Title Page
 Table of Contents
 List of Tables
 List of Figures
 Results and discussion
 Biographical sketch

Group Title: role of the charge-transfer complex in the alternating copolymerization of N-substituted maleimides and vinyl ethers
Title: The role of the charge-transfer complex in the alternating copolymerization of N-substituted maleimides and vinyl ethers
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00099237/00001
 Material Information
Title: The role of the charge-transfer complex in the alternating copolymerization of N-substituted maleimides and vinyl ethers
Physical Description: xiii, 214 leaves : ill. ; 28 cm.
Language: English
Creator: Olson, Kurt Gordon, 1954-
Copyright Date: 1981
Subject: Electron donor-acceptor complexes   ( lcsh )
Polymers and polymerization   ( lcsh )
Maleimide   ( lcsh )
Vinyl ethers   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis (Ph. D.)--University of Florida, 1981.
Bibliography: Bibliography: leaves 204-213.
General Note: Typescript.
General Note: Vita.
Statement of Responsibility: by Kurt Gordon Olson.
 Record Information
Bibliographic ID: UF00099237
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000316134
oclc - 08559535
notis - ABU2925


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Table of Contents
    Title Page
        Page i
        Page ii
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
    List of Tables
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    List of Figures
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    Results and discussion
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    Biographical sketch
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Full Text







Copyright 1981


Kurt Gordon Olson

To Leslie


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.


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

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

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

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


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

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

General . . . .

Reagents and Solvents. .

Model Compound Synthesis

Malpimidp Svnthp'si .

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

Copolymer Synthesis and Characterization . . . . .

Copolymer Epimerization . . . . . . . .

Complexation Studies . . . . . . . . .


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 . . . . .... .




















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

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




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
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



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



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



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



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



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


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.



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-
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


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-


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


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-


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


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
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.


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.




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-


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


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),


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,


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,

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,


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-

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,


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


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

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.


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

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


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

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.

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

and trans 11.

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.



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],


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),
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-

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-

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


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

Conditions for N-Phenvlmaleimide-2-Chloroethvl Vinyl Ether Cooolvmerizations


























Ma Xb

Temp. (OC)

-78 to -68







25 35



25 35








25 35





















1.56 x 10-3










Footnotes for this table appear at the end of Table 5.

0.699 i.in rn.77~1

^ .











































1.10 (

1.09 (

1.09 (

1.10 (

x 103c























Vol. (ml)d






















Time (Hr.)








1 mo.



1 mo.








S6 mos.





02nn 71.R

0.9 1 _1 (0.2% 200 2

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.























0.585 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






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


Data for Copolymers in Table 4

Yield Analysis
Sample Grams % %N Avg. m % C1 Avg. m Avg. mM
No. Grams % 1 N mMJ ~ mM


93.3 94.6















































































,. 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

















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
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-









d '


4-1 0


o E-

4 -

o -.
0 ro


I- .L.




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


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.


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

MT = 0.501 20.2 42.43 1.49

XM = 0.200 25.0 52.80 1.86
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
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
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
XM = 0.499 25.0 64.25 2.24
Wd = 286.25 30.0 81.75 2.86

35.0 88.07 3.07

MT = 0.500 26.1 23.66 0.808
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
XM = 0.699 30.5 40.99 1.38
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)].


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


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
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


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


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).

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),
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.

Copolymer Decomposition Temperatures (Td)

Copolymer Td (C) Copolymer Td (oC)

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
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-


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


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-


The IR spectrum of the epimerized copolymer was nearly identical

to that of the copolymer before epimerization, except for a small de-
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-

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