Studies on the mechanisms of copolymerization of electron-donor dienes and electron-acceptor dienes

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Title:
Studies on the mechanisms of copolymerization of electron-donor dienes and electron-acceptor dienes
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xii, 126 leaves : ill. ; 28 cm.
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Chen, Jen-Chi, 1954-
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Polymers   ( lcsh )
Polymerization   ( lcsh )
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Thesis:
Thesis (Ph. D.)--University of Florida, 1985.
Bibliography:
Includes bibliographical references (leaves 123-125).
Statement of Responsibility:
by Jen-Chi Chen.
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Typescript.
General Note:
Vita.

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STUDIES ON THE MECHANISMS OF
COPOLYMERIZATION OF ELECTRON-DONOR DIENES
AND ELECTRON-ACCEPTOR DIENES






BY






JEN-CHI CHEN


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


UNIVERSITY OF FLORIDA


1985


















To my family, for their love,

patience and encouragement














ACKNOWLEDGMENTS


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

research director, Professor George B. Butler, for his encouragement

and guidance during the course of this work. I would also like to

acknowledge the members of my supervisory committee for their

valuable time.

The friendship and cooperation provided by my colleagues in the

polymer chemistry laboratories are greatly appreciated.

I would like to thank Miss Cindy Zimmerman for her skillful

typing of this manuscript. I also wish to thank my wife, Weng-Jang,

for her encouragement and patience.















TABLE OF CONTENTS



Page

ACKNOWLEDGMENTS................................................. iii

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

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

ABSTRACT.........................................................xi

CHAPTERS

I INTRODUCTION.......................... ..................... 1

General Background.......................................1
Mulliken's Valence Bond Treatment.......................1
Molecular Orbital Treatment .............................4
Basic Principles of Copolymerization....................6
Diels-Alder Reaction....................................12
Copolymerization of Conjugated Diene and Dienophile.....13
The Research Objectives...............................17

II EXPERIMENTAL...........................................18

General Information....................................18
Reagents and Solvents.................................19
Monomer Synthesis......................................19
Copolymer Synthesis...................................34
Copolymerizations in Aqueous Phase......................45
Monomer Reactivity Ratios..............................46
Copolymer Characterization............................48
Complexation Studies.. .................................54
Diels-Alder Reactions with Inverse Electron Demand.......58

III RESULTS AND DISCUSSION... .............................. 60

Polymerizations of Electron-Poor Dienes with
Electron-Rich Dienophiles............................60
Copolymerizations of Electron-Rich Dienes with
Electron-Poor Dienophiles............................75








Copolymerizations of Electron-Rich Dienes with
Electron-Poor Dienes................................111
Copolymerizations in Aqueous Phase.....................118
Summary and Conclusions...............................121

REFERENCES........................................................123

BIOGRAPHICAL SKETCH..............................................126














LIST OF TABLES


Table Page

1 Conditions for the Polymerizations of Methyl
2,4-Pentadienoate (MPD) with Electron-Rich Dienophiles.....35

2 Yields and Analysis Data for Polymers in Table 1...........36

3 Conditions for the Polymerizations of 1-Carbethoxy-
1-cyano-1,3-butadiene (CCB) with Electron-Rich
Dienophiles ................................................37

4 Yields and Analysis Data for Polymers in Table 3...........38

5 Conditions for the Copolymerizations of Acrylonitrile
(AN) with Electron-Rich Dienes............................39

6 Yields and Analysis Data for Copolymers in Table 5.........40

7 Conditions for the Copolymerizations of Electron-Rich
Dienes (ERD) with Electron-Poor Dienes (EPD)...............41

8 Yields and Analysis Data for Copolymers in Table 7.........42

9 Conditions for the Polymerizations of Some Electron-
Rich Monomers (ERM) with Some Electron-Poor Monomers
(EPM) .....................................................43

10 Yields and Analysis Data for Polymers in Table 9...........44

11 Conditions and Results of Polymerizations of Water
Soluble Monomers.........................................45

12 Conditions, Yields and Analysis Data for the
Copolymerizations of Acrylonitrile (AN) with
1-Ethoxy-1,3-butadiene (EBD)...............................46

