Citation
The role of the charge-transfer complex in the alternating copolymerization of N-substituted maleimides and vinyl ethers

Material Information

Title:
The role of the charge-transfer complex in the alternating copolymerization of N-substituted maleimides and vinyl ethers
Creator:
Olson, Kurt Gordon, 1954- ( Dissertant )
Butler, George B. ( Thesis advisor )
Brey, Wallace S. ( Reviewer )
Helling, John F. ( Reviewer )
Hogen-Esch, Thieo E. ( Reviewer )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
1981
Language:
English
Physical Description:
xiii, 214 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Carbon ( jstor )
Chemical equilibrium ( jstor )
Copolymerization ( jstor )
Copolymers ( jstor )
Ethers ( jstor )
Monomers ( jstor )
Polymers ( jstor )
Protons ( jstor )
Solvents ( jstor )
Stereochemistry ( jstor )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Electron donor-acceptor complexes ( lcsh )
Maleimide ( lcsh )
Polymers and polymerization ( lcsh )
Vinyl ethers ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Abstract:
The aim of this research was to determine whether or not a comonomer charge-transfer complex participates significantly in the propagation steps of free-radically initiated alternating copolymerizations. Various N-substituted maleimides were shown to copolymerize alternately with several vinyl ethers. Both the sequence distribution and the stereochemistry of these copolymers were found to depend on such copolymerization conditions as temperature, solvent, total monomer concentration, the initial ratio of comonomers, and the relative donor and acceptor strengths of the comonomers. Carbon-13 nuclear magnetic resonance (NMR) spectroscopy was used extensively for the determination of copolymer stereoregularity. Copolymer epimerization studies and the comparison of copolymer 13 C NMR chemical shifts with those of a series of stereospecific model compounds indicated that the stereochemistry at the succinimide units in the copolymer was predominantly cis. In general, copolymerization conditions that were expected to enhance the fraction of maleimide monomer in complexed form (e.g., low temperature, excess vinyl ether, "inert" solvent, higher total monomer concentration, and stronger donor-acceptor character of the comonomer pair) yielded copolymers possessing a higher cis:trans stereochemical ratio at the succinimide units. A weak interaction between the comonomers was shown to exist by the appearance of a new absorption in the electronic spectra of comonomer mixtures, which did not appear in the spectrum of either component alone. The observed preference for cis stereochemical placements in these copolymers was opposite to what was expected if a mechanism involving consecutive alternate monomer additions to the radical chain end was operational. Thus, it was proposed that succinimide unit stereochemistry is dependent on the fraction of maleimide monomer in complexed form, and that the comonomer complex was participating in the propagation steps. Although the stereochemistry at the succinimide units was mostly cis, the relative stereochemistry between the vinyl ether methine carbons in the copolymers, and the methine carbons of adjacent succinimide units proved to be nearly random. The results were interpreted by invoking a concerted addition of the complex to the radical chain end, with radical attack occurring preferentially on the maleimide portion of the complex, on the side syn to the vinyl ether.
Thesis:
Thesis (Ph. D.)--University of Florida, 1981.
Bibliography:
Includes bibliographic references (leaves 204-213).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Kurt Gordon Olson.

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University of Florida
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University of Florida
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Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
028500194 ( AlephBibNum )
08559535 ( OCLC )
ABU2925 ( NOTIS )

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THE ROLE OF THE CHARGE-TRANSFER COMPLEX
IN THE ALTERNATING COPOLYMERIZATION OF
N-SUBSTITUTED MALEIMIDES AND VINYL ETHERS







BY

KURT GORDON OLSON





















A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

1981





























Copyright 1981

by

Kurt Gordon Olson































To Leslie
















ACKNOWLEDGEMENTS

I would like to express my deep appreciation and gratitude to my

research director, Dr. George B. Butler, for his encouragement and

guidance during the course of this work.

I would also like to thank Dr. Roy W. King for teaching me how

to use the FX-100 NMR spectrometer, and for many helpful discussions.

Thanks are also due to Dr. Thieo E. Hogen-Esch for numerous discus-

sions. I would like to thank Dr. Wallace Brey and Mr. Paul Kanyha

for running the 15N, 19F, and 300 MHz IH NMR spectra described herein.

The friendship and cooperation of my coworkers in the polymer

chemistry laboratories are greatly appreciated. Discussions with

Mr. David P. Vanderbilt were especially helpful during the course of

this research.

I would like to thank Miss Patty Hickerson for the skillful typ-

ing of this manuscript. Special thanks are due to my wife, Leslie,

for her constant encouragement and help.

Financial support for this work from the Department of Chemistry,

the National Science Foundation (Grant No. DMR80-20206), Tennessee

Eastman Co., Gulf Oil Co., and the University of Florida Graduate

School is gratefully acknowledged.

















TABLE OF CONTENTS


ACKNOWLEDGEMENTS . . . . . . . . . . . .

LIST OF TABLES . . . . . . . . . . . . .

LIST OF FIGURES . . . . . . . . . . . .

ABSTRACT . . . . . . . . . . . . . .

CHAPTER

I. INTRODUCTION . . . . . . . . . . . .

II. EXPERIMENTAL . . . . . . . . . . . .


General . . . .

Reagents and Solvents. .

Model Compound Synthesis

Malpimidp Svnthp'si .


... ...... .. ... ... . . . . . . . . . . .

Copolymer Synthesis and Characterization . . . . .

Copolymer Epimerization . . . . . . . .

Complexation Studies . . . . . . . . .

III. RESULTS AND DISCUSSION . . . . . . . . .

Copolymer Composition . . . . . . . .

Copolymerization Kinetics . . . . . . .

Maleimide-CEVE Complexation Studies . . . . .

Carbon-13 NMR Structural Studies on N-Substituted Male-
imide Vinyl Ether Copolymers . . . . . . .

Model Compound Synthesis and Stereochemical Assignments..

Summary and Conclusions . . . . .... .


PAGE

iv

vii

ix

xii



1

14


14

15

16

38

54

82

85

96

96

98

102












PAGE

REFERENCES .................... ...... 204

BIOGRAPHICAL SKETCH... .................. . .214











































vi
















LIST OF TABLES


TABLE PAGE

1 13C Chemical Shifts (6, ppm from TMS) for cis and trans
11. (DMSO-d6, internal reference DMSO-d6 = 39.5)......... 36
2 Conditions for N-Phenylmaleimide-2-Chloroethyl Vinyl
Ether Copolymerizations....................... .... ... 57

3 Yield and Analysis Data for Copolymers in Table 2......... 58

4 Polymerization Conditions for Other Maleimide Polymers.... 59

5 Yield and Analysis Data for Copolymers in Table 4......... 60

6 Reactivity Ratios for the Free Radical Initiated Copoly-
merization of N-Phenylmaleimide (M1) and 2-Chloroethyl
Vinyl Ether (M2) in Dichloromethane....................... 65

7 Kinetic Data for N-Phenylmaleimide 2-Chloroethyl Vinyl
Ether Copolymerizations................ .. ...... ....... 68

8 Initial Copolymerization Rates for the Copolymerization of
N-Phenylmaleimide and 2-Chloroethyl Vinyl Ether in Di-
chloromethane............................................. 70

9 Carbon-13 Spin-Lattice Relaxation Times (T1) and Nuclear
Overhauser Enhancement Factors (NOEF) For an NPM-CEVE -
Copolymer ............................................... 76

10 Copolymer Decomposition Temperatures (Td)................. 80

11 Absorbance Data for Maleimide, 2-Chloroethyl Vinyl Ether
Complexes at 295 nm....................................... 93

12 Slopes of A295/([M] x z) vs. [CEVE] Plots................. 95
c
13 Chemical Shifts (6, ppm From TMS) for the Olefinic Protons
of N-Phenylmaleimide in CDC13 Solutions of Varying
2-Chloroethyl Vinyl Ether Concentration................... 108

14 The Effect of Solvent on the Chemical Shift of NPM Ole-
finic Protons (100 MHz, 6, ppm From TMS).................. 110

vii











TABLE PAGE

15 The Mole Fraction of cis Succinimide Units in NPM-CEVE
Copolymers as a Function of the Mole Fraction of NPM
in the Initial Comonomer Feed (XM)........................ 146

16 Mole Fraction of cis Succinimide Units in NPM-CEVE Copoly-
mers Prepared at Various Temperatures..................... 155

17 The Effect of Solvent on the Mole Fraction of cis Succin-
imide Units in NPM-CEVE Copolymers........................ 157

18 Carbon-13 NMR Chemical Shifts of Some N-Substituted Male-
imides.................................................. .. 161

19 The Mole Fraction cis Succinimide Units in Various N-Sub-
stituted Maleimide-CEVE Copolymers....................... 165

20 The Mole Fraction of cis Succinimide Units in NPM-Vinyl
Ether Copolymers.......................................... 173

















LIST OF FIGURES


FIGURE PAGE

1 Kelen-Tudos Plot for the Free-Radical Initiated Copoly-
merization of N-Phenylmaleimide and 2-Chloroethyl Vinyl
Ether in Dichloromethane............................. .. 64

2 Electronic Absorption Spectra of Various N-Substituted
Maleimides in Dichloromethane........................... 87

3 Electronic Absorption Spectra of Various N-Substituted
Maleimide 2-Chloroethyl Vinyl Ether Charge-Transfer
Complexes, [CEVE] = 1.3 in all cases..................... 90

4 Effect of Varying CEVE Concentration on the Intensity of
the NPM-CEVE Charge-Transfer Band........................ 91

5 Copolymer Composition Diagram for the NPM-CEVE System.... 99

6 Initial Copolymerization Rate vs. XM for the System NPM,
CEVE, AIBN, CH2C12, 600C................................. 100

7 K295 vs. Hammett a Constants for Various Para Substi-
tuted Maleimide-CEVE Complexes in Dichloromethane........ 107

8 Noise Decoupled 13C NMR Spectrum of an NPM-CEVE Copoly-
mer, Obtained in DMSO-d6 at 1100C....................... 115

9 Complete a) and Off-resonance b) Decoupled 13C NMR Spec-
tra of NPM-Methyl Vinyl Ether Copolymer.................. 117

10 Model Compound 13C NMR Chemical Shifts................... 121

11 Homo- and Copolymer 13C NMR Chemical Shifts.............. 123

12 "Dyad" Stereochemical Possibilities for NPM-CEVE Alter-
nating Copolymers (i.e., Relative Stereochemistry Between
Two Adjacent Chiral Centers)............................. 125

13 "Triad" Stereochemical Possibilities for Alternating
Sequences in NPM-CEVE Copolymers.......................... 126

ix











FIGURE PAGE

14 Effect of the Mole Fraction of NPM in the Initial
Comonomer Feed (xM) on the Appearance of Copolymer 13C
NMR Carbonyl Peaks....................................... 132

15 Effect of Copolymer Epimerization on the Carbonyl Region
of the C NMR Spectra of NPM-CEVE Copolymers............ 134

16 Effect of Copolymer Epimerization on the 1C NMR Reso-
nances Due to Carbons a to Oxygen in NPM-CEVE Copolymers. 136

17 Expanded Carbonyl Regions of the 13C NMR Spectra of Low
(a) and High (b) Conversion NPM-CEVE Copolymers.......... 138

18 Mole Fraction cis Succinimide Units in NPM-CEVE Copoly-
mers vs. XM..................................... 142

19 Nitrogen-15 NMR Spectrum of an NPM-CEVE Copolymer (20%
15N Enriched) in Acetone-d6..................... ... .. 148

20 Expanded Carbonyl Regions of the 13C NMR Spectra of NPM-
CEVE Copolymers Prepared with Different Total Monomer
Concentrations (MT) in the Initial Feed.................. 152

21 Expanded Carbonyl Regions of the 13C NMR Spectra of NPM-
CEVE Copolymers Prepared at Various Temperatures......... 154

22 Expanded Carbonyl Regions of NPM-CEVE Copolymers Prepared
in Bulk (a), Dichloromethane (b), and Benzene (c)........ 158

23 Expanded Carbonyl Regions of the 13C NMR Spectra of Some
N-(4-Substituted)-Arylmaleimide-CEVE Copolymers.......... 164

24 Mole Fraction cis Succinimide Units in N-Arylmaleimide -
CEVE Copolymers vs. Hammett o Constant................... 166

25 KE295 vs. Mole Fraction Cis Succinimide Units in N-Sub-
stituted Maleimide-CEVE Copolymers....................... 167

26 Expanded Carbonyl Regions of the 13C NMR Spectra of Co-
polymers Prepared from Several N-Substituted Maleimides
and CEVE............................................... 169

27 Expanded Carbonyl Regions of the 13C NMR Spectra of Co-
polymers Prepared from NPM and Various Vinyl Ether Co-
monomers............................................. .. 172

28 Carbon-13 NMR Spectrum of N-Phenylcitraconimide CEVE
Copolymer .............................................. 179

x












FIGURE PAGE

29 Expanded Regions of the 13C NMR Spectrum of Maleic
Anhydride-CEVE Copolymer................................... 182

30 Synthetic Scheme for Model Compound 16................... 184

31 Possible Conformations of Endo Diels-Alder Adduct 13..... 185

32 Proton NMR Spectrum (300 MHz) of Model Compound 16....... 190

33 Expansions of the Ring Proton Resonances Appearing in the
300 MHz 1H NMR Spectrum Shown in Figure 32............... 191

34 Synthetic Scheme for Model Compound 11................... 198
















Abstract of Dissertation Presented to the
Graduate Council of the University of Florida
in Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy

THE ROLE OF THE CHARGE-TRANSFER COMPLEX
IN THE ALTERNATING COPOLYMERIZATION OF
N-SUBSTITUTED MALEIMIDES AND VINYL ETHERS

By

Kurt Gordon Olson

December 1981

Chairman: Dr. George B. Butler
Major Department: Chemistry

The aim of this research was to determine whether or not a co-

monomer charge-transfer complex participates significantly in the

propagation steps of free-radically initiated alternating copolymeri-

zations. Various N-substituted maleimides were shown to copolymerize

alternately with several vinyl ethers. Both the sequence distribu-

tion and the stereochemistry of these copolymers were found to depend

on such copolymerization conditions as temperature, solvent, total

monomer concentration, the initial ratio of comonomers, and the rela-

tive donor and acceptor strengths of the comonomers. Carbon-13 nu-

clear magnetic resonance (NMR) spectroscopy was used extensively for

the determination of copolymer stereoregularity.

Copolymer epimerization studies and the comparison of copolymer

C NMR chemical shifts with those of a series of stereospecific model

compounds indicated that the stereochemistry at the succinimide units











in the copolymer was predominantly cis. In general, copolymerization

conditions that were expected to enhance the fraction of maleimide

monomer in completed form (e.g., low temperature, excess vinyl ether,

"inert" solvent, higher total monomer concentration, and stronger

donor-acceptor character of the comonomer pair) yielded copolymers

possessing a higher cis:trans stereochemical ratio at the succinimide

units.

A weak interaction between the comonomers was shown to exist by

the appearance of a new absorption in the electronic spectra of co-

monomer mixtures, which did not appear in the spectrum of either

component alone.

The observed preference for cis stereochemical placements in

these copolymers was opposite to what was expected if a mechanism

involving consecutive alternate monomer additions to the radical

chain end was operational. Thus, it was proposed that succinimide

unit stereochemistry is dependent on the fraction of maleimide mono-

mer in completed form, and that the comonomer complex was participat-

ing in the propagation steps.

Although the stereochemistry at the succinimide units was mostly

cis, the relative stereochemistry between the vinyl ether methine

carbons in the copolymers, and the methine carbons of adjacent succin-

imide units proved to be nearly random. The results were interpreted

by invoking a concerted addition of the complex to the radical chain

end, with radical attack occurring preferentially on the maleimide

portion of the complex, on the side syn to the vinyl ether.
















CHAPTER I

INTRODUCTION

The concept of "molecular association" has long been recognized

as important in virtually all fields of chemistry. This fact is

underscored by the appearance of a plethora of books and reviews de-

voted to the subject during the past two decades.1 The concept is

that of a relatively electron poor molecule, or acceptor (A), inter-

acting in some way with an electron rich molecule, or donor (D). The

interaction is such that the binding between the components is weaker

than a covalent bond.lk This definition is sufficiently broad so as

to take in the gamut of both weak and strong interactions between

both ionic and uncharged species.

The concept has been utilized in many diverse fields of chemis-

try. Lewis acid-Lewis base interactions are, in principle, inter-

actions between donors and acceptors. i Inorganic and organometallic

chemists have used the concept to describe metal-ligand interactions.

Ion solvation, ionization equilibria, and catalysis are also fields

of chemistry where donor-acceptor interactions play important roles.1

Organic chemists have applied the terms electrophilic and nucleo-

philic to acceptor and donor molecules, respectively. The literature

abounds with such terms as "molecular complexes," "o and a complexes,"

and "charge-transfer complexes," which all refer to some sort of

donor-acceptor interaction.la










Modern interest in donor-acceptor complexes has blossomed since

the discovery by Benesi and Hildebrand in 1949 of a new absorption

band in the electronic spectrum of a solution of benzene and iodine

in n-heptane, which did not appear in the spectrum of either compo-
2
nent alone. The explanation of this phenomenon was provided by

Mulliken in a series of papers published in 1950-1952 (reprinted in

reference le). His conclusion was that the new band was due to an

iodine-benzene complex possessing a 1:1 stoichiometry. A new elec-

tronic transition such as that described above is typical of mixtures

of donor and acceptor molecules in relatively "inert" solvents (sol-

vents which do not interact to an appreciable extent with either the

donor or acceptor component). Thus, if the new band is in the visi-

ble region, solutions of colorless donors and acceptors may appear

colored.

The relatively weak interaction between donors and acceptors,

such as the iodine-benzene system described above, is generally viewed

as an equilibrium

A + D K C

where the equilibrium constant K describes the strength of the inter-

action. The theoretical groundwork for such weak interactions has

been adequately described in the works of Mulliken and Person,le and

Kosower. c While the details of this theory will not be discussed,

several points are pertinent and will be briefly covered.

The interaction between the components of the complex was de-

scribed in the valence bond formulation.3 The ground state wave func-

tion (YN) and the excited state wave function (YE) are approximated by











N = a [O(D,A) + b YI(D+,A-) (1)


E = a T((D+,A-) b yO(D,A) (2)

where 1((D+,A-) represents the contribution to the bonding of the

components from the resonance form where there has been complete

transfer of one electron from donor to acceptor, and 0(D,A) repre-

sents the contribution from all other bonding interactions. For weak

molecular interactions, the relationship between the coefficients a

and b is, a >> b, so h0 is the major contributor in the ground state

and T1 takes precedence in the excited state. The electronic transi-

tion between these two levels is thought to be the origin of the

charge-transfer transition. One of the justifications for this theory

is the applicability of empirical relationships between the energy of

the charge-transfer transition (hv), the ionization potential of the

donor (ID), and the electron affinity of the acceptor (EA).4


hv = ID EA + C (3)

The constant C represents coulombic forces between the donor and

acceptor. The values ID and EA reflect the relative strength of

donors and acceptors, respectively, strong donors having low ID and

strong acceptors having high EA.

Another important consequence of Equations (1) and (2) is that

complexes are predicted to have favored orientations, since b2 (a

measure of the amount of charge-transfer) is proportional to the over-

lap integral between the highest occupied molecular orbital of the












donor (HOMO), and the lowest unoccupied molecular orbital (LUMO) of

the acceptor.5 In other words, since the "charge-transfer" is from

the HOMO of the donor to the LUMO of the acceptor, the maximum amount

of charge-transfer stabilization of the complex is to be expected

when the overlap between these orbitals is greatest.

It should also be mentioned that the observation of a new elec-

tronic band in a solution of donor and acceptor molecules does not

necessarily imply the existence of a complex. Such bands are ob-

served even when the equilibrium constant (K) for complex formation

is zero. The absorption is due to donor-acceptor pairs that are

merely close or in contact, and can be fairly intense. This phenom-

enon is known as "contact charge-transfer" and has been recently re-

viewed in an excellent article by Tamres and Strong.6 Thus, the mere

observation of a charge-transfer band in a reaction system should not

be taken as evidence for the participation of charge-transfer com-

plexes as reaction intermediates.

Kosower cd has reviewed the organic reactions in which charge-

transfer complexes may be reaction intermediates. The types of reac-

tions discussed include solvolysis, thermal electron transfer (e.g.,

the formation of radical anion-cation pairs), and reactions which

follow light absorption by a charge-transfer complex. Recent examples

of organic reactions in which charge-transfer complexes have been

postulated as intermediates include the electrophilic addition of

bromine and mercuric salts to olefins,7 and the cleavage of alkyltin

compounds by mercuric salts.8










Especially pertinent to this work are reactions that Kosowerlcd

categorizes as class G reactions, or reactions that depend on the ge-

ometry of the charge-transfer complex. He describes these reactions

as reactions which lead to a product structure other than that which

might have been expected on the basis of random collision of the reac-

tants or a knowledge of similar reactions in related molecules. He

includes as examples the stereospecific hydrolysis of substrates by

enzymes and Diels-Alder reactions. A recent example of the applica-

tion of the charge-transfer concept to asymmetric induction in intra-

molecular Diels-Alder reactions is given by Trost, O'Krongly and

Belletire. Stereoselectivity has also been observed in photochemical

2+2 cycloadditions, where only the charge-transfer band was irradi-

ated.10

Charge-Transfer Complexes in Polymerization Processes

Several recent reviews have dealt with the influence of charge-

transfer complexes on polymerization processes.11,12 This disserta-

tion deals with the influence of the charge-transfer complex on the

propagation steps in alternating, radical-initiated copolymerizations.

Alternating copolymerizations are characteristic in that a

nearly 1:1 ratio of comonomers is found in copolymers produced from

a wide variety of comonomer mole fractions in the initial monomer

solution (referred to as the monomer feed). In a random copolymeri-

zation, the monomer ratio in the copolymer corresponds closely to

that in the feed. The degree of alternation depends strongly on the

polarity differences between the comonomers. If one monomer is a

donor, while the other is an acceptor, the copolymer resulting from











the polymerization of these monomers will possess a certain amount of

alternation, which depends on the strength of the interaction between

the comonomers. This effect was noticed very early in the develop-

ment of copolymerization theory, and the Q,e scheme was introduced in

order to provide a quantitative, empirical comparison of the polarity

of various monomers.13 The e value (polar parameter) is positive for

electron-deficient olefins and negative for electron-rich olefins.

The Q value is determined by resonance effects.

The influence of the charge-transfer complex in alternating co-

polymerizations has been the subject of debate for many years. Sev-

eral mechanisms have been proposed to explain the alternation ob-

served. First, the postulate was put forth by Walling et al.14 that

polarity differences between the radical chain end and the incoming

monomer would lower the energy of activation of a cross-propagation

reaction, as opposed to a homopropagation reaction, thus producing

alternating copolymers when the comonomers have widely different

polarities. This mechanism will henceforth be referred to as the

"free monomer" mechanism.

The second possible explanation for alternation in these systems

was first proposed by Bartlett and Nozaki in 1946.15 These workers

postulated that donor and acceptor monomers formed a charge-transfer

complex which, due to an inherently higher reactivity of the complex

relative to the free monomers, preferentially added to the chain end.

In other words, the alternating nature of the copolymer results from

a "homopolymerization" of the charge-transfer complex. Support for

this theory may be found in the works of Butler and coworkers 19










maleicc anhydride-divinyl ether and maleic anhydride-furan copoly-

mers), Iwatsuki, Yamashita and Kokubo20,21,22 maleicc anhydride-

vinyl ether and maleic anhydride-anethole copolymers), Gaylord and

coworkers23,24 maleicc anhydride-conjugated diene copolymers) and

Caze and Loucheux25 maleicc anhydride-vinyl acetate copolymers). This

mechanism has been termed the "complex" mechanism.

A third possibility is that both of the mechanisms described

above are important in alternating copolymerizations. Tsuchida and

Tomono,26 and Tsuchida et al.27 introduced this concept to explain re-

sults obtained for the styrene-maleic anhydride system. Seiner and

Litt,28 Litt,29 and Litt and Seiner331 derived a series of kinetic

equations that included the complex as a propagating species and ob-

tained better fits to experimental copolymer composition data than

could be obtained by using the classical "terminal" copolymerization
32 33
model developed by Mayo and Lewis,3 and Alfrey and Goldfinger.33 The

terminal model predicts copolymer compositions based on a kinetic

scheme which does not include a complex, and assumes random introduc-

tion of comonomers into the chain (i.e., only four possible propaga-

tion steps are included for two comonomers). Karad and Schneider34

have extended the Seiner-Litt equations to systems (e.g., styrene-

fumaronitrile) where the assumption of a small charge-transfer equi-

librium constant does not hold. Still more recently, Cais, Farmer,

Hill and O'Donnell35 have presented an alternative to the Seiner-Litt

complex participation model in which either copolymer composition data

or triad fractions can be used to test the various copolymerization

models. This treatment is unique in that it treats sequence number

fractions in terms of transition probabilities as well as reactivity

ratios.










Perhaps one of the strongest pieces of evidence for complex

participation in alternating copolymerizations is that the overall

rate of polymerization (R ) exhibits a maximum at a monomer feed

ratio of nearly 1:1, where the concentration of the complex is great-

est. Shirota et al.,36 and Yoshimura et al.37'38 have pointed out

that the rate maximum for alternating copolymerizations seldom occurs

at exactly 1:1 feed ratio. They also point out that the rate of

polymerization at constant feed ratio and initiator concentration is

generally greater than first order in total monomer concentration.

If only the cross-propagation of free monomers operates, the rate

should be proportional to the total monomer concentration. Thus,

they also support the theory that both completedd" and "free" monomers

participate in the propagation reactions. They have also derived a

scheme based on the change of R with total monomer concentration

(at constant feed ratio), whereby a quantitative separation of the

rate due to complex addition, and that due to free monomer addition,

can be achieved. These workers applied their method to the systems

N-vinylcarbazole (VCZ)-diethyl fumarate (DEF), and VCZ-fumaronitrile

(FN). They concluded that the overall rate of copolymerization was,

at most, 17% due to the addition of the complex in the VCZ-DEF sys-

tem. Ten percent of the overall rate was due to complex addition for

the VCZ-FN system. Georgiev and Zubov39 have also developed a scheme

that allows the determination of the ratio of rate constants for

addition of completedd" and "free" monomers. Their method utilizes

the shift in the overall rate maximum as a function of the total mono-

mer concentration. They found that a significant amount of complex











participation occurs in the copolymerization of maleic anhydride and

vinyl acetate.

The last copolymerization theories to be considered are the

penultimate and antepenultimate models first suggested by Mertz,

Alfrey and Goldfinger,40 and later by Barb41 and Ham.42 These work-

ers felt that deviations in copolymer composition from that predicted

by the terminal model could be explained by invoking the effect of

the penultimate or antepenultimate units in the copolymer chain. In

other words, the reactivity of the chain end radical may differ de-

pending on which monomer unit is in the penultimate or antipenulti-

mate position.

In spite of the large amount of data that has been amassed on

systems that produce alternating copolymers (especially the styrene-

maleic anhydride system), there is still disagreement as to what the

exact mechanism is. Hyde and Ledwith11 have pointed out that the

actual concentration of complex in systems that show a tendency to

alternately copolymerize is invariably very low (equilibrium con-

stants for complex formation (K) are generally in the range 0.01 -

0.5). Thus, if the complex has any role in the propagation steps,

it necessarily must have an extremely high reactivity relative to the

free monomers. This is a point that is still open to some debate.

Dodgson and Ebdon43 have reanalyzed styrene-maleic anhydride copoly-

mer composition as a function of initial feed ratio. They conclude

that the penultimate model gives as good a fit to the experimental

data as the complex model. Regel and Canessa4 have examined the

complexation and copolymerization behavior of difluoromaleic anhydride










with a variety of donors, and have come to the conclusion that donor-

acceptor complexes have no significant involvement in the copolymeri-

zation.

It should be kept in mind that in nearly all of the studies dis-

cussed in this section, only two basic sources of experimental data

have been used to make a large number of conclusions. These sources

of data are copolymer composition (and sequence analysis) and kinetic

data. As Hyde and Ledwith11 point out, these kinetic analyses in-

variably assume relative values of certain rate constants in order to

obtain good fits with experimental data. Copolymer composition is

generally calculated from either elemental analysis data or integra-

tion of copolymer NMR spectra. Copolymerization rates are typically

calculated from a single copolymer weight obtained after a certain

polymerization time. The polymers are routinely isolated by precipi-

tation into a nonsolvent, so an implicit assumption is that the co-

polymers are completely insoluble in this nonsolvent. All of these

experimental techniques are subject to errors which are seldom dis-

cussed. While the derivations, schemes and analyses discussed above

are not questioned, it seems necessary to have accurate and copious

data in order to distinguish between such mechanistic subtleties as

complex formation prior to addition to the chain end, and complex

formation with the chain end itself.

Thus, it was thought that some new source of data was needed in

order to help resolve the question of whether or not charge-transfer

complexes play a significant role in alternating copolymerizations.










Since, according to Mulliken theory, a donor-acceptor complex is

expected to have a preferred geometry videe supra), it may be that

if the complex adds to the chain end in a concerted manner (as op-

posed to stepwise addition of the complex components), a certain de-

gree of stereoregularity may be introduced into the copolymer chain.

As mentioned earlier, in organic reactions where charge-transfer com-

plexation between components has been observed, stereoselectivity is

often observed in the product distribution. If the "free" monomers

preferentially add to the chain end, the resulting copolymer stereo-

chemistry may be expected to be nearly random since the chain end is

expected to be either planar or possess a rapidly inverting pyramidal

structure.45

Thus, a detailed study of copolymer structure and stereochemis-

try as a function of copolymerization conditions was carried out.

Conditions were selected so as to shift the complex equilibrium one

way or the other. The system N-phenylmaleimide (NPM) 2-chloro-

ethyl vinyl ether (CEVE) was selected for study. Nitrogen and chlo-

rine elemental analysis allowed relatively accurate determination of

the composition of copolymers produced from these monomers. N-Phenyl-

maleimide is an acceptor monomer with an e value of +3.24.46 CEVE
46
is a donor monomer with an e value of -1.58.46 Thus, they were ex-

pected to form alternating copolymers. Indeed, NPM has been shown to

form alternating copolymers with styrene.47 Maleic anhydride copoly-

merizes alternately with CEVE.26'48

Several interesting reports have appeared that deal with asym-

metric induction into alternating copolymers. Kurokawa et al.49










copolymerized NPM with optically active menthyl vinyl ether and found

that the copolymer retained some optical activity even after cleavage

of the optically active side chain. Beredjick and Schuerch50 obtained

similar results with the system (-)-a-methylbenzyl methacrylate -

maleic anhydride, although Chiellini et a1.51 have questioned whether

they obtained complete hydrolysis of the side groups. Optically ac-

tive N-bornylmaleimide was copolymerized with styrene, methyl meth-

acrylate and vinylidene chloride by Yamaguchi and Minoura.52 They

found that more optical activity was observed in the copolymers which

had a higher degree of alternation. It may be that a charge-transfer

complex between the monomers plays an important role in these asym-

metric inductions. Kurokawa and Minoura,53 however, have explained

such induction of asymmetry as being the result of the influence of

the chiral chain end on the incoming monomer. Asakura, Yoshihara

and Maeshima54 have recently published an interesting report in which

they describe the copolymerization of maleic anhydride with isobutyl

vinyl ether, styrene, methacrylic acid, methyl acrylate, and methyl

methacrylate in optically active solvents such as 1-menthol. They

found that optically active copolymers were produced only for the

systems that copolymerized alternately maleicc anhydride-styrene and

maleic anhydride-isobutyl vinyl ether). They postulate that the chi-

ral solvent may interact with the charge-transfer complex, forming

a trimolecular complex that may be important in the asymmetric induc-

tion observed. In spite of some disagreement about the results ob-

tained in these studies, it seems at least plausible that an associa-

tion of the monomers prior to addition to the chain end may influence

the resulting stereochemistry.






13



Hirai et al.,55 and Okuzawa et al.56 have shown that in polymers

prepared in the presence of a Lewis acid, stereoregularity often

accompanies rate enhancement. This observation may also mean that

the formation of molecular complexes has an effect on polymer stereo-

chemistry. To the best of our knowledge, a detailed study of the

stereochemistry of alternating copolymers prepared by using conven-

tional free radical initiation, has thus far not appeared.

Carbon-13 NMR was used for the study of NPM-CEVE copolymer ster-

eochemistry. Synthesis of a series of stereospecific model compounds

aided in the interpretation of the copolymer 1C results.

















CHAPTER II

EXPERIMENTAL

General

All temperatures are uncorrected and are reported in degrees

centigrade. Melting points were determined in open capillary tubes

using a Thomas-Hoover Melting Point Apparatus. Pressures are ex-

pressed as millimeters of mercury.

Infrared (IR) spectra were obtained by using a Perkin Elmer

Model 281 Infrared Spectrophotometer. Spectra were calibrated using

the 1601 cm- line of a polystyrene film. Spectra of oils and liq-

uids were performed neat as a smear on a sodium chloride plate, and

those of solids were obtained by using KBr pellets. Vibrational

transition frequencies are expressed in wavenumbers (cm- ), with

bands being assigned the following classifications: weak (w), medi-

um (m), strong (s), very strong (vs) and broad (b).

Proton nuclear magnetic resonance (NMR) spectra (60 MHz) were

obtained on either a Varian A-60A or a Jeol JNM-PMX-60 spectrometer.

Carbon-13 (25.00 MHz) and 100 MHz proton NMR spectra were recorded

on a Jeol JNM-FX-100 instrument. Chemical shifts are expressed in

parts per million (ppm) downfield from tetramethylsilane (TMS) unless

stated otherwise. Multiplicities of proton and off-resonance de-

coupled 1C resonances are designated as singlet (s), doublet (d),










triplet (t), quartet (q) or multiple (m). Coupling constants (J)

are expressed in Hertz (Hz).

Mass spectra [low resolution (LRMS) and high resolution (HRMS)]

were recorded on an Associated Electronics Industries (AEI) Model

MS-30 spectrometer.

Ultraviolet (UV) spectra were run on a Beckman ACTA V Spectro-

photometer using 1 cm or 2 mm quartz cells.

Catalytic hydrogenations were carried out in a low pressure,

shaker type Parr Series 3910 Catalytic Hydrogenation Apparatus.

Polymer number average molecular weights (M ) were determined

using a Wescan 233 Molecular Weight Apparatus (vapor pressure osmo-

meter).

Chemical analyses were performed by Atlantic Microlab, Inc.,

Atlanta, Georgia.

Compound headings appear with the common name listed first,

followed by the systematic name (according to Chemical Abstracts) in

parentheses. Registry numbers are given in brackets for known com-

pounds. The Chemical Abstracts numbering scheme is used throughout

to designate protons or carbons (e.g., coupling constants in NMR

data).

Reagents and Solvents

Unless otherwise noted, reagents were obtained from Aldrich

Chemical Co. Dichloromethane (CH2C12) was distilled from P4010 im-

mediately before use. Purification of other solvents was carried out

using standard procedures57 and is described in the text. Deuterated

solvents [chloroform-d (CDC13), d6-acetone, dimethylsulfoxide-d6










(DMSO-d6), and dichloromethane-d2 (CD2C12)] for NMR spectra were

obtained from either Merck and Co. Inc., Stohler Isotope Chemicals

or Aldrich Chemical Co., and were used without further purification.

N-Phenylmaleimide was obtained from Aldrich Chemical Co., and was

recrystallized from cyclohexane before use.

Model Compound Synthesis

N-Phenylsuccinimide (l-Phenyl-2,5-pyrrolidine-dione), [83-25-0], (1)

Method A. The procedure of Umrigar58 was used for the synthesis

of this compound. Exactly 10.0 g succinic anhydride (0.1 mole)

(Aldrich) and 18.6 g distilled aniline (0.2 mole) were dissolved in

approximately 100 ml dimethylformamide (DMF) in a 250 ml round-bot-

tomed flask. The flask was fitted with a reflux condenser, and the

solution was refluxed for six hours. The bulk of the solvent was

then removed via rotary evaporation. The deep red residue was dis-

solved in hot ethanol (95%), and about 1 g decolorizing carbon was

added to the solution. After boiling for about ten minutes, the solu-

tion was filtered hot. The filtrate was allowed to cool slowly, and

N-phenylsuccinimide (1) crystallized as nearly colorless needles.

The needles were suction filtered and washed with cold ethanol. The

product was recrystallized again from ethanol to give 9.0 g 1 (51.4%),

mp 154-1550C literaturee9 mp 1560C).

H NMR (60 MHz,CDC13) 6 2.79(s, 4H), 7.38(m, 5H).

3C NMR (CDC13) 6 28.21(t), 126.32(d), 128.42(d), 128.95(d), 131.83(s),

176.03(s).

IR (KBr) 3439(w), 3030(w), 2921(w), 1779(w), 1705(vs), 1593(w),

1500(m), 1391(s), 1290(m), 1190(vs), 1148(m), 1077(w), 1030(w),

1002(w), 927(m), 819(m), 766(m), 696(s), 670(m), 625(w) cm-1










Method B. N-Phenylmaleimide (NPM) could be reduced to N-phenyl-

succinimide (1) by using the procedure of Medvedeva and Belotsvetov.60

To a 125 ml Erlenmeyer flask containing a solution of 25 ml glacial

acetic acid and 50 ml deionized water was added 1.0 g NPM (5.8 mmole)

and 3.0 g iron powder (53.7 mmole). The resulting slurry was stirred

magnetically and heated on a hot plate to 900C. After stirring for

about twenty minutes, the yellow solution turned light green. After

forty-five minutes, the solution had a red-brown color. At the end

of one hour of stirring, the flask was allowed to cool, and the red-

brown precipitate was filtered. The filtrate was neutralized with

solid NaHCO3 and then extracted with CHC13 (2 x 25 ml). The organic

layer was dried over anhydrous MgS04, and then filtered. The solvent

was removed on a rotary evaporator, and the residue recrystallized

from 95% ethanol to yield 0.4 g 1 (39%) as colorless needles. The

spectral properties (IR, NMR) and melting point were identical to

those of 1 synthesized via Method A.

3,4-Dimethyl-N-phenylmaleimide (3,4-Dimethyl-l-phenyl-IH-pyrrole-2,5-

dione) (2)

Dimethyl maleic anhydride (Aldrich) (5.0 g, 39.6 mmole) was dis-

solved in 75 ml CHC13. This solution was stirred magnetically while

5.0 g (53.7 mmole) freshly distilled aniline was added dropwise. This

solution was stirred on a hot plate at 40-45C for ninety-one hours.

No precipitation of the expected maleamic acid was noted. The CHC13

was removed on a rotary evaporator to leave an orange crystalline

mass. This residue was dissolved in a small amount of acetone and

precipitated dropwise into rapidly stirred acidic water (100 ml +










5 drops 18 M H2S04). The precipitate was suction filtered, washed

with water, and dried in a vacuum oven (50C) overnight. After dry-

ing, the residue was recrystallized from cyclohexane to yield 4.6 g

(57.6%) of pale green needles, mp 90-91C.

1H NMR (60 MHz, CDC13) 6 2.05(s, 6H), 7.38(s, broad, 5H).

1C NMR (CDC13) 6 8.82, 125.69, 127.33, 128.94, 132.03, 137.39,

170.85.

IR (KBr) 3450(w), 3048(w), 2987(w), 2953(w), 2920(w), 1750(w),

1699(vs), 1594(m), 1490(s), 1438(m), 1392(vs), 1123(m), 1090(s),

1070(m), 926(m), 769(s), 727(m), 700(s), 633(m).

LRMS (70eV, m/z, relative intensity) 202 (13.7), 201 (M 100.0),

157 (7.9), 142 (28.0), 119 (19.0), 91 (16.9), 77 (11.0), 64

(12.5), 54 (62.0), 53 (25.0).

cis-3,4-Dimethyl-N-phenylsuccinimide (DMNPS) (3.4-Dimethyl-1-phenyl-

2.5-pyrrolidinedione),[6144-74-7], (3)

To a 250 ml capacity hydrogenation bottle was added 1.0 g (5.0

mmole) 3,4-dimethyl-N-phenylmaleimide, approximately 150 ml 95%

ethanol, and 0.01 g PtO2 (Englehard Industries). The bottle was

placed on the Parr shaker, and the system was pressurized to 55 PSI

with hydrogen gas. The solution was shaken for about five minutes,

and the apparatus was then evacuated (aspirator). The system was

pressurized with H2 and evacuated twice more, then pressurized to

55 PSI. The solution was shaken for 18.5 hours at room temperature.

The catalyst was removed by filtration, and the solvent removed via

rotary evaporation. The residue was recrystallized from CC14 to

yield 0.97 g (95%) very fine, colorless needles, mp 128-1290C










literaturee1 mp 1270C). The cis:trans isomer ratio (calculated

from 13C NMR peak intensities) was > 14, or expressed as a percent-

age, the product was > 94% cis.

1H NMR (100 MHz, CDC13) 6 1.27(d, 6H, broad), 3.04(m, 2H), 7.35(m,5H).

1C NMR (CDC13) 6 11.55, 38.40, 126.38, 128.28, 128.57, 128.96,

132.08, 179.35.

IR (KBr) 3455(w), 3046(w,b), 2980(w), 1750(shoulder), 1700(vs),

1591(m), 1490(s), 1452(w), 1427(m), 1395(vs), 1375(shoulder),

1203(m), 1125(m), 1090(s), 1070(m), 935(b), 769(s), 750(m),

727(m), 697(s), 632(w), 615(w) cm-1

trans-3,4-Dimethyl-N-phenylsuccinimide (DMNPS) (trans-3,4-Dimethyl-

l-phenyl-2,5-pyrrolidinedione), [35393-95-4], (4)

The trans isomer of 3,4-dimethyl-N-phenylsuccinimide could be

conveniently prepared by epimerization of the cis compound. Thus,

approximately 0.2 g of the cis isomer was dissolved in 0.4 ml DMSO-d6,

and the resulting solution was filtered into a clean NMR tube. A 13C

NMR spectrum was run (see below for chemical shifts of cis isomer in

DMSO-d6). A drop of 2,2,6,6-tetramethylpiperidine (TMP) (Aldrich)

was then added to the tube, and the tube was placed in a 600C water

bath. After being heated overnight, another 1C spectrum was run.

The peaks due to the small amount of the trans isomer originally pre-

sent (- 5-6%) had grown at the expense of the peaks attributed to the

cis compound. Indeed, the trans isomer was in excess. Continued

epimerization at 600C (monitored periodically with 13C NMR) for about

one week gave a maximum trans:cis ratio of about 6 (86% trans), as

judged from 13C NMR peak intensities. That no epimerization took










place in the absence of TMP was verified by heating another sample of

the cis isomer at 600C in DMSO-d6 for several days and observing the
C3 NMR spectrum. No change was observed. An analytical sample of

4 was isolated by evaporation of most of the DMSO-d6, followed by

extraction of the residue with boiling cyclohexane. The hot cyclo-

hexane was decanted from the residue and on cooling, 4 crystallized

as colorless needles, mp 145-1470C literaturee1 mp 1460C).

Compound 3 13C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562)

6 11.28, 37.99, 127.18, 128.30, 128.88, 132.69, 179.72.

Compound 4 13C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562

6 13.94, 42.42, 126.98, 128.06, 128.71, 132.78, 178.45.

1H NMR (100 MHz, DMSO-d6, internal reference DMSO-d6 = 2.4962) 6

1.33(d, broad, 6H), 2.67(m, 2H), 7.37(m, 5H).

IR (KBr) 3450(w), 3062(w,b), 2980(w), 2937(w), 2875(w), 1780(w),

1710(vs), 1598(w), 1493(m), 1456(w), 1398(s), 1375(m), 1314(w),

1193(s), 1169(m), 1156(w), 1103(w), 1077(w), 948(m), 912(w),

852(w), 775(m), 738(m), 693(s), 620(w), 611(w) cm- .

cis-Hexahydrophthalanilic acid (2-[(Phenylamino)-carbonyl]cyclohexane-

carboxylic acid) (5)

Cis-1,2-cyclohexanedicarboxylic anhydride (Aldrich) (5.0 g, 32.4

mmole) was dissolved in 200 ml CHC13 in a 500 ml Erlenmeyer flask.

Freshly distilled aniline (3.0 g, 32.2 mmole) was slowly added (drop-

wise over ten minutes) while rapidly stirring the solution. The

solution was stirred for three hours. During this time a white pow-

dery precipitate formed. The precipitate was suction filtered and

dried in a 50C vacuum oven to yield 7.0 g 5 (87.4%), mp 176-177C

literaturee3 mp 172-173C).










H NMR (60 MHz, DMSO-d6) 6 1.52(s, broad, 4H), 1.83(m, 4H), 2.57(m,

1H), 2.99(m, 1H), 6.85-7.73(m, 5H), 9.63(s, 1H), 11.78(s, broad,

1H).
13C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562) 6 22.49, 24.10,

25.32, 27.85, 42.13, 42.67, 119.19, 122.74, 128.54, 139.66,

172.70, 175.18.

IR (KBr) 3388(s), 3060(s,b), 2935(s), 2860(m), 1718(vs), 1647(vs),

1597(vs), 1532(vs), 1498(m), 1433(vs), 1400(m), 1327(m), 1238(m),

1210(s), 1188(vs), 1130(m), 962(w), 938(w), 890(w), 860(w),

774(m), 746(m), 731(m), 691(s), 610(w) cm-1

cis-Hexahydrophthalimide (cis-Hexahydro-2-phenyl-1H-isoindole-1,3(2H)-

dione) (cis-HHPI), [26491-47-4], (6)

Compound 5 (6.7 g, 27.1 mmole) was dissolved in 300 ml acetic

anhydride and stirred magnetically at 80C for twenty-four hours.

The solution was cooled and slowly added to vigorously stirred water

(dropwise over 1.5 hours). The cream colored precipitate that formed

was suction filtered and dried in a 500C vacuum oven overnight. The

precipitate was mixed with 100 ml CHC13, filtered, and washed several

times with CHC13. The chloroform insoluble part proved to be un-

reacted starting material (2.6 g). The chloroform was removed from

the filtrate on a rotary evaporator, leaving 3.8 g residue. This

residue was recrystallized from CC14 to give 3.2 g fine white needles

(84.2% based on recovered starting material), mp 130-133C (litera-

ture63 mp 132-133C).
H NMR (CDC13, 100 MHz) 6 1.48(m, 4H), 1.85(s, broad, 4H), 2.98(m,

2H), 7.35(m, 5H).










C NMR (CDC13) 6 21.81, 23.93, 40.06, 126.25, 128.28, 129.03, 132.15,

178.55.

IR (KBr) 3468(w), 2942(m), 2911(m), 2858(m), 1775(w), 1709(vs),

1592(w), 1491(m), 1460(w), 1433(w), 1378(s), 1356(m), 1342(w),

1327(w), 1295(w), 1227(w), 1193(m), 1181(s), 1172(s), 1159(m),

1130(s), 1087(m), 921(w), 902(w), 887(m), 830(m), 776(m), 743(m),

698(m), 617(w) cm-'

trans-Hexahydrophthalanilic acid (2-[(Phenylamino)carbonyl]-cyclohex-

anecarboxylic acid) (7)

To a 125 ml Erlenmeyer flask was added 2.0 g (13.0 mmole) trans-

cyclohexanedicarboxylic anhydride (Aldrich) and 75 ml CHC13. The

resulting solution was stirred magnetically while 1.3 g (14.0 mmole)

distilled aniline was added dropwise. The solution was stirred at

500C for one hour. During this time, a white powdery precipitate

formed. The precipitate was suction filtered and dried in a vacuum

oven to yield 2.9 g of product (90.2%), mp 206-2120C literaturee3

mp 224-2250C).
1H NMR (100 MHz, DMSO-d6) 6 1.30(s, broad, 4H), 1.75(s, broad),

1.98(s, broad), 2.54(s, broad, 2H), 6.93-7.78(m, 5H), 9.92(s,

1H), 12.06(s, broad, 1H).
1C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562) 6 24.93, 25.12,

28.58, 28.88, 29.53, 44.35, 44.47, 46.54, 119.12, 122.79, 128.47,

139.53, 173.48, 175.94, 176.04.
IR (KBr) 3325(m), 3060(b), 2950(m), 2927(m), 2862(w), 1699(vs),

1655(s), 1601(m), 1533(s), 1500(w), 1443(m), 1416(m), 1328(m),

1313(m), 1262(m), 1205(m), 1186(w), 1115(w), 920(m), 900(w),

770(w), 745(m), 692(m), 672(w) cm-1










trans-Hexahydrophthalimide (trans-Hexahydro-2-phenyl-1H-isoindole-

1,3(2H)-dione) (8)

To a 125 ml Erlenmeyer flask was added 2 g 8 and 100 ml acetic

anhydride. The resulting solution was stirred at 80C for twenty-

two hours and then allowed to cool to room temperature. The solution

was added dropwise to a vigorously stirred aqueous NaC1 solution (500

ml). Some white precipitate formed. The mixture was cooled in an

ice bath for several hours, and the white crystalline solid that

formed was suction filtered, washed with water, and dried overnight

in a 50C vacuum oven. Recrystallization from CC14 yielded 1.2 g

colorless, very fine crystals, mp 194-1960C literaturee3 mp 195-

196C).
H NMR (CDC13, 100 MHz) 6 1.32-1.67(m, 4H), 1.7-2.3(m, 4H), 2.3-2.5

(m, 2H), 7.2-7.5(m, 5H).

C NMR (CDC13) 6 25.15, 25.54, 47.52, 126.25, 128.03, 128.98, 132.15,

175.77.

IR (KBr) 3462(w), 3060(w), 2922(m), 2860(w), 1773(w), 1711(vs),

1595(w), 1490(m), 1446(w), 1375(s), 1292(w), 1270(w), 1229(w),

1212(w), 1174(s), 1105(s), 1072(w), 1046(w), 922(w), 877(m),

753(m), 692(m), 670(w), 620(w) cm-1

1-Methoxy-1,3,3-triethoxybutane (9)

To a 125 ml Erlenmeyer flask was added 20 g (200 mmole) 4-

methoxy-3-buten-2-one (Aldrich), 30 g (202 mmole) triethyl ortho-

formate (Aldrich), 0.1 g p-toluenesulfonic acid monohydrate (Aldrich)

and 50 ml absolute ethanol. The solution turned deep black soon after

the addition of the p-toluenesulfonic acid. The reaction was somewhat










exothermic. The flask was stoppered and allowed to stand at room

temperature for sixteen hours. At the end of this time, the mixture

was fractionally distilled through a Vigreaux column. Distillation

at atmospheric pressure yielded a fraction boiling at 52-570C (~ 20

ml) presumed to be ethyl format literaturee4 bp 54.50C). Excess

ethanol was also removed at atmospheric pressure. The distillation

flask was allowed to cool and the pressure reduced to 10mmHg. Con-

tinued distillation gave 16.6 g (37.7%) colorless liquid with a boil-

ing range 85-95C (10 mm). The product proved to be a mixture of

isomers (various monomethoxy-triethoxybutanes).

H NMR (100 MHz, acetone-d6) 6 1.02-1.32(m, 4 overlapping triplets,

J = 7.0 Hz, 9H), 1.25(s, 3H), 1.88(d, J = 4.7 Hz, 2H), 3.09,

3.10, 3.21 and 3.23 (4 singlets, combined area 3H), 3.26-3.65

(m, overlapping quartets, J = 7.0 Hz, 6H), 4.50-4.60(m, over-

lapping triplets, J = 4.7 Hz, 1H).

C NMR (acetone-d6) 6 15.64, 15.74, 22.51, 22.56, 23.03, 23.07,

41.18, 41.64, 42.13, 47.86, 47.91, 51.73, 55.75, 60.58, 60.67,

60.94, 61.16, 100.54, 100.59, 101.40.

IR (thin film) 2980(vs), 2938(s), 2883(s), 1614(w), 1512(m), 1483(w),

1445(m), 1393(m), 1377(m), 1306(m), 1276(w), 1247(m), 1172(m),

1160(m), 1120(s,b), 1092(m), 1058(s,b), 999(w,b), 948(m),

838(m) cm-1

cis-2a,6a,3,4-Tetrahydro-3,5-diethoxy-N-phenylphthalimide (4,6-Di-

ethoxy-2-phenyl-3a,7a,4,5-tetrahydro-1H-isoindole-1,3(2H)-dione) (10)

The N-phenylmaleimide (NPM) used in this preparation was obtained

from Aldrich Chemical Co., and was recrystallized from cyclohexane










before use. N-Phenylmaleimide (5.0 g, 29.0 mmole) and 1-methoxy-1,3,

3-triethoxybutane (6.7 g, 30.4 mmole) were mixed in a 100 ml, one-

necked round-bottom flask. Hydroquinone (0.3 g) and Na2HPO3 (0.3 g)

were also added. The flask was evacuated to 25 mmHg with a vacuum

pump and immersed in a 70C oil bath. The yellow crystalline mass

soon dissolved, and the resulting solution was stirred magnetically

at 70-80C and 25 mmHg, until its weight decreased by about 2.5 g

(2 equivalents of ethanol). This took about one week (6.8 days). The

temperature was controlled so that it did not exceed 85C at any time.

The flask was cooled to room temperature, and the yellow solid mass

was triturated with absolute ethanol. The cream colored precipitate

that formed was filtered, and the ethanol was removed from the fil-

trate via rotary evaporation. The residue was triturated again to

yield more cream colored powder, which was filtered. This process

was repeated again, and the combined precipitates were recrystallized

from ethanol:water (3:1) to yield 5.2 g (56.9%) colorless plates, mp

156-1570C.

H NMR (100 MHz, CDC13) 6 1.09(t, J = 6.96, 3H), 1.31(t, J = 6.96,

3H), 2.35(broad AB quartet, 2H), 3.20(dd, J3a,4 = 3.9, J3a,7a

8.9, 1H), 3.24-3.98(complex m, 5H), 4.21(apparent q, J4,5 = 2.8,

J4,5a J4,3a = 3.9, 1H), 4.95(dd, J7,5 = 1.5, J7,7a = 3.9,

J7,5 = 0, 1H), 7.20-7.55(m, 5H).
C NMR (CDC13) 6 14.45(q), 15.30(q), 30.85(t), 39.21(d), 44.47(d),

62.53(t), 65.02(t), 72.50(d), 86.68(d), 126.60(d), 128.33(d),

129.01(d), 132.35(d), 152.72(s), 176.16(s), 176.94(s).










IR (KBr) 3480(w), 3059(w), 2973(m), 2938(m), 2890(m), 1779(w),

1717(vs), 1668(m), 1594(w), 1492(m), 1450(m), 1386(s), 1342(w),

1324(w), 1300(m), 1279(m), 1260(m), 1233(m), 1210(s), 1194(s),

1183(s), 1170(s), 1163(s), 1150(m), 1076(m), 1045(m), 1020(m),

924(w), 895(w), 864(w), 838(w), 789(m), 777(m), 744(s), 687(m),

626(w), 610(w) cm-1

LRMS (70 eV, m/z, relative intensity) 315(M 10.0), 271 (18.8), 242

(15.2), 168 (12.3), 139 (21.5), 119 (100.0).

HRMS (C18H21N04 requires 315.14706) found 315.14699.

Analysis. Calculated for C 8H21N04: C, 68.55; H, 6.71; N, 4.44.

Found: C, 68.54; H, 6.74; N, 4.44.

cis-3,5-Diethoxyhexahydro-N-phenylphthalimide (4,6-Diethoxyhexahydro-

2-phenyl-1H-isoindole-1,3(2H)-dione) (11)

Raney nickel catalyst was prepared65 by slowly adding 70 ml 16%

aqueous NaOH to 10 g Raney nickel alloy (PCR) in a 250 ml beaker. The

beaker was cooled in an ice bath if the generation of hydrogen became

too violent. After the addition of the NaOH solution was complete,

the beaker was heated gently on a hot plate until the evolution of

hydrogen stopped (~ 2 hours). The solution was diluted with water and

the black, active catalyst was isolated by suction filtration, and

washed with water until the filtrate was neutral to litmus. Care was

taken so as not to let the catalyst become dry, since Raney nickel

ignites spontaneously when dry.

Compound 10 (1.75 g, 5.5 mmole) was dissolved in 200 ml 95%

ethanol in a 250 ml hydrogenation bottle, and the moist, freshly made

catalyst was added. The solution was heated to 700C with a heating










tape wrapped around the bottle, and the bottle was placed in the Parr

hydrogenation apparatus. The apparatus was pressurized with hydrogen,

evacuated (aspirator) several times, and finally pressurized to 51

PSI. The solution was shaken at this hydrogen pressure and 70-80C

for 1.5 hours. At the end of this time, the solution was cooled to

room temperature and the pressure released. The solution was filtered

into a round-bottom flask, and the solvent was removed by rotary evap-

oration to leave 1.6 g oily residue. NMR analysis showed that the

residue was about 25% starting material. The residue was treated

with absolute ethanol, and the cream colored precipitate that formed

was isolated by filtration (0.25 g). Rotary evaporation of the fil-

trate left 1.2 g (91.4% based on recovered starting material) pale

green oil. This oil was purified further by percolation through a

short (~ 15 cm) silica gel column using isooctane:CH2C12:methanol

(50:20:1).
1H NMR (100 MHz, CDC13) 6 1.10(t, J = 7.0, 3H), 1.20(t, J = 7.0, 3H),

1.75-2.35(m, J5,4 = 2.2, J5,6 = 6.5, 4H), 2.79-3.07(m, J3a,4 =

3.5, J7a,7 = 6.3, Ja, 76 = 10.6, J3 ,7a = 9.5, 2H), 3.20-3.81

(m, 5H), 4.01-4.16(m, J4,3a = 3.5, 1H), 7.20-7.50(m, 5H).
13C NMR (CDC13) 6 15.30(q), 15.55(q), 25.98(t), 32.58(t), 37.48(d),

43.72(d), 63.75(t), 64.43(t), 72.89(d), 74.03(d), 126.57(d),

128.40(d), 129.03(d), 132.30(s), 176.67(s), 178.43(s).

IR (smear on NaC1 plate) 3480(w), 3070(w), 2979(m), 2925(m), 2880(m),

1778(w), 1715(vs), 1598(w), 1500(s), 1457(w), 1445(w), 1376(s),

1290(w), 1262(w), 1230(w), 1190(s), 1160(m), 1105(s), 1079(m),

922(w), 840(w), 797(w), 758(m), 736(m), 690(m), 620(m) cm-1










LRMS (70 eV, m/z, relative intensity) 317 (3.5, M+), 273 (57.6, meta-

stable), 227 (100.0).

HRMS (C18H23NO4 requires 317.1627) found: 317.1625.

Analysis. Calculated for C18H23N04: C, 68.12; H, 7.30; N, 4.41.

Found: C, 67.98; H, 7.32; N, 4.36.

1-Methoxy-3-(trimethylsiloxy)butadiene, [59414-23-2], (12)

This compound was made according to the procedure of Danishefsky

and Kitahara.66 Freshly fused ZnC12 (1.0 g) and 58.0 g triethylamine

(distilled from KOH) were added to a dry 500 ml Erlenmeyer flask. The

flask was stoppered, and the contents magnetically stirred for one

hour to form a white, milky suspension. At the end of the hour, 25.0

g (0.25 mole) of 4-methoxy-3-buten-2-one (Aldrich) dissolved in 75 ml

benzene was added to the suspension. Then 54.2 g (0.50 mole) chloro-

trimethylsilane (Pierce Chemical Co.) was added with a 30 ml syringe.

An exothermic reaction took place on addition of the chlorotrimethyl-

silane, and an orange precipitate formed immediately. This suspension

was stirred at 40-500C overnight and then poured into 500 ml of anhy-

drous ether. The precipitate was suction filtered and washed several

times with anhydrous ether. The filtrate was concentrated on a ro-

tary evaporator and then distilled. The colorless fraction distilling

at 48-500C (4.5mmHg) was collected to yield 24.3 g (56.5%) 1-methoxy-

3-(trimethylsiloxy)butadiene literaturee6 bp 54-55C, 5mm Hg).
H NMR (100 MHz, CDC13) 6 0.22(s, 9H), 3.54(s, 3H), 4.06(d, J = 3.4,

2H), 5.32(d, J = 12.3, 1H), 6.81(d, J = 12.3, 1H).
1C NMR (CDC13, internal reference CDC13 = 77.062) 6 -0.34(q), 55.87

(q), 90.62(t), 102.85(d), 150.06(d), 153.71(s).











IR (thin film) 3120(w), 3080(w), 3006(w), 2963(m), 2903(w), 2837(w),

1652(s), 1596(m), 1453(w), 1323(vs), 1257(s), 1213(vs), 1167(s),

1133(m), 1022(vs), 994(m), 960(w), 939(m), 921(m), 850(vs),

753(m), 682(w), 638(m), 617(m) cm-1.

cis-3-Methoxy-N-phenyl-2a,3,6,6a-tetrahydro-5-trimethylsiloxyphthal-

imide (cis-4-Methoxy-2-phenyl-3a,4,7,7a-tetrahydro-6-trimethylsiloxy-

1H-isoindole-1,3(2H)-dione) (13)

The procedure used was analogous to that used by Danishefsky

et al.67 To a 125 ml Erlenmeyer flask was added 10.0 g solid N-

phenylmaleimide (57.8 mmole), then 11.1 g l-methoxy-3-(trimethylsil-

oxy)butadiene. The flask was swirled, and evolution of heat was

noted. A homogeneous, light yellow solution resulted. After about

five minutes, the solution began to cool. A yellowish white crystal-

line mass formed on cooling. This crude product was broken up and

washed with a small amount of cold absolute ether. The product was

filtered, yielding 16.3 g pure white crystals. The ether washings

were evaporated, yielding more crystalline product. This residue was

washed, this time with a smaller amount of ether, and filtered to

yield 1.5 g more product. The total yield was 17.8 g (89.4%) of

white crystals, mp 114-116C. Repeated recrystallization from cyclo-

hexane failed to yield product that gave a satisfactory elemental

analysis. This was probably due to partial hydrolysis of the silyl

ether.
H NMR (100 MHz, CDC13) 6 0.25(s, 9H), 2.28-2.55(dd, "B" part of AB

quartet, J73,7 = 16.9, J7,7a = 10.1, J76,5 0, 1H), 2.66-2.93










(ddd, "A" part of AB quartet, J7a,76 = 16.9, J7a,7a = 6.4,
/a,/[j 7a,7a
7a,5 = 2.4, 1H), 2.98-3.16(dd, "B" part of AB quartet, J3a,7a
9.5, 3a,4 = 4.0, 1H), 3.20(s, 3H), 3.20-3.47(6 lines of ex-
pected 8 line pattern, "A" part of AB quartet, J7a,75 = 10.1,

J7a,3a = 9.5, J7a,7a = 6.4, 1H), 4.35(dd, J4,5 = 6.4, J4,3a =
4.0), 5.18(dd, J5,7 = 2.4, J ,4 = 6.4, J5,7 0, 1H), 7.20-

7.51(m, 5H).
1C NMR (CDC13) 6 0.121(q), 27.07(t), 37.43(d), 45.69(d), 55.54(q),

73.06(d), 100.94(d), 126.64(d), 128.35(d), 128.98(d), 132.35(s),

156.20(s), 176.06(s), 178.77(s).

IR (KBr) 3477(w), 3075(w), 2985(w), 2958(w), 2922(w), 2900(w),

2820(w), 1775(w), 1712(vs), 1643(m), 1597(w), 1496(m), 1455(w),

1388(s), 1360(m), 1342(m), 1308(m), 1271(m), 1257(m), 1228(m),

1197(s), 1182(s), 1097(m), 1081(m), 1021(w), 975(m), 928(m),

896(m), 854(s), 822(m), 748(m), 693(.m), 622(m) cm-1

LRMS (70 eV, m/z, relative intensity) 345 (3.1), 345 (M+, 12.1), 330

(39.4), 314 (41.6), 296 (12.2), 172 (30.4), 157 (100.0).

Analysis. Calculated for C18H23N04Si: C, 62.58; H, 6.71; N, 4.05.

Found: C, 63.63; H, 6.54; N, 3.90.

cis-Hexahydro-3-methoxy-5-oxo-N-phenylphthalimide (cis-Hexahydro-4-
methoxy-6-oxo-2-phenyl-lH-isoindole-1,3(2H)-dione) (14)

Silyl enol ether 13 was hydrolyzed to ketone 14 via two different

methods. The first uses the procedure of Danishefsky et al.67 Thus,

10.0 g (29.0 mmole) of silyl enol ether 13 was treated with 100 ml of

a solution comprised of 0.1N HC1 and tetrahydrofuran (THF) (1:4 by

volume). After stirring for 0.5 hour, the pale yellow solution was











poured into 300 ml 5% NaHCO3. The resulting deep yellow aqueous solu-

tion was extracted with CHC13 (4 x 75 ml). The combined organic

layers were dried over anhydrous MgSO4 overnight. The MgSO4 was

separated by filtration, and the solvent removed by rotary evapora-

tion. The resulting pale green oil was placed in a dessicator that

was subsequently evacuated. After drying at reduced pressure for

twenty-four hours, the oil solidified, yielding 7.2 g (90.9%) very

pale green solid.

The method of Semmelhack et al.68 was preferable for the desilyl-

ation of 13 because the reaction is easy and the product very clean.

Enough unactivated 3 A molecular sieves (Linde) were added to a 125

ml Erlenmeyer flask to cover the bottom. Then 1.0 g 13 dissolved in

100 ml of a solution of methanol:CHC13 (1:1) was added to the flask.

The flask was stoppered and allowed to stand at room temperature over-

night. The molecular sieves were removed by filtration and the sol-

vent evaporated on a rotary evaporator, to leave 0.80 g pale green

oil (101%). The product was dissolved in 5 ml of absolute ethanol:

chloroform (1:1). Slow evaporation of this solution yielded color-

less crystals which were isolated by filtration and washed with cold

absolute ethanol. After drying in a vacuum oven (50C) overnight,

the product weighed 0.70 g. Another workup of the ethanol washings

yielded an additional 0.05 g colorless crystals for a total isolated

yield of 0.75 g (95%), mp 107-1080C. Both of the above methods pro-

duced products with identical spectral properties.










H NMR (100 MHz, CDC13) 6 2.17(dd, "B" part of AB quartet, J58,4

2.2, J5,5a = 18.3, 1H), 2.50-3.50(m, J73,7a = 7.5, 7,7a ~

9.5, J,4 3.2, 3a,7a 9.4, J3a,4 3.5, 5H), 4.18 (appar-
ent q, 1H), 7.19-7.53(m, 5H).
1C NMR (CDC13) 6 36.10(d), 36.83(t), 40.46(t), 44.38(d), 57.25(q),

75.21(d), 126.54(d), 128.65(d), 129.09(d), 132.02(s), 175.31(s),

177.56(s), 205.91(s).

IR (KBr) 3480(w), 3078(w), 3054(w), 2998(w), 2965(w), 2952(w),

2935(w), 2904(w), 2838(w), 1778(w), 1710(vs), 1598(w), 1494(m),

1458(w), 1409(m), 1389(s), 1347(m), 1328(w), 1308(w), 1263(w),

1240(w), 1230(w), 1203(s), 1181(m), 1098(m), 1082(m), 1041(w),

1021(w), 968(w), 913(w), 897(w), 889(w), 814(m), 779(w), 758(m),

732(m), 693(m), 624(m) cm-1

LRMS (70 eV, m/z, relative intensity) 273(M 72.4), 243 (28.1), 188

(100.0).

Analysis. Calculated for C15H15N04: C, 65.92; H, 5.53; N, 5.12.

Found: C, 65.98; H, 5.54; N, 5.09.

cis-Hexahydro-5-hydroxy-3-methoxy-N-phenylphthalimide (cis-Hexahydro-

6-hydroxy-4-methoxy-2-phenyl-1H-isoindole-1,3(2H)-dione) (15)

Ketone 14 was reduced to alcohol 15 by catalytic hydrogenation.

Thus, 2.5 g (9.15 mmole) ketone 14 was dissolved in 200 ml 95% etha-

nol in a 500 ml capacity hydrogenation bottle. A catalytic amount

(~ 0.01 g) of PtO2 (Englehard Industries) was added to the solution,

and the bottle was placed in the Parr shaker. The hydrogenation

apparatus was flushed with hydrogen several times and finally pres-

surized to 46 PSI with hydrogen. The shaker was started, and the










solution was shaken at room temperature for four hours. At the end

of this time, the apparatus was depressurized, and the catalyst was
removed by filtration. The solvent was removed by rotary evaporation

to yield a pale green oil that crystallized on standing in a dessi-
cator for several days. This procedure yielded 2.5 g (99%) colorless

crystals of alcohol 15, mp 125-1270C.
H NMR (100 MHz, CDC13) 6 1.6-2.4(m, J5,4 = 3.8, J5s,6 : 6.1, J5,5 =

15.1, J7u,6 : 7.2, J7a,7a = 6.0, 4H), 2.76-3.10(m, 2H), 3.2(s,
broad, 1H), 3.33(s, 3H), 3.6-4.2(m, 2H), 7.10-7.54(m, 5H).
1C NMR (CDC13) 6 28.80(t), 32.21(t), 36.48(d), 43.86(d), 57.73(q),

64.97(d), 76.18(d), 126.60(d), 128.52(d), 129.11(d), 132.18(s),

176.33(s), 178.16(s).
IR (KBr) 3507(s), 3043(w), 2979(w), 2960(w), 2915(w), 2892(w),

2856(w), 2808(w), 1772(w), 1704(vs), 1596(w), 1493(m), 1457(w),
1392(s), 1352(w), 1292(m), 1279(m), 1263(m), 1230(w), 1200(m),

1178(s), 1151(m), 1099(m), 1084(m), 1064(m), 973(w), 938(w),
918(w), 901(w), 846(w), 805(m), 761(m), 736(m), 691(w), 618(w),
610(w) cm-1
LRMS (70 eV, m/z, relative intensity) 275(M+, 57.0), 245 (24.9), 227

(11.4), 188 (23.3), 119 (24.5), 103 (91.5), 84 (100.0).

Analysis. Calculated for C15H17N04: C, 65.44; H, 6.22; N, 5.09.
Found: C, 65.42; H, 6.22; N, 5.09.

cis-3,5-Dimethoxyhexahydro-N-phenylphthalimide (cis-4,6-Dimethoxy-
hexahydro-2-phenyl-lH-isoindole-1,3(2H)-dione) (16)

This compound was prepared by methylation of alcohol 15 using
trimethyloxonium tetrafluoroborate.69 Alcohol 15 (1.5 g, 5.45 mmole)











was dissolved in 250 ml freshly distilled (from P205) CH2C12 in a

500 ml Erlenmeyer flask with a ground glass stopper. Excess (~ 3 g)

trimethyloxonium tetrafluoroborate (Alfa) was added under a blanket

of dry nitrogen, i.e., the bottle was opened and the transfer made

under an inverted funnel connected to a nitrogen line. The trimethyl-

oxonium tetrafluoroborate was largely insoluble in CH2CI2. The flask

was tightly stoppered, and the suspension was stirred magnetically

for sixty hours at room temperature. At the end of this time, 100 ml

H20 was added. Then, solid NaHCO3 was added to the stirred solution

in small increments until further additions no longer resulted in the

evolution of CO2 bubbles. The organic layer was separated, and the

aqueous layer was extracted further with CHC13 (2 x 20 ml). The com-

bined organic layers were dried over anhydrous MgSO4 for several

hours. The MgSO4 was separated by filtration and the solvent removed

by rotary evaporation to yield a yellow orange oil. This oil was

purified by percolation through a short (15 cm) silica gel column

using hexane:CH2C12:MeOH (50:20:1). A pale yellow oil remained after

solvent evaporation. This oil solidified on standing in a dessicator

(~ 1 week). Recrystallization of this solid residue from absolute

ethanol gave 1.4 g (89%) colorless crystals, mp 120-1220C.

H NMR (300 MHz, CDC13) 6 1.841-2.072(dddd, J5,4 = 2.8, J5,6 = 5.6,

J5a,4 = 4.7, J5a,6 = 8.6, J5,58 15.3, 2H), 1.914-2.029 (appar-
ent q, center peakssplit, J7,7 = 11.9, J7,7a = 10.7, J7 ,6

11.2, 1H), 2.303-2.383(ddd, J7a,77 = 11.9, J7a,7a = 7.1, J7a,6

4.3, 1H), 2.878-2.923(dd, J3a,4 = 3.8, J3a,7a = 9.6, 1H), 2.949-

3.040(ddd, J7a,3a = 9.6, J7a,7 = 10.7, J7a,7 = 7.1, 1H),
7a,3a 7a,73 7a,7a










3.306(s, 3H), 3.333(s, 3H), 3.430-3.529(dddd, J6,7: = 11.2,

J6,5a = 8.6, J6,5 = 5.6, J6,7, = 4.3, 1H), 3.959-3.996(ddd,

J4,5 = 4.7, J4,3a = 3.8, J4,5 = 2.8, 1H), 7.244-7.484(m, 5H).
3C NMR (CDC13) 5 25.46(t), 31.19(t), 37.16(d), 43.42(d), 55.95(q),

56.71(q), 74.25(d), 75.59(d), 126.60(d), 128.35(d), 128.69(d),

132.32(s), 176.33(s), 178.33(s).
IR (KBr) 3470(w), 3066(w), 2991(w), 2940(m), 2895(m), 2812(m), 1775(w),

1709(vs), 1594(w), 1497(s), 1470(w), 1452(m), 1420(w), 1388(vs),
1362(m), 1320(w), 1292(m), 1252(m), 1192(s), 1180(s), 1160(s),
1100(s), 1078(vs), 1032(w), 987(w), 973(w), 940(w), 903(w),

846(w), 805(w), 792(w), 769(m), 753(w), 738(m), 695(m), 623(w),

610(w) cm-1

LRMS (70 eV, m/z, relative intensity) 289 (M+, 13.2), 259 (26.8),

227 (30.3), 175 (28.5), 173 (50.4), 119 (20.8), 111 (14.3),

110 (15.7), 109 (15.5), 101 (17.0), 93 (23.2), 85 (27.9), 84

(100.0).
HRMS. Required for C16H19N04: 289.13141 Found: 289.13189.

Analysis. Calculated for C16H19N04: C, 66.42; H, 6.62; N, 4.84.

Found: C, 66.32; H, 6.64; N, 4.82.

Epimerization of cis-4,6 Diethoxyhexahydro-2-phenyl-1H-isoindole-
1,3(2H)-dione (11)
Compound 11 (- 200 mg) was dissolved in 0.4 ml DMSO-d6, and the
solution was transferred to an NMR tube. A 13C NMR spectrum was ob-
tained on this sample. Several drops of 2,2,6,6-tetramethylpiperidine
(Aldrich) were then added to the tube, and the tube was placed in a

600C water bath. The epimerization was monitored by periodically










obtaining 1C spectra over a period of several weeks (fifty-four

days). Nine peaks with distinctly different chemical shifts from

the original compound were observed to increase in intensity with

time. The final cis/trans ratio was about three (75% cis). The 13C

chemical shifts and their assignments are given in Table 1. Carbons

not included in Table 1 did not exhibit a readily observable chemi-

cal shift change on epimerization.


TABLE 1
1C Chemical Shifts (6, ppm from TMS) for cis
(DMSO-d6, internal reference DMSO-d6 =


and trans 11.
39.5)


Carbon 6 cis 6 trans 6 cis-6 trans


1 178.65 177.72 0.93

3 176.55 176.23 0.32

7a 36.84 38.40 1.56

4* 73.93 74.74 0.81

5 25.98 27.24 1.26

71.11 1.09
7 32.24 34.63 2.39

3a 43.20 45.62 2.42

1' 132.71 132.44 0.27


* Assignments could be reversed.










5-Methoxy-8-[(phenylamino)carbonyl]-2-oxabicyclo[2.2.2]octan-3-one

(17)

Attempted reduction of ketone 14 to alcohol 15 by using sodium

borohydride (NaBH4) as a reducing agent led to bicyclic lactone 17

instead. Thus, 0.2 g (5.3 mmole) NaBH4 (Eastman) was added to a

stirred solution of 1.0 g (3.7 mmole) ketone 14 in 75 ml of 95% etha-

nol. The solution was stirred for 0.5 hour at room temperature. At

the end of this time, 12 M HC1 was slowly added (dropwise) until the

solution was acidic to litmus. Upon rotary evaporation of the bulk

of the solvent, a crystalline material formed. This material was

broken up and washed several times with water. The residue was

treated with chloroform, but was largely insoluble. Recrystalliza-

tion of the residue from ethanol:water (3:1) yielded colorless crys-

tals that had a sharp melting point (201-202C). On the basis of

the spectral information given below, the compound was assigned the

bicyclic lactone structure 17.
H NMR (100 MHz, DMSO-d6) 6 1.66-2.28(m, 4H), 2.91(ddd, 1H), 3.11(dd,

1H), 3.29(s, 3H), 3.80-3.95(m, 1H), 4.74(m, 1H), 6.95-7.63(m,

5H), 10.08(s, 1H).
13C NR (DMSO-d6) 6 27.78(t), 33.26(t), 38.28(d), 43.23(d), 55.54(q),

73.01(d), 75.91(d), 119.19(d), 123.31(d), 128.59(d), 138.93(s),

170.58(s), 170.65(s).

IR (KBr) 3302(m), 3282(m), 3138(w), 3067(w), 2978(w), 2967(w), 2942(w),

2877(w), 2840(w), 1736(vs), 1689(vs), 1601(s), 1540(s), 1493(m),

1443(s), 1381(m), 1362(m), 1334(m), 1320(m), 1302(m), 1279(w),

1247(m), 1212(m), 1190(m), 1150(m), 1108(s), 1088(m), 1052(m),











1018(m), 963(m), 930(w), 917(w), 788(w), 762(s), 701(m), 655(w),

609(w) cm-1

LRMS (70 eV, m/z, relative intensity) 275 (M+, 50.2), 245 (7.6), 188

(9.2), 174 (4.9), 119 (13.0), 103 (36.8), 93 (100.0).

Analysis. Calculated for C15H17NO4: C, 65.44; H, 6.22; N, 5.09.

Found: C, 65.53; H, 6.38; N, 5.05.

Maleimide Synthesis: General

Many of the maleimides used in this study [N-(4-fluorophenyl),

N-(4-chlorophenyl), N-(4-bromophenyl), N-(4-nitrophenyl), N-(4-carbo-

ethoxyphenyl), N-(4-methylphenyl), N-(4-acetoxyphenyl), N-(4-methoxy-

phenyl)] had been previously synthesized in these laboratories.70

They were purified by recrystallization from cyclohexane and charac-

terized by various spectral techniques. Only the spectral data for

these maleimides are given here. The N-acetoxymaleimide used was

synthesized in these laboratories by David P. Vanderbilt,1 and was

used without further purification. N-phenylmaleimide was obtained

from Aldrich Chemical Company, and was recrystallized from cyclohex-

ane before use.

In general, the synthetic procedure first developed by Searle72

and detailed by Barrales-Rienda et al.73 was used. The procedure

involves the reaction of the appropriately substituted aniline with

maleic anhydride to form an intermediate maleanilic acid. The male-

anilic acid is then dehydrated to the maleimide using acetic anhy-

dride:sodium acetate.










N-Phenyl[15N]maleanilic acid([15N}4-Oxo-4-[phenylamino]-[Z]-2-

butenoic acid) (18)

The contents of a 1.0 g ampule of 97.5% 15N-enriched aniline
(Merck and Co., Inc.) were mixed with 4.0 g freshly distilled regu-

lar aniline (5.0 g total, 53.7 mmole). The mixture was dissolved in

10 ml of chloroform, and the resulting solution was added dropwise

to a rapidly stirred solution of 6.0 g maleic anhydride (61.8 mmole)

in chloroform. A cream colored precipitate formed immediately on

addition of the aniline solution. The mixture was stirred for one

hour and allowed to stand at room temperature overnight. The mixture

was suction filtered and washed with chloroform several times.. After

drying in a 50C vacuum oven for several hours, the yield of cream

colored powder was 10.3 g (100.3%), mp 203-204C literaturee4 mp

206C). The approximate percentage of 15N in this compound could be

determined by integration of the N-H resonance of the 1H NMR spec-

trum. The 15N-H resonance appears as a doublet, whereas the 14N-H

resonance is a singlet appearing at the midpoint of the 15N-H doub-
let (approximately 20% 15N).
H NMR (DMSO-d6) 6 6.41 (AB quartet, J = 12.1, 2H), 6.87-7.70(m, 5H),

10.44[d, J(15NH) = 90.3, s, 1H (d+s)], CO2H not observed.
1C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562) 6 119.72(d),

124.10(d), 128.93(d), 130.59(d), 131.86[d, 2 ( 15N-CO-C) = 9.7],

138.58(s, 1 15N-C(quat. aromatic)] = 13.4), 163.39[s, 1J(15N-CO)

= 15.9], 166.95(s).

IR (KBr) 3254(m), 3193(m), 3060(m,b), 2863(w), 2240(m), 2075(w),
1876(m), 1697(s), 1620(s), 1635(vs,b), 1489(s), 1449(s), 1429(m),










1330(m), 1267(m), 1223(w), 1189(w), 998(m), 970(m), 900(m),

849(s), 800(m), 754(s), 686(m), 652(m), 605(s) cm-1

N-Phenyl[15N]maleimide([15N]-1-Phenyl-1H-pyrrole-2,5-dione) (19)

Finely divided 15N-enriched N-phenyl maleanilic acid (10.3 g,

53.9 mmole) was combined with 3.1 g freshly fused sodium acetate in

a 250 ml, three-necked, flame dried, N2 flushed round-bottom flask

equipped with a mechanical stirrer and a reflux condenser. Acetic

anhydride (32.0 g) was added, and the mixture was stirred while the

flask was heated to 80C in an oil bath. The bright yellow solution

was stirred at 800C for one hour. The flask was then allowed to cool

to room temperature while stirring was continued for two additional

hours. The reaction mixture was then added dropwise to rapidly

stirred ice water in which a small amount of salt (NaC1) had been

dissolved. The crude yellow precipitate that formed was suction

filtered, washed with water, and dried in a 50C vacuum oven over-

night. Vacuum sublimation (aspirator pressure) of the crude crystals

gave 6.4 g (68.8%) bright yellow needles, mp 87-89C literaturee5

mp 89-900C). An approximate percent enrichment was calculated by

obtaining a high resolution mass spectrum of the enriched maleimide

and comparing the observed intensity of the M+1 peak with the theo-

retical intensity [calculated from the known76 natural abundances of
13C (1.08%), 2H (0.016%), and 170 (0.04%)]. Thus, for C10H702, (1.08

x 10) + (0.016 x 7) + (0.04 x 2) = 11% of the intensity of the M+1

peak is not due to ions containing 15N. The following equation was

used for the calculation:









15 (M+1)Total 0.11 (M)
S (M) + 0.11 (M)


where the quantities in parentheses are the observed absolute inten-

sities of the corresponding ions. The calculated approximate % 15N
was 18.8.
1H NMR (100 MHz, CDC13) 5 6.75(s, 2H), 7.22-7.52(m, 5H).
13C NMR (CDCI3) 6 126.08(d), 127.89(d), 129.11(d), 133.93(s, 1J 15N-C

(quat. aromatic)] = 14.2), 134.08[d, 2( 15N-CO-13CH) = 7.7],
169.51[s, 1J(15N-13CO) = 14.6].
IR (KBr) 3090(w), 1775(w), 1704(vs), 1592(m), 1504(m), 1383(s),
1141(m), 1071(w), 1029(w), 941(w), 904(w), 829(s), 753(m),

692(s), 622(m) cm-1
LRMS (70 eV, m/z, relative intensity) 174 (M+1, 35.2), 173 (M,

100.0), 145 (8.3), 129 (26.3), 117 (15.1).

HRMS. Required for C10H702N: 173.0477. Found: 173.0484. Molecu-

lar ion absolute intensity (M) = 908, (M+1) = 289.

15N NMR (10.11 MHz, 1H decoupled, CDC13) 217.8(s, upfield from ex-

ternal CH3N02).

N-Cyclohexylmaleanilic acid [4-(Cyclohexylamino)-4-oxo-(Z)-2-butenoic
acid] [21477-59-8] (20)
Slow, dropwise addition of 31.0 g cyclohexylamine (313 mmole)
to a stirred solution of 31.0 g maleic anhydride (316 mmole) in 300
ml chloroform resulted in an exothermic reaction. The amine was
added slowly enough to avoid boiling of the chloroform. The solution
was allowed to stand at room temperature overnight. A white crystal-
line mass filled the flask the next morning. This mass was broken










up, filtered, and washed with cold chloroform and hexane. Evapora-

tion of the washings produced more hexane insoluble product which was

similarly filtered and washed. Removal of the residual solvent from

the combined precipitates in a 500C vacuum oven yielded 63.1 g (102%)

pure white product, mp 153-1540C literaturee7 mp 182C).
H NMR (60 MHz, DMSO-d6) 6 0.9-2.1(broad m, 10H), 3.4-4.0(m, 1H),

6.35 (AB q, J = 12.1, 2H), 9.10(broad d, 1H), CO2H not observed.

IR (KBr) 3240(m), 3075(m), 2940(s), 2861(m), 1920(w, b), 1702(vs),

1635(s), 1578(s), 1521(vs, b), 1480(vs, b), 1406(s), 1350(m),

1320(m), 1296(m), 1256(m), 1245(m), 1150(m), 1083(s), 983(m),

925(w), 910(w), 888(w), 877(w), 855(s), 790(w), 755(w), 635(m),

604(m) cm-1

N-Cyclohexylmaleimide (l-Cyclohexyl-1H-pyrrole-2,5-dione), [1631-25-0],

(21)

This compound was synthesized by thermal dehydration of the

corresponding maleamic acid.78 Thus, 15.0 g N-cyclohexylmaleamic

acid (76 mmole) and 50 ml xylene (mixed isomers) were added to a 250

ml, three-necked, round-bottom flask equipped with a nitrogen inlet,

mechanical stirrer, and reflux condenser. The suspension was stirred

as the flask and contents were heated to reflux in an oil bath. The

reflux was maintained for five hours. The flask was allowed to cool,

and most of the xylene was evaporated in vacuo. The residue was

treated with acetone, and the acetone insoluble portion (unreacted

starting material) was separated by filtration (~ 7.5 g). The acetone

was evaporated from the filtrate, and the residue was sublimed to

yield 1.5 g (22%, based on recovered starting material) colorless

needles, mp 86-87C literaturee9 mp 890C).










H NMR (100 MHz, CDCI3) 6 1.2-2.1(m, 10H), 3.75-4.03(tt, J = 3.9,

11.8, 1H), 6.66(s, 2H).

C NMR (CDC13) 6 25.10, 25.98, 29.95, 50.74, 133.91, 170.85.

IR (KBr) 3445(w), 3089(m), 2931(s), 2860(m), 1773(w), 1700(vs),

1598(w), 1579(w), 1465(w), 1457(w), 1396(w), 1403(s), 1382(m),

1371(m), 1348(m), 1265(w), 1178(m), 1140(m), 1113(m), 1018(w),

986(m), 892(w), 826(s), 748(w), 692(s), 638(m) cm-1

LRMS (70 eV, m/z, relative intensity) 179 (M 35.5), 136 (40.2),

123 (8.5), 99 (100.0).

N-Phenylcitraconamic acid [2(or 3)-Methyl-4-oxo-4-(phenylamino)-(Z)-

2-butenoic acid], [39734-91-3], (22)

Slowly adding 15.0 g aniline (161 mmole) to a stirred solution

of 17.5 g citraconic anhydride (Aldrich, 156 mmole) in CHC13 resulted

in an exothermic reaction and the immediate formation of a cream

colored precipitate. After stirring for one hour, the suspension was

filtered, washed with CHC13 and suspended in boiling CHC13 for an

additional thirty minutes. The suspension was cooled and filtered.

The precipitate was placed in a 500C vacuum oven overnight. The iso-

lated yield was 32.0 g (100%) of an off white powder, mp 175-176C

literaturee4 mp 171C). The product proved to be a mixture of the

two possible isomers (methyl substitution at the 2 or 3 position);

however, no attempt was made to separate them.
H NMR (60 MHz, DMSO-d6) 6 2.02(d, J = 1.2, 3H), 6.19(q, 3 peaks re-

solved, J = 1.2, 1H), 6.85-7.85(m, 5H), 10.13(broad s, 1H),

COOH not observed.










13C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562) 6 20.83, 21.66,

119.62, 119.82, 123.67, 123.82, 128.88, 128.98, 139.12, 139.36,

142.97, 150.38, 163.10, 165.97, 168.11, 170.36.

IR (KBr) 3284(m), 3210(m), 3120(m), 2340(w), 2200(w), 1701(s),

1630(s), 1571(s), 1530(vs), 1497(vs), 1490(vs), 1442(s), 1395(m),

1378(m), 1330(s), 1253(w), 1138(w), 1041(w), 1028(w), 972(m),
-1
896(m), 860(w), 788(w), 755(m), 688(m), 637(w) cm-1

Analysis. Calculated for C11H11N03: C, 64.38; H, 5.40; N, 6.82.

Found: C, 64.17; H, 5.49; N. 6.77.

N-Phenylcitraconimide (3-Methyl-l-phenyl-lH-pyrrole-2,5-dione),

[3120-04-5], (23)

Heating 10.0 g N-phenylcitraconamic acid (48.7 mmole) and 1.8 g

fused sodium acetate in 15 ml acetic anhydride at 900C for thirty

minutes produced a deep yellow solution. The solution was allowed

to cool to room temperature, and stirring was continued for two hours.

Precipitation of the reaction mixture into a rapidly stirred ice:

salt:water mix, followed by recrystallization of the precipitate from

cyclohexane, gave 3.5 g (38.4%) pale yellow needles, mp 92-940C (lit-

erature80 mp 94-960C).
H NMR (60 MHz, acetone-d6) 6 2.08(d, J = 1.8, 3H), 6.53(q, J = 1.8,

1H), 7.2-7.5(m, 5H).
C NMR (acetone-d6) 6 10.92, 126.91, 127.98, 128.08, 129.45, 133.10,

146.50, 170.09, 171.17.

IR (KBr) 3460(w), 3082(w), 2984(w), 2924(w), 1704(vs), 1640(m),

1596(w), 1502(m), 1400(s), 1290(w), 1205(w), 1188(m), 1140(w),

1114(m), 1073(w), 1038(w), 1012(w), 1000(w), 992(w), 888(m),

873(m), 762(m), 753(m), 708(m), 690(m), 651(w), 618(w) cm-1










LRMS (70 eV, m/z, relative intensity) 187(M 100.0), 143 (23.2), 130

(10.9), 119 (15.3), 117 (14.3), 91 (23.8).

Analysis. Calculated for C11H9N02: C, 70.06; H, 4.85; N, 7.48.

Found: C, 70.21; H, 5.40; N, 7.44.

N-(4-Trifluoromethylphenyl)maleamic acid (4-0xo-4-[(4-trifluoromethyl-

phenyl)amino]-(Z)-2-butenoic acid) (24)

A solution of 4.9 g p-aminobenzyltrifluoride (30.4 mmole, PCR)

dissolved in 10 ml CHC13 was added dropwise to a stirred solution of

3.6 g maleic anhydride in 125 ml CHC13. The solution started to be-

come turbid about five minutes after the addition was complete. The

solution-suspension was stirred for seventeen hours at room tempera-

ture and for seven hours at ~ 500C. After cooling, the bright yellow

precipitate was filtered and washed with chloroform. The powder was

added to 100 ml CHC13, and the mixture was boiled for about an hour.

The suspension was cooled, filtered and washed with CHC13. This pro-

cedure was repeated two more times. The pale, lemon yellow powder

was placed in a 500C vacuum oven overnight. This procedure yielded

7.5 g (95.2%) pale yellow product, mp 183-1840C literaturee1 mp 183-

1860C).
H NMR (100 MHz, DMSO-d6) 6 6.64(AB q, J = 12.0, 2H), 7.20-8.27(m,

4H), 10.50 and 10.66 (2 unequal s, 1H).

IR (KBr) 3275(w), 3205(w), 3117(m), 3069(m), 3020(w), 2260(w, b),

1890(w, b), 1715(s), 1630(m), 1590(s), 1548(vs), 1487(m),

1427(m), 1408(m), 1322(vs), 1222(m), 1169(m), 1130(s), 1070(m),

1018(w), 975(w), 900(w), 858(m), 842(m), 755(w, b), 669(w),

610(w) cm-1










N-(4-Trifluoromethylphenyl)maleimide [1-(4-Trifluoromethylphenyl)-1H-

pyrrole-2,5-dione], [54647-09-5], (25)

To a 100 ml, three-necked round-bottom flask equipped with a

mechanical stirrer and nitrogen inlet was added 3.0 g N-(4-trifluoro-

methylphenyl)maleamic acid (11.6 mmole), 0.75 g freshly fused sodium

acetate, and 10 ml acetic anhydride. The mixture was slowly heated

with an oil bath. At 60C, the slurry dissolved to form a bright

yellow solution. At 65C, the solution turned red. The flask was

immediately cooled to room temperature and allowed to stand for six

hours. The reaction mix was then precipitated into 300 ml rapidly

stirred ice water. The precipitate was then filtered, dried in vacuo

and recrystallized twice from cyclohexane. Activated charcoal was

added during the first recrystallization. This preparation yielded

2.4 g (86.0%) colorless needles, mp 153-155C literaturee1 mp 150-

1520C).
H NMR (100 MHz, CDC13) 6 6.87(s, 2H), 7.63(AB q, broad lines, 4H).

3C NMR (acetone-d6, letters denote actual multiplicities, J's are
13C-19F coupling constants in Hertz) 6 125.03(q, J = 271.0),

126.90(q, J = 3.7), 127.52(s), 129.40(q, J = 33.0), 135.74(s),

136.49(s), 170.02(s). Off resonance decoupling caused all peaks

to split into doublets, relative to the completely decoupled

spectrum, except for those at 125.03, 129.40, 136.49 and 170.02,

which remained singlets. Selective irradiation of the ethyl-

eneic protons resulted in a much greater intensity for the 13C

peak at 135.74, relative to the other carbon resonances.










C NMR (CDC13)6123.82(q, J = 272.2), 125.79(s), 126.26(q, J = 3.7),

129.64(q, J = 33.0), 134.42(s), 134.59(s), 168.92(s).
1F NMR (CDCI3, internal CFC13) 6 -63.2(m).

IR (KBr) 3480(w), 3112(w), 3079(w), 2963(w), 1780(vs), 1705(s),

1612(w), 1521(w), 1412(m), 1372(w), 1330(s), 1260(w), 1160(s),

1127(s), 1108(s), 1069(s), 1058(m), 1020(w), 952(w), 839(m),

821(m), 815(m), 737(w), 710(w), 690(m) cm-1

LRMS (70 eV, m/z, relative intensity) 242(M+1, 12.3), 241(M+, 100.0),

197 (25.6), 185 (10.3), 172 (18.2), 171 (15.4), 54 (73.4).

N-(4-Cyanophenyl)maleamic acid (4-[(4-Cyanophenyl)amino]-4-oxo-(Z)-

2-butenoic acid), [31460-28-3], (26)

Finely ground maleic anhydride (5.0 g, 51.0 mmole) was dissolved

in 75 ml CHC13, and a solution of 5.0 g 4-aminobenzonitrile (Aldrich)
in 100 ml CHC13 was added dropwise. The immediate formation of a

cream colored precipitate was noted. The suspension was stirred at

room temperature overnight, filtered, washed with CHC13, and placed

in a 700C vacuum oven for four hours. The powder thus obtained was

purified by stirring in boiling CHCl3 for one hour, followed by fil-

tering and removal of the residual solvent in a vacuum oven. This

procedure yielded 8.55 g (93.4%) cream colored, finely divided pow-

der, mp 193-1940C.
H NMR (100 MHz, DMSO-d6, internal reference DMSO-d6 = 2.4962) 6

6.40(AB q, J = 12.0, 2H), 7.76(broad s, 4H), 10.65(s, 1H), COOH
not observed.

13C NMR (DMSO-d6, internal reference DMSO-d6 = 39.562) 6 105.47,

118.65, 119.48, 129.76, 131.93, 132.93, 142.65, 163.78, 166.29.










IR (KBr) 3297(m), 3210(m), 3112(w), 3054(w), 2235(m), 1712(s),

1618(s), 1595(vs), 1540(vs), 1490(s), 1411(w), 1407(m), 1326(s),

1262(m), 1230(w), 1210(w), 1177(w), 972(m), 899(w), 858(m),

838(m), 758(w), 617(m) cm-1

N-(4-Cyanophenyl)maleimide [l-(4-Cyanophenyl)-lH-pyrrole-2,5-dione],

[31489-18-6], (27)

A suspension of 7.0 g (4-cyanophenyl)maleamic acid (32.4 mmole)

and 1.7 g freshly fused sodium acetate in 25 ml acetic anhydride was

slowly heated in an oil bath. The maleanilic acid dissolved when the
temperature reached 650C. Stirring (mechanical) of the solution was

continued while the temperature gradually increased to 900C. This

temperature was maintained for thirty minutes, and then the reaction

mix was allowed to cool to room temperature. On cooling, the mixture

crystallized to a cream colored mass. Water (~ 75 ml) was added to

this mass of crystals, which were then separated by filtration and

washed with copious amounts of water. After drying in a 60C vacuum

oven overnight, the powdery product was recrystallized from heptane

to yield 5.2 g (81.2%) pale yellow needles, mp 131-134C.
IH NMR (100 MHz, CDC13) 6 6.92(s, 2H), 7.66(AA'BB', 4H).

13C NR (CDC13) 6 110.98(s), 118.16(s), 125.69(d), 132.93(d),

134.54(d), 135.54(s), 168.59(s). Selective decoupling of the

ethyleneic protons resulted in a dramatically greater intensity

for the peak at 134.54, relative to the other protonated carbons.
IR (KBr) 3470(w), 3170(w), 3100(m), 3095(m), 2219(m), 1770(w),

1727(vs), 1605(m), 1587(w), 1515(m), 1415(m), 1392(s), 1376(s),

1320(w), 1280(w), 1216(w), 1146(m), 1079(m), 1031(m), 951(w), 841
(s), 829(m), 818(w), 762(w), 720(m), 687(m), 656(w), 622(w) cm-1
(s), 829(m), 813(w), 762(w), 720(m), 687(m), 656(w), 622(w) cm-










LRMS (70 eV, m/z, relative intensity) 199(M+1, 12.8), 198(M 100.0),

154 (34.0), 142 (12.1), 128 (15.0), 54 (38.4).
N-(4-Fluorophenyl)maleimide [l-(4-Fluorophenyl)-1H-pyrrole-2,5-dione],

[6633-22-3], (28)
Recrystallization from cyclohexane yielded long, pale green

needles, mp 155-156C literaturee3 mp 155C).
H NMR (100 MHz, CDC13) 6 6.83(s, 2H), 7.05-7.40(m, 4H).

13C NMR (CDC13, letters denote actual multiplicities, J's are 13C-19F

coupling constants in Hertz) 6 116.13(d, J = 22.6), 127.22(d,

J = 3.1), 127.91(d, J = 8.54), 134.22(s), 161.81(d, J = 247.8),

169.36(s). Selective irradiation of the ethyleneic protons re-
sulted in enhancement of the intensity of the resonance at

134.22, relative to the other protonated carbons.
19F NMR (CDC13, internal CFC13) 6 -113.7(m).

IR (KBr) 3460(w), 3165(w), 3101(m), 3071(w), 1900(w), 1710(vs),

1599(w), 1586(w), 1517(s), 1410(s), 1392(s), 1374(m), 1312(m),
1300(w), 1290(w), 1261(w), 1234(s), 1150(s), 1089(w), 1072(m),

1046(w), 1022(w), 950(w), 935(w), 836(s), 819(m), 765(w), 710(m),

685(s) cm-'
LRMS (70 eV, m/z, relative intensity) 192(M+1, 11.4), 191(M 100.0),

147 (13.3), 121 (20.0), 109 (10.7), 82 (10.3), 54 (40.8).
N-(4-Chlorophenyl)maleimide [1-(4-Chlorophenyl)-1H-pyrrole-2,5-dione],

[1631-29-4], (29)
Recrystallization from cyclohexane gave light yellow needles,

mp 113-115"C literaturee5 mp 114C).









H NMR (100 MHz, CDC13) 6 6.78(s, 2H), 7.34(AA'BB', 4H).
C NMR (CDC13) 6 127.08(d), 129.18(d), 129.88(s), 133.39(s),
134.17(d), 169.05(s). Irradiation of the ethyleneic protons
resulted in enhancement of the intensity of the peak at 134.17,
relative to the other carbon resonances.
IR (KBr) 3465(w), 3163(w), 3118(w), 3083(m), 1776(w), 1714(vs),
1585(w), 1497(s), 1453(w), 1402(s), 1388(s), 1372(m), 1310(m),
1278(w), 1211(w), 1149(m), 1097(m), 1071(m), 1031(m), 1019(m),
949(m), 836(s), 765(w), 743(m), 707(m), 685(m), 646(w) cm-1
LRMS (70 eV, m/z, relative intensity) 209 (31.9), 208 (11.6), 207
(M+, 100.0), 163 (15.2), 153 (10.1), 137 (19.4), 90 (11.9),
54 (44.6).
N-(4-Bromophenyl)maleimide [1-(4-Bromophenyl)-lH-pyrrole-2,5-dione],

[13380-67-1], (30)
Recrystallization of this compound from cyclohexane yielded
bright yellow needles, mp 123-124C literaturee2 mp 118-120C).
1H NMR (100 MHz, CDCI3) 6 6.81(s, 2H), 7.40(AA'BB', 4H).
1C NMR (CDC13) 6 121.43(s), 127.33(d), 130.32(s), 132.18(d),

134.20(d), 168.97(s). Selective irradiation of the ethyleneic
protons resulted in enhancement of the 13C resonance at 134.20,
relative to the other carbon resonances.
IR (KBr) 3461(w), 3160(w), 3111(w), 3089(m), 1717(vs), 1589(w),
1570(w), 1490(s), 1441(w), 1398(s), 1385(s), 1367(m), 1306(w),
1275(w), 1208(w), 1147(s), 1065(m), 1029(w), 1011(m), 945(m),
828(s), 811(m), 761(w), 729(w), 705(m), 681(m), 638(w) cm-1










LRMS (70 eV, m/z, relative intensity) 254 (11.0), 253 (98.6), 252

(11.7), 251 (M+, 100.0), 209 (10.3), 207 (10.2), 197 (11.2),
183 (12.6), 181 (11.8), 116 (19.9), 90 (19.3), 86 (15.3), 82
(14.3), 63 (17.6), 54 (59.2).
N-(4-Nitrophenyl)maleimide [l-(4-Nitrophenyl)-1H-pyrrole-2,5-dione],
[4338-06-1], (31)
Recrystallization of this compound from ethanol:cyclohexane (1:3)
gave colorless crystals, mp 167.5-169.50C literaturee5 mp 163-165C).
H NMR (100 MHz, CDC13) 6 6.94(s, 2H), 8.01(AA'BB', 4H).
1C NMR (CDC13) 6 124.48(d), 125.45(d), 134.61(d), 137.10(s),

146.21(s), 168.49(s).
IR (KBr) 3468(w), 3118(w), 3095(w), 1724(vs), 1682(m), 1612(m),
1594(m), 1518(s), 1500(s), 1447(w), 1398(m), 1388(m), 1373(m),
1347(s), 1300(m), 1268(w), 1217(w), 1144(m), 1107(w), 1062(m),
1030(w), 949(w), 851(m), 823(m), 761(w), 747(w), 719(w), 694(m),
639(w) cm-1
N-(4-Carboethoxyphenyl)maleimide [4-(2,5-Dihydro-2,5-dioxo-1H-pyrrol-
l-yl)benzoic acid, ethyl ester], [14794-06-0], (31)
This compound was kindly provided by David P. Vanderbilt. Re-
crystallization from cyclohexane yielded pale yellow needles, mp 112-
113C literaturee3 mp 113C).
H NMR (100 MHz, CDC13) 6 1.39(t, J = 7.1, 3H), 4.39(q, J = 7.1, 2H),

6.86(s, 2H), 7.81(AA'BB', 4H).
13C NR (CDC13) 6 14.30(q), 61.16(t), 125.18(d), 129.47(s), 130.35(d),

134.37(d), 135.37(s), 165.71(s), 168.95(s).