13 Conditions, Yields and Analysis Data for the
Copolymerizations of Acrylonitrile (AN) with
1-Diethylamino-1,3-butadiene (DABD) .......................47

14 1H NMR Data for Determination of Formation Constant
of Complexation of AN-EBD System at 25C ..................55









15 1H NMR Data for Determination of Formation Constant
of Complexation of AN-EBD System at 600C ..................56

16 1H NMR Data for Determination of Formation Constant
of Complexation of AN-DABD System at 25C .................57

17 13C NMR Data for the Complexed and Uncomplexed
EBD Molecules ..............................................57

18 13C NMR Data for the Complexed and Uncomplexed
DABD Molecules....................... ..... ...... ... ... .. 58

19 Conditions and Results for Diels-Alder Reactions with
Inverse Electron Demand..................................59

20 Monomer Reactivity Ratios and Alfrey-Price Q and e
Values for the Free Radical Initiated Copolymerization
of EBD and AN.......................... .. ........ ..... 82

21 Assignments of Chemical Shifts in H NMR Spectrum
of AN-EBD Copolymer......................................84

22 Assignments of Chemical Shifts in 13C NMR Spectrum
of AN-EBD Copolymer......................................86

23 Monomer Reactivity Ratios for the Free Radical
Initiated Copolymerization of DABD and AN..................97

24 Assignments of Chemical Shifts in 1H NMR Spectrum
of AN-DABD Copolymer..................................... 100

25 Assignments of Chemical Shifts in 13C NMR Spectrum
of AN-DABD Copolymer.................................... 100

26 Assignments of Chemical Shifts in 1H NMR Spectrum
of AN-TSBD Copolymer....................................105

27 Assignments of Chemical Shifts in 13C NMR Spectrum
of AN-TSBD Copolymer....................................106

28 Assignments of Chemical Shifts in 1C NMR Spectrum
of AN-ATBD Copolymer....................................110













LIST OF FIGURES


Figure Page

1 The Energy-Level Diagram of the Weak Charge-Transfer
Complex..................................................3

2 Molecular Orbital Representation of a Weak Charge-
Transfer Complex...........................................4

3 The Possible Reaction Pathways Form Alternating
Copolymers ..................................................9

4 The Reaction Pathways of Diels-Alder Reaction..............12

5 Frontier Orbital Interactions in the Diels-Alder
Reactions............................................... 14

6 1H NMR (60 MHz) Spectrum of Methyl 2,4-Pentadienoate
in CDC13 at 25 C .............................. .... .... 63

7 1H Decoupled 13C NMR (25.2 MHz) Spectrum of Methyl
2,4-Pentadienoate in CDC13 at 25"C........................64

8 1H NMR (60 MHz) Spectrum of Poly(Methyl
2,4-Pentadienoate) in CDC13 at 25C.......................65

9 1H Decoupled 13C NMR (25.2 MHz) Spectrum of Poly(Methyl
2,4-Pentadienoate) in CDC13 at 25'C .......................66

10 1H NMR (60 MHz) Spectrum of Poly(l-Carbethoxy-1-
cyano-1,3-butadiene) in CDC13 at 25C......................70

11 1H Decoupled 13C NMR (25.2 MHz) Spectrum of
Poly(1-Carbethoxy-l-cyano-1,3-butadiene) in
CDC13 at 25"C.............................................71

12 Frontier Orbital Energies and Coefficients for
1-Substituted Dienophile Donors and 1-Substituted
Diene Acceptors...........................................73

13 Monomer Feed-Copolymer Composition Curve for
Copolymerization System of EBD and AN......................76


viii








14 1H NMR Spectra of AN-EBD Copolymers, Except D
(Spontaneous Initiation), the Others Prepared with
Free Radical Catalysts. Copolymer Compositions of
EBD(%): (A) 14.9; (B) 49.6; (C) 50.6; (D) 52.3;
(E) 54.0; (F) 57.5 .......................................77

15 1H Decoupled 13C NMR Spectra of AN-EBD Copolymers,
Except D (Spontaneous Initiation), the Others Prepared
with Free Radical Catalysts. Copolymer Compositions of
EBD(%): (A) 14.9; (B) 49.6; (C) 50.6; (D) 52.3;
(E) 54.0; (F) 57.5................................ .. .... 78