Selective irradiation of the ethyleneic protons resulted in en-
hanced intensity for the 13C peak at 134.37, relative to the
other carbon resonances.

IR (KBr) 3120(w), 3091(w), 3001(w), 1718(vs), 1710(vs), 1607(m),

1509(m), 1476(w), 1417(m), 1398(m), 1386(m), 1369(m), 1310(m),

1286(s), 1217(w), 1177(m), 1146(m), 1130(m), 1110(m), 1070(w),
1025(m), 1013(w), 950(w), 857(m), 832(m), 827(m), 767(m), 701(m),

687(m), 641(w), 625(w) cm-
N-(4-Methylphenyl)maleimide [l-(4-Methylphenyl)-1H-pyrrole-2,5-dione],

[1631-28-3], (32)

Recrystallization from cyclohexane yielded yellow needles, mp
151.5-152C literaturee4 mp 148.5-150C).
1H NMR (100 MHz, CDCI3) 6 2.37(s, 3H), 6.79(s, 2H), 7.18-7.25(m, 4H).

13C NMR (CDCI3) 6 21.10(q), 126.01(d), 128.57(s), 129.74(d), 134.13(d),

137.98(s), 169.63(s).

Selective irradiation of the ethyleneic protons resulted in en-

hancement of the 1C signal at 134.13, relative to the other
carbon resonances.

IR (KBr) 3461(w), 3170(w), 3095(m), 2928(w), 1710(vs), 1588(w),

1528(m), 1410(s), 1390(s), 1324(m), 1318(w), 1290(w), 1212(w),
1182(w), 1154(s), 1079(w), 1038(w), 952(w), 833(s), 822(m),
810(m), 710(m), 686(s), 674(m) cm-1
LRMS (70 eV, m/z, relative intensity) 188 (12.9), 187 (M+, 100.0),

143 (12.5), 130 (17.7), 117 (18.7), 54 (15.1).










N-(4-Acetyloxyphenyl)maleimide [1-(4-Acetyloxyphenyl)-1H-pyrrole-2,5-

dione], [6637-46-3], (33)

Recrystallization from cyclohexane yielded pale yellow needles,
mp 160-161C literaturee5 mp 156C).
1H NMR (100 MHz, CDC13) 6 2.28(s, 3H), 6.80(s, 2H), 7.27(AA'BB', 4H).

13C NMR (CDC13) 6 21.03(q), 122.23(d), 126.91(d), 128.76(s), 134.17(d),

149.79(s), 169.00(s), 169.29(s).
Selective irradiation of the ethyleneic protons resulted in en-

hanced intensity for the 1C peak at 134.17, relative to the

other carbon resonances.

IR (KBr) 3095(w), 1754(s), 1709(vs), 1589(w), 1508(s), 1473(w),

1412(m), 1400(m), 1387(w), 1368(m), 1216(s), 1197(s), 1163(m),

1153(m), 1099(w), 1016(w), 957(w), 915(w), 853(w), 840(m),
732(w), 702(w), 690(m), 651(w) cm-1

LRMS (70 eV, m/z, relative intensity) 231 (M 2.4), 190 (11.5),

189(100.0), 119 (10.0), 54 (12.6).
N-(4-Methoxyphenyl)maleimide [1-(4-Methoxyphenyl)-1H-pyrrole-2,5-

dione], [1081-17-0], (34)

Recrystallization from cyclohexane yielded very bright yellow
needles, mp 148-151C literaturee5 mp 1460C).
1H NMR (100 MHz, COCI3) 6 3.80(s, 3H), 6.79(s, 2H), 7.09(AA'BB', 4H).
13C NMR (CDC13) 6 55.44(q), 114.44(d), 123.84(s), 127.57(d), 134.08(d),

159.13(s), 169.78(s).

Selective irradiation of the ethylenic protons resulted in en-
hancement of the intensity of the 13C peak at 134.08, relative


to the other carbons.










IR (KBr) 3460(w), 3109(w), 3080(w), 3011(w), 2970(w), 2939(w),

2919(w), 2838(w), 1770(w), 1706(vs), 1607(w), 1586(w), 1507(s),

1477(w), 1449(w), 1439(m), 1415(m), 1398(s), 1305(m), 1248(s),

1180(m), 1169(m), 1156(s), 1148(s), 1106(m), 1053(w), 1027(m),

950(w), 938(w), 836(m), 826(m), 816(m), 810(m), 797(w), 720(m),

685(m), 602(w) cm-1

LRMS (70 eV, m/z, relative intensity) 204 (12.3), 203 (M 100.0),

188 (35.4), 160 (19.8), 134 (9.3), 133 (9.3), 106 (8.6), 54

(11.9).

Copolymer Synthesis and Characterization

Copolymer Synthesis

All copolymers were synthesized in roughly the same manner. Azo-

bisisobutyronitrile (AIBN, Aldrich) was used as the initiator in all

cases, except where noted otherwise. The initiator was purified by

recrystallization from methanol.

Purification of 2-chloroethyl vinyl ether (Aldrich), ethyl vinyl

ether (Aldrich), and n-butyl vinyl ether (Aldrich) was carried out by

stirring over calcium hydride for at least twenty-four hours, fol-

lowed by distillation. Methyl vinyl ether (Matheson) was condensed

from a gas cylinder into a 250 ml round-bottomed flask cooled with

an ice:water:salt mixture. The round-bottomed flask was then con-

nected to a dry polymerization tube and allowed to warm to room temp-

erature while the polymerization tube was cooled in a dry ice:iso-

propanol bath.

Maleimides were recrystallized from cyclohexane before use.

Maleic anhydride was sublimed before use. Dichloromethane was










distilled from phosphorous pentoxide. Benzene was stirred over 18 M

H2SO4 for twenty-four hours, decanted, and distilled.

Typically, solutions of the desired concentrations were made by

weighing appropriate amounts of the initiator, maleimide and vinyl

ether into a volumetric flask and diluting to the mark with solvent.

The desired volume of this solution was then introduced into a clean

polymerization tube with a pipette. The tube was connected to a high

vacuum line and degassed by at least five freeze-pump-thaw cycles,

then sealed off at < 10-5 mm Hg. Tubes thus prepared were placed in

a bath (water, oil, or isopropanol:dry ice) of the appropriate temp-

erature for the desired amount of time. At the end of this time, the

tube was removed from the bath, cooled to -78C in a dry ice:isopro-

panol bath, and opened. The solution was then added slowly (drop-

wise) to a large excess of rapidly stirred precipitation solvent

(methanol was used unless otherwise noted). In some cases it was

necessary to redissolve the copolymer in acetone and precipitate it

again in order to obtain a pure white product.

It was noted that monomer solutions containing initiator de-

colorized on standing in bright light. Precipitation of these solu-

tions, as described above, yielded pure white copolymers. Thus,

polymerizations described from now on as being carried out at "room

temperature" took place in the presence of oxygen without careful

temperature control.

In the copolymerization carried out at -780C, a Hanovia Utility

Quartz Ultraviolet Lamp was used as a light source. The degassed

monomer solution was placed in a dry ice:isopropanol bath,











and the light was shone through a recrystallizing dish containing

about three inches of water, which was placed on top of the dewar

containing the cold bath and tube. The water served as insulation,

so that rapid heating of the bath by the hot lamp was avoided. Inde-

pendent experiments showed that no copolymerization took place in the

absence of initiator under these conditions. A UV scan showed that

AIBN has an absorption maximum near 345 nm which is well above the

pyrex glass cutoff of about 280 nm.5

All 4-substituted phenyl maleimides copolymerized with 2-chloro-

ethyl vinyl ether, except for N-(4-nitrophenyl) maleimide, which

yielded no copolymer after being heated in the presence of initiator

and CEVE for forty-two hours in a 60.0C bath. The unreacted male-

imide could be recovered unchanged (as judged by IR spectroscopy).

A Sargent Thermonitor (Model S-W) constant temperature bath was

used to control the temperature of the water bath used to 60.00.10C.

The homopolymer of N-phenylmaleimide was prepared in exactly the

same way as the copolymers (i.e., AIBN, CH2Cl2, 60.0C).

The copolymerization conditions, yields and analysis data for

all copolymerizations, except for those performed in kinetic studies,

are given in Tables 2 5.

2-Chloroethyl Vinyl Ether Homopolymer

The 2-chloroethyl vinyl ether (CEVE) homopolymer was synthesized

by storing distilled CEVE over unactivated molecular sieves (Linde).

The viscosity of the CEVE increased with the length of time that it

was stored over the sieves. Indeed, after several months the vinyl

ether had become a brown, solid mass. This mass was dissolved in









TABLE 2
Conditions for N-Phenvlmaleimide-2-Chloroethvl Vinyl Ether Cooolvmerizations


Sample
No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14q

15e

16

17

18

19

20P

21

22

23

24


Ma Xb
T M


Copolym.
Temp. (OC)

-78 to -68

60.00.1

60.00.1

60.00.1

60.00.1

60.00.1

60.00.1

25 35

60.00.1

60.00.1

25 35

60.00.1

60.00.1

60.00.1

60.00.1

60.00.1

100.01.0

60.00.1

25 35

60.00.1

60.00.1

60.00.1

60.00.1

60.00.1


I


0.501

0.501

0.501

0.501

0.501

0.501

0.500

0.500

0.500

0.500

0.507

0.500

0.500

1.774

1.56 x 10-3

2.018

0.549

0.501

0.500

0.500

0.500

0.500

0.501

0.501


Footnotes for this table appear at the end of Table 5.


0.699 i.in rn.77~1


^ .


0.100

0.100

0.100

0.100

0.200

0.200

0.260

0.260

0.300

0.350

0.395

0.400

0.400

0.399

0.400

0.400

0.454

0.499

0.496

0.499

0.600

0.600

0.699


[AIBN]

1.11

1.11

1.11

1.11

1.10

1.10

1.10

1.09

1.10

1.10

1.28

1.08

1.08

21.7

(

100.0

6.09

1.09
c

1.10 (

1.09 (

1.09 (

1.10 (


x 103c

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.22%)

(0.25%)

(0.22%)

:0.22%)

:1.2%)

:0.18%)

5.0%)

:1.1%)

0.22%)



0.22%)

0.22%)

0.22%)

0.22%)


Vol. (ml)d

100.0

10.0

10.0

10.0

10.0

20.0

20.0

5.0

20.0

20.0

5.0

10.0

20.0

50.0



50.0

50.0

20.0



50.0

10.0

20.0

10.0


Copolym.
Time (Hr.)

703.4

0.335

0.598

17.75

0.337

23.7

24.5

1 mo.

23.7

30.0

1 mo.

0.250

23.7

60.0

14.5

48.0

48.0

21.8

S6 mos.

1.0

0.502

21.8

0.687


02nn 71.R


0.9 1 _1 (0.2% 200 2









TABLE 3
Yield and Analysis Data for Copolymers in Table 2
Yield Analysis
Sample h i k Avg. m
No. Grams 1 % N M % C1 mM Av.


0.9287
0.03084
0.06208
0.1040
0.04243
0.4342
0.6068
0.1879
0.7216
0.8276
0.2732
0.03336
0.9658
7.75
1.6791
10.0
2.80
1.1857


0.257
0.03794
1.2736
0.06077
1.2614


16.4
5.44
10.9
18.3
7.07
36.2
49.0
60.7
57.0
69.07
81.2
5.01
72.5
65.7
80.6
74.3
74.6
84.7


7.34
5.18
86.9
7.93
82.3


0.490
0.507
0.510
0.506
0.519


0.504
0.474
0.517
0.513


0.555
0.531
0.523


12.33
12.52
12.53
12.59
11.22


11.43
13.17
11.27
11.13


10.72
11.15
11.68


66.3
21.9
44.2
74.0
15.14
77.4
83.4
103.3
86.0
84.5
97.5
5.96
86.3
78.3
96.0
88.6
80.3
84.8


7.35
5.18
86.9
7.93
82.3


4.93
5.06
5.08
5.05
5.15
-

5.04
4.81
5.14
5.11


5.42
5.24
5.18



5.45
5.39
5.40


5.63


5.96
6.26


0.511
0.505
0.505
0.503
0.546


0.540
0.484
0.547
0.550


0.564
0.550
0.532



0.573
0.547
0.564


0.585 9.32 0.611 0.598


0.633 9.10 0.620 0.626
0.679 8.04 0.659 0.669


Footnotes for this table appear at the end of Table 5.


0.560 10.46
0.551 11.22
0.553 10.72


0.500
0.506
0.507
0.504
0.532


0.522
0.479
0.532
0.532


0.560
0.540
0.528



0.566
0.549
0.558










TABLE 4

Polymerization Conditions for Other Maleimide Polymersr

Sample Monomerm M a b 3c Vol.d Copolym.
No. Pair T M [AIBN] x 10 (ml) Time(Hr.)

25 NPM MVE ? 0.
[NPM]=0.250 1.14 25.0 16.0

26 NPM EVE 0.512 0.488 1.12 (0.22%) 50.0 22.5

27 NPM BVE 0.521 0.520 9 20.0 19.5

28 NPC-CEVE 0.535 0.467 2.4 (0.45%) 50.0 163.5

29 NCHX-CEVE 0.500 0.500 1.11 (0.22%) 25.0 49.8

30 PCN-CEVEn 0.500 0.500 1.10 (0.22%) 25.0 43.5

31 PCF3-CEVE 0.500 0.500 1.11 (0.22%) 25.0 50.8

32 PCO2ET-CEVE 0.501 0.499 1.06 (0.21%) 5.0 43.5

33 PF CEVE 0.500 0.498 1.14 (0.23%) 10.0 60.0

34 PC1 -CEVE 0.501 0.499 1.09 (0.22%) 25.0 42.5

35 PBr-CEVE 0.500 0.500 1.12 (0.22%) 25.0 42.0

36 POAc-CEVE 0.500 0.500 1.11 (0.22%) 15.0 42.0

37 PCH3-CEVE 0.508 0.492 1.22 (0.24%) 25.0 42.5

38 POMe-CEVE 0.502 0.498 1.14 (0.23%) 25.0 42.5

39 NOAc-CEVE 0.500 0.500 1.09 (0.22%) 100.0 61.0

40 MAH-CEVEn 0.500 0.500 1.13 (0.23%) 50.0 66.5

41 MAH-CEVEn 0.500 0.500 1.11 (0.22%) 50.0 66.5

42 PNO2-CEVE 0.500 0.500 1.11 (0.22%) 25.0 42.0


table appear at the end of Table 5.


Footnotes for this












Yield and Analysis


TABLE 5

Data for Copolymers in Table 4


Yield Analysis
Sample Grams % %N Avg. m % C1 Avg. m Avg. mM
No. Grams % 1 N mMJ ~ mM


76.1

93.3 94.6


1.10

2.90



1.60

1.40

1.5827

2.10

0.3120

0.4553

1.6647

1.0172

1.0968

1.6135

0.6102

5.90

2.30

2.00

0.00


6.21



5.24

5.62

9.52

4.27

4.18

5.12

4.83


0.579



0.571

0.603

0.526

0.551

0.542

0.564

0.564


0.0

11.06

9.41

9.99

8.64

8.32

9.72

21.19


43.6

78.4

83.1

96.6

71.0

61.4

84.8

45.4

86.6

87.9

33.2

90.2

89.9

94.0


0.534

0.601

0.556

0.558

0.565

0.575

0.572



0.587

0.592

0.570

0.557

0.538


0.552

0.602

0.541

0.554

0.554

0.570

0.568



0.558

0.574

0.569

0.554


,. LU U.3/ -

4.30 0.530 8.15

5.15 0.557 9.39

4.93 0.568 9.43

5.79 0.551 11.75

- 16.06


41.3

78.4

83.1

96.6

70.9

61.4

84.7

45.4

86.6

86.9

31.5

90.2

89.9

94.0


L
Z



Z










Footnotes for Tables 2, 3, 4 and 5:
a Total monomer concentration = [M1] + [M2].

bMole fraction maleimide (or other acceptor) in the initial feed.

c Concentration of AIBN in moles/1 (mole % AIBN based on MT).

dVolume of the solution that was polymerized.

e No solvent.

Total moles of monomer.

9 Initiator was 2,4-dichlorobenzoyl peroxide (Lucidol), 1.1 x 10-3M.
hYield (%) based on theoretical maximum weight of polymer determined
from total weight of monomers initially present.
Yield (%) based on the knowledge that vinyl ethers do not homopoly-
merize under the present conditions, i.e., when [vinyl ether] >
[maleimide], the theoretical maximum conversion is 2[maleimide];
when [maleimide] > [vinyl ether], the maximum conversion is [male-
imide] + [CEVE].

SMole fraction maleimide in the copolymer calculated from nitrogen
analysis.
kMole fraction maleimide in the copolymer calculated from chlorine
analysis, i.e., 1-mCEVE.

Average mM from nitrogen and chlorine analyses.
m Abbreviations used:

NPM, N-phenylmaleimide
CEVE, 2-chloroethyl vinyl ether
BVE, n-butyl vinyl ether
EVE, ethyl vinyl ether
MVE, methyl vinyl ether
MAH, maleic anhydride
NPC, N-phenylcitraconimide
NCHX, N-cyclohexylmaleimide
PCF3, N-(4-trifluoromethylphenyl)maleimide
PCN, N-(4-cyanophenyl)maleimide
PF, N-(4-fluorophenyl)maleimide
PCI, N-(4-chlorophenyl)maleimide
PBr, N-(4-bromophenyl)maleimide
POAc, N-(4-acetyloxyphenyl)maleimide










PCH3, N-(4-methylphenyl)maleimide
PCO2ET, N-(4-carboethoxyphenyl)maleimide
POMe, N-(4-methoxyphenyl)maleimide
NOAc, N-acetyloxymaleimide
PNO2' N-(4-nitrophenyl)maleimide.
SCopolymerization proceeded heterogeneously, i.e., the copolymer was
insoluble in dichloromethane.
0 This copolymer was soluble in methanol, so petroleum ether was used
as the precipitating solvent.

P Benzene solvent.

q N-Phenylmaleimide was 20% 15N-enriched.
r Copolymerization temperature was 60.0 0.1C in all cases.


methylene chloride and precipitated into stirred methanol cooled in a

dry ice:isopropanol bath. The white precipitate was rapidly filtered

before it warmed to room temperature. On warming, the precipitate

changed to a viscous, pale yellow, transparent mass. The NMR data for

this material were consistent with that reported86 for the CEVE homo-

polymer prepared in methylene chloride using boron trifluoride ether-

ate catalyst.

H NMR (60 MHz, CDC13) 6 1.82 (broad s, 2H), 3.50 (broad s, 5H).

1C NMR (CDC13, internal reference CDC13 = 77.062)639.3 (t, broad),

40.5 (t, broad), 43.64 (t), 68.57 (t), 73.49 (d).

IR (thin film) 2930(vs), 2882(s), 2860(s), 1725(w), 1462(m), 1429(s),

1370(s), 1298(s), 1252(m), 1195(m), 1110(vs), 1150(s), 969(m),

890(w), 864(w), 825(w), 780(w), 740(m), 661(vs) cm-1











Copolymer Reactivity Ratios

The reactivity ratios for the NPM-CEVE copolymerization were

calculated using the copolymer composition data in Table 3. Two

separate methods were used to evaluate these ratios. The methods

used were those developed by Joshi and Joshi,87 and Kelen and Tudos.88

Although it is generally accepted89 that only composition data from

low conversion (< 10%) polymers should be used for these calcula-

tions, it can be seen from Table 3 that the copolymer composition

does not change significantly with conversion when the monomer feed

is rich in vinyl ether. Thus, both low and high conversion data (for

those copolymers prepared from vinyl ether-rich feeds) were used for

these calculations. The Kelen-Tudos plot is shown in Figure 1. The

numbers indicate data calculated from the corresponding samples in

Table 3. It can be seen that the plot is fairly linear, although

there are some points that deviate significantly from the line. Most

of the data that did not fall on the line were calculated from the

composition data for polymers prepared using different polymerization

conditions. Recalculation of the reactivity ratios using the ten

"best" data points did not change the results significantly. All

sixteen data points were used in the Joshi-Joshi calculation. The

results are summarized in Table 6.

Copolymerization Kinetics

The initial rate of copolymerization for the system NPM, CEVE,

CH2CI2, AIBN, 60.00C was measured as a function of the mole fraction

of maleimide in the initial comonomer feed (XM) at constant total

monomer concentration ([Mi] + [M2] = MT). A gravimetric technique was

















r- r-





E



CU

Q.



C94-

0
0

4-,



-




0




L.
d '









C CO

4-1 0
-o






















C-)C-
*u





,L
o E-
r-





LU
0
4 -





o -.
0 ro


4-'






I- .L.
I I


i*







LU



LL-










TABLE 6
Reactivity Ratios for the Free Radical Initiated Copolymerization
of N-Phenylmaleimide (Ml) and 2-Chloroethyl Vinyl Ether (M2)
in Dichloromethane

Calculation Method rl r2


Joshi-Joshi 0.286 0.012 -0.0000024

Kelen-Tudosa 0.284 -0.0079

Kelen-Tudosb 0.275 +0.00041

a Calculated using all data points.

bCalculated using ten "best" data points.


used to follow the conversion of monomers to polymer, i.e., the mass

of copolymer formed was monitored as a function of time.

Solutions of the desired concentrations were made by weighing

the appropriate amounts of monomers and initiators into clean 100 ml

volumetric flasks and diluting to the mark with freshly distilled

(from P4010) dichloromethane. Exactly 10 ml portions of these solu-

tions were transferred via pipette into clean, dry polymerization

tubes. The tubes were connected to a high vacuum line, degassed via

five freeze-pump-thaw cycles, and sealed at < 10-5 mm Hg. The tubes

were then immersed in a 60.0 0.10C water bath. After the desired

amount of time had elapsed, a tube was removed from the bath and

immediately plunged into a dry ice:isopropanol bath. The time inter-

val between immersions in the 60.0C and -780C baths was taken as the

polymerization time, and was measured with a stopwatch. The polymer-

ization times were such that the conversion to polymer was low











(k 10% of the initial weight of monomers present), so that the ratio

of monomer concentrations was approximately constant. The cold tube

was opened as quickly as possible, and the contents were quickly added

to 100 ml of methanol in one portion. The tube was carefully rinsed

with several small portions of dichloromethane. The rinsings were

added to the methanol. The pure white precipitated polymer was then

filtered into clean, previously weighed fine porosity, fritted glass

filters. The filters were cleaned in a chromic acid bath followed by

rinsing with deionized water. Concentrated nitric acid was then

passed through the filters, which were then rinsed with copious

amounts of deionized water. The filters were then dried in a 140C

oven overnight, cooled, and weighed accurately. Tongs were used to

handle the filters after they were dried. After the polymers were

filtered, the filter and polymer were dried in vacuo at 60C overnight.

After cooling to room temperature, the filters containing polymers

were reweighed, and the weight of the polymer was calculated by

difference.

Sometimes it was necessary to digest the polymer suspension in

order to increase the particle size and facilitate filtration. This

was done by gentle heating (- 35-45C) of the suspension for about one

hour, then allowing it to stand undisturbed at room temperature for

one to three days.

The NPM used for kinetic studies was vacuum distilled (bp 109-

111C @ 0.25 mm Hg), followed by recrystallization from cyclohexane.

A high efficiency spinning band column was used to distill CEVE (bp

109C) from calcium hydride.










The initial conditions, copolymerization times, and polymer

weights obtained are given in Table 7. These weights were converted

to the concentration of polymer at the corresponding time by using

the average molecular weight of the copolymer repeat unit calculated

from the copolymer composition data in Table 3. The following equa-

tion was used for the calculation:

MW = 2[mM (173.17) + mCEVE (106.55)]

where mM and mCEVE are the mole fractions of NPM and CEVE incorporated

into the copolymer, respectively.

The slope of a [polymer] vs. time plot gives the rate of copoly-

merization (R in mole/l-min). The results are shown in Table 8,

along with the standard deviation of the slope (Sm) and the x-inter-

cept (x) of the concentration vs. time plots. The slope and the x-

intercept were calculated by a linear least squares procedure. The

x-intercept was invariably non-zero and positive, indicating that

there was an induction period during which no polymerization took

place. The dependence of the rate (R ) on the initial mole fraction

maleimide is shown graphically in Figure 6.

Copolymer Characterization
13C NMR. Carbon-13 NMR analysis of the copolymers proved to be

vastly superior to proton (1H) NMR because of greater spectral sim-

plicity resulting from the lack of coupling and the greater spectral

width (typically 200 ppm for 13C and 0 ppm for 1H). Indeed, 1H NMR

spectra of the maleimide-vinyl ether copolymers prepared in this

study generally appear as a series of overlapping broad humps.










TABLE 7

Kinetic Data for N-Phenylmaleimide -
2-Chloroethyl Vinyl Ether Copolymerizations

Mole Pl. 2
Initial Conditions Time (Min.) Wt. Pol. (mg) lP. x 102


Mb = 0.500 20.1 30.84 1.10

c = 0.100 22.3 36.06 1.28
MWd = 280.52 25.0 40.38 1.44

27.5 47.10 1.68

30.1 49.78 1.77

35.9 62.08 2.21

b
MT = 0.501 20.2 42.43 1.49

XM = 0.200 25.0 52.80 1.86
d
MW = 283.98 30.0 66.55 2.34

35.1 76.95 2.71

rb = 0.500 15.1 32.97 1.16

XM = 0.300 20.0 46.24 1.63
d
MW = 283.98 25.0 62.90 2.21

30.0 73.44 2.59

MTb = 0.500 15.0 33.36 1.16

XM = 0.400 20.9 48.25 1.68
d
MW = 286.38 25.0 59.78 2.08

30.0 77.95 2.72











TABLE 7-Continued


Initial Conditions Time (Min.) Wt. Pol. (mg) MolePol. x 102


MT = 0.501 20.0 48.27 1.69
C
XM = 0.499 25.0 64.25 2.24
Wd = 286.25 30.0 81.75 2.86

35.0 88.07 3.07

b
MT = 0.500 26.1 23.66 0.808
c
XM = 0.600 30.1 37.94 1.30

MW = 292.78 31.8 41.39 1.41

38.1 50.06 1.71


MTb = 0.501 26.6 36.04 1.22
c
XM = 0.699 30.5 40.99 1.38
d
MW = 296.51 35.0 48.62 1.64

41.2 60.77 2.05


MTb = 0.500 69.4 20.15 2.33

XM = 1.00 84.2 23.61 2.73
MW = 173.17 106.1 29.30 3.38

120.4 32.53 3.76

150.1 41.75 4.82

156.0 39.58 4.57

aAll sample volumes were 10.00 ml, and the solvent was dichloro-
methane in all cases.
bTotal monomer concentration in moles/l.











TABLE 7-Continued
CMole fraction of maleimide.

dAverage molecular weight of repeat units calculated from composition
data in Table 3, i.e., MW = 2[(mM)(173.17) + (mCEVE)(106.55)].


TABLE 8

Initial Copolymerization Rates for the Copolymerization of
N-Phenylmaleimide and 2-Chloroethyl Vinyl Ether in Dichloromethane

XM R imle )a S b (min.)c
p 1-min m m
x 104 x 104

0.10 6.92 0.115 3.98

0.20 8.33 0.102 2.36

0.30 9.80 0.213 3.16

0.40 10.3 0.272 4.12

0.50 9.52 0.421 1.61

0.60 7.22 0.334 13.41

0.70 5.75 0.103 5.98

1.00 2.81 0.112 13.54

aRp d[P]/dt = -i d([M1]+[M2])/dt; for XM = 1.00, Rp = -d[M1]/dt;

P represents polymer.
bStandard deviation in the slope of the mole polymer/l vs. time plot.

CX-intercept of the mole polymer/l vs. time plot.











Careful sample preparation proved to be essential in obtaining

good quality "high resolution" spectra. All spectra were obtained

in solution, and the solvents used were either DMSO-d6 or tetrachlolo-

ethane (TCE). Because of the low natural abundance of 13C nuclei

(1.1%90) and the complexity of the copolymer structure (numerous

magnetic environments for similar types of carbon), a very high con-

centration of copolymer was needed in order to obtain a good signal

to noise ratio in a reasonable amount of time. Thus, samples were

generally prepared by adding solid copolymer to a small amount of

solvent (0.3-0.4 ml) until the resulting solution was viscous enough

to barely flow at room temperature. Usually 200-400 mg of copolymer

was enough to achieve the desired concentration. The solution was

filtered into a clean 5 mm NMR tube through a plug of glass wool,

using heat (heat gun) and positive nitrogen pressure. When TCE was

used as the solvent, 10-15 drops of benzene-d6 or toluene-d8 was added

for internal deuterium lock. Hexamethyldisiloxane (Merck & Co., 1-2

drops) was used as a reference (2.03 ppm from TMS91) when TCE was

used as the solvent. The middle peak of the solvent heptet (39.50

ppm from TMS62) was used as the reference peak when DMSO-d6 was the

solvent.

In order to minimize the dipolar line broadening caused by aniso-

tropic motion92 in the viscous polymer solution, all spectra were run

at high temperature. Acceptable line widths could be obtained at

100-110C for copolymers dissolved in DMSO-d6, and at 70-800C for

those dissolved in TCE.











Since the 13C NMR spectra of the NPM-CEVE copolymers had a large

dynamic range (difference between the intensity of the most intense

and the least intense peaks), and the Jeol-FX100 has limited space in

the computer memory for data storage, the computer word length would

overflow before an adequate signal to noise ratio was attained. For

a discussion of this effect, see Reference 90, p. 18, Reference 91,

p. 100 or Reference 93. This problem was overcome by using the fre-

quency domain (or block) averaging technique.93 This technique

amounts to the accumulation of a relatively small number of scans,

followed by Fourier transformation of the free induction decay, and

storage of the result in a separate block of computer memory. This

process is repeated, and the result of the Fourier transformation is

added to the previous result. The whole process is continued until

the desired signal to noise ratio is attained.

Since polymer carbon-13 nuclei generally have short spin-lattice

relaxation times (TI) relative to small molecules,90,91'94 a short

pulse delay (PD) and large pulse width (PW) were used to obtain 13C

spectra of the NPM-CEVE copolymers. Typical instrument parameters

for obtaining polymer spectra follow:

Number of accumulations: 20,000-35,000

Observation frequency: 47.0 KHz (TCE solvent)
47.3 KHz (DMSO-d6 solvent)

Pulse width: 12-18 ps (60-90)

Pulse delay: 180-360 ms

Acquisition time: 0.819 s

Spectral width: 5000 Hz

Exponential line broadening: 0.97 Hz











Each spectrum required eight to ten hours of accumulation. Accept-

able signal to noise ratio was not attained when the 13C NMR spectrum

of NPM homopolymer was run, until 250,000 scans had accumulated.

Copolymer TI and NOE determination. The spin-lattice relaxation

times (Ti) were determined for the carbons in the NPM-CEVE copolymer

prepared in bulk (sample 15 in Table 2). The method used for this

determination was the saturation recovery method developed by McDonald
95
and Leigh.95 This method proved to be superior to the inversion re-

covery (IRFT)96 or the fast inversion recovery (FIRFT)97 techniques

because of its relative insensitivity to mis-set 900 pulse angles,

the lack of a long wait time after each pulse sequence, and the very

short T1 values determined for some of the carbons in the copolymer.

Determining the 90 pulse width is a tedious, trial and error process

in which the pulse width is varied until the observed signal is nulled

(1800 pulse, the pulse width for a 900 pulse is ~ i that correspond-

ing to a 180C pulse). For the copolymer, it took ten to fifteen

minutes of accumulation to observe any signal at all, so such a trial

and error process was clearly unacceptable. The number of scans

necessary to obtain a polymer spectrum with good signal to noise ratio

(at least 2,000 under very favorable conditions) necessitated the use

of a short pulse sequence. Because of the short T1 values of some

polymer carbons, inversion of the broad carbon resonances (IRFT and

FIRFT methods) required extremely short pulse intervals, (T); and for

many values of T, some peaks did not appear above (or below) the

noise.











The saturation recovery experiment consisted of a 900 pulse

followed by a homospoil pulse (to dephase the spins). After the

system was allowed to relax for a time period -, another 900 pulse

was applied in order to sample the magnitude of the magnetization

vector. After the signal was acquired, another homospoil pulse was

applied, and the sequence was repeated until the desired signal to

noise ratio was achieved. A series of spectra were obtained using

different pulse intervals (-'s). The signal intensity was an expo-

nential function of T, with time constant T1. The relaxation times

were calculated by plotting In[SI S(T)] vs. T,95 where S and S(T)

were the signal areas corresponding to pulse intervals of infinity

and T, respectively.

By using a 10 mm tube and a high copolymer concentration, a

fairly good signal to noise ratio was obtained after 2,000 scans had

been accumulated. Thus, up to 10 spectra could be obtained (each

resulting from a different T) in a reasonable amount of time (12-

24 hours). The spectra were automatically accumulated and stored on

magnetic tape by the spectrometer. After completion of the run, each

spectrum was read off the tape, and the peaks were integrated elec-

tronically. Since the peaks were generally broad, and the signal to

noise ratio was low (especially when short T's were used), the inte-

gration was subject to large errors. Several experiments were run

using various combinations of pulse intervals and T This was neces-

sary because of the large range of T1 values encountered for different

carbon types in the copolymer (22-3,000 ms), i.e., the T's needed to

measure the short Tl's were not suitable for the measurement of long











T1's and vice versa. A linear least squares procedure was used to

calculate the slopes of the In(S S ) vs. T plots. Sometimes these

plots appeared nonlinear; however, due to the large errors involved

in the area determination, this observation was not considered signif-

icant. In these cases, the points corresponding to short T values

(and the least accurate area determinations) were invariably the

points that deviated significantly from the line, and were simply

neglected in the T1 calculation.

When using the semilogarithmic procedure described above, it is

essential that the Tm value chosen is at least five times as long as

the longest T1 to be measured.98 The results of the T1 determinations

are given in Table 9. The T1 values are shown as the range of values

determined from at least three separate experiments. The longest T

used in these experiments was 12,000 ms, which is not five times the

T1 values determined for the nonprotonated carbons. The use of a T_

value that is less than the time value results in an underestimation

of T1.98 Thus, the T1 values for the carbonyl and quaternary aromatic

carbons are probably greater than the values shown. The large varia-

tion in T1 values obtained for the same carbon in different experi-

ments underscores the inaccuracies inherent in the determination of

polymer relaxation times. The observed values are only useful for

qualitative comparisons.

Determination of Copolymer Nuclear Overhauser Enhancements (NOE).

Copolymer carbon-13 NOE's were determined by using the gated decoup-

ling technique.99 A spectrum was obtained using complete decoupling,

i.e., with the proton decoupler on all the time. The pulse delay used











TABLE 9

Carbon-13 Spin-Lattice Relaxation Times (T1) and
Nuclear Overhauser Enhancement Factors (NOEF)
For an NPM-CEVE Copolymera

Carbonb 5 (ppm)c T1 Range (ms) Avg. T1 (ms) NOEd NOEFe


1 177.1 1400-2200 2000 1.82 0.82

2 174.4-175.6 1400-1900 1400 1.81 0.81

3 131.9 2100-3000 2500 1.82 0.82

4,5f 127.7-128.3 200-560 334 2.92 1.92

6 126.3 160-330 250 2.86 1.86

7 75.7-76.7 28-68 56 2.03 1.03

8 69.2-70.1 64-186 142 2.28 1.28

9 48.3-49.9 62-99 76 2.30 1.30

10 42.9 98-264 164 3.03 2.03

11 37.0-39.5 Under solvent (DMSO-d6) resonance

12 32.4-34.7 22-35 29 2.59 1.59


a Prepared in bulk (sample 15, Tables 2,3).

b
Numbered as in Figure 8 (low to high field).

c Internal reference DMSO-d6 = 39.5 ppm.62

dTheoretical maximum value 2.988.6

e Theoretical maximum value 1.987.9
e Theoretical maximum value 1.987.90


fThese peaks overlap.
These peaks overlap.











to obtain this spectrum was fifteen seconds (> 5 times the longest

T1). The areas for all of the carbon resonances were measured.

Another spectrum was run under exactly the same conditions, except

the decoupler was gated on during data acquisition and off during

the pulse delay. Thus, a proton decoupled spectrum was obtained,

but without the NOE. The ratio of the areas obtained by using com-

plete decoupling, and those obtained using gated decoupling, gives

the NOE ratio. The quantity NOE-1 gives the amount of signal enhance-

ment and is known as the nuclear Overhauser enhancement factor

(NOEF).90 Repeating the gated decoupled spectrum after adding some

chromium tris-acetylacetonate [Cr(acac)3]99 paramagnetic relaxation

reagent had no effect on the integrated areas relative to those ob-

tained without Cr(acac)3. The results are presented in Table 9.

Infrared Spectroscopy. Generally, the IR spectra of NPM-CEVE

copolymers did not differ significantly with varying copolymerization

conditions. Thus, only one set of spectral data is reported below.

The abbreviations used below for the various monomer pairs used to

synthesize the copolymers are the same as those used in Tables 2-5.

All spectra were obtained using the KBr pellet technique.

NPM-CEVE, 3470(w, b), 3060(w), 2958(w), 2920(w), 2880(w), 1777(w),

1709(vs), 1595(w), 1498(m), 1457(w), 1432(w), 1382(s), 1300(w),

1185(s), 1110(m), 752(m), 690(m), 662(w), 620(w) cm-1

NPM-MVE, 3460(w, b), 3060(w), 2930(w), 2812(w), 1776(w), 1707(vs),

1595(w), 1497(m), 1456(w), 1382(s), 1180(s), 1098(m), 750(m),

688(m), 618(w) cm1.










NPM-EVE, 3465(w, b), 3062(w), 2973(w), 2915(w), 2880(w), 1779(w),
1710(vs), 1596(w), 1498(m), 1455(w), 1383(s), 1290(w), 1183(s),
1090(m), 751(m), 688(m), 619(w) cm-1
NCHX-CEVE, 3455(w, b), 2938(m), 2860(w), 1773(w), 1699(vs), 1452(w),
1400(m), 1377(m), 1348(m), 1260(w), 1200(m), 1190(m), 1148(m),
1110(w, b), 1055(w, b), 986(w), 894(w), 669(w), 631(w) cm-'
NOAc-CEVE, 3450(w, b), 2940(w), 1820(m), 1787(m), 1734(vs), 1540(w),
1430(w), 1372(m), 1220(m), 1164(m), 1110(m), 1057(m), 827(w),
740(w, b), 668(w) cm-1
NPC-CEVE, 3470(w, b), 3062(w), 2910(w, b), 1775(w), 1710(vs), 1594(w),
1497(m), 1454(w), 1428(w), 1390(s), 1373(s), 1297(w), 1200(m),
1140(m), 1108(m), 750(m), 688(m), 662(w), 618(w) cm-1
PF-CEVE, 3475(w, b), 3080(w), 2960(w), 2925(w), 2870(w), 1779(w),
1708(vs), 1601(w), 1508(s), 1388(m), 1290(w), 1230(m), 1183(m),
1157(m), 1100(m), 1050(w), 1013(w), 932(w), 831(m), 750(w, b),
908(w), 660(w) cm-1
PC1-CEVE, 3480(w, b), 3100(w), 2965(w), 2920(w), 2870(w), 1780(w),
1710(vs), 1493(s), 1384(s), 1300(w), 1278(w), 1180(m), 1092(m),
1018(m), 940(w), 823(m), 731(w), 707(w), 665(w), 638(w) cm-1
PBr-CEVE, 3470(w, b), 3018(w), 2960(w), 2923(w), 2880(w), 1778(w),
1710(vs), 1490(s), 1385(s), 1303(w), 1278(w), 1181(m), 1110(m),
-1
1073(m), 1013(m), 822(m), 704(w), 665(w), 632(w) cm-1
PCO2ET-CEVE, 3440(w, b), 2980(w), 2935(w), 2910(w), 1778(w), 1710(vs),
1608(m), 1509(m), 1414(w), 1380(m), 1280(s), 1180(m), 1110(m),
1021(m), 851(w), 767(w), 693(w), 667(w) cm-1









PCN-CEVE, 3480(w, b), 3102(w), 3060(w), 2965(w), 2927(w), 2878(w),
2218(m), 1780(w), 1711(vs), 1605(m), 1507(m), 1380(s), 1288(w),
1180(m), 1110(m), 1050(w), 954(w), 838(m), 800(w), 750(w),
650(w) cm-1
POAc-CEVE, 3480(w, b), 2930(w, b), 1769(m), 1711(vs), 1600(w),
1509(m), 1390(m), 1374(m), 1200(s), 1170(m), 1110(m), 1047(w),
1020(m), 941(w), 910(w), 848(w), 640(w, b) cm-.
PCH3-CEVE, 3470(w, b), 3040(w), 2960(w), 2927(w), 2870(w), 1779(w),
1708(vs), 1515(m), 1390(s), 1300(w), 1188(m), 1110(m), 1050(w),
812(w), 910(w), 660(w) cm-1.
POMe-CEVE, 3480(w, b), 3005(w), 2960(w), 2940(w), 2920(w), 2842(w),
1778(w), 1710(vs), 1611(m), 1592(w), 1515(s), 1465(w), 1445(w),
1390(m), 1303(m), 1257(s), 1188(m), 1172(m), 1110(m), 1030(m),
830(m), 806(w), 662(w) cm-.
PCF3-CEVE, 3480(w, b), 3070(w), 2925(w), 2860(w), 1780(w), 1714(vs),
1612(m), 1517(w), 1418(m), 1382(m), 1327(s), 1172(m), 1125(m),
1110(m), 1067(m), 1019(m), 950(w), 838(m), 757(w), 697(w),
662(w), 627(w) cm-1
MAH-EVE, 2980(m), 2935(w), 2900(w), 1860(m), 1780(vs), 1732(m),
1440(w), 1405(w), 1377(w), 1350(w), 1223(m), 1093(m), 1070(m),
928(m), 730(w), 620(w) cm-1
MAH-CEVE, 2960(w), 2925(w), 2870(w), 1855(m), 1779(vs), 1732(m),
1432(w), 1350(w), 1298(w), 1220(m), 1104(m), 1048(m), 923(m),
930(w), 660(w) cm-1.
NPM Homopolymer, 3480(w), 3060(w), 2900(w, b), 1775(w), 1705(vs),
1597(w), 1496(m), 1457(w), 1387(s), 1185(m, b), 749(m), 732(m),
688(m), 657(w), 621(m), 611(w) cm-1










A peak appears at 1110-1100 cm-1 in all copolymer spectra that

is absent in the NPM homopolymer spectrum. This peak was therefore

assigned to the C-0 stretch of the ether unit in the copolymers. The

appearance of this peak was thus indicative of copolymer formation.

Differential Scanning Calorimetry (DSC). The thermal properties

of many of the copolymers that were synthesized were investigated by

use of the DSC method. The copolymers generally did not have a well-

defined crystalline melting point or glass transition temperature (T ).

Although several thermal transitions were evident in most DSC runs,

they generally were not reproducible and they were always poorly de-

fined. The temperature of decomposition, however, proved to be fairly

reproducible. The thermal stability runs were performed in air with

a Perkin Elmer DSC-1B instrument. Several runs were performed in a

helium atmosphere with no apparent effect on the decomposition temp-

erature (Td). The Td's of the copolymers tested are given in Table

10. The abbreviations used are the same as those used in Tables 2-5.

TABLE 10
Copolymer Decomposition Temperatures (Td)

Copolymer Td (C) Copolymer Td (oC)

NPM-CEVE 272 PBr-CEVE 286
NPM-EVE 322 [ PCO2ET-CEVE 279
NPC-CEVE 285 PCH3-CEVE 265
NCHX-CEVE 280 POAc-CEVE 277
PCF3-CEVE 275 POMe-CEVE 280
PCN-CEVE 276 NOAc-CEVE 220
PF-CEVE 274 MAH-CEVE 237
PC1-CEVE 277 MAH-EVE 245










Copolymer molecular weight determinations. Although a great

deal of time was not spent on copolymer molecular weight determina-

tion, several copolymers were characterized by gel permeation chro-

matography (GPC) or vapor pressure osmometry (VPO). A low conversion

NPM-CEVE copolymer (XM = 0.2, MT = 0.5, AIBN, 600C) was analyzed on

a Waters Model 6000A GPC which was equipped with a Model 440 Absorb-

ance Detector. A Waters 104 Styragel column was used for the analy-

sis. A solution of copolymer concentration 2.3 g/l in CH2Cl2 was in-

jected. Dichloromethane was also used as the elution solvent. A

single, broad peak, typical of polymers produced by a free-radical
100
mechanism, was the result. The peak maximum corresponded to a

molecular weight of about 6300, based on polystyrene calibration

curves. This molecular weight corresponds to a degree of polymeri-

zation (D ) of 22-23 (based on 1:1 repeat unit).

Vapor pressure osmometry analysis of a high conversion NPM-

CEVE copolymer (sample 16, Table 2) in acetone, using a benzil cali-

bration standard, gave a number average molecular weight (Mn) of

13,250, which corresponds to a D of 47-48.

Solubility. The NPM-CEVE copolymers synthesized in this study

proved to be soluble in many organic solvents such as CHC13, CH2C12,

tetrahydrofuran, DMSO, nitromethane, ethyl acetate, acetone, aceto-

nitrile, and dimethyl formamide (DMF). The copolymers were insoluble

in benzene, alcohols, toluene, CC14 and water.

The NPM homopolymer, on the other hand, was generally insoluble

in the solvents listed above, dissolving only in DMSO, DMF and tetra-

chloroethane.











Copolymer Epimerization

Maleimide-vinyl ether copolymers were epimerized by using several

different bases and various reaction conditions. These conditions are

detailed below.

Copolymer epimerization with 2,2,6,6-tetramethylpiperidine (TMP)

in dimethylsulfoxide. The copolymer to be epimerized was dissolved in

DMSO-d6 (_ 0.25 g copolymer/0.3 ml DMSO-d6), and several drops of TMP

were added to the solution. Within 10-15 minutes, the solution turned

from colorless to a deep cobalt blue color. The solution was filtered

through a plug of glass wool into a clean, 5 mm NMR tube, which was

capped and placed in a 60.0C water bath. The progress of the epimeri-

zation could thus be monitored by periodically obtaining a 13C NMR

spectrum of the sample.

Copolymer epimerization with lithium diisopropylamide (LDA) in

tetrahydrofuran (THF). A three-necked, 200 ml round-bottomed flask

equipped with a magnetic stirring bar, addition funnel, and nitrogen

inlet was dried for several hours in a 1400C oven and then allowed to

cool in a dry nitrogen stream. One gram copolymer was dissolved in 20

ml THF (freshly distilled from lithium aluminum hydride), and the re-

sulting solution was placed in the addition funnel. About 1.0 g

solid LDA (Alfa) was added to 75 ml distilled THF which had been added

to the reaction flask. The transfer of the LDA was performed under a

blanket of dry nitrogen (inverted funnel). The reaction flask was

cooled to -750C with a dry ice:isopropanol bath. The LDA solution

was stirred magnetically under positive nitrogen pressure as the co-

polymer solution was slowly added over ten minutes. The solution











turned from colorless to deep red, and finally black opaque as the

copolymer solution was added. This solution was stirred at -750C

for one hour. At the end of this time, the solution was a deep green

color. Approximately 30 ml of saturated aqueous ammonium chloride

was quickly added while the solution temperature was still -750C.

The ammonium chloride solution froze on contact with the cold THF.

The dry ice was allowed to evaporate, so the solution slowly warmed

to room temperature with continued stirring. The organic layer of

the resulting two-phase system was now a deep cobalt blue color. The

organic layer was separated and added dropwise to rapidly stirred

methanol. The resulting light blue precipitate was filtered and

dried at reduced pressure (50C) overnight. The yield was 0.9 g

light blue powder. About one-half of this powder was treated with

20 ml hot (800C) acetic anhydride for three hours. The deep green

copolymer solution that resulted was allowed to cool, and 75 ml of

water was added. The resulting precipitate was filtered and dried

in vacuo. The resulting light green powder was dissolved in acetone

and precipitated into methanol. Three additional precipitations from

acetone into methanol failed to rid the product of all of its green

color.

IR analysis of the original blue copolymer showed a broad peak

at 3150 cm-1, which may be due to an amide N-H stretch resulting from

partial hydrolysis of the succinimide units of the copolymer. This

band disappeared on treatment of the copolymer with hot acetic anhy-

dride. Otherwise, the IR spectrum of the epimerized copolymer was

unchanged from that of the copolymer before epimerization.











Copolymer epimerization with potassium t-butoxide in DMSO. Po-

tassium t-butoxide was synthesized by using high vacuum techniques.

About 5 ml of t-butyl alcohol was distilled from calcium oxide and

sealed into a breakseal. About 20 ml freshly distilled (from KOH)

DMSO was used to dissolve 3.5 g copolymer (sample 16, Table 3), and

the resulting solution was sealed into a clean breakseal. A solution

of 1 g ammonium chloride in 10 ml distilled DMSO was sealed into a

third breakseal. The three breakseals were attached to a 200 ml

round-bottomed flask that could be attached to a vacuum line by means

of a 14/20 ground glass joint. The flask was also equipped with a

side arm that had several constrictions through which potassium metal

could be distilled. A small test tube with a ground glass joint con-

taining a pea-sized piece of potassium metal under hexane was con-

nected to the side arm of the inverted apparatus. The whole appara-

tus was again inverted, quickly connected to the vacuum line, and

evacuated. The potassium was gently heated with a yellow flame,

causing it to melt and flow down the side arm. The reaction flask

was cooled in ice water. Continued heating of the potassium metal

caused it to distill onto the inside wall of the cool flask, forming

a blueish silver mirror. The side arm was sealed off, and the t-

butyl alcohol was introduced by breaking the corresponding breakseal.

The metal was quickly consumed. Hydrogen gas was evolved, and a

clear, colorless solution resulted. The breakseal containing the

copolymer solution was then broken, allowing the solution to flow

into the potassium t-butoxide solution. Within two minutes, the com-

bined solutions had gone from nearly colorless, to deep green, to a










deep cobalt blue color. The blue solution was stirred at room temp-

erature for forty-three hours, and the breakseal containing the ammo-

nium chloride solution was broken. No color change was noted when

the ammonium chloride solution was added. The bulk of the solvent

was removed on the vacuum line with heat (heat gun). The apparatus

was removed from the vacuum line, chloroform was added to the bright

blue residue, and the chloroform solution was extracted with water.

The organic layer was dried over anhydrous MgSO4 overnight. The MgSO4

was separated from the solution by filtration. The blue chloroform

solution was slowly added to rapidly stirred hexane (dropwise) to

yield a blue precipitate. This precipitate was filtered and dried

in a 500C vacuum oven overnight to yield 3.0 g light blue powder.

This polymer was somewhat soluble in methanol, as evidenced by the

fact that attempted precipitation of copolymer solutions into metha-

nol yielded a fine dispersion that could not be separated by filtra-

tion.

The IR spectrum of the epimerized copolymer was nearly identical

to that of the copolymer before epimerization, except for a small de-
-1
crease in the relative intensity of the peak at 1110 cm-

Complexation Studies

Ultraviolet (UV) spectroscopy was used to study the complexation

behavior of maleimides and CEVE. Dichloromethane (CH2Cl2) was used

as the solvent in all cases. Invariably, the solvent was distilled

from P4010immediately prior to its use. CEVE was distilled from cal-

cium hydride immediately before use. The maleimides used were re-

crystallized from cyclohexane.










Solutions of CEVE in CH2C12 have absorption with Amax 275, 262,

and 254 nm. Dichloromethane solutions of N-arylmaleimides have ab-

sorptions with Amax in the range 300-320 nm and \max 255-275 nm,

depending on the maleimide. In contrast to solutions of N-arylmale-

imides, N-cyclohexylmaleimide solutions did not have an absorption at

255 nm. The absorption spectra of several maleimides are shown in

Figure 2. Addition of equal amounts of CEVE to a maleimide solution

in the sample beam of the UV spectrometer and a solvent blank in the

reference beam results in a slight intensification of the absorbance

in the 255-300 nm region. This increase in absorbance was attributed

to the formation of a charge-transfer complex and was therefore in-

vestigated further. This quantification proved to be a formidable

task due to the overlap of the charge-transfer band with the absorp-

tions of both monomers.

The experiments involved monitoring the absorbance of maleimide-

CEVE solutions of constant maleimide concentration and varying CEVE

concentration. The [CEVE] was always much greater than the [male-

imide]. In a typical procedure, the spectrum of the pure maleimide

in CH2C12 was measured against a reference of pure CH2C12 by using a

pair of 2 mm quartz cuvettes. Next, the spectrum of the solution of

the maleimide and vinyl ether was measured against a reference con-

taining the vinyl ether at the same concentration. The first spec-

trum was substracted from the second to afford the spectrum of the

charge-transfer complex. Absorbances were read directly from the dig-

ital display at 5 nm intervals, using care to optimize the slit width

before each reading so as to minimize noise. Absorbances read in this

manner were considered accurate to + 0.002 absorbance units.









































SC- C.- 0- a- C-

I
I
I I
S I
i- C.1I *


0 0 0




01 x 3


O
.O










*- 0


SEo
C 0

C 4-

ro ai




+0..-








2U C

,CO



S- -0

C

C0 4-1





(O3
UC'
-0 10






C'

C-
C


o



C S- -
--- 4

0 2)l
C C




CMD
U ->

LQ10L


0 0
C\J T Ci


I I I I I I


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I 1




Full Text

PAGE 1

THE ROLE OF THE CHARGE-TRANSFER COMPLEX IN THE ALTERNATING COPOLYMERIZATION OF N-SUBSTITUTED MALEIMIDES AND VINYL ETHERS BY KURT GORDON OLSON A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1981

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Copyright 1981 by Kurt Gordon Olson

PAGE 3

To Leslie

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ACKNOWLEDGEMENTS I would like to express my deep appreciation and gratitude to my research director, Dr. George B. Butler, for his encouragement and guidance during the course of this work. I would also like to thank Dr. Roy W. King for teaching me how to use the FX-100 NMR spectrometer, and for many helpful discussions. Thanks are also due to Dr. Thieo E. Hogen-Esch for numerous discussions. I would like to thank Dr. Wallace Brey and Mr. Paul Kanyha 15 19 1 for running the N, F, and 300 MHz H NMR spectra described herein. The friendship and cooperation of my coworkers in the polymer chemistry laboratories are greatly appreciated. Discussions with Mr. David P. Vanderbilt were especially helpful during the course of this research. I would like to thank Miss Patty Hickerson for the skillful typing of this manuscript. Special thanks are due to my wife, Leslie, for her constant encouragement and help. Financial support for this work from the Department of Chemistry, the National Science Foundation (Grant No. DMR80-20206) , Tennessee Eastman Co., Gulf Oil Co., and the University of Florida Graduate School is gratefully acknowledged. IV

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TABLE OF CONTENTS PAGE ACKNOWLEDGEMENTS iv LIST OF TABLES vii LIST OF FIGURES ix ABSTRACT xii CHAPTER I. INTRODUCTION 1 II. EXPERIMENTAL 14 General 14 Reagents and Solvents 15 Model Compound Synthesis 16 Maleimide Synthesis 38 Copolymer Synthesis and Characterization 54 Copolymer Epimerization 82 Complexation Studies 85 III. RESULTS AND DISCUSSION 96 Copolymer Composition 96 Copolymerization Kinetics 98 Maleimide-CEVE Complexation Studies 102 Carbon-13 NMR Structural Studies on N-Substituted Maleimide Vinyl Ether Copolymers 112 Model Compound Synthesis and Stereochemical Assignments. . 183 Summary and Conclusions 201 v

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PAGE REFERENCES 204 BIOGRAPHICAL SKETCH 214 VI

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LIST OF TABLES TABLE PAGE 13 1 C Chemical Shifts (6, ppm from TMS) for cis and trans 11. (DMSO-dg, internal reference DMSO-dg = 39.5) 36 2 Conditions for N-Phenylmaleimide-2-Chloroethyl Vinyl Ether Copolymerizations 57 3 Yield and Analysis Data for Copolymers in Table 2 58 4 Polymerization Conditions for Other Maleimide Polymers 59 5 Yield and Analysis Data for Copolymers in Table 4 60 6 Reactivity Ratios for the Free Radical Initiated Copolymerization of N-Phenylmaleimide (Mj) and 2-Chloroethyl Vinyl Ether (MJ in Dichloromethane 65 7 Kinetic Data for N-Phenylmaleimide 2-Chloroethyl Vinyl Ether Copolymeri zations 68 8 Initial Copolymerization Rates for the Copolymerization of N-Phenylmaleimide and 2-Chloroethyl Vinyl Ether in Dichloromethane 70 9 Carbon-13 Spin-Lattice Relaxation Times (Tj) and Nuclear Overhauser Enhancement Factors (NOEF) For an NPM-CEVE • Copolymer 76 10 Copolymer Decomposition Temperatures (T,) 80 11 Absorbance Data for Maleimide, 2-Chloroethyl Vinyl Ether Complexes at 295 nm 93 12 Slopes of A"7([M] x l) vs. [CEVE] Plots 95 13 Chemical Shifts (6, ppm From TMS) for the Olefinic Protons of N-Phenylmaleimide in CDCI3 Solutions of Varying 2-Chloroethyl Vinyl Ether Concentration 108 14 The Effect of Solvent on the Chemical Shift of NPM Olefinic Protons (100 MHz, 6, ppm From TMS) 110 Vll

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TABLE PAGE 15 The Mole Fraction of cis Succinimide Units in NPM-CEVE Copolymers as a Function of the Mole Fraction of NPM in the Initial Comonomer Feed (x^) 146 16 Mole Fraction of cis Succinimide Units in NPM-CEVE Copolymers Prepared at Various Temperatures 155 17 The Effect of Solvent on the Mole Fraction of cis Succinimide Units in NPM-CEVE Copolymers 157 18 Carbon-13 NMR Chemical Shifts of Some N-Substituted Maleimides 161 19 The Mole Fraction cis Succinimide Units in Various N-Substituted Maleimide-CEVE Copolymers 165 20 The Mole Fraction of cis Succinimide Units in NPM-Vinyl Ether Copolymers 173 vm

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LIST OF FIGURES FIGURE PAGE 1 Kelen-Tudos Plot for the Free-Radical Initiated Copolymerization of N-Phenylmaleimide and 2-Chloroethyl Vinyl Ether i n Di chl oromethane 64 2 Electronic Absorption Spectra of Various N-Substituted Maleimides in Dichloromethane 87 3 Electronic Absorption Spectra of Various N-Substituted Maleimide 2-Chloroethyl Vinyl Ether Charge-Transfer Complexes, [CEVE] = 1.3 in all cases 90 4 Effect of Varying CEVE Concentration on the Intensity of the NPM-CEVE Charge-Transfer Band 91 5 Copolymer Composition Diagram for the NPM-CEVE System 99 6 Initial Copolymerization Rate vs. x M for tne System NPM, CEVE, AIBN, CH 2 C1 2 , 60°C " 100 295 7 Ke vs. Hammett a Constants for Various Para Substituted Maleimide-CEVE Complexes in Dichloromethane 107 8 Noise Decoupled 13 C NMR Spectrum of an NPM-CEVE Copolymer, Obtained in DMSO-dg at 110°C 115 9 Complete a) and Off-resonance b) Decoupled C NMR Spectra of NPM-Methyl Vinyl Ether Copolymer 117 10 Model Compound 13 C NMR Chemical Shifts 121 1 3 11 Homoand Copolymer °C NMR Chemical Shifts 123 12 "Dyad" Stereochemical Possibilities for NPM-CEVE Alternating Copolymers (i.e., Relative Stereochemistry Between Two Adjacent Chiral Centers) 125 13 "Triad" Stereochemical Possibilities for Alternating Sequences in NPM-CEVE Copolymers 126 ix

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FIGURE PAGE 14 Effect of the Mole Fraction of NPM in the Initial n Comonomer Feed (x^) on the Appearance of Copolymer C NMR Carbonyl Peaks 132 15 Effect of Copolymer Epimerization on the Carbonyl Region of the 13 C NMR Spectra of NPM-CEVE Copolymers 134 13 16 Effect of Copolymer Epimerization on the C NMR Resonances Due to Carbons a to Oxygen in NPM-CEVE Copolymers. 136 13 17 Expanded Carbonyl Regions of the C NMR Spectra of Low (a) and High (b) Conversion NPM-CEVE Copolymers 138 18 Mole Fraction cis Succinimide Units in NPM-CEVE Copolymers vs . X M 142 19 Nitrogen-15 NMR Spectrum of an NPM-CEVE Copolymer (20% 15m Enriched) in Acetone-d g 148 20 Expanded Carbonyl Regions of the 13 C NMR Spectra of NPMCEVE Copolymers Prepared with Different Total Monomer Concentrations (My) in the Initial Feed 152 21 Expanded Carbonyl Regions of the 13 C NMR Spectra of NPMCEVE Copolymers Prepared at Various Temperatures 154 22 Expanded Carbonyl Regions of NPM-CEVE Copolymers Prepared in Bulk (a), Dichloromethane (b), and Benzene (c) 158 13 23 Expanded Carbonyl Regions of the C NMR Spectra of Some N-(4-Substituted)-Arylmaleimide-CEVE Copolymers 164 24 Mole Fraction cis Succinimide Units in N-Arylmaleimide CEVE Copolymers vs. Hammett a Constant 166 295 25 Ktvs. Mole Fraction Cis Succinimide Units in N-Substituted Maleimide-CEVE Copolymers 167 13 26 Expanded Carbonyl Regions of the C NMR Spectra of Copolymers Prepared from Several N-Substituted Maleimides and CEVE 169 13 27 Expanded Carbonyl Regions of the C NMR Spectra of Copolymers Prepared from NPM and Various Vinyl Ether Comonomers 172 28 Carbon-13 NMR Spectrum of N-Phenylcitraconimide CEVE Copolymer 179

PAGE 11

FIGURE PAGE 29 Expanded Regions of the C NMR Spectrum of Maleic Anhydride-CEVE Copolymer 182 30 Synthetic Scheme for Model Compound _16^ 184 31 Possible Conformations of Endo Diels-Alder Adduct 13 185 32 Proton NMR Spectrum (300 MHz) of Model Compound ^6 190 33 Expansions of the Ring Proton Resonances Appearing in the 300 MHz lH NMR Spectrum Shown in Figure 32 191 34 Synthetic Scheme for Model Compound 11 198 XT

PAGE 12

Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THE ROLE OF THE CHARGE-TRANSFER COMPLEX IN THE ALTERNATING COPOLYMERIZATION OF N-SUBSTITUTED MALEIMIDES AND VINYL ETHERS By Kurt Gordon Olson December 1981 Chairman: Dr. George B. Butler Major Department: Chemistry The aim of this research was to determine whether or not a comonomer charge-transfer complex participates significantly in the propagation steps of free-radically initiated alternating copolymerizations. Various N-substituted maleimides were shown to copolymerize alternately with several vinyl ethers. Both the sequence distribution and the stereochemistry of these copolymers were found to depend on such copolymerization conditions as temperature, solvent, total monomer concentration, the initial ratio of comonomers, and the relative donor and acceptor strengths of the comonomers. Carbon-13 nuclear magnetic resonance (NMR) spectroscopy was used extensively for the determination of copolymer stereoregularity. Copolymer epimerization studies and the comparison of copolymer 13 C NMR chemical shifts with those of a series of stereospecific model compounds indicated that the stereochemistry at the succinimide units XI 1

PAGE 13

in the copolymer was predominantly cis. In general, copolymerization conditions that were expected to enhance the fraction of maleimide monomer in complexed form (e.g., low temperature, excess vinyl ether, "inert" solvent, higher total monomer concentration, and stronger donor-acceptor character of the comonomer pair) yielded copolymers possessing a higher cis:trans stereochemical ratio at the succinimide units. A weak interaction between the comonomers was shown to exist by the appearance of a new absorption in the electronic spectra of comonomer mixtures, which did not appear in the spectrum of either component alone. The observed preference for cis stereochemical placements in these copolymers was opposite to what was expected if a mechanism involving consecutive alternate monomer additions to the radical chain end was operational. Thus, it was proposed that succinimide unit stereochemistry is dependent on the fraction of maleimide monomer in complexed form, and that the comonomer complex was participating in the propagation steps. Although the stereochemistry at the succinimide units was mostly cis, the relative stereochemistry between the vinyl ether methine carbons in the copolymers, and the methine carbons of adjacent succinimide units proved to be nearly random. The results were interpreted by invoking a concerted addition of the complex to the radical chain end, with radical attack occurring preferentially on the maleimide portion of the complex, on the side syn to the vinyl ether.

PAGE 14

CHAPTER I INTRODUCTION The concept of "molecular association" has long been recognized as important in virtually all fields of chemistry. This fact is underscored by the appearance of a plethora of books and reviews devoted to the subject during the past two decades. The concept is that of a relatively electron poor molecule, or acceptor (A), interacting in some way with an electron rich molecule, or donor (D). The interaction is such that the binding between the components is weaker Ik than a covalent bond. This definition is sufficiently broad so as to take in the gamut of both weak and strong interactions between both ionic and uncharged species. The concept has been utilized in many diverse fields of chemistry. Lewis acid-Lewis base interactions are, in principle, interactions between donors and acceptors. Inorganic and organometallic chemists have used the concept to describe metal-ligand interactions. Ion solvation, ionization equilibria, and catalysis are also fields of chemistry where donor-acceptor interactions play important roles. Organic chemists have applied the terms electrophilic and nucleophilic to acceptor and donor molecules, respectively. The literature abounds with such terms as "molecular complexes," "o and tt complexes," and "charge-transfer complexes," which all refer to some sort of donor-acceptor interaction.

PAGE 15

Modern interest in donor-acceptor complexes has blossomed since the discovery by Benesi and Hildebrand in 1949 of a new absorption band in the electronic spectrum of a solution of benzene and iodine in n-heptane, which did not appear in the spectrum of either compo2 nent alone. The explanation of this phenomenon was provided by Mull i ken in a series of papers published in 1950-1952 (reprinted in reference le). His conclusion was that the new band was due to an iodine-benzene complex possessing a 1:1 stoichiometry. A new electronic transition such as that described above is typical of mixtures of donor and acceptor molecules in relatively "inert" solvents (solvents which do not interact to an appreciable extent with either the donor or acceptor component). Thus, if the new band is in the visible region, solutions of colorless donors and acceptors may appear colored. The relatively weak interaction between donors and acceptors, such as the iodine-benzene system described above, is generally viewed as an equilibrium A + D „ K a C where the equilibrium constant K describes the strength of the interaction. The theoretical groundwork for such weak interactions has le been adequately described in the works of Mulliken and Person, and lc Kosower. While the details of this theory will not be discussed, several points are pertinent and will be briefly covered. The interaction between the components of the complex was de3 scribed in the valence bond formulation. The ground state wave function (tO and the excited state wave function (4V) are approximated by

PAGE 16

4V, = a * n (D,A) + b MD + ,A") (1] ^ = a ^(D + ,A") b Y Q (D,A) (2) where ^(D ,A~) represents the contribution to the bonding of the components from the resonance form where there has been complete transfer of one electron from donor to acceptor, and ^„(D,A) represents the contribution from all other bonding interactions. For weak molecular interactions, the relationship between the coefficients a and b is, a >> b, so V~ is the major contributor in the ground state and •, takes precedence in the excited state. The electronic transition between these two levels is thought to be the origin of the charge-transfer transition. One of the justifications for this theory is the applicability of empirical relationships between the energy of the charge-transfer transition (hv), the ionization potential of the 4 donor (I n )> and the electron affinity of the acceptor (E.). hv = I D E A + C (3) The constant C represents coulombic forces between the donor and acceptor. The values I n and E„ reflect the relative strength of donors and acceptors, respectively, strong donors having low Ir. and strong acceptors having high E„. Another important consequence of Equations (1) and (2) is that 2 complexes are predicted to have favored orientations, since b (a measure of the amount of charge-transfer) is proportional to the overlap integral between the highest occupied molecular orbital of the

PAGE 17

donor (HOMO), and the lowest unoccupied molecular orbital (LUMO) of 5 the acceptor. In other words, since the "charge-transfer" is from the HOMO of the donor to the LUMO of the acceptor, the maximum amount of charge-transfer stabilization of the complex is to be expected when the overlap between these orbitals is greatest. It should also be mentioned that the observation of a new electronic band in a solution of donor and acceptor molecules does not necessarily imply the existence of a complex. Such bands are observed even when the equilibrium constant (K) for complex formation is zero. The absorption is due to donor-acceptor pairs that are merely close or in contact, and can be fairly intense. This phenomenon is known as "contact charge-transfer" and has been recently reviewed in an excellent article by Tamres and Strong. Thus, the mere observation of a charge-transfer band in a reaction system should not be taken as evidence for the participation of charge-transfer complexes as reaction intermediates. lc d Kosower ' has reviewed the organic reactions in which chargetransfer complexes may be reaction intermediates. The types of reactions discussed include solvolysis, thermal electron transfer (e.g., the formation of radical anion-cation pairs), and reactions which follow light absorption by a charge-transfer complex. Recent examples of organic reactions in which charge-transfer complexes have been postulated as intermediates include the electrophil ic addition of bromine and mercuric salts to olefins, and the cleavage of alkyltin o compounds by mercuric salts.

PAGE 18

lc d Especially pertinent to this work are reactions that Kosower ' categorizes as class G reactions, or reactions that depend on the geometry of the charge-transfer complex. He describes these reactions as reactions which lead to a product structure other than that which might have been expected on the basis of random collision of the reactants or a knowledge of similar reactions in related molecules. He includes as examples the stereospecific hydrolysis of substrates by enzymes and Diels-Alder reactions. A recent example of the application of the charge-transfer concept to asymmetric induction in intramolecular Diels-Alder reactions is given by Trost, O'Krongly and 9 Belletire. Stereoselectivity has also been observed in photochemical 2+2 cycloadditions, where only the charge-transfer band was irradiated. Charge-Transfer Complexes in Polymerization Processes Several recent reviews have dealt with the influence of charge11 12 transfer complexes on polymerization processes. ' This dissertation deals with the influence of the charge-transfer complex on the propagation steps in alternating, radical -initiated copolymerizations. Alternating copolymerizations are characteristic in that a nearly 1:1 ratio of comonomers is found in copolymers produced from a wide variety of comonomer mole fractions in the initial monomer solution (referred to as the monomer feed). In a random copolymerization, the monomer ratio in the copolymer corresponds closely to that in the feed. The degree of alternation depends strongly on the polarity differences between the comonomers. If one monomer is a donor, while the other is an acceptor, the copolymer resulting from

PAGE 19

the polymerization of these monomers will possess a certain amount of alternation, which depends on the strength of the interaction between the comonomers. This effect was noticed very early in the development of copolymerization theory, and the Q,e scheme was introduced in order to provide a quantitative, empirical comparison of the polarity 13 of various monomers. The e value (polar parameter) is positive for electron-deficient olefins and negative for electron-rich olefins. The Q value is determined by resonance effects. The influence of the charge-transfer complex in alternating copolymerizations has been the subject of debate for many years. Several mechanisms have been proposed to explain the alternation ob14 served. First, the postulate was put forth by Walling et al . that polarity differences between the radical chain end and the incoming monomer would lower the energy of activation of a cross-propagation reaction, as opposed to a homopropagation reaction, thus producing alternating copolymers when the comonomers have widely different polarities. This mechanism will henceforth be referred to as the "free monomer" mechanism. The second possible explanation for alternation in these systems 15 was first proposed by Bartlett and Nozaki in 1946. These workers postulated that donor and acceptor monomers formed a charge-transfer complex which, due to an inherently higher reactivity of the complex relative to the free monomers, preferentially added to the chain end. In other words, the alternating nature of the copolymer results from a "homopolymerization" of the charge-transfer complex. Support for this theory may be found in the works of Butler and coworkers

PAGE 20

(maleic anhydride-di vinyl ether and maleic anhydride-furan copoly20 21 22 mers), Iwatsuki , Yamashita and Kokubo ' ' (maleic anhydridevinyl ether and maleic anhydride-anethole copolymers), Gaylord and 23 24 coworkers ' (maleic anhydride-conjugated diene copolymers) and Caze and Loucheux (maleic anhydride-vinyl acetate copolymers). This mechanism has been termed the "complex" mechanism. A third possibility is that both of the mechanisms described above are important in alternating copolymerizations. Tsuchida and Tomono, and Tsuchida et al . introduced this concept to explain results obtained for the styrene-maleic anhydride system. Seiner and 2° 29 30 31 Litt, Litt, and Litt and Seiner ' derived a series of kinetic equations that included the complex as a propagating species and obtained better fits to experimental copolymer composition data than could be obtained by using the classical "terminal" copolymerization 32 33 model developed by Mayo and Lewis, and Alfrey and Goldfinger. The terminal model predicts copolymer compositions based on a kinetic scheme which does not include a complex, and assumes random introduction of comonomers into the chain (i.e., only four possible propaga34 tion steps are included for two comonomers). Karad and Schneider have extended the Seiner-Litt equations to systems (e.g., styrenefumaronitrile) where the assumption of a small charge-transfer equilibrium constant does not hold. Still more recently, Cais, Farmer, 35 Hill and O'Donnell have presented an alternative to the Seiner-Litt complex participation model in which either copolymer composition data or triad fractions can be used to test the various copolymerization models. This treatment is unique in that it treats sequence number fractions in terms of transition probabilities as well as reactivity ra t i o s .

PAGE 21

Perhaps one of the strongest pieces of evidence for complex participation in alternating copolymerizations is that the overall rate of polymerization (R ) exhibits a maximum at a monomer feed ratio of nearly 1:1, where the concentration of the complex is greatest. Shirota et al . , and Yoshimura et al . ' have pointed out that the rate maximum for alternating copolymerizations seldom occurs at exactly 1:1 feed ratio. They also point out that the rate of polymerization at constant feed ratio and initiator concentration is generally greater than first order in total monomer concentration. If only the cross-propagation of free monomers operates, the rate should be proportional to the total monomer concentration. Thus, they also support the theory that both "complexed" and "free" monomers participate in the propagation reactions. They have also derived a scheme based on the change of R with total monomer concentration (at constant feed ratio), whereby a quantitative separation of the rate due to complex addition, and that due to free monomer addition, can be achieved. These workers applied their method to the systems N-vinylcarbazole (VCZ)-diethyl fumarate (DEF), and VCZ-fumaronitrile (FN). They concluded that the overall rate of copolymerization was, at most, 17% due to the addition of the complex in the VCZ-DEF system. Ten percent of the overall rate was due to complex addition for 39 the VCZ-FN system. Georgiev and Zubov have also developed a scheme that allows the determination of the ratio of rate constants for addition of "complexed" and "free" monomers. Their method utilizes the shift in the overall rate maximum as a function of the total monomer concentration. They found that a significant amount of complex

PAGE 22

participation occurs in the copolymerization of maleic anhydride and vinyl acetate. The last copolymerization theories to be considered are the penultimate and antepenultimate models first suggested by Mertz, Alfrey and Goldfinger, and later by Barb and Ham. These workers felt that deviations in copolymer composition from that predicted by the terminal model could be explained by invoking the effect of the penultimate or antepenultimate units in the copolymer chain. In other words, the reactivity of the chain end radical may differ depending on which monomer unit i-s in the penultimate or antipenultimate position. In spite of the large amount of data that has been amassed on systems that produce alternating copolymers (especially the styrenemaleic anhydride system), there is still disagreement as to what the exact mechanism is. Hyde and Ledwith have pointed out that the actual concentration of complex in systems that show a tendency to alternately copolymerize is invariably very low (equilibrium constants for complex formation (K) are generally in the range 0.01 0.5). Thus, if the complex has any role in the propagation steps, it necessarily must have an extremely high reactivity relative to the free monomers. This is a point that is still open to some debate. 43 Dodgson and Ebdon have reanalyzed styrene-maleic anhydride copolymer composition as a function of initial feed ratio. They conclude that the penultimate model gives as good a fit to the experimental 44 data as the complex model. Regel and Canessa have examined the complexation and copolymerization behavior of difluoromaleic anhydride

PAGE 23

10 with a variety of donors, and have come to the conclusion that donoracceptor complexes have no significant involvement in the copolymerization. It should be kept in mind that in nearly all of the studies discussed in this section, only two basic sources of experimental data have been used to make a large number of conclusions. These sources of data are copolymer composition (and sequence analysis) and kinetic data. As Hyde and Ledwith point out, these kinetic analyses invariably assume relative values of certain rate constants in order to obtain good fits with experimental data. Copolymer composition is generally calculated from either elemental analysis data or integration of copolymer NMR spectra. Copolymerization rates are typically calculated from a single copolymer weight obtained after a certain polymerization time. The polymers are routinely isolated by precipitation into a nonsolvent, so an implicit assumption is that the copolymers are completely insoluble in this nonsolvent. All of these experimental techniques are subject to errors which are seldom discussed. While the derivations, schemes and analyses discussed above are not questioned, it seems necessary to have accurate and copious data in order to distinguish between such mechanistic subtleties as complex formation prior to addition to the chain end, and complex formation with the chain end itself. Thus, it was thought that some new source of data was needed in order to help resolve the question of whether or not charge-transfer complexes play a significant role in alternating copolymerizations.

PAGE 24

11 Since, according to Mul liken theory, a donor-acceptor complex is expected to have a preferred geometry (vide supra), it may be that if the complex adds to the chain end in a concerted manner (as opposed to stepwise addition of the complex components), a certain degree of stereoregularity may be introduced into the copolymer chain. As mentioned earlier, in organic reactions where charge-transfer complexation between components has been observed, stereoselectivity is often observed in the product distribution. If the "free" monomers preferentially add to the chain end, the resulting copolymer stereochemistry may be expected to be nearly random since the chain end is expected to be either planar or possess a rapidly inverting pyramidal 45 structure. Thus, a detailed study of copolymer structure and stereochemistry as a function of copolymerization conditions was carried out. Conditions were selected so as to shift the complex equilibrium one way or the other. The system N-phenylmaleimide (NPM) 2-chloroethyl vinyl ether (CEVE) was selected for study. Nitrogen and chlorine elemental analysis allowed relatively accurate determination of the composition of copolymers produced from these monomers. N-Phenyl46 maleimide is an acceptor monomer with an e value of +3.24. CEVE 46 is a donor monomer with an e value of -1.58. Thus, they were expected to form alternating copolymers. Indeed, NPM has been shown to form alternating copolymers with styrene. Maleic anhydride copolymerizes alternately with CEVE. 26 ' 48 Several interesting reports have appeared that deal with asym49 metric induction into alternating copolymers. Kurokawa et al .

PAGE 25

12 copolymerized NPM with optically active menthyl vinyl ether and found that the copolymer retained some optical activity even after cleavage 50 of the optically active side chain. Beredjick and Schuerch obtained similar results with the system (-)-a-methylbenzyl methacrylate 51 maleic anhydride, although Chiellini et al . have questioned whether they obtained complete hydrolysis of the side groups. Optically active N-bornylmaleimide was copolymerized with styrene, methyl meth52 acrylate and vinyl idene chloride by Yamaguchi and Minoura. They found that more optical activity was observed in the copolymers which had a higher degree of alternation. It may be that a charge-transfer complex between the monomers plays an important role in these asym53 metric inductions. Kurokawa and Minoura, however, have explained such induction of asymmetry as being the result of the influence of the chiral chain end on the incoming monomer. Asakura, Yoshihara 54 and Maeshima have recently published an interesting report in which they describe the copolymerization of maleic anhydride with isobutyl vinyl ether, styrene, methacrylic acid, methyl acrylate, and methyl methacrylate in optically active solvents such as 1 -menthol. They found that optically active copolymers were produced only for the systems that copolymerized alternately (maleic anhydride-styrene and maleic anhydride-isobutyl vinyl ether). They postulate that the chiral solvent may interact with the charge-transfer complex, forming a trimolecular complex that may be important in the asymmetric induction observed. In spite of some disagreement about the results obtained in these studies, it seems at least plausible that an association of the monomers prior to addition to the chain end may influence the resulting stereochemistry.

PAGE 26

13 55 56 Hirai et al . , and Okuzawa et al . have shown that in polymers prepared in the presence of a Lewis acid, stereoregularity often accompanies rate enhancement. This observation may also mean that the formation of molecular complexes has an effect on polymer stereochemistry. To the best of our knowledge, a detailed study of the stereochemistry of alternating copolymers prepared by using conventional free radical initiation, has thus far not appeared. Carbon-13 NMR was used for the study of NPM-CEVE copolymer stereochemistry. Synthesis of a series of stereospecific model compounds 13 aided in the interpretation of the copolymer C results.

PAGE 27

CHAPTER II EXPERIMENTAL General All temperatures are uncorrected and are reported in degrees centigrade. Melting points were determined in open capillary tubes using a Thomas-Hoover Melting Point Apparatus. Pressures are expressed as millimeters of mercury. Infrared (IR) spectra were obtained by using a Perkin Elmer Model 281 Infrared Spectrophotometer. Spectra were calibrated using the 1601 cm" line of a polystyrene film. Spectra of oils and liquids were performed neat as a smear on a sodium chloride plate, and those of solids were obtained by using KBr pellets. Vibrational transition frequencies are expressed in wavenumbers (cm" ), with bands being assigned the following classifications: weak (w), medium (m), strong (s), very strong (vs) and broad (b). Proton nuclear magnetic resonance (NMR) spectra (60 MHz) were obtained on either a Varian A-60A or a Jeol JNM-PMX-60 spectrometer. Carbon-13 (25.00 MHz) and 100 MHz proton NMR spectra were recorded on a Jeol JNM-FX-100 instrument. Chemical shifts are expressed in parts per million (ppm) downfield from tetramethyl silane (TMS) unless stated otherwise. Multiplicities of proton and off-resonance de13 coupled C resonances are designated as singlet (s), doublet (d), 14

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15 triplet (t), quartet (q) or multiplet (m). Coupling constants (J) are expressed in Hertz (Hz). Mass spectra [low resolution (LRMS) and high resolution (HRMS)] were recorded on an Associated Electronics Industries (AEI) Model MS-30 spectrometer. Ultraviolet (UV) spectra were run on a Beckman ACTA V Spectrophotometer using 1 cm or 2 mm quartz cells. Catalytic hydrogenations were carried out in a low pressure, shaker type Parr Series 3910 Catalytic Hydrogenation Apparatus. Polymer number average molecular weights (M ) were determined using a Wescan 233 Molecular Weight Apparatus (vapor pressure osmometer). Chemical analyses were performed by Atlantic Microlab, Inc., Atlanta, Georgia. Compound headings appear with the common name listed first, followed by the systematic name (according to Chemical Abstracts) in parentheses. Registry numbers are given in brackets for known compounds. The Chemical Abstracts numbering scheme is used throughout to designate protons or carbons (e.g., coupling constants in NMR data) . Reagents and Solvents Unless otherwise noted, reagents were obtained from Aldrich Chemical Co. Dichloromethane (CH 2 C1 2 ) was distilled from P^g immediately before use. Purification of other solvents was carried out 57 using standard procedures and is described in the text. Deuterated solvents [chloroform-d (CDCK), d fi -acetone, dimethyl sulfoxide-dg

PAGE 29

16 (DMSO-dg), and dichloromethane-d 2 (CD 2 C1 2 )] for NMR spectra were obtained from either Merck and Co. Inc., Stonier Isotope Chemicals or Aldrich Chemical Co., and were used without further purification. N-Phenylmaleimide was obtained from Aldrich Chemical Co., and was recrystall ized from cyclohexane before use. Model Compound Synthesis N-Phenylsuccinimide (l-Phen.y1-2,5-pyrro! idine-dione) , [83-25-0], (1) CO Method A . The procedure of Umrigar was used for the synthesis of this compound. Exactly 10.0 g succinic anhydride (0.1 mole) (Aldrich) and 18.6 g distilled aniline (0.2 mole) were dissolved in approximately 100 ml dimethyl formamide (DMF) in a 250 ml round-bottomed flask. The flask was fitted with a reflux condenser, and the solution was refluxed for six hours. The bulk of the solvent was then removed via rotary evaporation. The deep red residue was dissolved in hot ethanol (95%), and about 1 g decolorizing carbon was added to the solution. After boiling for about ten minutes, the solution was filtered hot. The filtrate was allowed to cool slowly, and N-phenylsuccinimide (Jj crystallized as nearly colorless needTes. The needles were suction filtered and washed with cold ethanol. The product was recrystall ized again from ethanol to give 9.0 g _1 (51.4%), 59 mp 154-155°C (literature mp 156°C). l H NMR (60 MHz,CDCl 3 ) 5 2.79(s, 4H), 7.38(m, 5H). 13 C NMR (CDC1 3 ) 5 28.21(f), 126.32(d), 128.42(d), 128.95(d), 131.83(s), 176.03(s). IR (KBr) 3439(w), 3030(w), 2921(w), 1779(w), 1705(vs), 1593(w), 1500(m), 1391(s), 1290(m), 1190(vs), 1148(m), 1077(w), 1030(w), 1002(w), 927(m), 819(m), 766(m), 696(s), 670(m), 625(w) cm" 1 .

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17 Method B . N-Phenylmaleimide (NPM) could be reduced to N-phenylsuccinimide (I) by using the procedure of Medvedeva and Belotsvetov. To a 125 ml Erlenmeyer flask containing a solution of 25 ml glacial acetic acid and 50 ml deionized water was added 1.0 g NPM (5.8 mmole) and 3.0 g iron powder (53.7 mmole). The resulting slurry was stirred magnetically and heated on a hot plate to 90°C. After stirring for about twenty minutes, the yellow solution turned light green. After forty-five minutes, the solution had a red-brown color. At the end of one hour of stirring, the flask was allowed to cool, and the redbrown precipitate was filtered. The filtrate was neutralized with solid NaHCO-, and then extracted with CHCK (2 x 25 ml ) . The organic layer was dried o\/er anhydrous MgSO*, and then filtered. The solvent was removed on a rotary evaporator, and the residue recrystallized from 95% ethanol to yield 0.4 g _1 (39%) as colorless needles. The spectral properties (IR, NMR) and melting point were identical to those of 1^ synthesized via Method A. 3,4-Dimethyl-N-phenylmaleimide (3,4-Dimethyl-l-phenyl-lH-pyrrole-2,5dione) (2) Dimethyl maleic anhydride (Aldrich) (5.0 g, 39.6 mmole) was dissolved in 75 ml CHCK. This solution was stirred magnetically while 5.0 g (53.7 mmole) freshly distilled aniline was added dropwise. This solution was stirred on a hot plate at 40-45°C for ninety-one hours. No precipitation of the expected maleamic acid was noted. The CHC1-, was removed on a rotary evaporator to leave an orange crystalline mass. This residue was dissolved in a small amount of acetone and precipitated dropwise into rapidly stirred acidic water (100 ml +

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18 5 drops IS M hLS0 4 ). The precipitate was suction filtered, washed with water, and dried in a vacuum oven (50°C) overnight. After drying, the residue was recrystall ized from cyclohexane to yield 4.6 g (57.6%) of pale green needles, mp 90-91°C. ! H NMR (60 MHz, CDC1 3 ) 6 2.05(s, 6H), 7.38(s, broad, 5H). 13 C NMR (CDC1 3 ) 6 8.82, 125.69, 127.33, 128.94, 132.03, 137.39, 170.85. IR (KBr) 3450(w), 3048(w), 2987(w), 2953(w), 2920(w), 1750(w), 1699(vs), 1594(m), 1490(s), 1438(m), 1392(vs), 1123(m), 1090(s), 1070(m), 926(m), 769(s), 727(m), 700(s), 633(m). LRMS (70eV, m/z, relative intensity) 202 (13.7), 201 (M + , 100.0), 157 (7.9), 142 (28.0), 119 (19.0), 91 (16.9), 77 (11.0), 64 (12.5), 54 (62.0), 53 (25.0). cis-3,4-Dimethyl-N-pheny1succinimide (DMNPS) (3.4-Dimethyl-l-phenyl2.5-pyrrolidinedione), [6144-74-7], (3) To a 250 ml capacity hydrogenation bottle was added 1.0 g (5.0 mmole) 3,4-dimethyl -N-phenylmaleimide, approximately 150 ml 95% ethanol , and 0.01 g PtO(Englehard Industries). The bottle was placed on the Parr shaker, and the system was pressurized to 55 PSI with hydrogen gas. The solution was shaken for about five minutes, and the apparatus was then evacuated (aspirator). The system was pressurized with H ? and evacuated twice more, then pressurized to 55 PSI. The solution was shaken for 18.5 hours at room temperature. The catalyst was removed by filtration, and the solvent removed via rotary evaporation. The residue was recrystall ized from CC1* to yield 0.97 g (95%) very fine, colorless needles, mp 128-129°C

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19 £1 (literature nip 127°C). The cisrtrans isomer ratio (calculated from C NMR peak intensities) was > 14, or expressed as a percentage, the product was _> 94% cis. X H NMR (100 MHz, CDC1 3 ) 6 1.27(d, 6H, broad), 3.04(m, 2H), 7.35(m,5H). 13 C NMR (CDC1 3 ) 6 11.55, 38.40, 126.38, 128.28, 128.57, 128.96, 132.08, 179.35. IR (KBr) 3455(w), 3046(w,b), 2980(w), 1750(shoulder) , 1700(vs), 1591(m), 1490(s), 1452(w), 1427(m), 1395(vs), 1375(shoulder) , 1203(m), 1125(m), 1090(s), 1070(m), 935(b), 769(s), 750(m), 727(m), 697(s), 632(w), 615(w) cm" 1 . trans-3,4-Dimethyl-N-phenylsuccinimide (DMNPS) (trans-3,4-Dimethyll-phen,y1-2,5-p,yrro1idinedione), [35393-95-4], (4) The trans isomer of 3,4-dimethyl-N-phenylsuccinimide could be conveniently prepared by epimerization of the cis compound. Thus, approximately 0.2 g of the cis isomer was dissolved in 0.4 ml DMS0-d g , 13 and the resulting solution was filtered into a clean NMR tube. A C NMR spectrum was run (see below for chemical shifts of cis isomer in DMS0-d 6 ). A drop of 2,2,6,6-tetramethylpiperidine (TMP) (Aldrich) was then added to the tube, and the tube was placed in a 60°C water 13 bath. After being heated overnight, another C spectrum was run. The peaks due to the small amount of the trans isomer originally present (~ 5-6%) had grown at the expense of the peaks attributed to the cis compound. Indeed, the trans isomer was in excess. Continued 13 epimerization at 60°C (monitored periodically with C NMR) for about one week gave a maximum trans:cis ratio of about 6 (86% trans), as 1 3 judged from C NMR peak intensities. That no epimerization took

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20 place in the absence of TMP was verified by heating another sample of the cis isomer at 60°C in DMSO-cL for several days and observing the 13 C NMR spectrum. No change was observed. An analytical sample of 4 was isolated by evaporation of most of the DMSO-cL, followed by extraction of the residue with boiling cyclohexane. The hot cyclohexane was decanted from the residue and on cooling, _4 crystallized as colorless needles, mp 145-147°C (literature 61 mp 146°C). Compound 3 13 C NMR (DMSO-dg, internal reference DMSO-cL = 39. 5 52 ) 5 11.28, 37.99, 127.18, 128.30, 128.88, 132.69, 179.72. Compound 4 13 C NMR (DMSO-dg, internal reference DMSO-dg = 39. 5 62 ) 6 13.94, 42.42, 126.98, 128.06, 128.71, 132.78, 178.45. l ti NMR (100 MHz, DMS0-d 6 , internal reference DMSO-dg = 2.49 62 ) 6 1.33(d, broad, 6H), 2.67(m, 2H), 7.37(m, 5H). IR (KBr) 3450(w), 3062(w,b), 2980(w), 2937(w), 2875(w), 1780(w), 1710(vs), 1598(w), 1493(m), 1456(w), 1398(s), 1375(m), 1314(w), 1193(s), 1169(m), 1156(w), 1103(w), 1077(w), 948(m), 912(w), 852(w), 775(m), 738(m), 693(s), 620(w), 611(w) cm" 1 . cis-Hexahydroph thai anil ic acid (2-[(Phenylamino)-carbonyl]cyclohexanecarboxyl ic acid) (5) Cis-l,2-cyclohexanedicarboxyl ic anhydride (Aldrich) (5.0 g, 32.4 mmole) was dissolved in 200 ml CHCK in a 500 ml Erlenmeyer flask. Freshly distilled aniline (3.0 g, 32.2 mmole) was slowly added (dropwise over ten minutes) while rapidly stirring the solution. The solution was stirred for three hours. During this time a white powdery precipitate formed. The precipitate was suction filtered and dried in a 50°C vacuum oven to yield 7.0 g _5 (87.4%), mp 176-177°C (literature 63 mp 172-173°C).

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21 l H NMR (60 MHz, DMSO-dg) 6 1.52(s, broad, 4H), 1.83(m, 4H), 2.57(m, 1H), 2.99(m, 1H), 6.85-7.73(m, 5H), 9.63(s, 1H), 11.78(s, broad, 1H). 13 C NMR (DMS0-d 6 , internal reference DMSO-dg = 39. 5 62 ) 6 22.49, 24.10, 25.32, 27.85, 42.13, 42.67, 119.19, 122.74, 128.54, 139.66, 172.70, 175.18. IR (KBr) 3388(s), 3060(s,b), 2935(s), 2860(m), 1718(vs), 1647(vs), 1597(vs), 1532(vs), 1498(m), 1433(vs), 1400(m), 1327(m), 1238(m), 1210(s), 1188(vs), 1130(m), 962(w), 938(w), 890(w), 860(w), 774(m), 746(m), 731(m), 691(s), 610(w) cm -1 . cis-Hexahydrophthal imide (cis-Hexahydro-2-phenyl-lH-isoindole-l,3(2H)dione) (cis-HHPI), [26491-47-4], (6) Compound 5 (6.7 g, 27.1 mmole) was dissolved in 300 ml acetic anhydride and stirred magnetically at 80°C for twenty-four hours. The solution was cooled and slowly added to vigorously stirred water (dropwise over 1.5 hours). The cream colored precipitate that formed was suction filtered and dried in a 50°C vacuum oven overnight. The precipitate was mixed with 100 ml CHC1,, filtered, and washed several times with CHCK. The chloroform insoluble part proved to be unreacted starting material (2.6 g). The chloroform was removed from the filtrate on a rotary evaporator, leaving 3.8 g residue. This residue was recrystall ized from CC1, to give 3.2 g fine white needles (84.2% based on recovered starting material), mp 130-133°C (literature 53 mp 132-133°C). : H NMR (CDC1 3 , 100 MHz) 6 1.48(m, 4H), 1.85(s, broad, 4H), 2.98(m, 2H), 7.35(m, 5H).

PAGE 35

22 13 C NMR (CDC1 3 ) 6 21.81, 23.93, 40.06, 126.25, 128.28, 129.03, 132.15, 178.55. IR (KBr) 3468(w), 2942(m), 2911(m), 2858(m), 1775(w), 1709(vs), 1592(w), 1491(m), 1460(w), 1433(w), 1378(s), 1356(m), 1342(w), 1327(w), 1295(w), 1227(w), 1193(m), 1181(s), 1172(s), 1159(m), 1130(s), 1087(m), 921(w), 902(w), 887(m), 830(m), 776(m), 743(m), 698(m), 617(w) cm -1 . trans-Hexahydrophthalanil ic acid (2-[(Phenylamino)carbony1 ]-cyc!ohexanecarboxyl ic acid) (7) To a 125 ml Erlenmeyer flask was added 2.0 g (13.0 mmole) transcyclohexanedicarboxylic anhydride (Aldrich) and 75 ml. CHCU. The resulting solution was stirred magnetically while 1.3 g (14.0 mmole) distilled aniline was added dropwise. The solution was stirred at 50°C for one hour. During this time, a white powdery precipitate formed. The precipitate was suction filtered and dried in a vacuum oven to yield 2.9 g of product (90.2%), mp 206-212°C (literature 63 mp 224-225°C). l H NMR (100 MHz, DMSO-dg) 6 1.30(s, broad, 4H), 1.75(s, broad), 1.98(s, broad), 2.54(s, broad, 2H), 6.93-7.78(m, 5H), 9.92(s, 1H), 12.06(s, broad, 1H). 13 C NMR (DMS0-d 6 , internal reference DMS0-d 6 = 39. 5 62 ) 6 24.93, 25.12, 28.58, 28.88, 29.53, 44.35, 44.47, 46.54, 119.12, 122.79, 128.47, 139.53, 173.48, 175.94, 176.04. IR (KBr) 3325(m), 3060(b), 2950(m), 2927(m), 2862(w), 1699(vs), 1655(s), 1601(m), 1533(s), 1500(w), 1443(m), 1416(m), 1328(m), 1313(m), 1262(m), 1205(m), 1186(w), 1115(w), 920(m), 900(w), 770(w), 745(m), 692(m), 672(w) cm" 1 .