16 Plot According to the Method of Fineman-Ross for
the AN-EBD Copolymer System...............................80

17 Plot According to the Method of Kelen-Tudos for
the AN-EBD Copolymer System...............................81

18 1H NMR (60 MHz) Spectrum of AN-EBD Copolymer in CDC13
at 25C.... ............................................. 83

19 1H Decoupled 13C NMR (25.2 MHz) Spectrum of AN-EBD
Copolymer in CDC13 at 25C................................85

20 Frontier Orbital Energies and Coefficients for
1-Substituted Dienophile Acceptors and 1-Substituted
Diene Donors..............................................93

21 Plot According to the Method of Fineman-Ross for
the AN-DABD Copolymer System..............................95

22 Plot According to the Method of Kelen-Tudos for
the AN-DABD Copolymer System..............................96

23 1H NMR (60 MHz) Spectrum of AN-DABD Copolymer in
CDC13 at 25C...............................................98

24 1H Decoupled 13C NMR (25.2 MHz) Spectrum of AN-DABD
Copolymer in CDC13 at 25C.................................99

25 1H NMR (60 MHz) Spectrum of AN-TSBD Copolymer in
CDC13 at 25C ............................................103

26 1H Decoupled 13C NMR (25.2 MHz) Spectrum of AN-TSBD
Copolymer in CDC13 at 25C...............................104

27 1H NMR (60 MHz) Spectrum of AN-ATBD Copolymer in
CDC13 at 25 C.......................... ............ ... 108








28 1H Decoupled 13C NMR (25.2 MHz) Spectrum of AN-ATBD
Copolymer in CDC13 at 25C...............................109

29 1H NMR (60 MHz) Spectrum of MPD-EBD Copolymer in
CDC13 at 25C.................................. ........ 112

30 1H Decoupled 13C NMR (25.2 MHz) Spectrum of MPD-EBD
Copolymer in CDC13 at 25C...............................113

31 1H NMR (60 MHz) Spectrum of MPD-ATBD Copolymer in
CDC13 at 25C........................... ... .........116

32 1H Decoupled 13C NMR (25.2 MHz) Spectrum of MPD-ATBD
Copolymer in CDC13 at 25C...............................117

33 1H NMR (60 MHz) Spectrum of Poly(Trimethyl Vinyl
Ammonium Acrylate) in D20 at 25C........................119

34 1H Decoupled 13C NMR (25.2 MHz) Spectrum of
Poly(Trimethyl Vinyl Ammonium Acrylate) in D20 at 25C....120














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

STUDIES ON THE MECHANISMS OF
COPOLYMERIZATION OF ELECTRON-DONOR DIENES
AND ELECTRON-ACCEPTOR DIENES

BY

JEN-CHI CHEN

August, 1985

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


The aim of this research was to study the mechanism of

alternating copolymerizations of diene-dienophile systems.

The copolymerizations of electron-poor dienes with electron-rich

dienophiles, electron-rich dienes with electron-poor dienophiles, and

electron-rich dienes with electron-poor dienes were investigated.

The microstructure and sequence distributions of monomers in the

resulting polymers were analyzed by IR, H NMR and 13C NMR

techniques.

In the polymerization system of diene acceptors (methyl 2,4-

pentadienoate; 1-cyano-l,3-butadiene; and 1-carbethoxy-l-cyano-1,3-

butadiene) with several vinyl ethers, the resulting polymers were

found to be composed of diene monomer units only.








In the copolymerization system of diene donors (1-ethoxy-1,3-

butadiene; 1-diethylamino-1,3-butadiene; 1-trimethylsilyloxy-1,3-

butadiene; and 1-acetoxy-1,3-butadiene) with acrylonitrile, the

resulting copolymers were found to have a high alternating structure.

In the copolymerizations of acrylonitrile with 1-ethoxy-1,3-

butadiene and 1-diethylamino-1,3-butadiene, the monomer reactivity

ratios were determined by the Fineman-Ross and Kelen-Tudos methods.