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23 trans-Hexahydrophthalimide (trans-Hexahydro-2-phenyl-lH-isoindolel,3(2H)-dione) (8) To a 125 ml Erlenmeyer flask was added 2 g 8 and 100 ml acetic anhydride. The resulting solution was stirred at 80°C for twentytwo hours and then allowed to cool to room temperature. The solution was added dropwise to a vigorously stirred aqueous NaCl solution (500 ml). Some white precipitate formed. The mixture was cooled in an ice bath for several hours, and the white crystalline solid that formed was suction filtered, washed with water, and dried overnight in a 50°C vacuum oven. Recrystall ization from CC1. yielded 1.2 g colorless, very fine crystals, mp 194-196°C (literature 63 mp 195196°C). l H NMR (CDC1 3 , 100 MHz) 6 1.32-1.67(m, 4H), 1.7-2.3(m, 4H), 2.3-2.5 (m, 2H), 7.2-7. 5(m, 5H). 13 C NMR (CDC1 3 ) 6 25.15, 25.54, 47.52, 126.25, 128.03, 128.98, 132.15, 175.77. IR (KBr) 3462(w), 3060(w), 2922(m), 2860(w), 1773(w), 1711(vs), 1595(w), 1490(m), 1446(w), 1375(s), 1292(w), 1270(w), 1229(w), 1212(w), 1174(s), 1105(s), 1072(w), 1046(w), 922(w), 877(m), 753(m), 692(m), 670(w), 620(w) cm -1 . l-Methoxy-l,3,3-triethox,ybutane (9) To a 125 ml Erlenmeyer flask was added 20 g (200 mmole) 4methoxy-3-buten-2-one (Aldrich), 30 g (202 mmole) triethyl orthoformate (Aldrich), 0.1 g p-toluenesulfonic acid monohydrate (Aldrich) and 50 ml absolute ethanol . The solution turned deep black soon after the addition of the p-toluenesulfonic acid. The reaction was somewhat

PAGE 37

24 exothermic. The flask was stoppered and allowed to stand at room temperature for sixteen hours. At the end of this time, the mixture was fractionally distilled through a Vigreaux column. Distillation at atmospheric pressure yielded a fraction boiling at 52-57°C (~ 20 ml) presumed to be ethyl formate (literature bp 54.5°C). Excess ethanol was also removed at atmospheric pressure. The distillation flask was allowed to cool and the pressure reduced to lOmmHg. Continued distillation gave 16.6 g (37.7%) colorless liquid with a boiling range 85-95°C (10 mm). The product proved to be a mixture of isomers (various monomethoxy-triethoxybutanes) . l H NMR (100 MHz, acetone-dg) 6 1.02-1.32(m, 4 overlapping triplets, J = 7.0 Hz, 9H), 1.25(s, 3H), 1.88(d, J = 4.7 Hz, 2H), 3.09, 3.10, 3.21 and 3.23 (4 singlets, combined area 3H), 3.26-3.65 (m, overlapping quartets, J = 7.0 Hz, 6H), 4.50-4.60(m, overlapping triplets, J = 4.7 Hz, 1H). 13 C NMR (acetone-d 5 ) 6 15.64, 15.74, 22.51, 22.56, 23.03, 23.07, 41.18, 41.64, 42.13, 47.86, 47.91, 51.73, 55.75, 60.58, 60.67, 60.94, 61.16, 100.54, 100.59, 101.40. IR (thin film) 2980(vs), 2938(s), 2883(s), 1614(w), 1512(m), 1483(w), 1445(m), 1393(m), 1377(m), 1306(m), 1276(w), 1247(m), 1172(m), 1160(m), 1120(s,b), 1092(m), 1058(s,b), 999(w,b), 948(m), 838(m) cm" 1 . cis-2a,6a,3,4-Tetrahydro-3,5-diethoxy-N-phenylphthal imide (4,6-Diethoxy-2-pheny1-3a,7a,4,5-tetrahydro-lH-isoindo1e-l,3(2H)-dione) (10) The N-phenylmaleimide (NPM) used in this preparation was obtained from Aldrich Chemical Co., and was recrystall ized from cyclohexane

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25 before use. N-Phenylmaleimide (5.0 g, 29.0 mmole) and l-methoxy-1,3, 3-triethoxybutane (6.7 g, 30.4 mmole) were mixed in a 100 ml, onenecked round-bottom flask. Hydroquinone (0.3 g) and Na ? HP0 ? (0.3 g) were also added. The flask was evacuated to 25 mmHg with a vacuum pump and immersed in a 70°C oil bath. The yellow crystalline mass soon dissolved, and the resulting solution was stirred magnetically at 70-80°C and 25 mmHg, until its weight decreased by about 2.5 g (2 equivalents of ethanol). This took about one week (6.8 days). The temperature was controlled so that it did not exceed 85°C at any time. The flask was cooled to room temperature, and the yellow solid mass was triturated with absolute ethanol. The cream colored precipitate that formed was filtered, and the ethanol was removed from the filtrate via rotary evaporation. The residue was triturated again to yield more cream colored powder, which was filtered. This process was repeated again, and the combined precipitates were recrystall ized from ethanol :water (3:1) to yield 5.2 g (56.9%) colorless plates, mp 156-157°C. l ti NMR (tOO MHz, CDC1 3 ) 6 1.09(t, J = 6.96, 3H), 1.31(t, J = 6.96, 3H), 2.35(broad AB quartet, 2H), 3.20(dd, J , = 3.9, J , = oa ,4 da , /a 8.9, 1H), 3.24-3.98(complex m, 5H), 4.21(apparent q, J 4 g « 2.8, J 4,5a s J 4,3a = 3 ' 9 ' 1H >' 4 95 < dd > J 7,5 = ^ J 7,7a = 3 ' 9 ' J 7j5 = 0, 1H), 7.20-7.55(m, 5H). C NMR (CDC1 3 ) 6 14.45(q), 15.30(q), 30.85(f), 39.21(d), 44.47(d), 62.53(f), 65.02(f), 72.50(d), 86.68(d), 126.60(d), 128.33(d), 129.01(d), 132.35(d), 152.72(s), 176.16(s), 176.94(s). 13

PAGE 39

26 IR (KBr) 3480(w), 3059(w), 2973(m), 2938(m), 2890(m), 1779(w), 1717(vs), 1668(m), 1594(w), 1492(m), 1450(m), 1386(s), 1342(w), 1324(w), 1300(tn), 1279(m), 1260(m), 1233(m), 1210(s), 1194(s), 1183(s), 1170(s), 1163(s), 1150(m), 1076(m), 1045(m), 1020(m), 924(w), 895(w), 864(w), 838(w), 789(m), 777(m), 744(s), 687(m), 626(w), 610(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 315(M + , 10.0), 271 (18.8), 242 (15.2), 168 (12.3), 139 (21.5), 119 (100.0). HRMS (C 18 H 21 N0 4 requires 315.14706) found 315.14699. Analysis. Calculated for C^H^KL: C, 68.55; H, 6.71; N, 4.44. Found: C, 68.54; H, 6.74; N, 4.44. cis-3,5-Diethoxyhexahydro-N-phenylphthal imide (4,6-Diethoxyhexahydro2-phenyl-lH-isoindole-l,3(2H)-dione) (11) 65 Raney nickel catalyst was prepared by slowly adding 70 ml 16% aqueous NaOH to 10 g Raney nickel alloy (PCR) in a 250 ml beaker. The beaker was cooled in an ice bath if the generation of hydrogen became too violent. After the addition of the NaOH solution was complete, the beaker was heated gently on a hot plate until the evolution of hydrogen stopped (~ 2 hours). The solution was diluted with water and the black, active catalyst was isolated by suction filtration, and washed with water until the filtrate was neutral to litmus. Care was taken so as not to let the catalyst become dry, since Raney nickel ignites spontaneously when dry. Compound _10 (1.75 g, 5.5 mmole) was dissolved in 200 ml 95% ethanol in a 250 ml hydrogenation bottle, and the moist, freshly made catalyst was added. The solution was heated to ~ 70°C with a heating

PAGE 40

27 tape wrapped around the bottle, and the bottle was placed in the Parr hydrogenation apparatus. The apparatus was pressurized with hydrogen, evacuated (aspirator) several times, and finally pressurized to 51 PSI. The solution was shaken at this hydrogen pressure and 70-80°C for 1.5 hours. At the end of this time, the solution was cooled to room temperature and the pressure released. The solution was filtered into a round-bottom flask, and the solvent was removed by rotary evaporation to leave 1.6 g oily residue. NMR analysis showed that the residue was about 25% starting material. The residue was treated with absolute ethanol , and the cream colored precipitate that formed was isolated by filtration (0.25 g). Rotary evaporation of the filtrate left 1.2 g (91.4% based on recovered starting material) pale green oil. This oil was purified further by percolation through a short (~ 15 cm) silica gel column using isooctaneiCHLC^methanol (50:20:1). l H NMR (100 MHz, CDCI3) 6 1.10(t, J = 7.0, 3H), 1.20(t, J = 7.0, 3H), 1.75-2.35(m, J 5M = 2.2, J^g = 6.5, 4H), 2.79-3.07(m, J 3a>4 = 3 5 ' J 7a,7a = 6 " 3 ' J 7a, 7B = 10 ' 6 ' J 3a,7a = 9 " 5 ' 2H >' 3 20 " 3 81 (m, 5H), 4.01-4. 16(m, J 4 3a = 3.5, 1H), 7.20-7. 50(m, 5H). 13 C NMR (CDC1 3 ) 6 15.30(q), 15.55(q), 25.98(f), 32.58(f), 37.48(d), 43.72(d), 63.75(f), 64.43(f), 72.89(d), 74.03(d), 126.57(d), 128.40(d), 129.03(d), 132.30(s), 176.67(s), 178.43(s). IR (smear on NaCl plate) 3480(w), 3070(w), 2979(m), 2925(m), 2880(m), 1778(w), 1715(vs), 1598(w), 1500(s), 1457(w), 1445(w), 1376(s), 1290(w), 1262(w), 1230(w), 1190(s), 1160(m), 1105(s), 1079(m), 922(w), 840(w), 797(w), 758(m), 736(m), 690(m), 620(m) cm" 1 .

PAGE 41

28 LRMS (70 eV, m/z, relative intensity) 317 (3.5, M + ), 273 (57.6, metastable), 227 (100.0). HRMS (C lg H 23 N0 4 requires 317.1627) found: 317.1625. Analysis. Calculated for C lg H 23 N0 4 : C, 68.12; H, 7.30; N, 4.41. Found: C, 67.98; H, 7.32; N, 4.36. l-Methoxy-3-(trimeth,ylsiloxy)butadiene, [59414-23-2], (12) This compound was made according to the procedure of Danishefsky and Kitahara. Freshly fused ZnCl 2 (1.0 g) and 58.0 g triethylamine (distilled from K0H) were added to a dry 500 ml Erlenmeyer flask. The flask was stoppered, and the contents magnetically stirred for one hour to form a white, milky suspension. At the end of the hour, 25.0 g (0.25 mole) of 4-methoxy-3-buten-2-one (Aldrich) dissolved in 75 ml benzene was added to the suspension. Then 54.2 g (0.50 mole) chlorotrimethylsilane (Pierce Chemical Co.) was added with a 30 ml syringe. An exothermic reaction took place on addition of the chlorotrimethylsilane, and an orange precipitate formed immediately. This suspension was stirred at 40-50°C overnight and then poured into 500 ml of anhydrous ether. The precipitate was suction filtered and washed several times with anhydrous ether. The filtrate was concentrated on a rotary evaporator and then distilled. The colorless fraction distilling at 48-50°C (4.5mmHg) was collected to yield 24.3 g (56.5%) 1-methoxy3-(trimethylsiloxy)butadiene (literature 66 bp 54-55°C, 5mm Hg). 1 H NMR (100 MHz, CDC1 3 ) 6 0.22(s, 9H), 3.54(s, 3H), 4.06(d, J = 3.4, 2H), 5.32(d, J = 12.3, 1H), 6.81(d, J = 12.3, 1H). 13 C NMR (CDC1 3 , internal reference CDC1 3 = 77. 62 ) 6 -0.34(q), 55.87 (q), 90.62(f), 102.85(d), 150.06(d), 153.71(s).

PAGE 42

29 IR (thin film) 3120(w), 3080(w), 3006(w), 2963(m), 2903(w), 2837(w), 1652(s), 1596(m), 1453(w), 1323(vs), 1257(s), 1213(vs), 1167(s), 1133(m), 1022(vs), 994 (m), 960(w), 939(m), 921(m), 850(vs), 753(m), 682(w), 638(m), 617(m) cm" 1 . cis-3-Methoxy-N-phenyl-2a,3,6,6a-tetrahydro-5-trimethyl siloxyphthalimide (cis-4-Methoxy-2-phenyl-3a,4,7,7a-tetrahydro-6-trimethylsiloxylH-isoindole-l,3(2H)-dione) (13) The procedure used was analogous to that used by Danishefsky r 7 et al . To a 125 ml Erlenmeyer flask was added 10.0 g solid Nphenylmaleimide (57.8 mmole), then 11.1 g l-methoxy-3-(trimethyl silbxy)butadiene. The flask was swirled, and evolution of heat was noted. A homogeneous, light yellow solution resulted. After about five minutes, the solution began to cool. A yellowish white crystalline mass formed on cooling. This crude product was broken up and washed with a small amount of cold absolute ether. The product was filtered, yielding 16.3 g pure white crystals. The ether washings were evaporated, yielding more crystalline product. This residue was washed, this time with a smaller amount of ether, and filtered to yield 1.5 g more product. The total yield was 17.8 g (89.4%) of white crystals, mp 114-116°C. Repeated recrystall ization from cyclohexane failed to yield product that gave a satisfactory elemental analysis. This was probably due to partial hydrolysis of the silyl ether. 1 H NMR (100 MHz, CDC1 3 ) 5 0.25(s, 9H), 2.28-2. 55(dd, "B" part of AB quartet, J 70 7 = 16.9, J 7p , = 10.1, J 7o c * 0, 1H), 2.66-2.93 / p , /ot / p , /a /p, j

PAGE 43

13 30 (ddd, "A" part of AB quartet, J 7 7o = 16.9, J 7 , = 6.4, /a»/p /a, /a J ?a 5 = 2.4, 1H), 2.98-3. 16 (dd, "B" part of AB quartet, J 3a ?& = 9.5, J 3a 4 = 4.0, 1H), 3.20(s, 3H), 3.20-3.47(6 lines of expected 8 line pattern, "A" part of AB quartet, J_ 7 = 10.1, J 7a,3a = 9 ' 5 ' J 7a,7a = 6 " 4 ' 1H >' 4 35 < dd ' J 4,5 = 6 ' 4 > J 4,3a = 4.0), 5.18(dd, J 5)7a = 2.4, J 5>4 = 6.4, J^^ z 0, 1H), 7.207.51(m, 5H). C NMR (CDC1 3 ) 6 0.121(q), 27.07(f), 37.43(d), 45.69(d), 55.54(q), 73.06(d), 100.94(d), 126.64(d), 128.35(d), 128.98(d), 132.35(s), 156.20(s), 176.06(s), 178.77(s). IR (KBr) 3477(w), 3075(w), 2985(w), 2958(w), 2922(w), 2900(w), 2820(w), 1775(w), 1712(vs), 1643(m), 1597(w), 1496(m), 1455(w), 1388(s), 1360(m), 1342(m), 1308(m), 1271(m), 1257(m), 1228(m), 1197(s), 1182(s), 1097(m), 1081(m), 1021(w), 975(m), 928(m), 896(m), 854(s), 822(m), 748(m), 693(.m), 622(m) cm -1 . LRMS (70 eV, m/z, relative intensity) 345 (3.1), 345 (M + , 12.1), 330 (39.4), 314 (41.6), 296 (12.2), 172 (30.4), 157 (100.0). Analysis. Calculated for c 18 H 23 N0 4 Si : C ' 62 58 i H > 6.71; N, 4.05. Found: C, 63.63; H, 6.54; N, 3.90. ci s-Hexahydro-3-methoxy-5-oxo-N-phenyl phthal imide (ci s-Hexahydro-4methoxy-6-oxo-2-phenyl-lH-isoindole-l,3(2H)-dione) (14) Silyl enol ether JJ was hydrolyzed to ketone 1A via two different r-J methods. The first uses the procedure of Danishefsky et al . Thus, 10.0 g (29.0 mmole) of silyl enol ether L3 was treated with 100 ml of a solution comprised of 0. IN HC1 and tetrahydrofuran (THF) (1:4 by volume). After stirring for 0.5 hour, the pale yellow solution was

PAGE 44

31 poured into 300 ml 5% NaHCO.,. The resulting deep yellow aqueous solution was extracted with CHCl, (4 x 75 ml). The combined organic layers were dried over anhydrous MgSO* overnight. The MgSO, was separated by filtration, and the solvent removed by rotary evaporation. The resulting pale green oil was placed in a dessicator that was subsequently evacuated. After drying at reduced pressure for twenty-four hours, the oil solidified, yielding 7.2 g (90.9%) very pale green solid. CO The method of Semmelhack et al . was preferable for the desilylation of JJ3 because the reaction is easy and the product \/ery clean. o Enough unactivated 3 A molecular sieves (Linde) were added to a 125 ml Erlenmeyer flask to cover the bottom. Then 1.0 g 13 dissolved in 100 ml of a solution of methanol : CHC1 ^ (1:1) was added to the flask. The flask was stoppered and allowed to stand at room temperature overnight. The molecular sieves were removed by filtration and the solvent evaporated on a rotary evaporator, to leave 0.80 g pale green oil (101%). The product was dissolved in 5 ml of absolute ethanol : chloroform (1:1). Slow evaporation of this solution yielded colorless crystals which were isolated by filtration and washed with cold absolute ethanol. After drying in a vacuum oven (50°C) overnight, the product weighed 0.70 g. Another workup of the ethanol washings yielded an additional 0.05 g colorless crystals for a total isolated yield of 0.75 g (95%), mp 107-108°C. Both of the above methods produced products with identical spectral properties.

PAGE 45

32 l \i NMR (100 MHz, CDC1 3 ) 6 2.17(dd, "B" part of AB quartet, J g 4 = 2 2 > J 53,5a = 18 3 ' 1H >' 2.50-3.50( m , J^ z 7.5, J^ z 9.5, J 5a>4 * 3.2, J 3aj7a s 9.4, J 3a>4 a 3.5, 5H), 4.18 (apparent q, 1H), 7.19-7.53(m, 5H). 13 C NMR (CDC1 3 ) 6 36.10(d), 36.83(t), 40.46(t), 44.38(d), 57.25(q), 75.21(d), 126.54(d), 128.65(d), 129.09(d), 132.02(s), 175.31(s), 177.56(s), 205.91(s). IR (KBr) 3480(w), 3078(w), 3054(w), 2998(w), 2965(w), 2952(w), 2935(w), 2904(w), 2838(w), 1778(w), 1710(vs), 1598(w), 1494(m), 1458(w), 1409(m), 1389(s), 1347(m), 1328(w), 1308(w), 1263(w), 1240(w), 1230(w), 1203(s), 1181(m), 1098(m), 1082(m), 1041(w), 1021(w), 968(w), 913(w), 897(w), 889(w), 814(m), 779(w), 758(m), 732(m), 693(m), 624(m) cm" 1 . LRMS (70 eV, m/z, relative intensity) 273(M + , 72.4), 243 (28.1), 188 (100.0). Analysis. Calculated for C.gH.gNO.: C, 65.92; H, 5.53; N, 5.12. Found: C, 65.98; H, 5.54; N, 5.09. cis-Hexahydro-5-hydroxy-3-methoxy-N-phenylphtha1 imide (cis-Hexahydro6-hydroxy-4-methoxy-2-pheny1-lH-isoindole-l,3(2H)-dione) (15) Ketone ]A was reduced to alcohol _^5 by catalytic hydrogenation. Thus, 2.5 g (9.15 mmole) ketone ^4 was dissolved in 200 ml 95% ethanol in a 500 ml capacity hydrogenation bottle. A catalytic amount (~ 0.01 g) of Pt0 ? (Englehard Industries) was added to the solution, and the bottle was placed in the Parr shaker. The hydrogenation apparatus was flushed with hydrogen several times and finally pressurized to 46 PSI with hydrogen. The shaker was started, and the

PAGE 46

33 solution was shaken at room temperature for four hours. At the end of this time, the apparatus was depressurized, and the catalyst was removed by filtration. The solvent was removed by rotary evaporation to yield a pale green oil that crystallized on standing in a dessicator for several days. This procedure yielded 2.5 g (99%) colorless crystals of alcohol _15, mp 125-127°C. X H NMR (100 MHz, CDC1 3 ) 6 1.6-2.4(m, J 5g 4 = 3.8, J 5 g : 6.1, J g fe : 15.1, J /a 6 z 7.2, J ?a 7a = 6.0, 4H), 2.76-3. 10(m, 2H), 3.2(s, broad, 1H), 3.33(s, 3H), 3.6-4.2(m, 2H), 7.10-7.54(m, 5H). 13 C NMR (CDC1 3 ) 6 28.80(t), 32.21(f), 36.48(d), 43.86(d), 57.73(q), 64.97(d), 76.18(d), 126.60(d), 128.52(d), 129.11(d), 132.18(s), 176.33(s), 178.16(s). IR (KBr) 3507(s), 3043(w), 2979(w), 2960(w), 2915(w), 2892(w), 2856(w), 2808(w), 1772(w), 1704(vs), 1596(w), 1493(m), 1457(w), 1392(s), 1352(w), 1292(m), 1279(m), 1263(m), 1230(w), 1200(m), 1178(s), 1151(m), 1099(m), 1084(m), 1064(m), 973(w), 938(w), 918(w), 901(w), 846(w), 805(m), 761(m), 736(m), 691(w), 618(w), 610(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 275(M + , 57.0), 245 (24.9), 227 (11.4), 188 (23.3), 119 (24.5), 103 (91.5), 84 (100.0). Analysis. Calculated for C 15 H 17 N0 4 : C, 65.44; H, 6.22; N, 5.09. Found: C, 65.42; H, 6.22; N, 5.09. cis-3,5-Dimethoxyhexahydro-N-phenylphthal imide (cis-4,6-Dimethoxyhexahydro-2-phenyl-lH-isoindole-l,3(2H)-dione) (16) This compound was prepared by methylation of alcohol _15_ using 69 trimethyloxonium tetrafluoroborate. Alcohol 15 (1.5 g, 5.45 mmole)

PAGE 47

34 was dissolved in ~ 250 ml freshly distilled (from P0O5) ChLCU in a 500 ml Erlenmeyer flask with a ground glass stopper. Excess (~ 3 g) trimethyloxonium tetrafluoroborate (Alfa) was added under a blanket of dry nitrogen, i.e., the bottle was opened and the transfer made under an inverted funnel connected to a nitrogen line. The trimethyloxonium tetrafluoroborate was largely insoluble in ChLCl ? . The flask was tightly stoppered, and the suspension was stirred magnetically for sixty hours at room temperature. At the end of this time, 100 ml FLO was added. Then, solid NaHCOwas added to the stirred solution in small increments until further additions no longer resulted in the evolution of CO2 bubbles. The organic layer was separated, and the aqueous layer was extracted further with CHC1-, (2 x 20 ml). The combined organic layers were dried over anhydrous MgS0» for several hours. The MgSO* was separated by filtration and the solvent removed by rotary evaporation to yield a yellow orange oil. This oil was purified by percolation through a short (15 cm) silica gel column using hexanerChLCl-^leOH (50:20:1). A pale yellow oil remained after solvent evaporation. This oil solidified on standing in a dessicator (~ 1 week). Recrystall ization of this solid residue from absolute ethanol gave 1.4 g (89%) colorless crystals, mp 120-122°C. l H NMR (300 MHz, CDC1 3 ) 6 1 .841-2. 072(dddd, J g 4 = 2.8, J 5g 6 = 5.6, J 5a,4 = 4 ' 7 ' J 5a,6 = 8 ' 6 ' J 5a,5 B = 15 ' 3 ' 2H) ' i" 914 " 2 " 029 ^^ ent q, center peaks spl it, J 7o 7 = 11.9, J 7o 7 „ = 10.7, J 7 _ c = r r ' 7(3, 7a 73,7a 73,6 11.2, 1H), 2.303-2.383(ddd, J 7 7D = 11.9, J 7 = 7.1, J 7 , = 7a, 7B 7a, 7a 7a, 6 4.3, 1H), 2.878-2.923(dd, J 3a 4 = 3.8, J 3a /a = 9.6, 1H), 2.9493.040(ddd, J 7a>3a = 9.6, 7aj7B = 10.7, J 7aj?a = 7.1, 1H),

PAGE 48

13 35 3.306(s, 3H), 3.333(s, 3H), 3.430-3.529(dddd, J, 7o = 11.2, 0,/g J, , = 8.6, J fi , = 5.6, J, 7 = 4.3, 1H), 3 . 959-3 . 996(ddd, o,ba 6,53 6,7a J 4,5a = 4 ' 7 ' J 4,3a = 3 ' 8 ' J 4,5g = 2 * 8 ' 1H) ' 7.244-7.484(m, 5H). C NMR (CDC1 3 ) 6 25.46(t), 31.19(t), 37.16(d), 43.42(d), 55.95(q), 56.71(q), 74.25(d), 75.59(d), 126.60(d), 128.35(d), 128.69(d), 132.32(s), 176.33(s), 178.33(s). IR (KBr) 3470(w), 3066(w), 2991(w), 2940(m), 2895(m), 2812(m), 1775(w) : 1709(vs), 1594(w), 1497(s), 1470(w), 1452(m), 1420(w), 1388(vs), 1362(m), 1320(w), 1292(m), 1252(m), 1192(s), 1180(s), 1160(s), 1100(s), 1078(vs), 1032(w), 987(w), 973(w), 940(w), 903(w), 846(w), 805(w), 792(w), 769(m), 753(w), 738(m), 695(m), 623(w), 610(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 289 (M + , 13.2), 259 (26.8), 227 (30.3), 175 (28.5), 173 (50.4), 119 (20.8), 111 (14.3), 110 (15.7), 109 (15.5), 101 (17.0), 93 (23.2), 85 (27.9), 84 (100.0). HRMS. Required for C 16 H ig N0 4 : 289.13141 Found: 289.13189. Analysis. Calculated for C 16 H 19 N0 4 : C, 66.42; H, 6.62; N, 4.84. Found: C, 66.32; H, 6.64; N, 4.82. Epimerization of cis-4,6 Diethoxyhexahydro-2-phenyl-lH-isoindolel,3(2H)-dione (11) Compound ]A (~ 200 mg) was dissolved in 0.4 ml DMS0-d g , and the 13 solution was transferred to an NMR tube. A C NMR spectrum was obtained on this sample. Several drops of 2,2,6,6-tetramethylpiperidine (Aldrich) were then added to the tube, and the tube was placed in a 60°C water bath. The epimerization was monitored by periodically

PAGE 49

36 13 obtaining C spectra over a period of several weeks (fifty-four days). Nine peaks with distinctly different chemical shifts from the original compound were observed to increase in intensity with 1 3 time. The final cis/trans ratio was about three (75% cis). The C chemical shifts and their assignments are given in Table 1. Carbons not included in Table 1 did not exhibit a readily observable chemical shift change on epimerization. TABLE 1 13 C Chemical Shifts (6, ppm from TMS) for cis and trans 11 . (DMS0-d 6 , internal reference DMSO-d, = 39.5) Carbon 6 cis 6 trans 6 cis6 trans 0.93 0.32 -1.56 0.81 -1.26 r0.75 ^.09 2.39 2.42 0.27 1

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37 5-Methoxy-S-[(phenylamino)carbonyl]-2-oxabicyclo[2.2.2]octan-3-one mi Attempted reduction of ketone _14 to alcohol 15_ by using sodium borohydride (NaBHJ as a reducing agent led to bicyclic lactone 17 instead. Thus, 0.2 g (5.3 mmole) NaBH, (Eastman) was added to a stirred solution of 1.0 g (3.7 mmole) ketone 14 in 75 ml of 95% ethanol . The solution was stirred for 0.5 hour at room temperature. At the end of this time, 12 M HC1 was slowly added (dropwise) until the solution was acidic to litmus. Upon rotary evaporation of the bulk of the solvent, a crystalline material formed. This material was broken up and washed several times with water. The residue was treated with chloroform, but was largely insoluble. Recrystall ization of the residue from ethanol :water (3:1) yielded colorless crystals that had a sharp melting point (201-202°C). On the basis of the spectral information given below, the compound was assigned the bicyclic lactone structure 17. ! H NMR (100 MHz, DMSO-d ) 6 1.66-2.28(m, 4H), 2.91(ddd, 1H), 3.11(dd, 1H), 3.29(s, 3H), 3.80-3. 95(m, 1H), 4.74(m, 1H), 6.95-7.63(m, 5H), 10.08(s, 1H). 13 C NMR (DMS0-d 6 ) 6 27.78(f), 33.26(f), 38.28(d), 43.23(d), 55.54(q), 73.01(d), 75.91(d), 119.19(d), 123.31(d), 128.59(d), 138.93(s), 170.58(s), 170.65(s). IR (KBr) 3302(m), 3282(m), 3138(w), 3067(w), 2978(w), 2967(w), 2942(w), 2877(w), 2840(w), 1736(vs), 1689(vs), 1601(s), 1540(s), 1493(m), 1443(s), 1381(m), 1362(m), 1334(m), 1320(m), 1302(m), 1279(w), 1247(m), 1212(m), 1190(m), 1150(m), 1108(s), 1088(m), 1052(m),

PAGE 51

38 1018(m), 963(m), 930(w), 917(w), 788(w), 762(s), 701(m), 655(w), 609(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 275 (M + , 50.2), 245 (7.6), 188 (9.2), 174 (4.9), 119 (13.0), 103 (36.8), 93 (100.0). Analysis. Calculated for C 15 H iy N0 4 : C, 65.44; H, 6.22; N, 5.09. Found: C, 65.53; H, 6.38; N, 5.05. Maleimide Synthesis: General Many of the maleimides used in this study [N-(4-fluorophenyl ) , N-(4-chlorophenyl ) , N-(4-bromophenyl ) , N-(4-nitrophenyl ) , N-(4-carboethoxyphenyl ) , N-(4-methyl phenyl ) , N-(4-acetoxyphenyl ) , N-(4-methoxyphenyl)] had been previously synthesized in these laboratories. They were purified by recrystallization from cyclohexane and characterized by various spectral techniques. Only the spectral data for these maleimides are given here. The N-acetoxymaleimide used was synthesized in these laboratories by David P. Vanderbilt, and was used without further purification. N-phenylmaleimide was obtained from Aldrich Chemical Company, and was recrystallized from cyclohexane before use. 72 In general, the synthetic procedure first developed by Searle 73 and detailed by Barrales-Rienda et al . was used. The procedure involves the reaction of the appropriately substituted aniline with maleic anhydride to form an intermediate maleanilic acid. The maleanil ic acid is then dehydrated to the maleimide using acetic anhydride:sodium acetate.

PAGE 52

39 N-Phenyl [ N]ma1eanil1c acid([ lb N>4-0xo-4-[phenylamino]-[Z]-2butenoic acid) (18) The contents of a 1.0 g ampule of 97.5% N-enriched aniline (Merck and Co., Inc.) were mixed with 4.0 g freshly distilled regular aniline (5.0 g total, 53.7 mmole). The mixture was dissolved in 10 ml of chloroform, and the resulting solution was added dropwise to a rapidly stirred solution of 6.0 g maleic anhydride (61.8 mmole) in chloroform. A cream colored precipitate formed immediately on addition of the aniline solution. The mixture was stirred for one hour and allowed to stand at room temperature overnight. The mixture was suction filtered and washed with chloroform several times.. After drying in a 50°C vacuum oven for several hours, the yield of cream colored powder was 10.3 g (100.3%), mp 203-204°C (literature 74 mp 15 206°C). The approximate percentage of N in this compound could be determined by integration of the N-H resonance of the H NMR spectrum. The N-H resonance appears as a doublet, whereas the N-H 15 resonance is a singlet appearing at the midpoint of the N-H doublet (approximately 20% 15 N). l H NMR (DMS0-d 6 ) 6 6.41 (AB quartet, J = 12.1, 2H), 6.87-7.70(m, 5H), 10.44[d, J(15 N _ H ) = 90.3, s, 1H (d+s)], CO^ not observed. 13 C NMR (DMS0-d 6 , internal reference DMSO-dg = 39. 5 62 ) 6 119.72(d), 124.10(d), 128.93(d), 130.59(d), 131.86[d, 2 J ( 15 N _ C0 _ C > = 9.7], 138.58(s, \l5 n _ c{quau aromatic)] = 13.4), 163.39[s, V^-CO) 15.9], 166.95(s). IR (KBr) 3254(m), 3193(m), 3060(m,b), 2863(w), 2240(m), 2075(w), 1876(m), 1697(s), 1620(s), 1635(vs,b), 1489(s), 1449(s), 1429(m),

PAGE 53

40 1330(m), 1267(m), 1223(w), 1189(w), 998(m), 970(m), 900(m), 849(s), 800(m), 754(s), 686(m), 652(m), 605(s) cm" 1 . N-Phenyl[ 15 N]ma1eimide([ 15 N]-l-Phenyl-lH-pyrrole-2,5-dione) (19) 15 Finely divided N-enriched N-phenyl maleanilic acid (10.3 g, 53.9 mmole) was combined with 3.1 g freshly fused sodium acetate in a 250 ml, three-necked, flame dried, N~ flushed round-bottom flask equipped with a mechanical stirrer and a reflux condenser. Acetic anhydride (32.0 g) was added, and the mixture was stirred while the flask was heated to 80°C in an oil bath. The bright yellow solution was stirred at 80°C for one hour. The flask was then allowed to cool to room temperature while stirring was continued for two additional hours. The reaction mixture was then added dropwise to rapidly stirred ice water in which a small amount of salt (NaCl ) had been dissolved. The crude yellow precipitate that formed was suction filtered, washed with water, and dried in a 50°C vacuum oven overnight. Vacuum sublimation (aspirator pressure) of the crude crystals 75 gave 6.4 g (68.8%) bright yellow needles, mp 87-89°C (literature mp 89-90°C). An approximate percent enrichment was calculated by obtaining a high resolution mass spectrum of the enriched maleimide and comparing the observed intensity of the M+l peak with the theo7fi retical intensity [calculated from the known natural abundances of 13 C (1.08%), 2 H (0.016%), and 17 (0.04%)]. Thus, for C^H^, (1.08 x 10) + (0.016 x 7) + (0.04 x 2) = 11% of the intensity of the M+l 15 peak is not due to ions containing N. The following equation was used for the calculation:

PAGE 54

41 15 N (M+1 >Total O11 W 10 " (M) + 0.11 (M) where the quantities in parentheses are the observed absolute intensities of the corresponding ions. The calculated approximate % N was 18.8. l H NMR (100 MHz, CDCI3) 6 6.75(s, 2H), 7.22-7.52(m, 5H). 13 C NMR (CDCI3) 6 126.08(d), 127.89(d), 129.11(d), 133.93(s, 1 J f -15 N _ c (quat. aromatic)] = 14 ' 2 >' 134 08 £ d ' V 5 N-C013 CH) = 7 ^' 169.51[s, ^(ISfj.lSj.QX = 14.6]. IR (KBr) 3090(w), 1775(w), 1704(vs), 1592(m), 1504(m), 1383(s), 1141(m), 1071(w), 1029(w), 941(w), 904(w), 829(s), 753(m), 692(s), 622(m) cm -1 . LRMS (70 eV, m/z, relative intensity) 174 (M+l, 35.2), 173 (M + , 100.0), 145 (8.3), 129 (26.3), 117 (15.1). HRMS. Required for C^H^N: 173.0477. Found: 173.0484. Molecular ion absolute intensity (M) = 908, (M+l) = 289. 15 (10.11 MHz, l H decoupled, CDC1 3 ) 217. 8(s, upfield from external CH 3 N0 2 ) N-Cyclohexylmaleanil ic acid [4-(Cyclohexy1amino)-4-oxo-(Z)-2-butenoic acid] [21477-59-8] (20) Slow, dropwise addition of 31.0 g cyclohexyl amine (313 mmole) to a stirred solution of 31.0 g maleic anhydride (316 mmole) in 300 ml chloroform resulted in an exothermic reaction. The amine was added slowly enough to avoid boiling of the chloroform. The solution was allowed to stand at room temperature overnight. A white crystalline mass filled the flask the next morning. This mass was broken

PAGE 55

42 up, filtered, and washed with cold chloroform and hexane. Evaporation of the washings produced more hexane insoluble product which was similarly filtered and washed. Removal of the residual solvent from the combined precipitates in a 50°C vacuum oven yielded 63.1 g (102%) pure white product, mp 153-154°C (literature 77 mp 182°C). X H NMR (60 MHz, DMSO-dg) 6 0.9-2. l(broad m, 10H), 3.4-4. 0(m, 1H), 6.35 (AB q, J = 12.1, 2H), 9.10(broad d, 1H), C0 2 H not observed. IR (KBr) 3240(m), 3075(m), 2940(s), 2861(m), 1920(w, b), 1702(vs), 1635(s), 1578(s), 1521(vs, b), 1480(vs, b), 1406(s), 1350(m), 1320(m), 1296(m), 1256(m), 1245(m), 1150(m), 1083(s), 983(m), 925(w), 910(w), 888(w), 877(w), 855(s), 790(w), 755(w), 635(m), 604(m) cm -1 . N-Cyclohexylmaleimide (l-C,yclohexyl-lH-pyrrole-2,5-dione) , [1631-25-0], (21) This compound was synthesized by thermal dehydration of the 78 corresponding maleamic acid. Thus, 15.0 g N-cyclohexylmaleamic acid (76 mmole) and 50 ml xylene (mixed isomers) were added to a 250 ml, three-necked, found-bottom flask equipped with a nitrogen inlet, mechanical stirrer, and reflux condenser. The suspension was stirred as the flask and contents were heated to reflux in an oil bath. The reflux was maintained for five hours. The flask was allowed to cool, and most of the xylene was evaporated in vacuo. The residue was treated with acetone, and the acetone insoluble portion (unreacted starting material) was separated by filtration (~ 7.5 g). The acetone was evaporated from the filtrate, and the residue was sublimed to yield 1.5 g (22%, based on recovered starting material) colorless needles, mp 86-87°C (literature 79 mp 89°C).

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43 l H NMR (100 MHz, CDC1 3 ) 6 1.2-2. l(m, 10H), 3.75-4.03(tt, J = 3.9, 11.8, 1H), 6.66(s, 2H). 13 C NMR (CDC1 3 ) 6 25.10, 25.98, 29.95, 50.74, 133.91, 170.85. IR (KBr) 3445(w), 3089(m), 2931(s), 2860(m), 1773(w), 1700(vs), 1598(w), 1579(w), 1465(w), 1457(w), 1396(w), 1403(s), 1382(m), 1371(m), 1348(m), 1265(w), 1178(m), 1140(m), 1113(m), 1018(w), 986(m), 892(w), 826(s), 748(w), 692(s), 638(m) cm" 1 . LRMS (70 eV, m/z, relative intensity) 179 (M + , 35.5), 136 (40.2), 123 (8.5), 99 (100.0). N-Phenylcitraconamic acid [2(or 3)-Methyl-4-oxo-4-(phenylamino)-(Z)2-butenoic acid], [39734-91-3], (22) Slowly adding 15.0 g aniline (161 mmole) to a stirred solution of 17.5 g citraconic anhydride (Aldrich, 156 mmole) in CHC1., resulted in an exothermic reaction and the immediate formation of a cream colored precipitate. After stirring for one hour, the suspension was filtered, washed with CHC1,. and suspended in boiling CHOIfor an additional thirty minutes. The suspension was cooled and filtered. The precipitate was placed in a 50°C vacuum oven overnight. The isolated yield was 32.0 g (100%) of an off white powder, mp 175-176°C 24 (literature mp 171°C). The product proved to be a mixture of the two possible isomers (methyl substitution at the 2 or 3 position); however, no attempt was made to separate them. l H NMR (60 MHz, DMSO-dJ 6 2.02(d, J = 1.2, 3H), 6.19(q, 3 peaks resolved, J = 1.2, 1H), 6.85-7.85(m, 5H), 10.13(broad s, 1H), C00H not observed.

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44 13 C NMR (DMS0-d 6 , internal reference DMSO-dg = 39. 5 62 ) 6 20.83, 21.66, 119.62, 119.82, 123.67, 123.82, 128.88, 128.98, 139.12, 139.36, 142.97, 150.38, 163.10, 165.97, 168.11, 170.36. IR (KBr) 3284(m), 3210(m), 3120(m), 2340(w), 2200(w), 1701(s), 1630(s), 1571(s), 1530(vs), 1497(vs), 1490(vs), 1442(s), 1395(m), 1378(m), 1330(s), 1253(w), 1138(w), 1041(w), 1028(w), 972(m), 896(m), 860(w), 788(w), 755(m), 688(m), 637(w) cm" 1 . Analysis. Calculated for (^H^O^ C, 64.38; H, 5.40; N, 6.82. Found: C, 64.17; H, 5.49; N. 6.77. N-Phenylcitraconimide (3-Methyl-l-phenyl-lH-pyrrole-2,5-dione) , [3120-04-5], (23) Heating 10.0 g N-phenylcitraconamic acid (48.7 mmole) and 1.8 g fused sodium acetate in 15 ml acetic anhydride at 90°C for thirty minutes produced a deep yellow solution. The solution was allowed to cool to room temperature, and stirring was continued for two hours. Precipitation of the reaction mixture into a rapidly stirred ice: salt:water mix, followed by recrystall ization of the precipitate from cyclohexane, gave 3.5 g (38.4%) pale yellow needles, mp 92-94°C (literature 80 mp 94-96°C). 1 H NMR (60 MHz, acetone-dg) 6 2.08(d, J 1.8, 3H), 6.53(q, J = 1.8, 1H), 7.2-7.5(m, 5H). 13 C NMR (acetone-d 6 ) 6 10.92, 126.91, 127.98, 128.08, 129.45, 133.10, 146.50, 170.09, 171.17. IR (KBr) 3460(w), 3082(w), 2984(w), 2924(w), 1704(vs), 1640(m), 1596(w), 1502(m), 1400(s), 1290(w), 1205(w), 1188(m), 1140(w), 1114(m), 1073(w), 1038(w), 1012(w), 1000(w), 992(w), 888(m), 873(m), 762(m), 753(m), 708(m), 690(m), 651(w), 618(w) cm" 1 .

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45 LRMS (70 eV, m/z, relative intensity) 187(M + , 100.0), 143 (23.2), 130 (10.9), 119 (15.3), 117 (14.3), 91 (23.8). Analysis. Calculated for C 1 .H g N0 2 : C, 70.06; H, 4.85; N, 7.48. Found: C, 70.21; H, 5.40; N, 7.44. N-(4-Trifluoromethyl phenyl )maleamic acid (4-Qxo-4-[(4-trifluoromethylphenyl )amino]-(Z)-2-butenoic acid) (24) A solution of 4.9 g p-aminobenzyltrifluoride (30.4 mmole, PCR) dissolved in 10 ml CHC1., was added dropwise to a stirred solution of 3.6 g maleic anhydride in 125 ml CHCU. The solution started to become turbid about five minutes after the addition was complete. The solution-suspension was stirred for seventeen hours at room temperature and for seven hours at ~ 50°C. After cooling, the bright yellow precipitate was filtered and washed with chloroform. The powder was added to 100 ml CHCK, and the mixture was boiled for about an hour. The suspension was cooled, filtered and washed with CHCloThis procedure was repeated two more times. The pale, lemon yellow powder was placed in a 50°C vacuum oven overnight. This procedure yielded Ol 7.5 g (95.2%) pale yellow product, mp 183-184°C (literature mp 183186°C). 1 H NMR (100 MHz, DMSO-dg) 6 6.64(AB q, J = 12.0, 2H), 7.20-8.27(m, 4H), 10.50 and 10.66 (2 unequal s, 1H). IR (KBr) 3275(w), 3205(w), 3117(m), 3069(m), 3020(w), 2260(w, b), 1890(w, b), 1715(s), 1630(m), 1590(s), 1548(vs), 1487(m), 1427(m), 1408(m), 1322(vs), 1222(m), 1169(m), 1130(s), 1070(m), 1018(w), 975(w), 900(w), 858(m), 842(m), 755(w, b), 669(w), 610(w) cm

PAGE 59

46 N-(4-Trifluorometh,ylphen,yl)maleimide [l-(4-Trifl uoromethyl phenyl )-lHpyrrole-2,5-dione], [54647-09-5], (25) To a 100 ml, three-necked round-bottom flask equipped with a mechanical stirrer and nitrogen inlet was added 3.0 g N-(4-trifluoromethyl phenyl )maleamic acid (11.6 mmole), 0.75 g freshly fused sodium acetate, and 10 ml acetic anhydride. The mixture was slowly heated with an oil bath. At 60°C, the slurry dissolved to form a bright yellow solution. At 65°C, the solution turned red. The flask was immediately cooled to room temperature and allowed to stand for six hours. The reaction mix was then precipitated into 300 ml rapidly stirred ice water. The precipitate was then filtered, dried in vacuo and recrystallized twice from cyclohexane. Activated charcoal was added during the first recrystall ization. This preparation yielded 2.4 g (86.0%) colorless needles, mp 153-155°C (literature 81 mp 150152°C). l H NMR (100 MHz, CDC1 3 ) 6 6.87(s, 2H), 7.63(AB q, broad lines, 4H). 13 C NMR (acetone-dg, letters denote actual multiplicities, J's are 13 C19 F coupling constants in Hertz) 6 125.03(q, J = 271.0), 126.90(q, J = 3.7), 127.52(s), 129.40(q, J = 33.0), 135.74(s), 136.49(s), 170.02(s). Off resonance decoupling caused all peaks to split into doublets, relative to the completely decoupled spectrum, except for those at 125.03, 129.40, 136.49 and 170.02, which remained singlets. Selective irradiation of the ethyl13 eneic protons resulted in a much greater intensity for the C peak at 135.74, relative to the other carbon resonances.

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47 13 C NMR (CDCl 3 )6123.82(q, J = 272.2), 125.79(s), 126.26(q, J = 3.7), 129.64(q, J = 33.0), 134.42(s), 134.59(s), 168.92(s). 19 F NMR (CDC1 3 , internal CFC1 3 ) 6 -63.2(m). IR (KBr) 3480(w), 3112(w), 3079(w), 2963(w), 1780(vs), 1705(s), 1612(w), 1521(w), 1412(m), 1372(w), 1330(s), 1260(w), 1160(s), 1127(s), 1108(s), 1069(s), 1058(m), 1020(w), 952(w), 839(m), 821(m), 815(m), 737(w), 710(w), 690(m) cm" 1 . LRMS (70 eV, m/z, relative intensity) 242(M+1, 12.3), 241(M + , 100.0), 197 (25.6), 185 (10.3), 172 (18.2), 171 (15.4), 54 (73.4). N-(4-Cyanopheny1 )maleamic acid (4-[(4-Cyanophenyl )amino]-4-oxo-(Z)2-butenoic acid), [31460-28-3], (26) Finely ground maleic anhydride (5.0 g, 51.0 mmole) was dissolved in 75 ml CHC1 3 , and a solution of 5.0 g 4-aminobenzonitrile (Aldrich) in 100 ml CHCl^ was added dropwise. The immediate formation of a cream colored precipitate was noted. The suspension was stirred at room temperature overnight, filtered, washed with CHCK, and placed in a 70°C vacuum oven for four hours. The powder thus obtained was purified by stirring in boiling CHCln for one hour, followed by filtering and removal of the residual solvent in a vacuum oven. This procedure yielded 8.55 g (93.4%) cream colored, finely divided powder, mp 193-194°C. l H NMR (100 MHz, DMSO-dg, internal reference DMS0-d 6 = 2.49 62 ) 6 6.40(AB q, J = 12.0, 2H), 7.76(broad s, 4H), 10.65(s, 1H), C00H not observed. lo C NMR (DMS0-d 6 , internal reference DMS0-d 6 = 39. 5 62 ) 6 105.47, 118.65, 119.48, 129.76, 131.93, 132.93, 142.65, 163.78, 166.29.

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IR (KBr) 3297(m), 3210(m), 3112(w), 3054(w), 2235(m), 1712(s), 1618(s), 1595(vs), 1540(vs), 1490(s), 1411(w), 1407(m), 1326(s), 1262(m), 1230(w), 1210(w), 1177(w), 972(m), 899(w), 858(m), 838 (m), 758(w), 617(m) cm" 1 . N-(4-Cyanophenyl )maleimide [l-(4-C,yanophenyl )-lH-pyrrole-2,5-dione], [31489-18-6], (27) A suspension of 7.0 g (4-cyanophenyl )maleamic acid (32.4 mmole) and 1.7 g freshly fused sodium acetate in 25 ml acetic anhydride was slowly heated in an oil bath. The maleanilic acid dissolved when the temperature reached 65°C. Stirring (mechanical) of the solution was continued while the temperature gradually increased to 90°C. This temperature was maintained for thirty minutes, and then the reaction mix was allowed to cool to room temperature. On cooling, the mixture crystallized to a cream colored mass. Water (~ 75 ml) was added to this mass of crystals, which were then separated by filtration and washed with copious amounts of water. After drying in a 60°C vacuum oven overnight, the powdery product was recrystallized from heptane to yield 5.2 g (81.2%) pale yellow needles, mp 131-134°C. ! H NMR (100 MHz, CDC1 3 ) 6 6.92(s, 2H), 7.66(AA'BB', 4H). 13 C NMR (CDC1 3 ) 5 110.98(s), 118.16(s), 125.69(d), 132.93(d), 134.54(d), 135.54(s), 168.59(s). Selective decoupling of the ethyleneic protons resulted in a dramatically greater intensity for the peak at 134.54, relative to the other protonated carbons. IR (KBr) 3470(w), 3170(w), 3100(m), 3095(m), 2219(m), 1770(w), 1727(vs), 1605(m), 1587(w), 1515(m), 1415(m), 1392(s), 1376(s), 1320(w), 1280(w), 1216(w), 1146(m), 1079(m), 1031(m), 951(w), 841 (s), 829(m), 818(w), 762(w), 720(m), 687(m), 656(w), 622(w) cm" 1 .

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49 LRMS (70 eV, m/z, relative intensity) 199(M+1, 12.8), 198(M + , 100.0), 154 (34.0), 142 (12.1), 128 (15.0), 54 (38.4). N-(4-Fluorophenyl )maleimide [l-(4-F1uorophenyl )-lH-pyrrole-2,5-dione], [6633-22-3], (28) Recrystall ization from cyclohexane yielded long, pale green needles, mp 155-156°C (literature 73 mp 155°C). l H NMR (100 MHz, CDC1 3 ) 6 6.83(s, 2H), 7.05-7.40(m, 4H). 13 13 19 C NMR (CDClo, letters denote actual multiplicities, J's are CF coupling constants in Hertz) 6 116. 13(d, J = 22.6), 127.22(d, J = 3.1), 127.91(d, J = 8.54), 134.22(s), 161.81(d, J = 247.8), 169.36(s). Selective irradiation of the ethyleneic protons resulted in enhancement of the intensity of the resonance at 134.22, relative to the other protonated carbons. 19 F NMR (CDC1 3 , internal CFC1 3 ) 6 -113. 7(m). IR (KBr) 3460(w), 3165(w), 3101(m), 3071(w), 1900(w), 1710(vs), 1599(w), 1586(w), 1517(s), 1410(s), 1392(s), 1374(m), 1312(m), 1300(w), 1290(w), 1261(w), 1234(s), 1150(s), 1089(w), 1072(m), 1046(w), 1022(w), 950(w), 935(w), 836(s), 819(m), 765(w), 710(m), 685(s) cm" 1 . LRMS (70 eV, m/z, relative intensity) 192(M+1, 11.4), 191(M + , 100.0), 147 (13.3), 121 (20.0), 109 (10.7), 82 (10.3), 54 (40.8). N-(4-Ch!orophenyl )maleimide [l-(4-Chlorophenyl ) -1Hpyrrol e-2,5-di one], [1631-29-4], (29) Recrystall ization from cyclohexane gave light yellow needles, mp 113-115°C (literature 75 mp 114°C).

PAGE 63

50 ! H NMR (100 MHz, CDC1 3 ) 6 6.78(s, 2H), 7.34(AA'BB', 4H). 13 C NMR (CDC1 3 ) 6 127.08(d), 129.18(d), 129.88(s), 133.39(s), 134.17(d), 169.05(s). Irradiation of the ethyleneic protons resulted in enhancement of the intensity of the peak at 134.17, relative to the other carbon resonances. IR (KBr) 3465(w), 3163(w), 3118(w), 3083(m), 1776(w), 1714(vs), 1585(w), 1497(s), 1453(w), 1402(s), 1388(s), 1372(m), 1310(m), 1278(w), 1211(w), 1149(m), 1097(m), 1071(m), 1031(m), 1019(m), 949(m), 836(s), 765(w), 743(m), 707(m), 685(m), 646(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 209 (31.9), 208 (11.6), 207 (M + , 100.0), 163 (15.2), 153 (10.1), 137 (19.4), 90 (11.9), 54 (44.6). N-(4-Bromophenyl )maleimide [l-(4-Bromopheny1 )-lH-pyrrole-2,5-dione] , [13380-67-1], (30) Recrystallization of this compound from cyclohexane yielded bright yellow needles, mp 123-124°C (literature 82 mp 118-120°C). ! H NMR (100 MHz, CDC1 3 ) 6 6.81(s, 2H) , 7.40(AA'BB\ 4H). 13 C NMR (CDC1 3 ) 6 121.43(s), 127.33(d), 130.32(s), 132.18(d), 134.20(d), 168.97(s). Selective irradiation of the ethyleneic 13 protons resulted in enhancement of the C resonance at 134.20, relative to the other carbon resonances. IR (KBr) 3461(w), 3160(w), 3111(w), 3089(m), 1717(vs), 1589(w), 1570(w), 1490(s), 1441(w), 1398(s), 1385(s), 1367(m), 1306(w), 1275(w), 1208(w), 1147(s), 1065(m), 1029(w), 1011(m), 945(m), 828(s), 811(m), 761(w), 729(w), 705(m), 681(m), 638(w) cm -1 .

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51 LRMS (70 eV, m/z, relative intensity) 254 (11.0), 253 (98.6), 252 (11.7), 251 (M + , 100.0), 209 (10.3), 207 (10.2), 197 (11.2), 183 (12.6), 181 (11.8), 116 (19.9), 90 (19.3), 86 (15.3), 82 (14.3), 63 (17.6), 54 (59.2). N-(4-Nitrophenyl )ma1eimide [l-(4-Nitrophenyl )-lH-pyrro1e-2,5-dione], [4338-06-1], (31) Recrystall ization of this compound from ethanol :cyclohexane (1:3) gave colorless crystals, mp 167. 5-169. 5°C (literature 75 mp 163-165°C). X H NMR (100 MHz, CDC1 3 ) 6 6.94(s, 2H), 8.01(AA'BB', 4H). 13 C NMR (CDC1 3 ) 6 124.48(d), 125.45(d), 134.61(d), 137.10(s), 146.21(s), 168.49(s). IR (KBr) 3468(w), 3118(w), 3095(w), 1724(vs), 1682(m), 1612(m), 1594(m), 1518(s), 1500(s), 1447(w), 1398(m), 1388(m), 1373(m), 1347(s), 1300(m), 1268(w), 1217(w), 1144(m), 1107(w), 1062(m), 1030(w), 949(w), 851(m), 823(m), 761(w), 747(w), 719(w), 694(m), 639(w) cm" 1 . N-(4-Carboethoxyphenyl )maleimide [4-(2,5-Dihydro-2,5-dioxo-lH-pyrroll-y1)benzoic acid, ethyl ester], [14794-06-0], (31) This compound was kindly provided by David P. Vanderbilt. Recrystallization from cyclohexane yielded pale yellow needles, mp 112113°C (literature 83 mp 113°C). l \i NMR (100 MHz, CDC1 3 ) 6 1.39(t, J = 7.1, 3H), 4.39(q, J = 7.1, 2H), 6.86(s, 2H), 7.81(AA'BB', 4H). 13 C NMR (CDC1 3 ) 6 14.30(q), 61.16(t), 125.18(d), 129.47(s), 130.35(d), 134.37(d), 135.37(s), 165.71(s), 168.95(s).

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52 Selective irradiation of the ethyleneic protons resulted in en1-3 hanced intensity for the C peak at 134.37, relative to the other carbon resonances. IR (KBr) 3120(w), 3091(w), 3001(w), 1718(vs), 1710(vs), 1607(m), 1509(m), 1476(w), 1417(m), 1398(m), 1386(m), 1369(m), 1310(m), 1286(s), 1217(w), 1177(m), 1146(m), 1130(m), 1110(m), 1070(w), 1025(m), 1013(w), 950(w), 857(m), 832(m), 827(m), 767(m), 701(m), 687(m), 641(w), 625(w) cm -1 . N-(4-Methylphenyl )maleimide [l-(4-Methyl phenyl )-lH-pyrrole-2,5-dione], [1631-28-3], (32) Recrystall ization from cyclohexane yielded yellow needles, mp 151.5-152°C (literature 84 mp 148.5-150°C) . l \i NMR (100 MHz, CDC1 3 ) 6 2.37(s, 3H), 6.79(s, 2H), 7.18-7.25(m, 4H). 13 C NMR (CDC1 3 ) 6 21.10(q), 126.01(d), 128.57(s), 129.74(d), 134.13(d), 137.98(s), 169.63(s). Selective irradiation of the ethyleneic protons resulted in en13 hancement of the C signal at 134.13, relative to the other carbon resonances. IR (KBr) 3461(w), 3170(w), 3095(m), 2928(w), 1710(vs), 1588(w), 1528(m), 1410(s), 1390(s), 1324(m), 1318(w), 1290(w), 1212(w), 1182(w), 1154(s), 1079(w), 1038(w), 952(w), 833(s), 822(m), 810(m), 710(m), 686(s), 674(m) cm" 1 . LRMS (70 eV, m/z, relative intensity) 188 (12.9), 187 (M + , 100.0), 143 (12.5), 130 (17.7), 117 (18.7), 54 (15.1).

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53 N-(4-Acetyloxyphenyl )maleimide [l-(4-Acetyloxyphenyl )-!H-pyrrole-2,5dione], [6637-46-3], (33) Recrystall ization from cyclohexane yielded pale yellow needles, mp 160-161°C (literature 85 mp 156°C). *H NMR (100 MHz, CDC1 3 ) 6 2.28(s, 3H), 6.80(s, 2H), 7.27(AA'BB\ 4H). 13 C NMR (CDC1 3 ) 6 21.03(q), 122.23(d), 126.91(d), 128.76(s), 134.17(d), 149.79(s), 169.00(s), 169.29(s). Selective irradiation of the ethyleneic protons resulted in en13 hanced intensity for the C peak at 134.17, relative to the other carbon resonances. IR (KBr) 3095(w), 1754(s), 1709(vs), 1589(w), 1508(s), 1473(w), 1412(m), 1400(m), 1387(w), 1368(m), 1216(s), 1197(s), 1163(m), 1153(m), 1099(w), 1016(w), 957(w), 915(w), 853(w), 840(m), 732(w), 702(w), 690(m), 651(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 231 (M + , 2.4), 190 (11.5), 189(100.0), 119 (10.0), 54 (12.6). N-(4-Methoxyphenyl )maleimide [l-(4-Methoxyphenyl )-!H-pyrrole-2,5dione], [1081-17-0], (34) Recrystall ization from cyclohexane yielded wery bright yellow needles, mp 148-151°C (literature 75 mp 146°C). X H NMR (100 MHz, CDC1 3 ) 6 3.80(s, 3H) , 6.79(s, 2H), 7.09(AA'BB', 4H). 13 C NMR (CDC1 3 ) 6 55.44(q), 114.44(d), 123.84(s), 127.57(d), 134.08(d), 159.13(s), 169.78(s). Selective irradiation of the ethylenic protons resulted in en13 hancement of the intensity of the C peak at 134.08, relative to the other carbons.

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54 IR (KBr) 3460(w), 3109(w), 3080(w), 3011(w), 2970(w), 2939(w), 2919(w), 2838(w), 1770(w), 1706(vs), 1607(w), 1586(w), 1507(s), 1477(w), 1449(w), 1439(m), 1415(m), 1398(s), 1305(m), 1248(s), 1180(m), 1169(m), 1156(s), 1148(s), 1106(m), 1053(w), 1027(m), 950(w), 938(w), 836(m), 826(m), 816(m), 810(m), 797(w), 720(m), 685 (m), 602(w) cm" 1 . LRMS (70 eV, m/z, relative intensity) 204 (12.3), 203 (M + , 100.0), 188 (35.4), 160 (19.8), 134 (9.3), 133 (9.3), 106 (8.6), 54 (11.9). Copolymer Synthesis and Characterization Copolymer Synthesis All copolymers were synthesized in roughly the same manner. Azobisisobutyronitrile (AIBN, Aldrich) was used as the initiator in all cases, except where noted otherwise. The initiator was purified by recrystall ization from methanol. Purification of 2-chloroethyl vinyl ether (Aldrich), ethyl vinyl ether (Aldrich), and n-butyl vinyl ether (Aldrich) was carried out by stirring over calcium hydride for at least twenty-four hours, followed by distillation. Methyl vinyl ether (Matheson) was condensed from a gas cylinder into a 250 ml round-bottomed flask cooled with an ice:water:sal t mixture. The round-bottomed flask was then connected to a dry polymerization tube and allowed to warm to room temperature while the polymerization tube was cooled in a dry ice:isopropanol bath. Maleimides were recrystall i zed from cyclohexane before use. Maleic anhydride was sublimed before use. Dichloromethane was

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55 distilled from phosphorous pentoxide. Benzene was stirred over 18 M H 2 S0 4 for twenty-four hours, decanted, and distilled. Typically, solutions of the desired concentrations were made by weighing appropriate amounts of the initiator, maleimide and vinyl ether into a volumetric flask and diluting to the mark with solvent. The desired volume of this solution was then introduced into a clean polymerization tube with a pipette. The tube was connected to a high vacuum line and degassed by at least five freeze-pump-thaw cycles, -5 then sealed off at < 10 mm Hg. Tubes thus prepared were placed in a bath (water, oil, or isopropanol :dry ice) of the appropriate temperature for the desired amount of time. At the end of this time, the tube was removed from the bath, cooled to -78°C in a dry ice: isopropanol bath, and opened. The solution was then added slowly (dropwise) to a large excess of rapidly stirred precipitation solvent (methanol was used unless otherwise noted). In some cases it was necessary to redissolve the copolymer in acetone and precipitate it again in order to obtain a pure white product. It was noted that monomer solutions containing initiator decolorized on standing in bright light. Precipitation of these solutions, as described above, yielded pure white copolymers. Thus, polymerizations described from now on as being carried out at "room temperature" took place in the presence of oxygen without careful temperature control . In the copolymerization carried out at -78°C, a Hanovia Utility Quartz Ultraviolet Lamp was used as a light source. The degassed monomer solution was placed in a dry ice: isopropanol bath,

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56 and the light was shone through a recrystall izing dish containing about three inches of water, which was placed on top of the dewar containing the cold bath and tube. The water served as insulation, so that rapid heating of the bath by the hot lamp was avoided. Independent experiments showed that no copolymerization took place in the absence of initiator under these conditions. A UV scan showed that AIBN has an absorption maximum near 345 nm which is well above the 57 pyrex glass cutoff of about 280 nm. All 4-substituted phenyl maleimides copolymerized with 2-chloroethyl vinyl ether, except for N-(4-nitrophenyl ) maleimide, which yielded no copolymer after being heated in the presence of initiator and CEVE for forty-two hours in a 60.0°C bath. The unreacted maleimide could be recovered unchanged (as judged by IR spectroscopy). A Sargent Thermonitor (Model S-W) constant temperature bath was used to control the temperature of the water bath used to 60.0±0.1°C. The homopolymer of N-phenylmaleimide was prepared in exactly the same way as the copolymers (i.e., AIBN, CH-CK, 60.0°C). The copolymerization conditions, yields and analysis data for all copolymerizations, except for those performed in kinetic studies, are given in Tables 2-5. 2-Chloroethyl Vinyl Ether Homopolymer The 2-chloroethyl vinyl ether (CEVE) homopolymer was synthesized by storing distilled CEVE over unactivated molecular sieves (Linde). The viscosity of the CEVE increased with the length of time that it was stored over the sieves. Indeed, after several months the vinyl ether had become a brown, solid mass. This mass was dissolved in

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'yi TABLE 2 Conditions for N-Phenylmaleimide-2-Chloroethyl Vinyl Ether Copolymerizations Sample Copolym. Z a No. Temp. (°C) H" . Copolym. V M [AIBN] x 10 J Vol. (ml) Time (Hr.) 1

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58 TABLE 3 Yield and Analysis Data for Copolymers in Table 2

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59 TABLE 4 Polymerization Conditions for Other Maleimide Polymers Sample No.

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60 TABLE 5 Yield and Analysis Data for Copolymers in Table 4

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61 Footnotes for Tables 2, 3, 4 and 5 : Total monomer concentration = [M, ] + [NL]. Mole fraction maleimide (or other acceptor) in the initial feed. c Concentration of AIBN in moles/1 (mole % AIBN based on VL) . Volume of the solution that was polymerized. No solvent. f Total moles of monomer. 9 Initiator was 2,4-dichlorobenzoyl peroxide (Lucidol), 1.1 x 10 M. Yield (%) based on theoretical maximum weight of polymer determined from total weight of monomers initially present. Yield (%) based on the knowledge that vinyl ethers do not homopolymerize under the present conditions, i.e., when [vinyl ether] > [maleimide], the theoretical maximum conversion is 2[maleimide] ; when [maleimide] > [vinyl ether], the maximum conversion is [maleimide] + [CEVE]. Mole fraction maleimide in the copolymer calculated from nitrogen analysis. k Mole fraction maleimide in the copolymer calculated from chlorine 1 analysis, i.e., l-m rr „ r . CEVE Average m,, from nitrogen and chlorine analyses, Abbreviations used: NPM, N-phenylmaleimide CEVE, 2-chloroethyl vinyl ether BVE, n-butyl vinyl ether EVE, ethyl vinyl ether MVE, methyl vinyl ether MAH, maleic anhydride NPC, N-phenylcitraconimide NCHX, N-cyclohexylmaleimide PCF-, N-(4-trifluoromethylphenyl )maleimide PCN, N-(4-cyanophenyl )maleimide PF, N-(4-fluorophenyl )maleimide PCI , N-(4-chlorophenyl jmaleimide PBr, N-(4-bromophenyl )maleimide POAc, N-(4-acetyloxyphenyl jmaleimide

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62 PCH,, N-(4-methyl phenyl )maleimide PCCLET, N-(4-carboethoxyphenyl )maleimide POMe, N-(4-methoxyphenyl )maleimide NOAc, N-acetyloxymaleimide PNOp, N-(4-nitrophenyl )maleimide. Copolymerization proceeded heterogeneously, i.e., the copolymer was insoluble in dichloromethane. This copolymer was soluble in methanol, so petroleum ether was used as the precipitating solvent. p Benzene solvent. q ir ^ N-Phenylmaleimide was ~ 20% N-enriched. Copolymerization temperature was 60.0 ± 0.1°C in all cases. r methylene chloride and precipitated into stirred methanol cooled in a dry ice:isopropanol bath. The white precipitate was rapidly filtered before it warmed to room temperature. On warming, the precipitate changed to a viscous, pale yellow, transparent mass. The NMR data for this material were consistent with that reported for the CEVE homopolymer prepared in methylene chloride using boron trifluoride etherate catalyst. 2 H NMR (60 MHz, CDC1 3 ) 6 1.82 (broad s, 2H), 3.50 (broad s, 5H). 13 C NMR (CDC1 3 , internal reference CDC1 3 = 77.0 62 )639.3 (t, broad), 40.5 (t, broad), 43.64 (t), 68.57 (t), 73.49 (d). IR (thin film) 2930(vs), 2882(s), 2860(s), 1725(w), 1462(m), 1429(s), 1370(s), 1298(s), 1252(m), 1195(m), 1110(vs), 1150(s), 969(m), 890(w), 864(w), 825(w), 780(w), 740(m), 661(vs) cm" 1 .

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63 Copolymer Reactivity Ratios The reactivity ratios for the NPM-CEVE copolymerization were calculated using the copolymer composition data in Table 3. Two separate methods were used to evaluate these ratios. The methods used were those developed by Joshi and Joshi, 87 and Kelen and Tudos. 88 89 Although it is generally accepted that only composition data from low conversion (< 10%) polymers should be used for these calculations, it can be seen from Table 3 that the copolymer composition does not change significantly with conversion when the monomer feed is rich in vinyl ether. Thus, both low and high conversion data (for those copolymers prepared from vinyl ether-rich feeds) were used for these calculations. The Kelen-Tudos plot is shown in Figure 1. The numbers indicate data calculated from the corresponding samples in Table 3. It can be seen that the plot is fairly linear, although there are some points that deviate significantly from the line. Most of the data that did not fall on the line were calculated from the composition data for polymers prepared using different polymerization conditions. Recalculation of the reactivity ratios using the ten "best" data points did not change the results significantly. All sixteen data points were used in the Joshi-Joshi calculation. The results are summarized in Table 6. Copolymerization Kinetics The initial rate of copolymerization for the system NPM, CEVE, CHgCI 2 , AIBN, 60.0°C was measured as a function of the mole fraction of maleimide in the initial comonomer feed (x») at constant total monomer concentration ([Mj] + [M 2 ] = My). A gravimetric technique was

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64 o cu to 10 +-> •ICL) +> E •rO E S1—1 O . • OJ OJ

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65 TABLE 6 Reactivity Ratios for the Free Radical Initiated Copolymerization of N-Phenylmaleimide (Mj) and 2-Chloroethyl Vinyl Ether (M„) in Dichloromethane Calculation Method r l

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66 {< 10% of the initial weight of monomers present), so that the ratio of monomer concentrations was approximately constant. The cold tube was opened as quickly as possible, and the contents were quickly added to 100 ml of methanol in one portion. The tube was carefully rinsed with several small portions of dichloromethane. The rinsings were added to the methanol. The pure white precipitated polymer was then filtered into clean, previously weighed fine porosity, fritted glass filters. The filters were cleaned in a chromic acid bath followed by rinsing with deionized water. Concentrated nitric acid was then passed through the filters, which were then rinsed with copious amounts of deionized water. The filters were then dried in a 140°C oven overnight, cooled, and weighed accurately. Tongs were used to handle the filters after they were dried. After the polymers were filtered, the filter and polymer were dried in vacuo at 60°C overnight. After cooling to room temperature, the filters containing polymers were rev/eighed, and the weight of the polymer was calculated by difference. Sometimes it was necessary to digest the polymer suspension in order to increase the particle size and facilitate filtration. This was done by gentle heating (~ 35-45°C) of the suspension for about one hour, then allowing it to stand undisturbed at room temperature for one to three days. The NPM used for kinetic studies was vacuum distilled (bp 109111°C @ 0.25 mm Hg), followed by recrystallization from cyclohexane. A high efficiency spinning band column was used to distill CEVE (bp 109°C) from calcium hydride.

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67 The initial conditions, copolymerization times, and polymer weights obtained are given in Table 7. These weights were converted to the concentration of polymer at the corresponding time by using the average molecular weight of the copolymer repeat unit calculated from the copolymer composition data in Table 3. The following equation was used for the calculation: MW = 2[m M (173.17) + m CEVE (106.55)] where m^ and nWwr are the mole fractions of NPM and CEVE incorporated into the copolymer, respectively. The slope of a [polymer] vs. time plot gives the rate of copolymerization (R in mole/1-min). The results are shown in Table 8, along with the standard deviation of the slope (S ) and the x-interv m cept (x) of the concentration vs. time plots. The slope and the xintercept were calculated by a linear least squares procedure. The x-intercept was invariably non-zero and positive, indicating that there was an induction period during which no polymerization took place. The dependence of the rate (R ) on the initial mole fraction maleimide is shown graphically in Figure 6. Copolymer Characterization 13 C NMR . Carbon-13 NMR analysis of the copolymers proved to be vastly superior to proton ( H) NMR because of greater spectral simplicity resulting from the lack of coupling and the greater spectral width (typically 200 ppm for 13 C and 10 ppm for l H) . Indeed, l H NMR spectra of the maleimide-vinyl ether copolymers prepared in this study generally appear as a series of overlapping broad humps.

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68 TABLE 7 Kinetic Data for N-Phenylmaleimide 2-Chloroethyl Vinyl Ether Copolymerizations Initial Conditions Time (Min.) Wt. Pol. (mg) ^ole^Pol. x 1Q 2 M T b = 0.500 20.1 30.8 1.10 X M C = 0.100 22.3 36. 0g 1.28 MW d = 280.52 25.0 40. 3 Q 1.44 27.5 47. 1 1.68 30.1 49. 7 8 1.77 35.9 62. 8 2.21 M T b = 0.501 20.2 42. 4 3 1.49 X M C = 0.200 25.0 52. 8 Q 1.86 MW d = 283.98 30.0 66. 5 C 2.34 o 35.1 76. 9 5 2.71 M T b = 0.500 15.1 32. 9 ? 1.16 X M C = 0.300 20.0 46. 2 4 1.63 MW d 283.98 25.0 62. 9 Q 2.21 30.0 73. 4 4 2.59 M T b = 0.500 15.0 33. 3g 1.16 X M C = 0.400 20.9 48. 2 5 1.68 MW d = 286.38 25.0 59. 7 g 2.08 30.0 77. 9 r 2.72

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69 TABLE 7-Continued

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70 TABLE 7-Continued Mole fraction of maleimide. Average molecular weight of repeat units calculated from composition data in Table 3, i.e., MW = 2[(m M )(173.17) + (m CEVE )(106.55)]. TABLE 8 Initial Copolymerization Rates for the Copolymerization of N-Phenylmaleimide and 2-Chloroethyl Vinyl Ether in Dichloromethane x M

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71 Careful sample preparation proved to be essential in obtaining good quality "high resolution" spectra. All spectra were obtained in solution, and the solvents used were either DMSO-d, or tetrachlolob 13 ethane (TCE). Because of the low natural abundance of C nuclei 90 (1.1% ) and the complexity of the copolymer structure (numerous magnetic environments for similar types of carbon), a very high concentration of copolymer was needed in order to obtain a good signal to noise ratio in a reasonable amount of time. Thus, samples were generally prepared by adding solid copolymer to a small amount of solvent (0.3-0.4 ml) until the resulting solution was viscous enough to barely flow at room temperature. Usually 200-400 mg of copolymer was enough to achieve the desired concentration. The solution was filtered into a clean 5 mm NMR tube through a plug of glass wool, using heat (heat gun) and positive nitrogen pressure. When TCE was used as the solvent, 10-15 drops of benzene-d,or toluene-d ft was added for internal deuterium lock. Hexamethyldisiloxane (Merck & Co., 1-2 91 drops) was used as a reference (2.03 ppm from TMS ) when TCE was used as the solvent. The middle peak of the solvent heptet (39.50 CO ppm from TMS ) was used as the reference peak when DMS0-d fi was the solvent. In order to minimize the dipolar line broadening caused by aniso92 tropic motion in the viscous polymer solution, all spectra were run at high temperature. Acceptable line widths could be obtained at 100-110°C for copolymers dissolved in DMSO-dg, and at 70-80°C for those dissolved in TCE.

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72 13 Since the C NMR spectra of the NPM-CEVE copolymers had a large dynamic range (difference between the intensity of the most intense and the least intense peaks), and the Jeol-FXIOO has limited space in the computer memory for data storage, the computer word length would overflow before an adequate signal to noise ratio was attained. For a discussion of this effect, see Reference 90, p. 18, Reference 91, p. 100 or Reference 93. This problem was overcome by using the fre93 quency domain (or block) averaging technique. This technique amounts to the accumulation of a relatively small number of scans, followed by Fourier transformation of the free induction decay, and storage of the result in a separate block of computer memory. This process is repeated, and the result of the Fourier transformation is added to the previous result. The whole process is continued until the desired signal to noise ratio is attained. Since polymer carbon-13 nuclei generally have short spin-lattice relaxation times (T-,) relative to small molecules, ' ' a short 13 pulse delay (PD) and large pulse width (PW) were used to obtain C spectra of the NPM-CEVE copolymers. Typical instrument parameters for obtaining polymer spectra follow: Number of accumulations: 20,000-35,000 Observation frequency: 47.0 KHz (TCE solvent) 47.3 KHz (DMS0-d 6 solvent) Pulse width: 12-18 ys (60-90°) Pulse delay: 180-360 ms Acquisition time: 0.819 s Spectral width: 5000 Hz Exponential line broadening: 0.97 Hz

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73 Each spectrum required eight to ten hours of accumulation. Acceptable signal to noise ratio was not attained when the C NMR spectrum of NPM homopolymer was run, until 250,000 scans had accumulated. Copolymer T , and NOE determination . The spin-lattice relaxation times (T\) were determined for the carbons in the NPM-CEVE copolymer prepared in bulk (sample 15 in Table 2). The method used for this determination was the saturation recovery method developed by McDonald 95 and Leigh. This method proved to be superior to the inversion recovery (IRFT) or the fast inversion recovery (FIRFT) techniques because of its relative insensitivity to mis-set 90° pulse angles, the lack of a long wait time after each pulse sequence, and the very short T, values determined for some of the carbons in the copolymer. Determining the 90° pulse width is a tedious, trial and error process in which the pulse width is varied until the observed signal is nulled (180° pulse, the pulse width for a 90° pulse is ~ £ that corresponding to a 180°C pulse). For the copolymer, it took ten to fifteen minutes of accumulation to observe any signal at all, so such a trial and error process was clearly unacceptable. The number of scans necessary to obtain a polymer spectrum with good signal to noise ratio (at least 2,000 under very favorable conditions) necessitated the use of a short pulse sequence. Because of the short T, values of some polymer carbons, inversion of the broad carbon resonances (IRFT and FIRFT methods) required extremely short pulse intervals, (t); and for many values of x, some peaks did not appear above (or below) the noise.

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74 The saturation recovery experiment consisted of a 90° pulse followed by a homospoil pulse (to dephase the spins). After the system was allowed to relax for a time period x, another 90° pulse was applied in order to sample the magnitude of the magnetization vector. After the signal was acquired, another homospoil pulse was applied, and the sequence was repeated until the desired signal to noise ratio was achieved. A series of spectra were obtained using different pulse intervals (t's). The signal intensity was an exponential function of x, with time constant T,. The relaxation times were calculated by plotting ln[S S(t)] vs. x, 95 where S and S( T ) oo oo were the signal areas corresponding to pulse intervals of infinity and t, respectively. By using a 10 mm tube and a high copolymer concentration, a fairly good signal to noise ratio was obtained after 2,000 scans had been accumulated. Thus, up to 10 spectra could be obtained (each resulting from a different x) in a reasonable amount of time (1224 hours). The spectra were automatically accumulated and stored on magnetic tape by the spectrometer. After completion of the run, each spectrum was read off the tape, and the peaks were integrated electronically. Since the peaks were generally broad, and the signal to noise ratio was low (especially when short t's were used), the integration was subject to large errors. Several experiments were run using various combinations of pulse intervals and Tco . This was necessary because of the large range of T, values encountered for different carbon types in the copolymer (22-3,000 ms), i.e., the t's needed to measure the short T^'s were not suitable for the measurement of long

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75 TVs and vice versa. A linear least squares procedure was used to calculate the slopes of the ln(S S ) vs. t plots. Sometimes these 1 x oo j' ' plots appeared nonlinear; however, due to the large errors involved in the area determination, this observation was not considered significant. In these cases, the points corresponding to short x values (and the least accurate area determinations) were invariably the points that deviated significantly from the line, and were simply neglected in the T, calculation. When using the semi logarithmic procedure described above, it is essential that the t value chosen is at least five times as long as 98 the longest T, to be measured. The results of the T, determinations are given in Table 9. The I, values are shown as the range of values determined from at least three separate experiments. The longest x^ used in these experiments was 12,000 ms, which is not five times the T, values determined for the nonprotonated carbons. The use of a x ro value that is less than the time value results in an underestimation 98 of T, . Thus, the T, values for the carbonyl and quaternary aromatic carbons are probably greater than the values shown. The large variation in T, values obtained for the same carbon in different experiments underscores the inaccuracies inherent in the determination of polymer relaxation times. The observed values are only useful for qualitative comparisons. Determination of Copolymer Nuclear Overhauser Enhancements (NOE) . Copolymer carbon-13 NOE's were determined by using the gated decoup99 ling technique. A spectrum was obtained using complete decoupling, i.e., with the proton decoupler on all the time. The pulse delay used

PAGE 89

76 TABLE 9 Carbon-13 Spin-Lattice Relaxation Times (T, ) and Nuclear Overhauser Enhancement Factors (NOEF) For an NPM-CEVE Copolymer 3 Carbon

PAGE 90

77 to obtain this spectrum was fifteen seconds (> 5 times the longest T,). The areas for all of the carbon resonances were measured. Another spectrum was run under exactly the same conditions, except the decoupler was gated on during data acquisition and off during the pulse delay. Thus, a proton decoupled spectrum was obtained, but without the NOE. The ratio of the areas obtained by using complete decoupling, and those obtained using gated decoupling, gives the NOE ratio. The quantity NOE-1 gives the amount of signal enhancement and is known as the nuclear Overhauser enhancement factor 90 (NOEF). Repeating the gated decoupled spectrum after adding some 99 chromium tris-acetylacetonate [Cr(acac)-,] paramagnetic relaxation reagent had no effect on the integrated areas relative to those obtained without Cr(acac)-,. The results are presented in Table 9. Infrared Spectroscopy . Generally, the IR spectra of NPM-CEVE copolymers did not differ significantly with varying copolymerization conditions. Thus, only one set of spectral data is reported below. The abbreviations used below for the various monomer pairs used to synthesize the copolymers are the same as those used in Tables 2-5. All spectra were obtained using the KBr pellet technique. NPM-CEVE, 3470(w, b), 3060(w), 2958(w), 2920(w), 2880(w), 1777(w), 1709(vs), 1595(w), 1498(m), 1457(w), 1432(w), 1382(s), 1300(w), 1185(s), 1110(m), 752(m), 690(m), 662(w), 620(w) cm" 1 . NPM-MVE, 3460(w, b), 3060(w), 2930(w), 2812(w), 1776(w), 1707(vs), 1595(w), 1497(m), 688 (m), 618(w) cm" 1595(w), 1497(m), 1456(w), 1382(s), 1180(s), 1098(m), 750(m), -1

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78 NPM-EVE, 3465(w, b), 3062(w), 2973(w), 2915(w), 2880(w), 1779(w), 1710(vs), 1596(w), 1498(m), 1455(w), 1383(s), 1290(w), 1183(s), 1090(m), 751(m), 688(m), 619(w) cm" 1 . NCHX-CEVE, 3455(w, b), 2938(m), 2860(w), 1773(w), 1699(vs), 1452(w), 1400(m), 1377(m), 1348(m), 1260(w), 1200(m), 1190(m), 1148(m), 1110(w, b), 1055(w, b), 986(w), 894(w), 669(w), 631(w) cm" 1 . NOAc-CEVE, 3450(w, b), 2940(w), 1820(m), 1787(m), 1734(vs), 1540(w), 1430(w), 1372(m), 1220(m), 1164(m), 1110(m), 1057(m), 827(w), 740(w, b), 668(w) cm" 1 . NPC-CEVE, 3470(w, b), 3062(w), 2910(w, b), 1775(w), 1710(vs), 1594(w), 1497(m), 1454(w), 1428(w), 1390(s), 1373(s), 1297(w), 1200(m), 1140(m), 1108(m), 750(m), 688(m), 662(w), 618(w) cm" 1 . PF-CEVE, 3475(w, b), 3080(w), 2960(w), 2925(w), 2870(w), 1779(w), 1708(vs), 1601(w), 1508(s), 1388(m), 1290(w), 1230(m), 1183(m), 1157(m), 1100(m), 1050(w), 1013(w), 932(w), 831(m), 750(w, b), 908(w), 66G(w) cm" 1 . PC1-CEVE, 3480(w, b), 3100(w), 2965(w), 2920(w), 2870(w), 1780(w), 1710(vs), 1493(s), 1384(s), 1300(w), 1278(w), 1180(m), 1092(m), 1018(m), 940(w), 823(m), 731(w), 707(w), 665(w), 638(w) cm" 1 . PBr-CEVE, 3470(w, b), 3018(w), 2960(w), 2923(w), 2880(w), 1778(w), 1710(vs), 1490(s), 1385(s), 1303(w), 1278(w), 1181(m), 1110(m), 1073(m), 1013(m), 822(m), 704(w), 665(w), 632(w) cm" 1 . PC0 2 ET-CEVE, 3440(w, b), 2980(w), 2935(w), 2910(w), 1778(w), 1710(vs), 1608(m), 1509(m), 1414(w), 1380(m), 1280(s), 1180(m), 1110(m), 1021(m), 851(w), 767(w), 693(w), 667(w) cm" 1 .

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79 PCN-CEVE, 3480(w, b), 3102(w), 3060(w), 2965(w), 2927(w), 2878(w), 2218(m), 1780(w), 1711(vs), 1605(m), 1507(m), 1380(s), 1288(w), 1180(m), 1110(m), 1050(w), 954(w), 838(m), 800(w), 750(w), 650(w) cm . POAc-CEVE, 3480(w, b), 2930(w, b), 1769(m), 1711(vs), 1600(w), 1509(m), 1390(m), 1374(m), 1200(s), 1170(m), 1110(m), 1047(w), 1020(m), 941(w), 910(w), 848(w), 640(w, b) cm" 1 . PCH 3 -CEVE, 3470(w, b), 3040(w), 2960(w), 2927(w), 2870(w), 1779(w), 1708(vs), 1515(m), 1390(s), 1300(w), 1188(m), 1110(m), 1050(w), 812(w), 910(w), 660(w) cm -1 . POMe-CEVE, 3480(w, b), 3005(w), 2960(w), 2940(w), 2920(w), 2842(w), 1778(w), 1710(vs), 1611(m), 1592(w), 1515(s), 1465(w), 1445(w), 1390(m), 1303(m), 1257(s), 1188(m), 1172(m), 1110(m), 1030(m), 830(m), 806(w), 662(w) cm -1 . PCF 3 -CEVE, 3480(w, b), 3070(w), 2925(w), 2860(w) , 1780(w), 1714(vs), 1612(m), 1517(w), 1418(m), 1382(m), 1327(s), 1172(m), 1125(m), 1110(m), 1067(m), 1019(m), 950(w), 838(m), 757(w), 697(w), 662(w), 627(w) cm" 1 . MAH-EVE, 2980(m), 2935(w), 2900(w), 1860(m), 1780(vs), 1732(m), 1440(w), 1405(w), 1377(w), 1350(w), 1223(m), 1093(m), 1070(m), 928(m), 730(w), 620(w) cm" 1 . MAH-CEVE, 2960(w), 2925(w), 2870(w), 1855(m), 1779(vs), 1732(m), 1432(w), 1350(w), 1298(w), 1220(m), 1104(m), 1048(m), 923(m), 930(w), 660(w) cm' 1 . NPM Homopolymer, 3480(w), 3060(w), 2900(w, b), 1775(w), 1705(vs), 1597(w), 1496(m), 1457(w), 1387(s), 1185(m, b), 749(m), 732(m), 688(m), 657(w), 621(m), 611(w) cm" 1 .

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A peak appears at 1110-1100 cm in all copolymer spectra that is absent in the NPM homopolymer spectrum. This peak was therefore assigned to the C-0 stretch of the ether unit in the copolymers. The appearance of this peak was thus indicative of copolymer formation. Differential Scanning Calorimetry (DSC) . The thermal properties of many of the copolymers that were synthesized were investigated by use of the DSC method. The copolymers generally did not have a welldefined crystalline melting point or glass transition temperature (T ), Although several thermal transitions were evident in most DSC runs, they generally were not reproducible and they were always poorly defined. The temperature of decomposition, however, proved to be fairly reproducible. The thermal stability runs were performed in air with a Perkin Elmer DSC-1B instrument. Several runs were performed in a helium atmosphere with no apparent effect on the decomposition temperature (T d ). The T d 's of the copolymers tested are given in Table 10. The abbreviations used are the same as those used in Tables 2-5. TABLE 10 Copolymer Decomposition Temperatures (T .) Copolymer

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81 Copolymer molecular weight determinations . Although a great deal of time was not spent on copolymer molecular weight determination, several copolymers were characterized by gel permeation chromatography (GPC) or vapor pressure osmometry (VPO). A low conversion NPM-CEVE copolymer ( x „ = 0.2, M T = 0.5, AIBN, 60°C) was analyzed on a Waters Model 6000A GPC which was equipped with a Model 440 Absorb4 ance Detector. A Waters 10 u Styragel column was used for the analysis. A solution of copolymer concentration 2.3 g/1 in ChLCl ? was injected. Dichloromethane was also used as the elution solvent. A single, broad peak, typical of polymers produced by a free-radical mechanism, was the result. The peak maximum corresponded to a molecular weight of about 6300, based on polystyrene calibration curves. This molecular weight corresponds to a degree of polymerization (D ) of 22-23 (based on 1:1 repeat unit). Vapor pressure osmometry analysis of a high conversion NPMCEVE copolymer (sample 16, Table 2) in acetone, using a benzil calibration standard, gave a number average molecular weight (M ) of 13,250, which corresponds to a D of 47-48. Solubility . The NPM-CEVE copolymers synthesized in this study proved to be soluble in many organic solvents such as CHCL, CH ? C1 ? , tetrahydrofuran, DMS0, nitromethane, ethyl acetate, acetone, acetonitrile, and dimethyl formamide (DMF). The copolymers were insoluble in benzene, alcohols, toluene, CC1. and water. The NPM homopolymer, on the other hand, was generally insoluble in the solvents listed above, dissolving only in DMS0, DMF and tetrachloroethane.

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82 Copolymer Epimerization Maleimide-vinyl ether copolymers were epimerized by using several different bases and various reaction conditions. These conditions are detailed below. Copolymer epimerization with 2,2,6,6-tetramethylpiperidine (TMP) in dimethylsulfoxide . The copolymer to be epimerized was dissolved in DMS0-d 6 (~ 0.25 g copolymer/0.3 ml DMSO-dg), and several drops of TMP were added to the solution. Within 10-15 minutes, the solution turned from colorless to a deep cobalt blue color. The solution was filtered through a plug of glass wool into a clean, 5 mm NMR tube, which was capped and placed in a 60.0°C water bath. The progress of the epimeri13 zation could thus be monitored by periodically obtaining a C NMR spectrum of the sample. Copolymer epimerization with lithium diisopropyl amide (LDA) in tetrahydrofuran (THF) . A three-necked, 200 ml round-bottomed flask equipped with a magnetic stirring bar, addition funnel, and nitrogen inlet was dried for several hours in a 140°C oven and then allowed to cool in a dry nitrogen stream. One gram copolymer was dissolved in 20 ml THF (freshly distilled from lithium aluminum hydride), and the resulting solution was placed in the addition funnel. About 1.0 g solid LDA (Alfa) was added to 75 ml distilled THF which had been added to the reaction flask. The transfer of the LDA was performed under a blanket of dry nitrogen (inverted funnel). The reaction flask was cooled to -75°C with a dry ice:isopropanol bath. The LDA solution was stirred magnetically under positive nitrogen pressure as the copolymer solution was slowly added over ten minutes. The solution

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83 turned from colorless to deep red, and finally black opaque as the copolymer solution was added. This solution was stirred at -75°C for one hour. At the end of this time, the solution was a deep green color. Approximately 30 ml of saturated aqueous ammonium chloride was quickly added while the solution temperature was still -75°C. The ammonium chloride solution froze on contact with the cold THF. The dry ice was allowed to evaporate, so the solution slowly warmed to room temperature with continued stirring. The organic layer of the resulting two-phase system was now a deep cobalt blue color. The organic layer was separated and added dropwise to rapidly stirred methanol. The resulting light blue precipitate was filtered and dried at reduced pressure (50°C) overnight. The yield was 0.9 g light blue powder. About one-half of this powder was treated with 20 ml hot (80°C) acetic anhydride for three hours. The deep green copolymer solution that resulted was allowed to cool, and 75 ml of water was added. The resulting precipitate was filtered and dried in vacuo. The resulting light green powder was dissolved in acetone and precipitated into methanol. Three additional precipitations from acetone into methanol failed to rid the product of all of its green color. IR analysis of the original blue copolymer showed a broad peak at 3150 cm , which may be due to an amide N-H stretch resulting from partial hydrolysis of the succinimide units of the copolymer. This band disappeared on treatment of the copolymer with hot acetic anhydride. Otherwise, the IR spectrum of the epimerized copolymer was unchanged from that of the copolymer before epimerization.

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84 Copolymer epimerization with potassium t-butoxide in DMSO. Potassium t-butoxide was synthesized by using high vacuum techniques. About 5 ml of t-butyl alcohol was distilled from calcium oxide and sealed into a breakseal . About 20 ml freshly distilled (from KOH) DMSO was used to dissolve 3.5 g copolymer (sample 16, Table 3), and the resulting solution was sealed into a clean breakseal. A solution of 1 g ammonium chloride in 10 ml distilled DMSO was sealed into a third breakseal. The three breakseal s were attached to a 200 ml round-bottomed flask that could be attached to a vacuum line by means of a 14/20 ground glass joint. The flask was also equipped with a side arm that had several constrictions through which potassium metal could be distilled. A small test tube with a ground glass joint containing a pea-sized piece of potassium metal under hexane was connected to the side arm of the inverted apparatus. The whole apparatus was again inverted, quickly connected to the vacuum line, and evacuated. The potassium was gently heated with a yellow flame, causing it to melt and flow down the side arm. The reaction flask was cooled in ice water. Continued heating of the potassium metal caused it to distill onto the inside wall of the cool flask, forming a blueish silver mirror. The side arm was sealed off, and the tbutyl alcohol was introduced by breaking the corresponding breakseal. The metal was quickly consumed. Hydrogen gas was evolved, and a clear, colorless solution resulted. The breakseal containing the copolymer solution was then broken, allowing the solution to flow into the potassium t-butoxide solution. Within two minutes, the combined solutions had gone from nearly colorless, to deep green, to a

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85 deep cobalt blue color. The blue solution was stirred at room temperature for forty-three hours, and the breakseal containing the ammonium chloride solution was broken. No color change was noted when the ammonium chloride solution was added. The bulk of the solvent was removed on the vacuum line with heat (heat gun). The apparatus was removed from the vacuum line, chloroform was added to the bright blue residue, and the chloroform solution was extracted with water. The organic layer was dried over anhydrous MgSCL overnight. The MgSCL was separated from the solution by filtration. The blue chloroform solution was slowly added to rapidly stirred hexane (dropwise) to yield a blue precipitate. This precipitate was filtered and dried in a 50°C vacuum oven overnight to yield 3.0 g light blue powder. This polymer was somewhat soluble in methanol, as evidenced by the fact that attempted precipitation of copolymer solutions into methanol yielded a fine dispersion that could not be separated by filtration. The IR spectrum of the epimerized copolymer was nearly identical to that of the copolymer before epimerization, except for a small decrease in the relative intensity of the peak at 1110 cm" . Complexation Studies Ultraviolet (UV) spectroscopy was used to study the complexation behavior of maleimides and CEVE. Dichloromethane (CHpClp) was used as the solvent in all cases. Invariably, the solvent was distilled from PfliQ immediately prior to its use. CEVE was distilled from calcium hydride immediately before use. The maleimides used were recrystallized from cyclohexane.

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86 Solutions of CEVE in CH C1 have absorptions with X 275, 262, c L max and 254 nm. Dichloromethane solutions of N-arylmaleimides have absorptions with A mav in the range 300-320 nm and X „ 255-275 nm, nidx max depending on the maleimide. In contrast to solutions of N-arylmaleimides, N-cyclohexylmaleimide solutions did not have an absorption at 255 nm. The absorption spectra of several maleimides are shown in Figure 2. Addition of equal amounts of CEVE to a maleimide solution in the sample beam of the UV spectrometer and a solvent blank in the reference beam results in a slight intensification of the absorbance in the 255-300 nm region. This increase in absorbance was attributed to the formation of a charge-transfer complex and was therefore investigated further. This quantification proved to be a formidable task due to the overlap of the charge-transfer band with the absorptions of both monomers. The experiments involved monitoring the absorbance of maleimideCEVE solutions of constant maleimide concentration and varying CEVE concentration. The [CEVE] was always much greater than the [maleimide]. In a typical procedure, the spectrum of the pure maleimide in CHpClp was measured against a reference of pure CHLClp by using a pair of 2 mm quartz cuvettes. Next, the spectrum of the solution of the maleimide and vinyl ether was measured against a reference containing the vinyl ether at the same concentration. The first spectrum was substracted from the second to afford the spectrum of the charge-transfer complex. Absorbances were read directly from the digital display at 5 nm intervals, using care to optimize the slit width before each reading so as to minimize noise. Absorbances read in this manner were considered accurate to ± 0.002 absorbance units.

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87 o o . ID •<•1o

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Solution concentrations were carefully controlled so that [maleimide] was the same in all runs and [CEVE] was exactly the same in both reference and sample cells. Stock solutions of maleimide and CEVE were made by weighing the desired amounts of monomers into clean, dry volumetric flasks and diluting to the mark with solvent. Experimental solutions were then made by transferring the appropriate amounts of the stock solutions to a series of volumetric flasks with glass pipettes, followed by dilution to the mark. Convenient final concentrations for the maleimide solutions were approximately 0.01 M. CEVE concentrations varied in the range 0.3 2.5 M. Higher concentrations were not practical because both monomers have absorptions in the region of interest. It was noticed that repetitive runs on a single sample did not give reproducible absorbance readings, even if the spectrometer was carefully zeroed before each run. Thus, all absorbance values were corrected by first taking the average of the absorbances at a specific wavelength (where the complex did not absorb) for a series of spectra as the "true" value of the absorbance at that wavelength. The deviations of individual spectra from this "true" value at the specified wavelength (335 nm) were then added (or subtracted) from all of the absorbance readings for each particular run. This procedure gave highly reproducible absorbance values over the entire wavelength range for repetitive runs on the same sample. While there may be some error in the observed absorbances due to deviations of the calculated "true" A (absorbance at 335 nm) value from the actual one, the relative absorbances within a series (constant [maleimide] and varying [CEVE]) are believed to be highly accurate.

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89 The maleimides that were investigated were N-(4-methoxyphenyl ) , N-(4-chlorophenyl ), N-phenyl , N(4-trifluoromethyl phenyl ) , N-(4-cyanophenyl ) , and N-cyclohexylmaleimides. The absorption bands due to the charge-transfer complex between the various maleimides and CEVE were obtained by subtracting the spectrum of pure maleimide from that of maleimide-CEVE solutions. The results are shown in Figure 3. The figure shows the normalized absorbance due to the complex (i.e., the absorbance due to the complex [A ], divided by the concentration of maleimide [M]) vs. wavelength (A) for the various maleimides studied. N-Arylmaleimides exhibit a very intense absorption beginning at 255 nm (see Figure 2), so investigation of the charge-transfer band was impossible at lower wavelengths. This was not a problem with N-cyclohexyl maleimide; however, CEVE has an intense absorption below 245 nm, thus precluding investigation of the charge-transfer band below this wavelength. The N-cyclohexylmaleimide-CEVE charge-transfer band has a definite maximum at 255 nm, but the corresponding maxima for the other maleimides is not evident and must be considered to be <_ 255 nm in all cases {< 265 nm for N-(4-chlorophenylmaleimide) . The intensity of the charge-transfer band was measured for at least five different CEVE concentrations for each maleimide. Invariably, the intensity of the band increased linearly with [CEVE] at all wavelengths. The results for the NPM-CEVE complex are shown in Figure 4. Absorbance measurements were considered to be least subject to error at 295 nm because the CEVE was nearly transparent at this wavelength, and none of the maleimides exhibited extremely intense

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90 20.0 r 15. Or 10.05.0 r .0.0 NCHX-CEVE NPM-CEVE PC1-CEVE PCF 3 -CEVE POMe-CEVE 265 275 285 Wavelength (nmj FIGURE 3. Electronic Absorption Spectra of Various N-Substituted Maleimide 2-Chloroethyl Vinyl Ether Charge-Transfer Complexes, [CEVE] = 1.3 in all cases.

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91 22. 5 T [CEVE] • 1.9397 9.988 x 10" 1.6164 a 1.2932 a 0.9699 • 0.6466 + 285 295 305 Wavelength A FIGURE 4. Effect of Varying CEVE Concentration on the Intensity of the NPM-CEVE Charge-Transfer Band

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92 absorptions at 295 nm. Thus, the normalized absorbance due to complex 295 formation at 295 nm (A ) , as a function of [CEVE], is given in Table 295 11. The slope of a plot of A /([M] x i) (where I represents the path length of the cell) vs. [CEVE] gives the relative sensitivity of the complex absorption to changes in [CEVE]. These slopes were calculated for the various complexes by using a linear least squares technique. The results are presented in Table 12. The slopes given in Table 12 are equivalent to the product of the equilibrium constant for complex formation and the extinction coefficient of the complex at 295 nm. This is discussed further in the next chapter.

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93 en cm u < 00 CM -_D O =-!co co r»» cxi ud r-~ r~-. uo en co i— I c\i en >-}• LD o o o o o o o o o o o CM lO i— I CM i— I CTi Ohwcooi^ui oooooooo o o o o o o o CM CM «3" -D UO CM OO «=*• LT) CO o o o o o o o o o o o CTii— ii_ni.no>— iota Ot— i cm n -j>* m uo cocococooocoooco oooooooo i— i oo co i_n vo i — oo uo us r~co cri CO CO CO CO CO CO o o o o o o <-D <-_>" 00 >— ( CD cd en cri en co OMiriNCfiH <-0 en cm Ln en O O i— I i-H I— I tJOOHHHN o i— i cm oo «-_iin c_n co en o uo o en en oh n -t co Noi o o o o o O i-H HHHWCVI -jo en cm ir> co o *-f co en t— i oo co en cm co en o o <-H t— I I— 4 j= cu +j -a QJ •!.— E E 2 O TSCU CM O r— I .3 ID C (O E X C >.•!CU O CU CM r— i r— en =-*
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94 un co co x> cri cm OO UD CD lO Ol CM n ^" LTHO o o o o o o o o o o o •tNOCfioci co x> r~~. i — en o x> vo <*Q ix) iX3 r^ o o o o o o r-^ i— i >3co •— i OU3 H ID W O .— i in cm r^ co i — o "=3r~^ r-i <— E X i— I CM CO ^JIX) o o o o o o o o o o o r^ cm o o r^* co (OCOOlOOrH r>. N N CO CO CO o o o o o o x> cr> cm ^ r^ ud en co ix> en O <3" X3 CTi r— I CO en cm ix) en .— i r^ r^ co O X) o o o o o o o o o o o o o CO Ol LO IX) < — ( CO ^*NCOCfiOHHM LT) IX) IT) X) X> IX) o o o o o o o r^ -sicm en x> «3^en "3co co co o i— ( cm >=tix) r^ co CO X) CM IX) CO O O O i— I i— * i— I X a; o -a .c: •!+-> E QJ -rs: cu *3fT3

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95 TABLE 12 Slopes of A" 3 /([M] x I) vs. [CEVE] Plots Complex 3 Slope = Ke 295 r b NCHX-CEVE 15.8 0.998 PCN-CEVE 17.1 0.989 PCF 3 -CEVE 17.0 1.000 PC1-CEVE 15.6 0.998 NPM-CEVE 13.6 0.998 POMe-CEVE 11.3 0.997 Abbreviations used are explained in the footnotes of Tables 2-5. Correlation coefficient of the data.

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CHAPTER III RESULTS AND DISCUSSION Copolymer Composition Copolymerizations are most simply described by the following kinetic scheme: ' \AAA/H[' + M 2 \AAA/M 2 + M 1 \AAA/M 2 * + M 2 k 12

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97 probably the nonlinear least-squares procedure developed by Tidwell and Mortimer. This procedure is, however, most tedious due to the computer iteration that is required. Equation (S) can be expressed as a linear equation in r, and r~. This linearization is the basis 102 of the Fineman-Ross technique for reactivity ratio determination. Of The Joshi-Joshi method is a refinement of the Fineman-Ross technique, where linear least-squares analysis minimizes the errors inherent in the graphical Fineman-Ross procedure. Another linearization of the terminal copolymerization equation has been developed by Kelen and Tudos. 88 It must be kept in mind that Equations (4)-(7) describe only the simplest possible copolymerization kinetic scheme, and several assumptions have been made in the derivation of Equation (8). These assumptions include the following: 1) all steps are irreversible, 2) there is no influence of the penultimate monomer units in the chain and 3) addition of a comonomer complex is not important. Thus, Kelen and QQ Tudos have stated that systematic deviation from linearity of a Kelen-Tudos plot indicates nonadherence to the terminal copolymerization model given by Equations (4)-(7). Copolymerization systems that exhibit a strong tendency to alternate (e.g., vinyl idene cyanidemaleic anhydride) often do not give linear Kelen-Tudos plots. The composition of NPM-CEVE copolymers (expressed as the mole fraction of NPM in the copolymer [m.,], see Table 3), as determined from chlorine and nitrogen elemental analysis, is shown in Figure 5 as a function of the initial mole fraction of NPM in the comonomer

PAGE 111

98 feed (xm)« It can be seen that the system shows a strong tendency to alternate, since 1:1 comonomer ratios in the copolymer were obtained for a wide variety of \. values. When x», > 0.5, the copolymers are rich in succinimide units, resulting from incorporation of NPM into the copolymer. This fact reflects the ability of maleimide monomers to homopolymerize under free-radical initiation, as shown in this work and by Cubbon and Tawney et al . The reactivity ratios calculated from the data in Figure 6 by 87 88 using the Joshi-Joshi method or the Kelen-Tudos method are r. m „ = NPM 0.28 and r CEVE » (see Table 6). Thus, CEVE shows no tendency to homopolymerize under these conditions. The Kelen-Tudos plot (Figure 1), calculated from the data shown in both Figure 6 and Table 3, is linear. This observation may mean that the terminal model adequately describes the copolymerization of NPM and CEVE. As McFarlane, Reilly and O'Driscoll point out, however, the use of a linear least-squares analysis of copolymer composition data should not, by itself, be used for copolymerization model discrimination. The authors reached this conclusion by showing that a random 2% error in copolymer composition data can cause a significant deviation from linearity in a Kelen-Tudos plot. Similarly, it is felt that the observation of linearity in these plots should not be taken as conclusive evidence for adherence to the terminal model. Copolymerization Kinetics Figure 6 shows the dependence of the overall rate of copolymerization (R ) on the mole fraction of NPM in the feed (xJ for NPM-CEVE copolymerizations initiated by the thermal decomposition of AIBN in

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99 1.0 T 0.9 • 0.8 0.7 • 0.6 0.5 0.4 .. 0.3 0.2 o.i 0.0 0.2 0.4 0.6 0.8 10.0 V NPM FIGURE 5. Copolymer Composition Diagram for the NPMCEVE System (m Np „ = Mole Fraction NPM in the Copolymer, xmdm = Initial Mole Fraction of NPM in the Feed)

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100 11.0 10. f 9.0-18.07.0-6.0 OJ

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101 CH 2 C1 2 at 60.0°C. This plot exhibits a clear maximum at x M = 0.4. Such a dependence of the copolymerization rate on the mole fraction of comonomers in the feed has been taken as evidence for the participation of intermolecular complexes in the propagation steps of alternating copolymerizations. It should be noted that plots of [polymer] formed vs. the time of polymerization invariably exhibited a nonzero x-intercept (see Experimental). This fact indicates that there was an induction period during which no copolymerization took place. This induction period is probably at least partially due to the finite amount of time necessary for the comonomer solution to reach thermal equilibrium after being inserted into the 60.0°C bath. The induction periods for various x M values are given in Table 8. These induction periods showed no regular dependence on x M> but were generally longer for maleimiderich feeds. This fact may or may not be significant, but it emphasizes a need for determining more than one copolymer mass when determining copolymerization rates by a gravimetric technique. It should also be noted that several other kinetic methods were employed in an attempt to determine the NPM-CEVE copolymerization rate. These methods included: 1) following the rate of disappearance of NPM by UV spectroscopy, 2) following the rate of CEVE disappearance by gas chromatography (GC), and 3) monitoring the copolymerization by means of H NMR spectroscopy. None of these methods gave reproducible results. The integration of GC and NMR peaks was not sufficiently accurate enough to follow the small changes in monomer concentration encountered in low conversion copolymerization kinetics. While UV

PAGE 115

102 spectroscopy proved to be very sensitive to changes in NPM concentration, the rates obtained by using this method were invariably much smaller (2-7 times) than those obtained by the gravimetric technique. In some cases, the absorbance being monitoring showed no change, or even increased, with time, even though solid copolymer could be isolated from the reaction mixture. These observations led to the supposition that either a by-product or low molecular weight oligomers were absorbing at the same wavelengths being used to monitor the NPM concentration. Thus, the UV kinetic studies were abandoned. Copolymerization kinetics are discussed in greater detail in a recent review by Wittmer. Maleimide-CEVE Complexation Studies Ultraviolet (UV) Spectroscopy The classical method for the determination of the equilibrium constant for charge-transfer complex formation is that of Benesi and Hildebrand, or some modification of it such as the Scott method, ] no or the Scatchard method. The use of the Scatchard method has been 109 advocated by Derenleau. For a general discussion of these methods, see References la, lb, lg (Chapter 3), and Ik (Chapter 5). The Benesi -Hildebrand equation follows from consideration of the following complex equilibrium. A + D — ^ C ^ The equilibrium constant is given by K = C/[(D -C)(A Q -C)] (9) where D and A are the initial concentrations of donor and acceptor, respectively, and C is the concentration of complex.

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103 2 If complexation is weak (C « CA or CD ), the reciprocal of Equation (9) becomes K" 1 = DA/C D A (10) K J Typical experimental conditions are adjusted so that D » A , so oo K" 1 = D o A o /C-D o (11) Rearrangement of (11) gives C = D A o K/(l + K D Q ) (12) Using the Beer-Lambert law to express the complex concentration C (C = A c /e£, where A c is the absorbance due to the complex, e is the molar absorptivity, and l is the path length of the cell) gives A c = D o A o K ^ /(1 + K D o } (13) Equation (13) has the form of the typical absorption isotherm described by Person. Thus, if the equilibrium constant K has a finite, nonzero value, a plot of A vs. D q (constant A ) should exhibit curvature and approach the line A = A Iz asymptotically for large values of D , and for strong complexation. An absorption appears in the UV spectra of methylene chloride solutions of N-substituted maleimides and CEVE, which does not appear in spectrum of either component alone. This absorption appears in the wavelength region < 255-300 nm (see Figures 3 and 4). For all the maleimides studied, the absorption due to complex (A ) increased linearly with CEVE concentration at all wavelengths (Figure 4 is typical of A /£ vs. wavelength plots for all of the maleimides studied). In such cases, K D << 1, and Equation (13) reduces to the form

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104 A c D A o K£ £ (14) which predicts a linear dependence of A on D (at constant A ). This co o means that either K is small or the range of donor concentrations used was not large enough. Unfortunately, higher CEVE concentrations were not practical in this study because CEVE absorbs in the same region as the complex. Only the product Ke, and not their separate values, can be determined when such a linear dependence is observed. Thus, Equation (14) predicts that a plot of A /A I vs. D will have a slope of Ke. These slopes are given in Table 12 for the various maleimides studied. It must be reemphasized that due to the overlap of the absorptions of both components with the charge-transfer band, the values determined must be considered as approximate. It is felt, however, that the present study indicates that the complexation between N-sub295 stituted maleimides and CEVE is weak, since the values of Ke determined are in the range 11-18. The weakness of the interaction also follows from the observation of linearity of the A vs. [CEVE] plots over the range of [CEVE] studied, which means K[CEVE] << 1 (vide supra). Since the maximum [CEVE] used was about 2 M (see Table 11), 2K « 1 or K « 0.5 M" 1 . 295 The e value may be small, since the complex absorptions were determined at 295 nm, while the maximum absorption was typically at shorter wavelengths {<_ 255 nm). This wavelength was used so that comparative values could be determined for all of the maleimides studied (see Experimental section). The e values may be small even at the A. for the complex, if an analogy can be drawn with the

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105 citraconic anhydride-CEVE complex. The value of e for this system has been determined as 252 1/mole/cm, compared to the value of 604 1/mole/cm determined for the citraconic anhydride-ethyl vinyl 21 ether system. Kukubo et al . studied the complexation behavior of maleic anhydride and CEVE in chloroform. These authors determined a value of 33 1/mole/cm for z at 340 nm (K = 0.105, 30°C) as compared to the value of 690 1/mole/cm determined for e at 350 nm for the paradioxene-maleic anhydride system. Thus, a small extinction coefficient seems to be typical of CEVE complexes. Several groups have also stated that no complexation was evident for N-aryl substituted maleimide-donor monomer systems. For example, Barrales-Rienda et 47 al . found no evidence of a charge-transfer band in solutions of NPM and styrene in benzene or cyclohexane. Oishi has also reported that no charge-transfer transitions were observable in the UV spectra 112 of styrene-N-(substituted phenyl )citraconimide, and styrene-N113 alkyl citraconimide solutions. These observations may indicate that e is small; but even if e is as small as 100, the K values would be in the range 0.11-0.17, indicating a weak complexation between the maleimides studied and CEVE. It should also be mentioned that a linear dependence of A /A £ CO on D is to be expected if the charge-transfer is of the "contact" variety, or, in other words, results from random collisions of the complex participants (see Reference Ik, Chapter 5). This possibility could not be ruled out by the experiments described herein.

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106 In spite of the experimental shortcomings discussed above, it 295 is felt that the Ke values determined in this study are comparable, at least within the series of N-(substituted aryl )maleimides. 295 It can be seen in Table 12 that the Ke values are relatively small for those N-arylmaleimides substituted with electron donating groups in the para position, and large for those with para electron with295 drawing groups. This relationship can be shown by plotting the Ke values vs. the Hammett substituent constants (a) for the para sub295 stituents. This plot is shown in Figure 7. If the e values are similar within the series of N-arylmaleimides, then the difference 295 in Ke values reflects a difference in the equilibrium constants for complex formation. It is also possible, however, that the dif295 295 ferences in Ke are due to differences in the e value for the various maleimides. It is noteworthy that the observation of a small equilibrium constant (K) for charge-transfer complex formation does not necessarily exclude the complex as a reaction intermediate. Similar linear dependencies of complex absorption on the concentration of added donor have been observed for a number of donor-acceptor systems in a series of recent papers by Fukuzumi and Kochi , ' ' ' and Fukuzumi et al . Even though these linear dependencies exist, the authors have also provided convincing evidence that the complex is an actual intermediate in many of the reactions studied. Complexation Studies Utilizing NMR Techniques Hanna and Ashbaugh have developed a technique similar to that 2 of Benesi and Hildebrand, whereby shifts of NMR resonances in

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107 to (13 O 4-> •rO) O S_ i— o .c (/I

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108 solutions of donors and acceptors relative to the resonances of the components themselves are used to evaluate the equilibrium constant for complex formation. The olefinic protons of NPM exhibit very small shifts upon mixing with CEVE in CDCl, or CD^Cl^. Typical data obtained in CDC1., at 100 MHz are shown in Table 13. TABLE 13 Chemical Shifts (6, ppm From TMS) for the Olefinic Protons of N-Phenylmaleimide in CDCI3 Solutions of Varying 2-Chloroethyl Vinyl Ether Concentration [NPM] [CEVE] 6 { l H) 0.100 0.0 6.856 0.100 0.995 6.849 0.104 1.952 6.842 0.100 2.956 6.842 0.100 5.640 6.824 0.0500 6.856 0.0497 2.469 6.846 0.0497 4.862 6.836 0.0501 5.654 6.833 0.0501 6.743 6.830 0.0501 7.359 6.829 It can be seen that the shifts are very small over a wide range of [CEVE]. Indeed, similar shifts were observed in solutions of NPM and 2-chloroethyl ethyl ether. Similar small shifts have been

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109 48 observed for maleic anhydride-CEVE solutions by Iwatsuki and I ton. These authors also found that the maleic anhydride-CEVE complexes are highly reactive in alternating copolymerizations. Thus, they attribute the small NMR shifts to the low concentration of the complex in the solution. Such an explanation may also apply to the NPM-CEVE system. It may also be possible that the complex geometry is such that the chemical shifts of the olefinic protons are not affected by complexation. 13 Mixtures of vinyl acetate and maleic anhydride exhibit small C NMR shifts as compared to the chemical shifts of the pure compo118 1 ? nents. The C chemical shifts of NPM-CEVE mixtures were nearly identical to those determined for the pure monomers. However, this observation does not prove that complexes are absent. A recent re119 13 port on the C NMR of solid crystalline complexes has shown that the shift induced by complexation is small, even in the solid state. 120 121 Indeed, several authors ' have pointed out that NMR studies of weak complexes can be highly misleading. The chemical shift of NPM olefinic protons is markedly solvent dependent. This effect is shown in Table 14 for NPM and NPM-CEVE solutions. The large upfield shift of NPM protons in C fi D fi relative to CC1, (1.05 ppm) or CDC1-, (1.15 ppm) is particularly interesting. Bryce122 Smith and Hems observed similar shifts for NPM, N-2,6-xylylmaleimide, and N-butylmaleimide in benzene solutions. They argued that these shifts were due to the formation of exo stereospecific complexes of the maleimides with benzene solvent, where the olefinic

PAGE 123

110 TABLE 14 cci 4

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Ill determined for the N-methylsuccinimide-durene complex was twice that found for the corresponding maleimide complex. Thus, it appears that the double bond of the maleimide is unimportant in complexes with 124 aromatic donors. Matsuo came to a similar conclusion by observing that aromatic solvent induced shifts were comparable in N-substituted maleimides and the corresponding succinimides. On the other hand, the downfield shift of the methylene protons of N-(p-chlorophenyl )succinimide in DMSO (compared with the shift in nonpolar solvents) was small compared with the chemical shift difference of the corresponding maleimide (DMSO solvent vs. CC1. or hexane). The author interpreted these results by invoking a specific interaction of the donor solvent (DMSO) with the methine carbons of the maleimide. The ethylenic protons of NPM exhibited a similar downfield shift in DMSO (see Table 14) as compared with the chemical shifts observed in CDC1 3 or CCL. The large solvent effects on the chemical shifts of NPM olefinic protons seem to indicate that one of the assumptions made in the traditional Benesi-Hildebrand treatment of complex equilibria, namely that of solution ideality, is probably invalid. Studies of weak complexes using either UV or NMR techniques often require measurements over the whole range of donor concentrations. Thus, the assumption 125 of solution ideality is questionable. Li tt and Wellinghoff have examined the influence of solution nonideality on complexation for the styrene-fumaronitrile system in a variety of solvents. They propose a model that explains curvature of Benesi-Hildebrand plots as being the result of strong solvent interaction with the donor or

PAGE 125

112 acceptor. They also propose a method whereby complexation equilibrium constants may be determined while taking these solvation effects l ?fi into account. As Bertrand points out, however, the method requires four adjustable parameters for the treatment of typically 5-10 data points, which casts doubt on the physical significance of the results. Bertrand proposed an alternative to the Li tt and Wellinghoff model based on purely nonspecific solvent-solute interactions. The above discussion emphasizes the fact that the treatment of UV or NMR data by using the classical Benesi-Hildebrand method can sometimes lead to misleading or even erroneous conclusions. On the basis of the results discussed above, however, it can be concluded that maleimides are capable of interacting with various donors. Indeed, solid crystalline complexes of maleimide with re104 127 sorcinol and hydroquinone have been isolated and shown to possess a 1:1 stoichiometry. An interaction between NPM and CEVE, however, cannot be concluded on the basis of the NMR studies described above, although some sort of interaction between the monomers is implied by the UV studies. These observations point out that the presence or absence of spectroscopic behavior expected when complex formation takes place is not sufficient evidence for the inclusion or exclusion of the complex on the reaction coordinate. Carbon-13 NMR Structural Studies on N-Substituted Maleimide-Vinyl Ether Copolymers 13 Since the appearance of commercial C NMR spectrometers in the early 1970' s, the technique has been widely used for the structural 90 elucidation of organic molecules. The technique has proven to be

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113 particularly useful in the field of polymer chemistry, because of the extreme structural and stereochemical complexity of many polymers and copolymers. In many cases, H NMR is of limited use in determining the microstructure of polymers, since the spectra often appear as a series of overlapping, broad humps. The possibility of the elimination of proton coupling through broadband high power decoupling, and 1 3 the large range of C chemical shifts (> 200 ppm), result in considerable spectral simplification as compared to H NMR spectra. The lack of CC coupling due to the low natural abundance of the C nuclei also contributes to spectral simplification. The low natural 13 abundance of the C nuclei is also a detriment in that the observa13 tion of C nuclei is inherently less sensitive. This fact, plus the fact that carbon types in large molecules can have a variety of magnetic environments (resulting in many lines for a single carbon resonance) necessitates the averaging of a large number of individual spectra in order to achieve an acceptable signal to noise ratio. This process became practical with the advent of Fourier transform NMR spectroscopy, which enables a large number of spectra to be automatically accumulated, averaged and stored by a dedicated computer. 13 The applications of Fourier transform C NMR have been discussed 90 99 128 both generally ' and specifically in reference to polymer sys91 94 terns ' by many authors. 91 129-136 Carbon-13 NMR has been used extensively by many authors, ' 'za129 132 133 especially Katritzky and Weiss, ' ' for copolymer characteri 13 tion. Several papers have appeared that discuss the C NMR spectra o1 maleic anhydride copolymers. ' These papers deal primarily with

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114 Q1 I^Q-l^^ copolymer sequence analysis, although in some cases ' tacticity is also determined. The above references constitute an excel 13 lent introduction to the utility of C NMR in copolymer analysis. Peak Assignments in N-Phenylmaleimide-Vinyl Ether Copolymers 13 The C NMR spectrum of an NPM-CEVE copolymer is shown in Figure 8. This copolymer was synthesized by using low temperature (-78°C), photochemical initiation (AIBN), and a large excess of vinyl ether in the initial monomer feed. Elemental analysis (CI and N) showed that the monomer ratio in this copolymer was very close to 1:1 (sample 1 in Tables 2 and 3). The peak assignments shown were made by utilizing several techniques. General assignments can be made by compari13 son with the considerable amount of C shift data available in the 90 literature. The three peaks appearing in the 173-178 ppm region may be confidently assigned to carbonyl carbons. The peaks appearing in the 126-132 ppm region are due to aromatic carbon resonances. The chemical shifts of the peaks appearing in the range 69-77 ppm are consistent with those of carbons that are alpha to an oxygen atom. An off-resonance decoupled spectrum of the copolymer was run, and the peaks appearing at 131.9, 174.4, 175.6 and 177.1 remained as singlets. This means that the carbons resonating at these positions have no directly bonded protons. This is consistent with the assignment of the carbonyl carbons. The resonance appearing at 131.9 was assigned to the quaternary aromatic carbon on the basis of this result. The other aromatic carbon peaks are split into doublets on off-resonance decoupling, and thus are assigned to the ortho, meta and para carbons of the phenyl ring. The small peak appearing as a

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115 o i— 0) E CO M

PAGE 129

116 shoulder at 127.7 ppm was assigned to the para carbon due to its small intensity. The ortho and meta carbons cannot be distinguished by this technique. The peaks centered at 76 ppm split into doublets on off -resonance decoupling, and were thus assigned to the methine carbon of the vinyl ether units in the copolymer. Similarly, the peaks centered at 69.7 ppm are split into a triplet, and were assigned to the methylene carbon of the side chain that is a to oxygen. The intense singlet appearing at 42.9 ppm was also split into a triplet in the off-resonance decoupled spectrum. This peak was assigned to the methylene carbon a to chlorine in the vinyl ether units. The large intensity of this peak also supports this assignment. This carbon is located on a side chain three bonds from the nearest chiral center in the copolymer backbone, and thus is not expected to be split or broadened significantly by the different magnetic environments produced by varying backbone stereochemistry. The remaining carbons (backbone methines of the succinimide units and the backbone methylene of the vinyl ether units) appear as fairly closely spaced broad resonances in the completely decoupled spectrum (31-50 ppm). The splitting induced by off-resonance decoupling causes these peaks to be even broader, and considerable overlap of peaks was observed. This problem is illustrated in Figure 9, which shows the completely decoupled (DMS0-d fi solvent) and off-resonance decoupled (TCE solvent) C spectra for the NPM-methyl vinyl ether (MVE) copolymers. Careful examination of expansions of this region allowed tentative assignment of the highest field resonance

PAGE 130

117 ^^ Wk^v^p WyW*!W" J I I DMSO-d, TCE a) 180 160 140 120 100 80 60 40 20 6 ppm FIGURE 9. Complete a) and Off-resonance b) Decoupled 13 C NMR Spectra of NPM-Methyl Vinyl Ether Copolymer

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118 (32-34 ppm) to the backbone methylene carbon of the vinyl ether units. 13 This assignment was supported by the C spin-lattice relaxation times (TjJ compiled in Table 9. Polymer backbone T,'s for methylene carbons are generally one-half the T, values of backbone methine carbons because of the greater efficiency of the dipolar relaxation mechanism resulting from two directly bonded protons (methylene) as op94 139 posed to a single directly bonded proton (methine). ' As seen in Table 9, the J^ of the resonance appearing farthest upfield (32-34 ppm) was about 29 ms, and the T. for the resonance at 48-50 ppm was about 76 ms. Thus, the resonance at 32-34 could more confidently be assigned to the backbone methylene of the vinyl ether units. The T,'s listed in Table 9 also support the assignments discussed _ 90 99 above. Quaternary carbons generally have long T, 's, ' and the values determined for the resonances assigned to the carbonyl and quaternary aromatic carbons are much longer (~ 10 times) than the rest of the values determined. The T, value of the resonance assigned to the methine a to oxygen (56 ms) is about one-half of the T, determined for the side chain methylene a to oxygen (142 ms). This finding supports the assignment for the reasons discussed above. The assignment of the intense resonance at 42.9 ppm to the side chain methylene carbon a to chlorine is supported by the NOEF values listed in Table 9. The NOEF values for polymer carbons are often less than the theoretical maximum of ~ 2, due to the fact that the effective correlation time (related to the tumbling rate or segmental reorientation rate) does not satisfy the extreme narrowing condition (cot_ << 1, where t is the correlation time, and uj is the Larmor o c c o

PAGE 132

119 . 94 frequency). This is true for all carbons listed in Table 9 except for the carbon resonating at 42.9 ppm (and the protonated aromatic carbons), which exhibit the full theoretical nuclear Overhauser enhancement. This is to be expected if the carbon is part of a rela90 94 tively flexible side chain. ' The distinction between the two methine and the two carbonyl carbons of the succinimide units cannot be made by use of the off-resonance decoupling technique or by comparing T, or NOEF values. A good estimate of the relative chemical shifts of such similar carbon types can be made by exploiting the chemical shift parameters first determined by Grant and Paul, and extended by Lindeman and Adams, 142 143 for various alkanes. Tonelli et al . ' have utilized simil ar 13 considerations to predict the C spectra of many homoand copolymers. In general, these authors have shown, by empirical comparison 13 of the C chemical shifts of a large number of compounds, that atoms other than protons a or 3 to a carbon of interest cause a downfield shift (~ 9 ppm for carbon atoms) relative to a similar compound without the substitution. Atoms other than protons that are y, and situated in a gauche relationship to the carbon of interest, on the other hand, cause an upfield shift, the magnitude of which depends on the atom and the probability that the y substituent is gauche to the carbon of interest. Examination of the copolymer structure (Figure 8) reveals that both carbonyl s of the succinimide units have the same number of a and 6 atoms, but carbonyl 2 has an extra y interaction (0 atom of the vinyl ether) in comparison with carbonyl 1. Thus, the upfield carbonyl resonance was assigned to carbonyl 2. Similarly,

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120 methine carbons 9 and 11 both are a to the same number of atoms. Carbon 9 has an extra 3 interaction compared to carbon 11, while carbon 11 has one more y interaction than carbon 9. Thus, the resonance overlapped by the solvent (DMSO-dg) at ~ 37-40 ppm was assigned to carbon 11, and the downfield methine (~ 48-50 ppm) was assigned to carbon 9. 13 The structures and C chemical shifts for the model compounds synthesized in this work are shown in Figure 10. The copolymer structure and the chemical shifts based on the above assignments are shown 13 in Figure 11, along with the C chemical shifts of the CEVE and NPM homopolymers. While it may be argued that the model compounds do not have structures that are strictly analogous to the copolymer structure because some of them have a bicyclic structure, it is felt that they are useful for qualitative comparisons. The model compounds could be synthesized in stereospecific form, and could be more easily characterized by proton NMR than the copolymers. The synthesis and stereochemical characterization of these compounds will be discussed in detail in a later section. It can be seen from Figures 10 and 11 that the chemical shifts of the model compounds are in qualitative agreement with the assignments of the copolymer resonances discussed above. The differences in the chemical shifts for similar carbons in the homoand copolymers (see Figure 11), coupled with the fact that the copolymers contain a nearly 1:1 mole ratio of the comonomers (see Figure 5), may be taken as evidence for the alternating nature of these copolymers.

PAGE 134

121 128.95,126.32 28.39 ^ 176.03 128.42 128.96,126.38 128.28 13.9 42.42 128.71,126. 178.45 132.78 >128.06 23.93 129.03,126.25 40.06"? 21.81 CH28 25.54 128.98,126.25 47.520 25.15 FIGURE 10. Model Compound 13 C NMR Chemical Shifts (CDC1-, ppm from TMS)

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122 * 15.30' y 63.75/ 37 48 129.03,126.57 { .,, , 7 1 32 58 l 38 40 72.89" W — -ry y lto.tu 27.24 132.44 25.98 15.55 11 74.74 f 45.620 (or other possible "trans' epimer) 56.00 31.19 '0 74.25 Y^ v
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123 TCE-d 2 Solvent CDC1 3 Solvent 129.2, 126.8 DMS0-d 6 Solvent 48.3-49.9 37.0-39.5 75.7-76.7 \ / 32.4-34.7 / 174.41177.1 175.6 1131.9 127.7 \\] 128.3,126.3 CI FIGURE 11. Homoand Copolymer 13 C NMR Chemical Shifts (ppm from TMS)

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124 13 Interpretation of Copolymer C Spectra 13 The copolymer whose C NMR spectrum is shown in Figure 8 contains a 1:1 ratio of comonomers and is believed to be totally alternating (vide supra). The spectrum exhibits fewer peaks than might be expected, based on the fact that there are three chiral centers per alternating repeat unit. Free radically initiated polymers are typically predominantly atactic, with a slight preference for syndio92 tactic placement. Thus, as a first approximation, all possible relative stereochemistries should be present to a greater or lesser extent. Carbon-13 NMR is very sensitive to differences in magnetic environment caused by differences in relative stereochemistry between 90 91 94 1 3 chiral centers in polymers. ' 'The sensitivity of C chemical shifts to different stereochemical environments usually decreases rapidly with distance. In other words, a carbon of interest is often most sensitive to differing relative stereochemistry between chiral centers situated one bond away, and less sensitive to relative stereochemistry between chiral centers two bonds distant, and so on. Sensitive, in this context, refers to the magnitude of the chemical shift difference caused by varying stereochemical placements. The possible relative stereochemistries between adjacent chiral centers ("dyad" stereochemistry) in NPM-CEVE alternating copolymers is shown in Figure 12. Figure 13 illustrates the various stereochemical possibilities for three adjacent chiral centers ("triads") for alternat13 ing sequences. As can be seen in Figure 8, many of the C resonances do not appear as singlets, but are split. Since this copolymer is not expected to exhibit complications due to varying sequence

PAGE 138

125 cis (erythro) \ r = racemic trans (threo' m = meso r' 1°; 4-OR 1-h FIGURE 12. "Dyad" Stereochemical Possibilities for NPM-CEVE Alternating Copolymers (i.e., Relative Stereochemistry Between Two Adjacent Chiral Centers)

PAGE 139

126 r' r

PAGE 140

127 distribution, these splittings are presumed to reflect dyad stereochemical sensitivity. Consider the carbonyl region. If carbonyl 1 is sensitive to stereochemistry two bonds removed, it would be expected to appear as two peaks [m or r (Figure 12)]. If this carbon is sensitive to stereochemistry three bonds distant, it would appear as eight peaks (r'mm", m'mm", r'mr", m'mr", r'rm", m'rm",r'rr" and m'rr"). If carbonyl 2 is sensitive to stereochemical differences two bonds removed, four peaks are expected [r'r, r'm, m'r and m'm (Figure 13)], since this carbon is situated two bonds from two chiral centers and one bond from another. The experimental observation is three peaks in the carbonyl region with approximate area ratios of 2:1:1 (measured by electronic integration and by cutting and weighing). This observation can only be explained if the stereochemistry at the succinimide units is either exclusively cis (r) or trans (m), and both carbonyls can "see" at most relative stereochemistry two bonds distant. If this is the case, carbonyl 1 should appear as a singlet, and carbonyl 2 should appear as two peaks (split only by the relative stereochemistry between carbons 7 and 9, r' or m'). The fact that the area ratio of the two peaks comprising the resonance ascribed to carbonyl 2 is about 1:1 (the downfield peak is slightly broader) may indicate that the relative stereochemistry between carbons 7 and 9 is random (~ 50% r 1 and ~ 50% m'). This contention is supported by the fact that the resonance assigned to carbon 7 also appears as two peaks with approximately 1:1 area ratio. Thus, it appears that carbon 7 is sensitive only to relative

PAGE 141

128 stereochemistry resulting from the chiral center that is one bond away (carbon 9) . Carbon 8 also appears as two peaks, but their area is clearly not 1:1. Apparently, carbon 8 exhibits different stereochemical sensitivity than carbon 7. This has been found to be true in the case of various vinyl ether homopolymers. The methine carbon of poly(ethyl vinyl ether) appears as a singlet, while the methylene in the side chain exhibits triad configurational sensitivity. The backbone methylene has dyad sensitivity. In the C NMR spectrum of poly(methyl vinyl ether), the methyl carbons show splitting which has been ascribed to pentad configurational sensitivity, while the meth144 me appears as a singlet. In view of the fact that the methoxy carbon in poly(methyl vinyl ether) is very sensitive to various configurational sequences, an NPMmethyl vinyl ether (MVE) copolymer was synthesized (sample 25 in 13 Tables 4 and 5). The C NMR spectrum of this copolymer is shown in Figure 9. The methoxy carbon is clearly split into three peaks, while the methine of the vinyl ether unit appears as a singlet. This observation may be taken as evidence that the side chain carbons of the vinyl ether units in NPM-vinyl ether copolymers are more sensitive to configurational sequences than the methine carbons. The approximate area ratio of the two peaks comprising the carbon resonance assigned to carbon 8 (NPM-CEVE, Figure 8) is 2:1 as measured by electronic integration, cutting and weighing, and planimetry. Since carbon 8 is believed to be sensitive to at least "triad" configurational sequences, at least four peaks are expected

PAGE 142

129 (m'V, m'V, r"m', r"r'), while only two are observed. Thus, any detailed analysis of this resonance is highly speculative. It is noteworthy, however, that a 2:1 area ratio is not expected based on the observed "dyad" probabilities [Pm 1 ~ 0.5, Pm" z 0.5 (vide infra)] 91 9? and the assumption of Bernoullian propagation statistics. ' Carbon 9 appears as two overlapping peaks having an approximate 13 area ratio of 2:1. The corresponding peak in the C NMR spectrum of the NPM-MVE copolymer is a complex resonance consisting of at least eight overlapping peaks. Thus, this carbon is thought to be sensitive to longer configurational sequences than "dyads." Carbon 11 also exhibits configurational splitting. This resonance was overlapped by the solvent peaks when the spectrum was run 13 in DMSO-dg. This problem could be circumvented by running the C NMR spectrum in tetrachloroethane (TCE). The resonance then appears as two peaks with approximate area ratio 1:1. It is possible that this splitting reflects the relative stereochemistry between carbons 11 and 7 (m" or r"); however, this conclusion must be regarded as speculative. It is reasonable to assume that the splitting observed for the backbone methylene carbon 12 reflects the relative stereochemistry between carbons 11 and 7. This resonance consists of two overlapping broad peaks. The approximate area ratio of these two peaks is 1:1 (the downfield peak is broader). Although the accuracy of the area determination for overlapping peaks may be questioned (cut and weigh, planimetry, and electronic integration), the corresponding peaks in 13 the C NMR spectrum of the NPM-MVE copolymer are not as broad, and

PAGE 143

130 exhibit baseline resolution. The area ratio for these peaks in the NPM-MVE copolymer are also 1:1, although the downfield peak is somewhat broader than the upfield peak. This observation is interpreted as indicating that the relative stereochemistry between chiral centers at carbons 7 and 11 is random. In other words, the probability for an m" placement (Pm") is 0.5. 13 In summary, on the basis of C NMR analysis, the stereochemistry at the succinimide units in the copolymers discussed is either all cis (Pr = 1.0, Pm = 0), or all trans (Pm = 1.0, Pr = 0), while the relative stereochemistry between chiral centers 7 and 9, and 7 and 11 appears to be random (Pm' z Pm" z 0.5). These findings are not consistent with a copolymerization mechanism involving consecutive alternate additions of "free" monomers. It would be hard to rationalize the high stereoselectivity observed at the succinimide units of the copolymers discussed if such a mechanism was operational. Radicals are generally postulated as having 45 either a planar or a rapidly inverting pyramidal structure. The stereochemistry at the chain end is therefore not determined until the next monomer adds. Monomer approach to either side of the radical end should be equally likely (or nearly so) in the absence of a large steric effect by the penultimate or antepenultimate units in the chain. Such steric effects are not uncommon in free radical polymerizations, as evidenced by the general preference for syndiotactic placements in traditional free radically initiated homopolymerizations go which increases with decreasing temperature of polymerization. The trend observed for the alternating copolymerizations studied in this

PAGE 144

131 work, however, is opposite to what is expected based on the consideration of such a steric effect. This will be discussed in upcoming sections. It should be mentioned that the possibility exists that the ob13 served simplicity of the C NMR spectra discussed herein could be due to the accidental equivalence of the chemical shifts due to the various relative stereochemistries possible in these copolymers. This possibility was ruled out by the epimerization studies described in the next section. 1 q The Effect of Composition and Stereochemistry on Copolymer C NMR Spectra 13 The appearance of copolymer C spectra depends markedly on the conditions used to synthesize the copolymers. Figure 14 shows expan13 sions of the carbonyl region of C spectra of copolymers obtained with various initial comonomer mole fractions (x M )Other conditions used to synthesize the copolymers whose spectra are shown in Figure 14 were exactly the same [temperature (60°C), AIBN, CH 2 C1 2 , NL = 0.5]. Several changes are obvious in the spectra as the initial mole fraction of NPM is varied. First, the intensity of the peak at about 176.4 ppm increases at the expense of the peak at 177.1 ppm as the fraction of NPM in the initial feed is increased. Second, the upfield peaks seem to broaden and increase in intensity relative to the downfield peaks as x M increases. As shown in Figure 5, the mole fraction of maleimide incorporated into the copolymer also increases as x M increases. Thus, one possible 1 o explanation for the observed changes in the C spectra is that the

PAGE 145

132 |/V>v^ 180 FIGURE 14. 175 170 6 ppm Effect of the Mole Fraction of NPM in the Initial Comonomer Feed (x..) on the Appearance of Copolymer ^C NMR Carbonyl Peaks

PAGE 146

133 sequence distribution changes with X m (i-e., carbonyl carbons in sequence of two or three consecutive succinimide units may exhibit different chemical shifts than the carbonyl s of succinimide units in alternating sequences). A second possibility is that the stereochemistry at the succinimide units affects the carbonyl 13 C chemical shifts, and varies with the initial mole fraction of NPM present in the feed. The changes shown in Figure 14 seem to be more dramatic than might be expected, based on the relatively small changes in copolymer composition in this range of x M (see Figure 5) if they are due to compositional sequence variations. Thus, it was thought that the ob13 served variations in the C NMR spectra were at least in part due to the differences in copolymer stereochemistry. This postulate was verified by epimerizing various NPM-CEVE copolymers by using different bases and epimerization conditions. These epimerizations presumably proceed via generation of the enolate of the succinimide by basic abstraction of the acidic proton a to the carbonyl. Protonation of the planar enolate should lead to a scrambling of the stereochemistry at the succinimide units of the copolymer. Figure 15 shows the expanded carbonyl regions of NPM-CEVE copolymers at various stages of epimerization. Also given in the figure are the epimerization conditions. Experimental details are given in Chapter II. It is obvious from these studies that the changes in the relative intensities of the peaks at 176.4 ppm and 177.1 ppm, and the broadening of the carbonyl peaks farther upfield, are due to changes in the stereochemistry at the succinimide units in the copolymers.

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134 No Epimerization 5 ppm FIGURE 15. Effect of Copolymer Epimerization on the Carbonyl Region of the 13c NMR Spectra of NPM-CEVE Copolymers

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135 Enolate generation with lithium diisopropyl amide (LDA) in THF at low temperature is generally irreversible. 145 Thus, on quenching with a proton source (NH 4 C1 in this case), approximately equal amounts of the possible diastereomers are expected. The copolymer carbonyl peaks at 176.4 and 177.1 ppm have a nearly 1:1 intensity ratio after epimerization with LDA. This result is exactly what is expected for carbonyl 1 (see Figure 8) if this carbonyl is sensitive to stereochemistry two bonds distant. The relative stereochemistry between carbons 9 and 11 is either all cis or all trans before epimerization, and the cis:trans ratio is about 1:1 after epimerization. As discussed in the preceding section, if the copolymer stereochemistry is random, then carbonyl 2 is expected to appear as four peaks. Four separate peaks are not clearly resolved in the LDA epimerized copolymer carbonyl region, but the peaks assigned to this carbon have clearly broadened upon epimerization. This observation is consistent with the expected result. 13 The other regions of the C NMR spectrum of NPM-CEVE copolymers are also changed drastically on epimerization. Since these other carbon resonances are not as well resolved as the carbonyl peaks, the changes observed on epimerization are generally a broadening of the peaks or slight changes in relative intensities, as compared with 13 the copolymer C NMR spectrum before epimerization. This effect is illustrated in Figure 16, which shows the effect of epimerization 13 (LDA) on the C resonances assigned to the carbons a to oxygen in the vinyl ether units. Such changes are much more difficult to interpret than the changes observed in the carbonyl region, and are not discussed extensively in this work.

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136 No Epimerization Epimerized LDA, -75°C 80 70 60 ppm 13 FIGURE 16. Effect of Copolymer Epimerization on the C NMR Resonances Due to Carbons a to Oxygen in NPM-CEVE Copolymers

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137 Another factor (aside from stereochemistry) that must be considered in the interpretation of the carbonyl region is the possibility of sequence irregularities. Copolymer composition data (Table 3) indicates that mole fraction of NPM in the copolymers increases slightly with the mole fraction of NPM in the feed. Thus, there are undoubtedly some sequences of two, three or more consecutive succinimide units in the copolymers. The carbonyls in these sequences could conceivably have different chemical shifts than carbonyls in succinimide units flanked by two ether units. The carbonyls of the NPM homopolymer appear as a fairly broad single peak with a maximum at 176.2 ppm. If the NPM homopolymer carbonyls have the same chemical shift as the homo repeat units in the copolymer, then the carbonyl resonances resulting from these homo repeat units would be expected to overlap the split resonance assigned to carbonyl 2. Thus, the apparent increase in intensity of the upfield carbonyl resonances relative to the downfield peaks with increasing mole fraction NPM in the feed (see Figure 12) could be due to an increase in the percentage of succinimide homo repeat units in the copolymers. Supporting evidence for this postulate is shown in Figure 17. This figure shows 13 the carbonyl regions of the C NMR spectra of two NPM-CEVE copolymers prepared under the conditions: M. = 0.5, x M = 0-7, AIBN, 60°C. Specif, n trum (a) was obtained on a high conversion copolymer (82%), while spectrum (b) was obtained on a low conversion copolymer (< 10%). Table 3 reveals that succinimide units comprise 67 and 62% of these two copolymers, respectively (samples 23 and 24). The difference in the comonomer ratio in the copolymers is clearly reflected by an

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138 170 6 ppm FIGURE 17, 13, Expanded Carbonyl Regions of the i,J C NMR Spectra of Low (a) and High (b) Conversion NPM-CEVE Copolymers (X M = 0.7)

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139 increased intensity of the upfield peaks, relative to those appearing downfield for the high conversion copolymer. 13 Examination of the C chemical shifts determined for the model compounds (Figure 10) reveals that in all cases the carbonyl chemical shifts are greater for the compounds that possess a cis stereochemistry at the succinimide methines, as opposed to the corresponding compounds that have trans stereochemistry. Figure 15 shows that the peak at 176.4 ppm grows at the expense of the downfield peak at 177.1 ppm upon epimerization. These observations suggest that the predominant relative stereochemistry at the succinimide units in NPM-CEVE copolymers is cis. This contention is supported by the epimerization results shown in Figure 15. Long term equilibrium epimerization of NPM-CEVE copolymers with the bases 2,2,6,6-tetramethylpiperidine (TMP) or potassium t-butoxide in DMSO resulted in the continued decrease of the intensity of the peak at 177.1, and continued increase of the peak at 176.4, until the downfield peak was the minor component. Trans stereochemistry at the succinimide units is expected to be favored thermodynamically since epimerization of model compound _3, under similar conditions (TMP, DMSO, 60°C), resulted in a six-fold excess of the trans isomer. This could be due to a relief of steric strain in the cis compound on transformation to the trans. Similar relief of steric strain should also favor the trans form in the copolymer. 13 As seen in Figure 15, the overlap of peaks in the C NMR spectra of the equilibrium epimerized copolymers is severe. It is felt, however, that the intensity at 177.1 ppm is definitely smaller than

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140 that at 176.4, and this fact is taken as solid evidence that NPM-CEVE copolymers possess predominantly cis stereochemistry at the succinimide units. Epimerization of the cis fused bicyclic model compounds 6, .U and ^6 with TMP in DMSO did not give an excess of the trans isomers. This suggests that the cis fused 5,6-membered ring bicyclic systems are more stable than the corresponding trans fused systems, as has been reported by several authors. ' Epimerization of compound _11 resulted in an increase in the proportion of trans:cis isomers over that originally present, but treatment of compound JJ5 with TMP in DMSO caused the small amount of trans isomer originally present (~ 1-2%) to disappear (presumably by transformation to the cis fused diastereomer) . Epimerization of trans compound 8^ using similar conditions resulted in the production of an excess of the cis isomer. The possibility of undesired side reactions under the epimerization conditions discussed above should be addressed. It is possible that the chlorine of the vinyl ether units in the copolymer could have been involved in an undesired side reaction such as dehydrohalogenation or nucleophilic displacement. That such reactions were not the cause of the observed changes in the carbonyl region of the C NMR spectra upon epimerization was verified by epimerizing an NPMethyl vinyl ether (EVE) copolymer. The same changes in the carbonyl region were noted. The appearance of several new peaks in the 167170 ppm and aromatic regions sometimes resulted upon copolymer epimerization. These peaks are thought to be the result of partial

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141 hydrolysis of the succinimide units to the corresponding acid-amide structure. The new peaks were well separated from the imide carbonyls and always exhibited low intensity (~ 10% of the imide carbonyl intensity at most). For these reasons, the fact that partial hydrolysis took place is not believed to effect the validity of the conclusions discussed above. In summary, NPM-CEVE copolymers seem to possess a predominantly cis stereochemistry at the succinimide units. The ratio of the areas of the copolymer carbonyl peaks appearing at 176.4 and 177.1 ppm (carbon 1) is related to the ratio of trans to cis succinimide units, respectively. The ratio of cis to trans succinimide units depends on the initial mole fraction of NPM in the feed. This latter effect was quantified by measuring the relative areas of the two peaks (177.1 and 176.4 ppm) for copolymers prepared at various Xm's, and expressing the result as the mole fraction cis succinimide units in the copolymers [Area (cis)/Area (cis) + Area (trans)]. The regularity of the change in this parameter with x M is exhibited by the linear relationship shown in Figure 18. The fact that more cis succinimide units result in copolymers prepared from vinyl ether rich feeds (small x«) may be significant. If comonomer complexation is viewed as a simple equilibrium, then the fraction of maleimide in complexed form is greater when the vinyl ether is in excess. If the stoichiometry of the complex is 1:1, the equilibrium constant for complex formation is given by Equation (9), as discussed previously.

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142 o.g r FIGURE 18. Mole Fraction cis Succinimide Units in NPM-CEVE Copolymers vs. Xm

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143 K = (V C)C ( D oC) (9) If the complex concentration (C) is small compared to the concentration of maleimide (A ) and the concentration of vinyl ether (D ), Equation (9) is approximated by K = C/A o D Q (15) The fraction of maleimide complexed is thus C/A Q = D Q K = (M T A Q )K (16) where M, is the total monomer concentration. Expressing A as the mole fraction of maleimide (x M ) leads to C/A Q = KM T (1 x M ) (17) If the polymer stereochemistry at the succinimide units is proportional to the fraction of maleimide that is complexed (C/A ), then the linear relationship shown in Figure 18 is predicted by Equation (17). Thus, it is possible that comonomer complexation has an effect on copolymer stereochemistry. It is prudent at this juncture to discuss the possible errors in 13 1? using C NMR for quantitative studies on polymers. When using C NMR for quantitative comparisons, it is important to account for any differences in the spin-lattice relaxation times (T, ) and nuclear Overhauser effects (NOE) in the resonances being compared. If such differences exist, then the determination of relative areas is likely 90 99 to be in error. ' Polymers are generally "well behaved," in that T^ and NOE values for similar carbon types are very nearly the same,

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144 although T, values may vary considerably from one carbon type to another 90 ' 94 ' 139 (see Table 9). It is generally recommended 90 ' 99 13 that if C NMR is to be used for quantitative purposes, the pulse delay (PD) should be at least five times the longest T, in the sample (> 99% relaxation before the next pulse). Due to the number of scans necessary to obtain polymer spectra, the time requirement for the use of such a long PD is prohibitive (e.g., the longest T, in Table 9 is 2.5 s; thus, 5 x 2.5 s x 25,000 scans * 87 hours). The PD's used to obtain copolymer spectra were typically 0.180-0.360 s, as compared to the T, values of about 1.5-2.0 s determined for the carbonyl carbons. Nevertheless, if the Tj values for all of the peaks in the carbonyl region are similar, their relative areas should be comparable. Such 94 13 behavior is often assumed in polymer C studies; however, polymer T 's that are dependent on stereochemical sequences have been reported. ' Freeman and Hill have shown that in a repetitive sequence of 90° pulses, a steady state is established in which an equilibrium exists between the effects of the radiofrequency pulses and spin relaxation. The equilibrium magnetization is a function of Tj, and differences in T. among various carbon types are reflected in varying relative peak areas with changes in the PD between the 90° pulses. An experiment was performed on an NPM-CEVE copolymer in which 13 a series of C spectra was obtained with different pulse delays varying in the range 0.1-2.0 s. No change in the relative intensities of the carbonyl peaks at 177.1 and 176.4 ppm was observed over the range of pulse delays used. Thus, it was concluded that there is no significant difference between the T,'s for carbonyl s (number 1 in

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145 Figure 8) in cis succinimide units as opposed to those in trans units. The relative areas of these peaks thus reflect the relative amounts of cis and trans succinimide units in the copolymers, even though the 13 PD used to obtain the copolymer C spectra discussed in this work was not five times the T, of the carbon in question. It is also note13 worthy that all C spectra that are compared quantitatively in this work were obtained by using the same PD (360 ms), temperature (110°C) and solvent (DMSO-dg). The error in the determination of the areas of these peaks should also be discussed. As can be seen in Figures 14 and 15, the peaks at 176.4 and 177.1 ppm are fairly broad (due to some sensitivity to longer configurational sequences), and there is often some overlap of these peaks, both with each other and with the other peaks in the carbonyl region. Thus, there is considerable error in the determination 91 of their relative areas. Randall has advocated the use of curvefitting procedures, utilizing pure Lorentzian peak shapes for the determination of the relative areas of overlapping resonances of poly13 mer C NMR spectra. Unfortunately, this procedure, which requires computer iteration, was not available during the course of this work. Areas were typically estimated by the use of relative peak heights and digital electronic integration. The electronic integration was carried out by first phasing the entire spectrum, and then adjusting the integration parameters to obtain the "best" integration over the whole spectral range. The carbonyl region was then expanded and integrated digitally. Individual peaks were integrated between peak minima, which amounts to dropping a perpendicular from the minima to

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146 the baseline, followed by integration of the resulting areas. The integral value of the peak farthest downfield was arbitrarily set to 1.00, and other peak areas were determined relative to this value. It is not known what the error inherent in this procedure actually is, but the areas are estimated to be within ±5% of the true values. The use of peak areas is thought to be more accurate than the use of peak intensities. Peak intensities are often used as estimates of the relative areas of polymer C NMR peaks. The results of the digital integration and peak intensity area determinations for the data presented in Figure 18 are compared in Table 15. The results calculated from the digital integration were used to plot Figure 18. TABLE 15 The Mole Fraction of cis Succinimide Units in NPM-CEVE Copolymers as a Function of the Mole Fraction of NPM in the Initial Comonomer Feed (x.,) M Sample Mole Fr a ction cis Succinimide Units Number 6 d 7 9 10 13 18 21 A.M

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147 TABLE 15 Continued For copolymerization conditions and analysis data, see corresponding sample numbers in Tables 2 and 3. Calculated from peak areas (digital integration). Calculated from peak intensities. This sample is not included in Tables 2 and 3; lower % conversion than sample 7. Nitrogen-15 NMR Studies Nitrogen-15 NMR has proven useful in the structure elucidation of both small molecules and polymers containing nitrogen atoms. 15 It has also been suggested that N NMR chemical shifts are about 1 3 five times more sensitive to stereoisomerism than C NMR chemical shifts. For this reason, N enriched (~ 20%) NPM was synthesized and copolymerized with CEVE (M T = 1.77, AIBN, 60.0°C, x M = 0-5). The 15 N NMR spectrum of this copolymer is shown in Figure 19. 15 The N resonance appears as two major peaks, each of which exhibits some fine structure. It is reasonable to assume that the difference in the chemical shift of these two major peaks is caused by different magnetic environments at the nitrogen, as a result of either cis or trans stereochemistry at the succinimide units in the copolymer. Partial epimerization of this copolymer resulted in a decrease of the area ratio of the downfield to the upfield peaks (as measured planimetrically) . This observation lends credence to the assumption mentioned above. 15 The area ratio of the two peaks in the N NMR spectrum of the non-epimerized copolymer is about 3:1. The area ratio of the peaks

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148

PAGE 162

149 13 assigned to cis and trans succim'mide units in the C NMR spectrum of this same polymer was about 6:1. This could mean that there are 13 two peaks in the C NMR spectra corresponding to carbonyl 1 in trans succim'mide units, one of which overlaps either the downfield peak at 177.1 ppm or the upfield peaks in the carbonyl region assigned to carbonyl 2. This must be regarded as speculative at this point be15 cause there are no data available on the relative T, values of N nuclei in trans vs. cis succinimide units. A difference in the T, values could cause a discrepancy in the relative areas, as discussed 15 in the previous section. The pulse delay used to obtain the N spectrum shown in Figure 19 was five seconds. Another possible source of the discrepancy in the cis:trans ratio 15 13 15 as determined by N and C NMR techniques is the possibility of N13 13 15 C coupling. Each C carbonyl in the N enriched copolymer is directly bonded to a nitrogen atom, 20% of which are N atoms. Thus, 20% of 13 C carbonyls should appear as a doublet. The 15 N13 C (carbonyl) coupling constant for the maleimide monomer was determined as 14.6 Hz. If the analogous coupling constant in the copolymer has a similar value, then some broadening of the carbonyl resonance in the 13 15 C NMR spectrum is expected. On the other hand, each N nucleus is 13 directly bonded to relatively few C nuclei (1.1% natural abun90 dance ), and the coupling should be relatively unimportant. 13 The validity of conclusions drawn based on the C NMR spectra would not be affected even if an overlap such as that described above existed. Changes in the stereochemistry are obvious, but cis:trans 13 ratios calculated from the C NMR spectra may be larger than the

PAGE 163

150 actual ratio. The calculated ratio is expected to be closer to the actual one when the percentage of trans succinimide units is low (less overlap), as opposed to when the calculated ratio is small (more overlap and therefore an overestimation of the cisrtrans ratio). If this is the case, changes in the cis:trans ratio, such as that depicted in Figure 18, would actually be larger than that shown. 15 The spectral simplicity evident in the N NMR spectrum shown in 13 Figure 19, as compared to the corresponding C NMR spectra, results from the fact that there is but one nitrogen atom per succinimide 15 unit. This simplicity, coupled with the apparent sensitivity of N NMR to stereochemical variations, may warrant further attempts to overcome such experimental difficulties as the need for nitrogen-15 enrichment and large sample sizes (3-5 g). 13 The Effect of Copolymerization Conditions on Copolymer C NMR Spectra In order to further probe the possibility that copolymer stereochemistry is dependent on the addition of a comonomer complex, a series of copolymerizations were carried out under various initial conditions that would be expected to shift the complex equilibrium A + D ^ — ^ C one way or the other. The stereochemistries of the resulting copoly13 mers were then investigated by using C NMR. The effect of the initial mole fraction of maleimide (x M ) on copolymer stereochemistry has already been discussed. The Effect of Total Monomer Concentration on Copolymer Stereochemistry An increase in the total monomer concentration should shift the above equilibrium to the right and thereby increase the concentration

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151 of the complex. Dilution of the reaction mix would be expected to cause the opposite effect. Walling et al . have argued against the participation of a molecular complex in copolymerizations because of an apparent absence of a dilution effect on monomer reactivities. Butler and Campus, however, have observed interesting dilution effects in the cyclocopolymerization of divinyl ether (DVE) and fumaronitrile (FN). The monomer ratio in the copolymers changed systematically from 2:1 (FN:DVE) toward 1:1 on dilution of the reac38 tion mix. Yoshimura et al . have observed that copolymerization rates are sometimes described by an order of total monomer concentration that is greater than one. The stereochemistry of NPM-CEVE copolymers also depends on the total monomer concentration. This effect is shown in Figure 20, which depicts the expanded carbonyl region of several copolymers prepared with different total monomer concentrations in the initial feed. The mole fractions of cis succinimide units calculated from these spectra are 0.855 for M y = 1.77 and 0.725 for M T = 0.5. Other con13 ditions used to synthesize the copolymers whose C NMR spectra are shown were exactly the same (60.0°C, AIBN, x M = 0.4, CHpClp). If the copolymer stereochemistry depends on the fraction of maleimide that is complexed, then the increase in the mole fraction of cis succinimide units with My observed is predicted by Equation (17). The observed increase in stereoselectivity with Mj is hard to rationalize if the "free monomer" mechanism is operational. The higher overall rates of copolymerization commonly observed at higher 38 total monomer concentrations might lead to the expectation of less selectivity and a more random stereochemistry.

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152 M T 1.78 180 175 6 ppm 170 FIGURE 20. 13, Expanded Carbonyl Regions of the iw, C NMR Spectra of NPM-CEVE Copolymers Prepared with Different Total Monomer Concentrations (M-) in the Initial Feed

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153 The Effect of Copolymerization Temperature on Copolymer Stereochemistry Temperature is also expected to perturb the complex equilibrium. Weak complex formation is generally slightly exothermic and disfavored entropically (-AH * 1-10 kcal/mole, -AS = 2-20 cal/mole/°K) . la Thus, an increase in temperature would be expected to decrease the complex 151 concentration. Seymour et al . have shown that complex formation between maleic anhydride and vinyl acetate is temperature dependent, and that no complex exists above ~ 90°C. Copolymers prepared from these monomers below 90°C were predominantly alternating, while those prepared at temperatures > 90°C had random sequence distributions. The stereochemistry of NPM-CEVE copolymers is also temperature dependent. The effect of copolymerization temperature on the appearance of the expanded carbonyl regions of NPM-CEVE copolymers is shown in Figure 21. The mole fractions of cis succinimide units for these 13 polymers, calculated from C NMR integrations, are given in Table 16. The mole fraction of cis succinimide units (x ) is also given for the copolymer prepared at -78°C, and several other copolymers. 'The data for these copolymers are not strictly comparable, because different initial conditions were used to synthesize them. It can be seen from Table 16, however, that lower copolymerization temperature invariably produces a more stereoregular copolymer. Lower temperature is also expected to lead to a higher equilibrium constant for complex formation (K). a ' Therefore, if copolymer stereochemistry depends on the fraction of maleimide that is in complexed form, then Equation (17) predicts that an increase in K will lead to an increase in copolymer stereoregularity.

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154 FIGURE 21. Expanded Carbonyl Regions of the C NMR Spectra of NPM-CEVE Copolymers Prepared at Various Temperatures

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155 TABLE 16 Mole Fraction of cis Succinimide Units in NPM-CEVE Copolymers Prepared at Various Temperatures Copolymerization Mole Fraction cis Temperature (°C) Succinimide Units Sample Number

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156 The temperature studies described here suggest that the enthalpy of activation is greater for production of trans stereochemical placements at the succinimide units in NPM-CEVE copolymers than it is for cis placements. Trans placements, however, are expected to be thermodynamically favored because of steric repulsion of the alkyl substituents (polymer chains in this case) in cis succinimide structures. Equilibrium epimerization of cis-dimethyl-N-phenylsuccinimide with 2,2,6,6-tetramethylpiperidine in DMSO led to an excess of the trans isomer (see Experimental). This finding supports the above contention. Thus, the cis stereochemistry results from kinetic control. Consecutive alternate addition of "free" comonomers would logically be expected to produce an excess of the more stable trans placements at the succinimide units. This follows from both thermodynamic considerations and the expectation of some steric hindrance to monomer approach from the side of the radical chain end cis to the polymer chain (higher enthalpy of activation). For these reasons, the temperature dependence of copolymer stereochemistry may indicate that a comonomer complex is involved in the propagation steps of NPM-CEVE copolymerization. The Effect of Copolymerization Solvent on Copolymer Stereochemistry The equilibrium constant for charge-transfer complex formation (K) is generally highly solvent dependent. The equilibrium can be perturbed if one or both of the complex participants is strongly solvated. In other words, K depends on the relative strengths of donor-acceptor interactions, donor-solvent interactions, and acceptorsolvent interactions. The solvent-solute interactions may also have

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157 donor-acceptor character, depending on the nature of the solvent. These facts, plus the observation that the chemical shifts of the olefinic protons of NPM are solvent-dependent, prompted a study of 13 the appearance of the C NMR spectra of NPM-CEVE copolymers prepared in different solvents. Figure 22 shows the expanded carbonyl regions of copolymers prepared in bulk (no solvent), benzene, and CH 2 C1 2 The mole fractions of cis succinimide units calculated from these spectra are shown in Table 17. The copolymers were prepared under similar conditions of temperature, initiator, and initial monomer ratio (x M = 0-5, AIBN, 60.0°C). The copolymerization carried out in benzene proved to be heterogenous, so the copolymerization was quenched at low conversion, when slight turbidity was first noticed. TABLE 17 The Effect of Solvent on the Mole Fraction of cis Succinimide Units in NPM-CEVE Copolymers co„«„+ Mole Fraction Solvent . _ . . ., .. .. cis Succinimide Units None 0.852 3 Benzene 0.505 a CH 2 C1 2 0.633 a Peak areas estimated by peak intensities These results indicate that copolymer stereochemistry is markedly dependent on the copolymerization solvent. The copolymer prepared in benzene exhibits a nearly 1:1 ratio of cis to trans succinimide units.

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158 ppm FIGURE 22. Expanded Carbonyl Regions of NPM-CEVE Copolymers Prepared in Bulk (a), Dichloromethane (b), and Benzene (c)

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159 This copolymer is also less regular as to sequence distribution, as evidenced by the large intensity of the upfield carbonyl peak at about 175.33 ppm. Such a large intensity is believed to be indicative of the presence of sequences of two or three consecutive succinimide units, as discussed previously. 128 Benzene has been shown to form complexes with NPM. Therefore, since benzene is also a donor in the NPM-CEVE-benzene system, the above results may be explained as being due to a competition between benzene solvent and CEVE monomer for the acceptor NPM. The overall concentration of NPM-CEVE complexes would thus be expected to be reduced, causing a decrease in both the stereoregularity and the alternation. The Effect of Donor and Acceptor Strength on the Stereochemistry of Maleimide-Vinyl Ether Copolymers It has been established that molecules possessing a high electron affinity (EA) form stronger complexes (larger K) with molecules possessing a low ionization potential (IP) relative to molecules with lower EA and higher IP. Thus, EA and IP are convenient measures of acceptor and donor strength, respectively. By appropriate variation of the structures of maleimides and vinyl ethers, it may be possible to alter their relative acceptor and donor strengths, causing the complex equilibrium to shift toward or away from complex formation (alter K) . With this in mind, a series of various N-substituted maleimides was copolymerized with CEVE by using constant conditions of temperature, solvent, concentration, monomer ratio, and initiator.

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160 13 The effect of the N-substituent on the C NMR spectra of the resulting copolymers was then investigated. Similarly, several vinyl ethers were copolymerized with NPM, and the resulting copolymer structures 13 were investigated by means of the C NMR technique. N-Substituted maleimide-CEVE copolymers . The maleimides used in 13 this study and their C NMR chemical shifts in CDC1are summarized in Table 18. All of the maleimides shown readily copolymerized with CEVE, except for N-(4-nitrophenyl )maleimide, which yielded no copolymer. The conditions used to synthesize all of the copolymers were similar (My = 0.5, x M = 0.5, 60.0°C, AIBN, CH 2 C1 2 ) and are given in Table 4. The yield and analysis data are given in Table 5. 13 It can be seen in Table 18 that the C chemical shifts of the olefinic and carbonyl carbons do not change very much with varying para substitution in the N-substituted phenyl maleimide series. A definite trend is observed, however. The maleimides bearing electron withdrawing substituents at the para aromatic carbon exhibit a small downfield shift at the olefinic carbon, relative to those maleimides with electron donating groups at the para position. The opposite trend is observed for the carbonyl carbon chemical shift. The carbonyls appearing farthest downfield are those contained in maleimides bearing electron donating groups. Larger changes in relative chemical shift are observed for the aromatic carbons. Changes in the olefinic and carbonyl chemical shifts are also noted on changing the Nsubstituent from aryl to alkyl or acetoxy. 13 Changes in C chemical shift have of 119 152 in electron density. ' Although the relative chemical shift 13 Changes in C chemical shift have often been related to changes

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161 TABLE IS Carbon-13 NMR Chemical Shifts of Some N-Substi tuted Maleimides 'CDC1.,, Ambient Temp., TMS Reference] R

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162 changes observed are very small, they may indicate that there are differences in electron density at the olefinic and carbonyl carbons within this series, even though these carbons are \/ery remote from the substituent. An increase in the fractional positive charge at 13 a carbon atom is expected to induce a downfield shift in the C NMR spectrum of that carbon. Thus, the olefinic carbons of N-(4-substituted)arylmaleimides bearing electron withdrawing substituents appear to be slightly more electron deficient than their counterparts having electron donating groups. This observation could possibly be related to the acceptor character of these monomers. The postulate that electron withdrawing para substituents increase the acceptor character of N-arylmaleimides is also supported 295 by the Ke values determined in the UV studies discussed earlier (see Table 12). It is also significant that a linear correlation has been observed between the polarographic half-wave potentials of a series of N-(substituted phenyl )maleimides and the corresponding 153 Hammett o constants. The radical reactivities of a series of N-(4-substituted phenyl )maleimides have also been correlated with Hammett's a constants in copolymerizations of these monomers with vinyl acetate and methyl154 methacrylate. No such correlation was found in the copolymerization of these maleimides with styrene, however. The results were interpreted as indicating that the interaction between the comonomers in the highly alternating N-(4-substituted phenyl )maleimide-styrene copolymerizations was stronger than the effects of the 4-substituent on the radical reactivities of the maleimides.

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163 Konovalov et al . and Samuilov et al . have shown that reactivity in Diels-Alder reactions of N-(substituted phenyl )maleimides with cyt a155 . «... . . ., 156,157,158 , , 159 clopentadiene, substituted anthracenes, phencyclone, pentacene, and isobenzofurans increases with the degree of charge-transfer between the diene and dienophile. Dienophile reac157 tivity was correlated both with Hammett's a constants and with the 155 electron affinity of the maleimides. Reactivity and selectivity 1 C 1 increased in the same order. The effect of the N-arylmaleimide para substituent on copolymer stereochemistry is illustrated in Figure 23. It can be seen that there is a greater preference for cis stereochemistry at the succinimide units when the maleimide is substituted with an electron withdrawing group (-CN), relative to substitution with an electron donating group (-OMe) . This effect is quantified in Table 19 which shows the mole fraction of cis succinimide units in the various N-substituted maleimideCEVE copolymers. The Hammett a constants for the various para substituents are included in Table 19 as an indication of the relative electron donating or accepting ability of the substituents. The correlation of copolymer stereochemistry with these o constants is shown in Figure 24. The correlation of the copolymer stereochemistry with 295 the Ke values determined for some of the maleimides is illustrated in Figure 25. It must be remembered that these correlations are at best, approximate due to the inaccuracies in the determination of the areas of the 13 C NMR resonances discussed previously. Nevertheless, it is felt that a definite trend is observed, and the differences in stereochemistry are beyond the experimental error in their determination.

PAGE 177

164 R = -CN -AA^-v 180 FIGURE 23. 175 170 ppm 13, Expanded Carbonyl Regions of the C NMR Spectra of Some N-(4-Substituted)Arylmaleimide-CEVE Copolymers

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165 TABLE 19 The Mole Fraction cis Succinimide Units in Various N-Substituted Maleimide-CEVE Copolymers Sample Number

PAGE 179

166 < o

PAGE 180

167 30 t 20 10 T 0.0 H A correlation coefficient = 0.977 0.4 0.5 0.6 0.7 0.8 0.9 Mole Fraction Cis 295 FIGURE 25. Ke vs. Mole Fraction Cis Succinimide Units in N-Substi tuted Maleimide-CEVE Copolymers

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168 While it may be argued that the interaction between the radical chain end and the incoming monomer may also be enhanced by the acceptor strength of the maleimide, it is not felt that the observed differences in the stereochemistry can be explained by such a mechanism. The radical chain end is achiral, and interaction with the incoming monomer is not expected to be favored on one side of either the chain end or the incoming monomer. If the stereochemistry is influenced by the fraction of maleimide that is complexed, and the equilibrium constant for complex formation (K) is affected by the acceptor strength of the maleimide, then an increase in stereoselectivity with increasing K is predicted by Equation (17). The stereochemistry of maleimide-CEVE copolymers also depends on the N-substituent. Figure 26 shows the expanded carbonyl regions of 13 the C NMR spectra of N-acetoxymaleimide, NPM, and N-cyclohexylmaleimide CEVE copolymers prepared under similar conditions (My = 0.5, X M = 0.5, 60.0°C, AIBN, CH^Cl ? ) . The mole fraction of cis succinimide units in these copolymers is given in Table 19. The N-cyclohexylmaleimide CEVE copolymer contains a considerable amount of trans succinimide units, which may indicate that it is 13 a relatively poor acceptor. The C NMR chemical shift of the olefinic carbons in this monomer appear farther upfield than the N-arylmaleimides. This may indicate that this monomer is a poorer acceptor, but in the absence of more data this conclusion must be regarded as 295 speculative. As can be seen in Figure 25, the Ke value determined for N-cyclohexylmaleimide CEVE complexation does not correlate with

PAGE 182

169 R = -OAc J L 180 FIGURE 26. 175 170 ppm 13, Expanded Carbonyl Regions of the C NMR Spectra of Copolymers Prepared from Several N-Substituted Maleimides and CEVE

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170 the copolymer stereochemistry in the same way that the values determined for the N-arylmaleimides do. It is felt that this observation 295 could reflect a difference in the e value for N-cyclohexylmaleimide relative to the N-arylmaleimides. The N-acetoxymaleimide CEVE copolymer, on the other hand, is fairly stereoregular, although the chemical shift of the monomer olefinic carbons is further upfield than any of the other maleimides studied. The reason for this result is not known, although extrapola13 tion of the C NMR shifts of N-arylmaleimides to other maleimides is probably a dangerous practice. Nevertheless, it can be concluded from these results that the copolymer stereochemistry depends on the N-substitution in the maleimide monomer. The effect of the vinyl ether comonomer on the stereochemistry of NPM-vinyl ether copolymers . Iwatsuki and Itoh have reported that various vinyl ethers differ in their mode of polymerization with tetracyanoquinodimethane (TCNQ), depending upon the electron-donating character of the vinyl ether. Cationic homopolymerization of nbutyl vinyl ether (BVE) occurred on mixing with TCNQ, while CEVE gave alternating copolymers with TCNQ when initiated with AIBN at 60°C. This difference was attributed to the greater donor character of BVE 1 CO relative to CEVE, as measured by Taft's a* substituent constants for vinyl oxy compounds. Since BVE is a better donor than CEVE, upon mixing with the strong acceptor, TCNQ, complete electron transfer takes place, producing a radical anion-cation pair, and thereby initiating the cationic homopolymerization of the BVE.

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171 This observation of a difference in the electron-donor ability of various vinyl ethers prompted a study of the copolymers of NPM with BVE, CEVE, ethyl vinyl ether (EVE) and methyl vinyl ether (MVE). The different donor character of the vinyl ethers may be expected to perturb the complex equilibrium, and thus effect copolymer stereochemistry. All of the vinyl ethers mentioned above readily copolymer!' zed with NPM. Similar copolymerization conditions were used in all cases (M T = 0.5, x M = 0.5, 60.0°C, CH 2 C1 2 ). The initiator used was AIBN in all cases, except the BVE-NPM copolymerization, where 2,4dichlorobenzoyl peroxide was used. Difficulty in weighing the gaseous MVE monomer precluded the determination of concentration, so a large excess of this monomer (relative to NPM) was used. 13 The expanded carbonyl regions of the C NMR spectra of the copolymers of NPM with BVE, EVE and CEVE are shown in Figure 27, and the mole fraction of cis succinimide units in the copolymers is given in Table 20. The Taft a* values for the substituents (R) in vinyloxy compounds (CH 2 = CHOR) and the e values for the vinyl ethers are also given in Table 20. Table 20 and Figure 27 show that copolymer stereochemistry depends on which vinyl ether comonomer is copolymerized with NPM. The trend in stereoselectivity correlates roughly with the e values, i.e., the most stereoregular copolymer results from copolymerization of NPM with EVE, which is the best donor (as judged by the e value). The NPM-BVE copolymer is the least stereoregular, and BVE has the largest e value in this series.

PAGE 185

172 ppm FIGURE 27. 13, Expanded Carbonyl Regions of the iw, C NMR Spectra of Copolymers Prepared from NPM and Various Vinyl Ether Comonomers

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173 TABLE 20 The Mole Fraction of cis Succinimide Units in NPM-Vinyl Ether Copolymers Sample Number

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174 The apparent nonstereoregularity of the BVE-NPM copolymer may reflect a steric inhibition to complex formation by the relatively bulky n-butyl group. Fukuzumi and Kochi ' ' ' and Fukuzumi et al . have determined that steric effects are very important in reactions in which charge-transfer complexes are intermediates. This postulate is speculative at this point, but it may deserve further investigation. It can be concluded from these results that the stereochemistry of NPM-vinyl ether copolymers depends on the vinyl ether comonomer, which -may reflect the ability of the vinyl ether to form complexes with NPM. 13 A mechanistic interpretation of the C NMR results . So far, it has been shown that copolymers of N-substituted maleimides and vinyl ethers have a stereochemistry that is predominantly cis (erythro) at the succinimide units, while the relative stereochemistry between the other chiral centers in the copolymer backbone (vinyl ether-maleimide junction bonds) is essentially random. The stereoselectivity varies with copolymerization conditions in the same way as might be expected if it were in some way related to the ease of formation of chargetransfer complexes between the comonomers. le As pointed out in Chapter I, Mulliken theory predicts that the most probable geometry of a charge-transfer complex is that in which there is maximum overlap between the HOMO of the donor and the LUMO of the acceptor. The LUMO of maleimide monomers and the HOMO of vinyl ethers are depicted below.

PAGE 188

175 -A Thus, the expected geometry of the complex may be visualized as Tf^A Q> 35 ^< R °s. The stereochemical results discussed above may be rationalized by invoking attack of the radical chain end on the side of the complex that is syn to the vinyl ether. AA/VW S% m ys

PAGE 189

176 This mechanism is, in effect, a concerted addition of the complex to the chain end. The next complex could conceivably add to either side of the vinyl ether radical, thus explaining the random relative stereochemistry between the vinyl ether methine carbon and the methines of adjacent succinimide units observed in the copolymers. Whether or not a preference for attack by the radical on the more sterically hindered side of the complex is reasonable, is open to question. Such a preference for bond formation on the more sterically hindered side of a substrate is not unknown, however. For example, cycloadditions of 1,2,3,4,5-pentachlorocyclopentadiene with various dienophiles lead preferentially to products resulting from addition of the dienophile to the sterically more hindered side of the diene, syn to the 5-chlorine atom. Jones has found that the cycloadditions of N-phenylmaleimide to a l-hydroxycyclopenta-2,4-diene and the corresponding acetate proceed via exclusive endo addition of the maleimide syn to the hydroxy (or acetate) group. Dienes favoring the syn orientation bear lone pair electrons on the substituent of the cyclopentadiene ring. Such behavior has been rationalized by Inagaki, Fujimoto and Fukui as being the result of "nonequivalent extension of the HOMO of the diene." In other words, the HOMO of the diene is biased towards the side of the molecule bearing the heteroatom. Similar reasoning has been utilized by the above authors to explain the exo stereoselectivity in free-radical reactions of 2-norbornyl and 7-oxa-2-norbornyl . Frontier molecular orbital theory has also been applied successfully to free-radical additions to olefins " and the copolymerization of maleic anhydride and vinyl acetate.

PAGE 190

177 The case at hand involves the interaction of the singly occupied molecular orbital (SOMO) of the nucleophilic, vinyl ether radical chain end with the LUMO of the complex (35) (or the LUMO of NPM which has been perturbed on complexation) . It is conceivable that the LUMO of NPM is biased in the region syn to the vinyl ether on mixing with the vinyl ether HOMO, thus inducing a preference for attack of the nucleophilic radical syn to the vinyl ether. The origin of the postulated preference for syn attack on the complex may also be related to secondary orbital interactions with 172 the vinyl ether comonomer. Caramella et al . have pointed out in a recent communication that interactions of a radical SOMO with the LUMO of propene can favor attack syn to the peri planar methyl C-H bond. This postulate is highly speculative at this point, and is only presented as a possible explanation of the observed copolymer stereochemistry. It is well known that vinyl ethers do not readily homopolymerize 173 under free-radical conditions, while NPM does homopolymerize under the same conditions used for the copolymerizations described in this work (see Experimental). Postulation of a mechanism such as that shown in Equation (18) does not seem to be in accord with these facts, since a vinyl ether radical is formed on complex addition. The reason for the inability of vinyl ethers to polymerize is thought to be kinetic, rather than thermodynamic. A radical a to an oxygen atom is expected to be stabilized by overlap with the filled 45 p-orbitals of the oxygen. Radicals a to oxygen have been observed

PAGE 191

178 at 20°C by electron spin resonance (ESR) spectroscopy. Di vinyl ether can be homopolymerized via a free-radically initiated cyclopolymerization mechanism, which requires the formation of radicals a 175 to oxygen. Therefore, vinyl ether radicals should be capable of forming based on the thermodynamic stability of a radical a to oxygen. Indeed, the heat of formation (AH f °) for the a tetrahydrofuryl radical has been reported as -4.3 ± 1.5 kcal/mole, and the AH° value of the radical derived from the abstraction of a hydrogen atom from dimethyl ether was found to be -2.8 ± 1.2 kcal/mole. 176 Therefore, it may be concluded that the reason that vinyl ethers do not homopolymerize free-radically is kinetic. It is reasonable that a concerted addition of the maleimide-vinyl ether complex as shown in Equation (18) could considerably lower the energy of activation for the formation of the radical a to oxygen, thus explaining the apparently anomalous results discussed above. 13 The C NMR Spectra of Some Other Alternating Copolymers 13 N-Phenylcitraconimide 2-chloroethyl vinyl ether . The C NMR spectrum of the N-phenylcitraconimide (NPC) 2-chloroethyl vinyl ether copolymer prepared under the conditions given in Table 4 (sample 28) is shown in Figure 28. There are two possible structures for the repeating units in this copolymer as shown below. The numbering scheme used below corresponds to that used to designate the corresponding carbons in the NPM-CEVE copolymer (Figure 8). 13 Structures 36 and 37 may be distinguished by comparison of the C NMR chemical shifts of the NPC-CEVE copolymer with those of the NPM-CEVE copolymer.

PAGE 192

179

PAGE 193

180 36 37 The resonances corresponding to carbons 1, 9, 11 and 12 in the 1 o NPC-CEVE copolymer appear downfield from the corresponding C reso13 nances in the C NMR spectrum of the NPM-CEVE copolymer, while carbons 2, 7 and 8 appear at higher field in the NPC-CEVE copolymer. These observations are consistent only with the structure 3_7 for the NPC-CEVE copolymer. This follows from the fact that the methyl group in _3_Z is y to the methine carbons of adjacent vinyl ether units and carbonyl 2, but either a or 3 to carbons 1, 9, 11 and 12. Such is 13 not the case for structure 36. The C chemical shift of carbon 10 is approximately the same in both copolymers. It is interesting to note the differences in the appearance of the carbon resonances assigned to carbons 7 and 8 in the NPC-CEVE copolymer, as opposed to the corresponding peaks in the NPM-CEVE copolymer. The methine of the vinyl ether units (carbon 7) appears as two peaks with an approximate area ratio of 1:2, while the methylene of the side chain (a to oxygen) appears as a 1:1 "doublet." This is exactly opposite to the observed intensity ratios in the NPM-CEVE copolymer. This observation may indicate that the stereochemistry of the NPC-CEVE copolymer is different from that of the NPM-CEVE

PAGE 194

181 copolymer. The carbonyl resonance assigned to carbon 2 is split into two overlapping peaks of approximate intensity ratio 1:1, however, suggesting a random stereochemistry between carbons 7 and 9. This discrepancy may reflect different conformational preferences in the two copolymers as a result of the steric requirements of the extra methyl group in the NPC-CEVE copolymer. 13 The methyl resonance in the C NMR spectrum of the NPC-CEVE copolymer appears as five major peaks, indicating that this carbon has more configurational sensitivity than the other carbons of this copolymer. Complete analysis of this result is difficult in the absence of more data (e.g., epimerization studies). Maleic anhydride (MAH) CEVE copolymer . The stereochemistry at the succinic anhydride units of MAH-isobutene copolymers has been 1 177 postulated as threo (trans) based on H NMR studies. In view of this finding, a MAH-CEVE copolymer was synthesized (see Tables 4 and 13 5 for copolymerization conditions and analysis data) and its C NMR spectrum was obtained. Expanded portions of the spectrum are presented in Figure 29. It can be seen that the appearance of the carbonyl region is markedly different from that of the NPM-CEVE copolymers discussed previously. While a priori conclusions may not be justified in the absence of epimerization studies, the chemical shifts of the MAH-CEVE copolymer carbonyl s might be similar to the corresponding carbonyls in NPM-CEVE copolymers. If this is the case, the peak appearing furthest downfield (-173.8 ppm) in the carbonyl region corresponds to carbonyl carbons in cis anhydride units, while the peak at -172.5 corresponds to carbonyls in trans units. The intensity

PAGE 195

182 ---YvvVy^ J L J L J L 75 6 ppm 13, 70 FIGURE 29. Expanded Regions of the C NMR Spectrum of Maleic Anhydride-CEVE Copolymer

PAGE 196

183 ratio of these peaks suggests that there is a preference for trans anhydride units in this copolymer, which is in accord with the findings of Bacskai et al . , whose work was mentioned above. These observations may suggest that the mode of complex addition to the chain end is different for the MAH-CEVE complex than for the NPM-CEVE complex. Model Compound Synthesis and Stereochemical Assignments The synthesis of model compounds J,, _3, 4_, 6^ and 8^ is adequately described in the experimental section (Chapter II). Assignment of the stereochemistry of these compounds could be made unambigously by comparison with literature melting points and spectral data. The synthesis of compound _16 will be discussed before that of compound _U, even though the latter compound was made first. This order was chosen because the stereochemistry of compound JJ_ proved to be easier to assign than that of compound j_l. Indeed, the reason for synthesizing 16 was to more firmly establish the stereochemistry of 11. The synthesis of _15 is outlined in Figure 30. Compound _12_ was made according to the procedure of Danishefsky and Kitahara (see Experimental). Simply mixing 1Z_ with NPM at room temperature produced 178 ]3 as a white crystalline product. Danishefsky et al . have pointed out that compounds such as JJ3 can exist in either of two stable conformations, which they have termed the "folded boat" and the "extended boat" conformations. These conformations are illustrated in Figure 31. The two possible conformations could be distinguished by examination of the proton-proton coupling constants, which were

PAGE 197

184 + (CH 3 ) 3 SiCl C 6 H 5 Et 3 N-ZnCl 2 (CHJ-SiO 40-50°C/overnight OCH, OCH, 12 12 (CH 3 ) 3 SiO ^^Ja^ 4 ^ ?" C 6 H 5 5 min. 13 MeOH:CHCl 3A Molecular Sieves HO ,., ^ 7a 7 7a P • C 6 H 5 H„(49 PSI) 7 I PtO £ EtOH ^g Y^ R.T., 5 5.5 hrs. >^tY " C 6 H 5 15 ;ch 3 ) 3 o bf 4 _ CH 2 C1 2 , R.T. 2 days 'o X7a ° W s 14 16 FIGURE 30. Synthetic Scheme for Model Compound J^

PAGE 198

185 (CH 3 ) 3 SiO "Extended Boat" Conformation 0Si(CH 3 ). 'Folded Boat" Conformation FIGURE 31. Possible Conformations of Endo Diels-Alder Adduct 13

PAGE 199

186 determined from the H NMR spectrum obtained at 100 MHz in CDCK. In this, and forthcoming NMR spectral determinations of coupling constants, homonuclear decoupling techniques were used extensively in order to establish which multiplets were coupled. This greatly facilitated spectral interpretation. Coupling constants were calculated directly from peak printouts after each spectrum was interpreted. Proton 4 appears as a doublet of doublets centered at 6 4.35. The observed couplings for this proton (J. r = 6.4, J 7 ~ = 4.0) imply a guache arrangement of protons 4 and 3a, and a nearly coplanar 128 relationship between protons 4 and 5. Proton 5 is seen as a doublet of doublets (JV 7a = 2.4, J 5 . = 6.4) at 6 5.18. The subscripts a or g are used in this work to denote protons bonded to the same carbon. The subscript a has arbitrarily been assigned to the proton of the pair which resonates at lower magnetic field in the proton NMR spectrum. The large allylic coupling between protons 5 and 7a implies 128 an ideal relationship for such coupling (-.90°). The 9.5 Hz coupling observed between protons 3a and 7a is consistent with either a nearly eclipsed or a nearly anti relationship. All of these couplings, taken together, are consistent only with the "extended boat" conformation of the endo adduct depicted in Figure 31. The observed couplings are also nearly identical to those determined by Danishefsky 178 et al . for the corresponding maleic anhydride adduct, and Overman 179 et al . for similar adducts. o Mildly acidic hydrolysis of trimethylsilyl enol ether _H with 3A 68 molecular sieves gave ketone _14 as colorless crystals. The 100 MHz H NMR spectrum of _14 proved to be very complicated with many

PAGE 200

187 overlapping multiplets. Some coupling constants could be determined, however. Proton 53 appears as a doublet of doublets centered at 6 2.17 (J 5B = 2.2, J 5 r = 18.3). Proton 4 appears at 6 4.18 as an apparent quartet with the center peaks slightly broader than the outer peaks. This is thought to reflect a near equivalence of the couplings 4,5a; 4,5$; and 4,3a (i.e., each center peak of the quartet is actually three overlapping peaks). The approximate coupling constant for these couplings is 2-4 Hz, suggesting a gauche arrangement of proton 4 with both 5a and 56, and also a gauche arrangement of 4 and 3a. These contentions are supported by the similarity of the appearance of the resonance due to proton 4 in compound _14, with the corresponding resonance in compound _16. A 300 MHz H NMR spectrum of _16 resolved the "quartet" into the expected eight peaks (vide infra). The above coupling constants are consistent with the stereochemistry for 14 shown in Figure 30 if its conformation is the "extended boat" type, similar to that shown for 13 in Figure 31. Thus, it was concluded that no epimerization took place at carbon 4 during the hydrolysis of 13. Ketone j^4 was catalytically reduced (Pt0 2 , Hp) to alcohol 15 , 13 which was isolated as colorless crystals. The C NMR spectrum of 15 exhibited the theoretical number of peaks, so the reduction was presumed to be stereospecific. The 100 MHz NMR spectrum of _15_ (CDCl^) is complicated by serious overlap of fairly complex multiplets. Protons bonded to carbons 4 and 6 appear as overlapping multiplets at 6 3.6-4.2. Protons 7a and 3a are overlapping multiplets at 6 2.76-3.10. Resonances due to protons 7a, 73, and 5a all overlap in the range

PAGE 201

188 : 1.9-2.4. Homonuclear decoupling allowed some estimates of relevant coupling constants to be made, however. For example, irradiation of protons 4 and 6 afforded considerable simplication of resonances due to 5a, 58, 3a, 7a, and 7(3, allowing approximate coupling constants to be determined. The 5S proton resonance is the only ring proton resonance that is not overlapped by other multiplets. It appears as a doublet of doublets of doublets centered at 6 1.85 (Jr c « 3.8, Jr fi fi = 6.1, Jr, r = 15.1). These coupling constants indicate that 5e is gauche to 4 and 6. Couplings for proton 7a (J-, c ~ 7.2, J-, -, v 6.0) are / a , d / a 5 / a suggestive of a dihedral angle of about 45° between protons 7a and 6, and 7a and 7a. These observations, along with the similarities between the couplings discussed above and those determined for compound 16 at 300 MHz (all of the ring coupling constants could be determined at this field strength, vide infra), suggest that the stereochemistry of 15_ is that shown in Figure 30. Support for the assigned stereochemistry at carbon 6 was obtained indirectly, by the isolation of bicyclic lactone _1_7 after attempted reduction of ketone _14 with sodium borohydride in ethanol , as shown below. 14 1) NaBH 4 ,EtOH 2) HC1 / £f^ H C 6 H 5 17

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189 The structure of j7 was deduced based on the appearance of an N-H stretch at 3302 cm" in its IR spectrum, and a resonance at 10.08 in its H NMR spectrum. The IR spectrum of 17 also exhibits two carbonyl absorptions; one at 1736, and the other at 1689 cm" . The absorption at 1689 cm" is characteristic of six-membered lactones. Lactonizations of this type, carried out with NaBH., are not uncommon. The production of 17 is possible only if the stereochemistry of the presumably intermediate alcohol is that shown for _15 in Figure 30. This evidence by itself cannot be regarded as conclusive, however, because the assumption must be made that the stereochemistry of the reduction of ketone 14 is the same whether NaBhU or Pt-HL is the reducing agent. Compound JL6 was prepared in crystalline form by methylation of alcohol JJ5 with trimethyloxonium tetrafluoroborate in ZWJ^o' The 100 MHz H NMR spectrum of \%_ exhibited the same extensive overlap of the ring proton resonances as did that of compound _15_. A 300 MHz H NMR spectrum of _16 was obtained on a Nicolet NTC-300 instrument. This spectrum is shown in Figure 32. Overlap was much less of a problem in the 300 MHz spectrum, and all of the couplings for the ring protons could be determined. Expansions of the ring proton resonances and the coupling constant analysis are illustrated in Figure 33. The coupling constants are consistent with the stereochemistry and conformation for compound _16, which is shown below. The large coupling constants observed for proton 73 (J 7 „ c ~ 11.2, J-, n -, = 3 K 73,6 73,7a 10.7) are particularly revealing. Such large coupling constants are

PAGE 203

190 ko S? \ X

PAGE 204

191 '4,5a 4.7 J 4,3a = 3 ' J 4,56 = 2 .03 4 .05 H .0i .30 3.93 1.95 3.94 3.92 1.90 3.83 FIGURE 33. Expansions of the Ring Proton Resonances Appearing in the 300 MHz *H NMR Spectrum Shown in Figure 32

PAGE 205

192 7a J 7 = 9.6 7a, 3a J 7a,73 = 10 7 A A A J 7a 7 = 7.1 7a, 7a 3a J 3a,7a = 9 " 6 J 3a,4 = 3 ' "iQOhZ EX°ftNSlGN 3..Z 3.10 3.08 3.16 3.04 3.C<» 3 . CO FIGURE 33. Continued 2.96 2. 94 2.32 2.30 2 . 08 2.85 2.84 2.32 2.30

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193 7a J 7a,7B = U ' 9 \ M A J 7a,7a ' 7A °7c6 4 3 2.i3 2.t5 2.44 2.i2 2. -10 2.38 2.36 2.34 2.32 2.30 2.29 2. 25 2.24 2.22 2.20 2.13 PPM FIGURE 33. Continued

PAGE 207

194 J 5a,56 =15 3 J c , = 8.6 5a, 6 Jc a = 4 7 5a, 4 Jc Q r = 15.3 53, ba FIGURE 33. Continued

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195 indicative of an anti relationship between the coupled protons. An anti relationship between 76 and both 7a and 6 is possible only for the stereochemistry and conformation shown below for 16. H 3 C0 7a N-C,H 6"5 16 The couplings observed for proton 7a (J-, r = 4.3, J-, -, = 7.1) r 7a, 6 7a, 7a ' imply a gauche arrangement of 7a with both 7a and 6, although the 7a, 7a coupling is larger than might be expected for such an arrangement. 178 Danishefsky et al . have observed correspondingly large coupling constants in somewhat similar compounds, and have obtained x-ray crystal structure analysis to support their stereochemical conclusions. Apparently, these types of molecules are twisted in such a way so as to allow large coupling between hydrogen 7a and its gauche related partner 7a. Proton 4 is coupled to junction hydrogen 3a and hydrogens 5a and 53 (J 4 3a = 3.8, J 4 5a = 4.7, J 4 r = 2.8). Thus, 4 is in a gauche relationship with all three of its neighboring protons, as in the conformation depicted above. Proton 6 appears as sixteen peaks, centered at : 3.48 (J, , = 4.3, J c ,, = 11.2, J c c = 8.6, J c Cd = 5.6). o , /a 6,7£ 6,ba 6,bS

PAGE 209

196 These couplings are also consistent with the conformation shown above. The large coupling constant between junction hydrogen 7a and 3a (9.6 Hz) is also consistent with the cis fused ring structure shown. The carbon-13 NMR assignments for compound ^6 (shown in Figure 10) were made by using selective decoupling techniques. Selective irradiation of proton 4 caused more of an increase in the intensity of the carbonyl peak at 6 176.33, relative to the peak at 6 178.33, due to the removal of the three bond coupling between proton 4 and carbonyl 3. Thus, the peak at 6 178.33 was assigned to carbonyl 1, and the peak at 176.33 was assigned to carbonyl 3. The same selective decoupling experiment described above caused a collapse of the doublet centered at 6 75.59, in the coupled spec13 trum of _16, to a singlet. Therefore, the methine C resonance at 6 75.59 was assigned to carbon 4, and the methine at 6 74.25 was assigned to carbon 6. Selective irradiation of protons 7a and 7B caused a collapse of the triplet centered at 31.19 in the coupled spectrum. This observation allowed assignment of the 6 31.19 resonance to carbon 7, and the remaining methylene carbon resonance (5 25.46) was assigned to carbon 5. Another experiment was performed by setting the decoupler frequency slightly downfield of the overlapping resonances due to protons 1 13 7a and 3a in the H NMR spectrum while observing the C NMR spectrum. 13 A greater intensity was observed for the C NMR methine peak at 6 37.16 than for the methine peak at 5 43.42. Since proton 7a appears at lower field than proton 3a, this experiment allows assignment of

PAGE 210

197 13 the C NMR resonance at 6 37.16 to carbon 7a, and the peak at 6 43.42 to carbon 3a. Compound ^U was synthesized via the route shown in Figure 34. Compound 9_ was obtained as a mixture of isomers by treating 4-methoxy3-butene-2-one with triethylorthoformate and an acid catalyst in absolute ethanol . 173 Attempts to synthesize 1,3-dialkoxybutadiene by pyrolysis of 9_ invariably yielded black polymeric material. Heating 9_ in the presence of NPM, radical (hydroquinone) , and acid (Na„HPCL) scavengers, however, produced _10 as a colorless crystalline material. It' is interesting that the double bond in JJD is not in the position expected for a typical Diels-Alder adduct. The position of the double bond in K) was established by H NMR homonuclear decoupling studies. Irradiation of the doublet of doublets centered at 6 4.95 (assumed to be due to a vinyl proton) did not affect the apparent quartet centered at <5 4.21, but did sharpen the broad AB quartet appearing at 6 2.35. Irradiation of the resonance at 6 2.35, however, caused both the doublet of doublets at 6 4.95 and the apparent quartet at 6 4.21 to collapse to doublets. Irradiation of the apparent quartet at 6 4.21 caused the collapse of a doublet of doublets centered at 6 3.20 to a doublet, and sharpened the broad AB quartet at 6 2.35. These observations are consistent with the assigned structure W shown in Figure 34, but not with the structure shown below. In both _10 and 38, the vinyl proton is expected to be most deshielded. In 38, however, the vinyl proton 5 should be coupled to proton 4 and, to some extent, with one or both of protons 7a and 7g.

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198 :\ + (C 2 H 5 0) 3 CH OCH, H (cat.) EtOH R.T. 24 hrs. 0^ + isomers 9 9 + | \-(/ } 70-85°C X ^y \=/ 25 Q 1 w week 4^(50 PSI) Ra Ni EtOH 80°C/1 hr. 10 4. A?a 3, N C 6 H 5 3a o 11 FIGURE 34. Synthetic Scheme for Model Compound 11

PAGE 212

199 38 Proton 4, on the other hand, cannot be coupled to the protons 7a and 73 in structure 38. The coupling relationships discussed above suggest that the methyl ene protons (AB quartet at 6 2.35) are coupled to the protons responsible for the resonances at 6 4.95 and 6 4.21. The latter resonances, however, are not coupled to each other. These relationships are only possible if the structure for _10 is as shown in Figure 34., and the peaks at c 4.95, 4.21, 3.20 and 2.35 are assigned to protons bonded to carbons 7, 4, 3a and 5, respectively. Proton 4 thus appears as an apparent quartet, which looks very similar to the corresponding proton resonances in compounds 14 and 16 (vide supra). This observation is indicative of similar, small (2-4 Hz) coupling constants between proton 4 and protons 3a, 5a, and 56. Such small couplings imply gauche relationships between the above mentioned protons. Stereochemical conclusions are difficult to make based on these observations, because a gauche relationship between proton 4 and 3a, and 4 and both 5a and 5£, is possible if the stereochemistry at carbon 4 shown in Figure 34 is reversed and the molecule adopts a "folded boat" conformation. The observed couplings are also consistent with the stereochemistry shown in Figure 34 for 10_, if the conformation is the "extended boat" type.

PAGE 213

200 The reason for the anomalous position of the double bond in _10 is unknown at present. It is reasonable to assume, however, that the "normal" Diels-Alder adduct 36 is formed first, followed by an allylic hydrogen shift. It is also interesting that the corresponding pyrolysis of 1,1, 3,3-tetramethoxy butane in the presence of NPM failed to produce any of the dimethoxy substituted compound analogous to JLO. Only a complex mixture of products was obtained. This mixture was thought to contain various isomers in which the double bond was located at all possible positions of the six-membered ring. Catalytic hydrogenation of _10_ in ethanol using Raney nickel catalyst and high temperature (70-80°C) produced U as a pale green oil. The similarity of the 13 C NMR chemical shifts of U and 16 (see Figure 10) suggests that the stereochemistry of these two compounds is very similar. The 100 MHz H NMR spectrum of _U proved to be even more complicated than that of compound _16, due to the overlap of the ethyl methylene quartets with the ring methine protons a to oxygen. Some couplings were observable, however. Proton 53 appears as a doublet of doublets of doublets centered at 6 1.85 (J 5B . = 2.2, J 5ft fi = 6.5). The resonances due to protons 3a and 7a comprise an AB quartet, which is further split by adjacent protons in the region 6 2.79-3.07 (JJa , 7a = 9 ' 5 ' J 3a,4 = 3 " 5 > J 7a,7 B = 10 ' 6 ' J 7a,7a = 6 ' 3 ^ A11 of the above coupling constants are almost exactly the same as those determined for the corresponding protons in compound _16_. These observations strongly suggest that the stereochemistry of compounds jl and _16 is the same.

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201 Summary and Conclusions 1-3 It has been shown in this work that the appearance of the C NMR spectra of N-substituted maleimide vinyl ether copolymers depends markedly on the copolymerization conditions. The copolymer 13 structure (as deduced from C NMR) varies with such conditions as temperature, solvent, total monomer concentration and comonomer ratio in the initial feed. Copolymer structure also varied with the maleimide N-substituent and the vinyl ether comonomer. 13 Comparison of the copolymer C NMR chemical shifts with those of a series of stereospecific model compounds, coupled with copolymer epimerization studies, has established that the aforementioned structural variations are stereochemical in nature. The predominant stereochemistry at the succinimide units in these copolymers was invariably cis (erythro) . The existence of a weak charge-transfer interaction between CEVE and N-substituted maleimides was confirmed by electronic spectroscopy of mixtures of the comonomers in CH ? C1 ? . In general, copolymerization conditions that were expected to increase the fraction of maleimide monomers in the complexed state, produced copolymers with a higher cis:trans ratio at the succinimide units. This observation led to the postulate that copolymer stereochemistry was related to the fraction of maleimide monomers that were complexed. This contention is supported by the observed preference for erythro placements at the copolymer succinimide units. If the "free monomer" mechanism is operational, succinimide unit stereochemistry

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202 is fixed on addition of the next monomer unit to the succinimidyl radical chain end. Monomer approach is expected to be favored from the less sterically hindered side of the chain end, which would produce threo succinimide units. This effect should be relatively greater at lower temperature (lower activation energy for production of threo vs. erythro placements). The observed effect was exactly opposite (greater preference for erythro placements at lower temperature). These results are nicely accommodated by a "complex" mechanism, however. If the activation energy for attack of the radical chain end on the side of the complex syn to the vinyl ether (see Equation [18]) is lower than that for anti attack, then a preference for cis (erythro) placements is expected. The observed increase in cis placements with decreasing temperature is also in accord with this mechanism. Given that the copolymer stereochemistry is dependent on the fraction of maleimide in complexed form, Equation (17) may be expressed as £= k Xc = KM T (1 x M ) (19) o where ;< is the mole fraction of cis succinimide units in the copolymer, and k is a proportionality constant. Equation (19) predicts that x r will depend on the total monomer concentration (M T ), the equilibrium constant for complex formation (K), and the mole fraction of maleimide in the initial feed (xm)The experimental results bore these expectations out in all cases.

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203 Thus, the conclusion of this work is that a comonomer chargetransfer complex participates to a significant extent in the propagation steps of the free-radical alternating copolymerization of Nsubstituted maleimides and vinyl ethers. This appears to be true in spite of the fact that the association between the comonomers is weak, and therefore the complex concentration small. It is also noteworthy that some of the more "traditional" methods for discerning the participation of a complex in copolymerization reactions (e.g., nonlinearity of Kelen-Tudos plots) are not adequate evidence, and can lead to erroneous conclusions.

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REFERENCES 1. a) Andrews, L.J.; Keefer, R.M. "Molecular Complexes in Organic Chemistry"; Holden-Day, Inc.: San Francisco, 1964. b) Foster, R. "Organic Charge Transfer Complexes"; Academic Press: New York. 1969. c) Kosower, E.M. in "Progress in Physical Organic Chemistry," Vol. 3, Cohen, S.G.; Streitwieser, A.; Taft, R.W., Ed.; Wiley-Interscience: New York, 1965. d) Kosower, E.M. "An Introduction to Physical Organic Chemistry"; John Wiley and Sons: New York, 1968. e) Mulliken, R.S.; Person, W.B. "Molecular Complexes: A Lecture and Reprint Volume"; Wiley-Interscience: New York, 1969. f) Foster, R., Ed. "Molecular Complexes," Vol. 1; Paul Elek: London, 1973. g) Foster, R., Ed. "Molecular Complexes," Vol. 2; Paul Elek: London, 1974. h) Gur'yanova, E.N.; Gol'dshtein, I. P.; Romm, I. P. "Donor-Acceptor Bond"; John Wiley and Sons: New York, 1975. i) Gutmann, V. "The Donor-Acceptor Approach to Molecular Interactions"; Plenum Press: New York, 1978. j) Foster, R., Ed. "Molecular Association," Vol. 1; Academic Press: London, 1977. k) Foster, R., Ed. "Molecular Association," Vol. 2; Academic Press: London, 1979. 2. Benesi, H.A. ; Hildebrand, J.H. J. Am. Chem. Soc . 1949, 71, 2703. 3. Mulliken, R.S. J. Phys. Chem . 1952, 56, 801. 4. McConnell, H.; Ham, J.S.; Piatt, J.R. J. Chem. Phys . 1953, 21, 66. 5. Mulliken, R.S. J. Am. Chem. Soc . 1950, 72, 600. 6. Tamres, M. ; Strong, R.L. in "Molecular Association," Vol. -2, Foster, R., Ed.; Academic Press: London, 1979. 7. Fukuzumi, S.; Kochi, J.K. J. Am. Chem. Soc . 1981, 1_03, 2783. 8. Fukuzumi, S.; Kochi, J.K. J. Phys. Chem . 1981, 85, 648. 9. Trost, B.M.; 0'Krongly, D.; Belletire, J.L. J. Am. Chem. Soc . 1980, JL02, 7595. 10. Robson, R.; Grubb, P.W.; Baltrop, J. A. J. Chem. Soc . 1964, 2153. 11. Hyde, P.; Ledwith, A., in "Molecular Complexes," Vol. 2, Foster, R., Ed.; Paul Elek: London, 1974. 12. Butler, G.B., in "Anionic Polymeric Drugs"; Donaruma, G.; Ottenbrite, R.M. ; Vogl , 0., Eds.; John Wiley and Sons: New York, 1980. 204

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205 13. Alfrey, T. Jr.; Price, C.C. J. Polym. Sci . 1947, 2, 101. 14. Walling, C; Briggs, E.; Wolfstirn, K.; Mayo, F.R. J. Am. Chem . Soc . 1948, _70, 1537. 15. Bartlett, P.D.; Nozaki , K. J. Am. Chem. Soc . 1946, 68, 1495. 16. Butler, G.B.; Campus, A.F. J. Polym. Sci.: Part A-l 1970, 8, 545, 17. Butler, G.B.; Joyce, K.C. J. Polym. Sci.: Part C(22) 1968, 45. 18. Butler, G.B.; Fujimori, K. J. Macromol . Sci. -Chem . 1972, 6, 1533. 19. Ragab, Y.A.; Butler, G.B. J. Polym. Sci.: Polym. Chem. Ed . 1981, 19, 1175. 20. Yamashita, Y.; Iwatsuki , S.; Kokubo, T. J. Polym. Sci.: Part C (23) 1968, 753. 21. Kokubo, T.; Iwatsuki, S.; Yamashita, Y. Macromol ecules 1968, 1, 482. 22. Kokubo, T.; Iwatsuki , S. ; Yamashita, Y. Macromol ecul es 1970, 3, 518. 23. Gaylord, N.G.; Stolka, M.; Takahashi , A.; Maiti, S. J. Macromol. Sci. -Chem . 1971, A5, 867. 24. Gaylord, N.G. ; Stolka, M. ; Patnaik, B.K. J. Macromol. Sci. -Che m. 1972, A6, 1435, 1521. 25. Caze, C; Loucheux, C. J. Macromol . Sci. -Chem . 1975, 9, 29. 26. Tsuchida, E.; Tomono, T. Makromol . Chem . 1971, j^J, 265. 27. Tsuchida, E.; Tomono, T.; Sano, M. Makromol. Chem . 1972, 151, 245. 28. Seiner, J. A.; Litt, M. Macromol ecules 1971, _4, 308. 29. Litt, M. Macromol ecules 1971, 4, 312. 30. Litt, M. ; Seiner, J. A. Macromol ecules 1971, 4, 314. 31. Litt, M.; Seiner, J. A. Macromolecules 1971, 4, 316. 32. Mayo, F.R,; Lewis, F.M. J. Am. Chem. Soc . 1944, 66, 1594. 33. Alfrey, T. Jr.; Goldfinger, G. J. Chem. Phys . 1944, \2, 205.

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BIOGRAPHICAL SKETCH Kurt Gordon Olson was born March 4, 1954, in Ridgway, Pennsylvania. He was a 1972 graduate of Northampton Senior High School, Northampton, Pennsylvania, and went on to attend Ursinus College, Collegeville, Pennsylvania, where he received a B.S. in chemistry in 1976. Upon graduation from Ursinus College, he enrolled in the Graduate School of the University of Florida. While working toward the degree of Doctor of Philosophy in organic chemistry, Mr. Olson served as a teaching and research assistant in the Department of Chemistry. During the summer of 1977, he was employed in the research laboratories of Tennessee Eastman Co., Kingsport, Tennessee, as a summer technical employee. Mr. Olson was married to the former Leslie Lovett in March, 1978. The author is a member of the American Chemical Society. 214

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. k „ 1 ^ r /< /.->. /J^UJl George B. Butler, Chairman Professor of Chemistry I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. V V r-A\cw: ---1Hk Wallace S. Brey Professor of Chemistry I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. 7 Eugene P.j Goldberg Professor of Materials \_ Science & Engineering I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. John F. Helling Professor of Chemistr

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Thieo E. Hogen-Esch Professor of Chemistry This dissertation was submitted to the Graduate Faculty of the Department of Chemistry in the College of Liberal Arts and Sciences and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. December, 1981 Dean for Graduate Studies and Research

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UNIVERSITY OF FLORIDA 3 1262 08553 1696