On the basis of chemical shift differences between the head-to-

tail and head-to-head monomer sequence distributions, the mechanism

of this alternating copolymerization system was suggested.

In the copolymerization system of several diene donors with

several diene acceptors, it was found that the mole fractions of

acceptors were much more than those of donors in the resulting

copolymers.

In order to explain all these copolymerization systems, a

frontier molecular orbital treatment was proposed. A good

qualitative correlation with experimental results was obtained.














CHAPTER I
INTRODUCTION



General Background

When electron donors and electron acceptors are brought

together, they usually form electron donor-acceptor complexes to

various extents. The term "electron donor-acceptor complex" is used

to describe a wide variety of intermolecular complexes. Its range

comprises Lewis acid-Lewis base interactions, ion pairs, and charge-

transfer complexes. The enthalpies of dissociation of these

complexes are much smaller than those of ordinary chemical reactions,

and are similar to hydrogen bondings and van der Waals forces.

In 1949, Benesi and Hildebrand1 measured the ultraviolet spectra

of iodine and benzene in n-heptane solutions and discovered a new

absorption band which is uncharacteristic of either of the component

molecules. Later, Mulliken2,3 successfully developed a now widely

accepted theoretical description of these phenomena. Mulliken's

contribution has stimulated a wide variety of theoretical and

experimental work in this area.


Mulliken's Valence Bond Treatment

On the basis of the valence bond theory, Mulliken described the

complex that exists in a resonance form between the no-bond and the








dative states of the donor molecule (D) and the acceptor molecule

(A).


K
D + A = [(D,A) + (D ,A )] (1)
no-bond dative


where (D,A) is the no-bond state of the complex, (D+,A-) is the

dative state of the complex, and K is the formation constant of the

complex.

The wave functions of the complex can be expressed as a linear

combination of wave functions of the no-bond state and the dative

state. The ground state:



N = a*0(D,A) + b1(D',A) (2)

with a >> b

and the excited state:



E = b*1(D+,A ) a* 0(D,A) (3)


with b* >> a*


where 0o(D,A) is the wave function for the molecular complex which is

held together by several physical electrostatic forces involving

dipole-dipole, dipole-induced dipole, London dispersion, and hydrogen

bonding types. The term 1[(D+,A-) correlates with a wave function

for the complex where one electron has been entirely transferred from

the donor molecule to the acceptor molecule. The transition between








these two states yields the characteristic charge-transfer absorption

band. The term "charge-transfer complex" is usually given to this

association pair.

For these weak charge-transfer complexes, their energy levels

can be treated by the perturbation theory. The energy-level diagram

of the relationship between the various terms is shown in Figure 1.


E*[ E]

41


El I (D+,A )]


E,[* D+*PA


E0 0(DA)I
S EO[oP(D,A)]


E[DN]


Fig. 1. The Energy-Level Diagram of the Weak Charge-Transfer
Complex.


Based on Mulliken's treatment, a relationship among the energy

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

the donor (ID), and the electron affinity of the acceptor (EA) can be

expressed by equation (4).









ECT = EA + G + X (4)


where G and X are coulomb and resonance energies, respectively, and

are considered to be constant for a given donor and acceptor. This

expression has been well proven experimentally.


Molecular Orbital Treatment

About the same year, an alternative approach to this

intermolecular charge-transfer transition was proposed by Dewar4 and

Fukui,5 respectively. In their approaches, the complex is treated as

a i-complex which is formed by the interaction of the w-orbitals of

the donor and the acceptor. Since the interaction between donor and

acceptor is very small, the charge-transfer interaction can also be

treated by the perturbation method. The energy-level diagram of the

molecular orbital representation of a weak charge-transfer complex is

shown in Figure 2.



Anti-
bonding Charge Anti-
transfer bonding
Locally transition --
excited | '
transition Locally
i excited
Bonding transition

E .- Bonding
E

DONOR ACCEPTOR



Fig. 2. Molecular Orbital Representation of a Weak Charge-Transfer
Complex.








Interactions between occupied bonding orbitals of donors and

acceptors produce no change in their total energy and no net transfer

of charge between donor and acceptor. Interactions of the occupied

orbitals of the donor with the unoccupied antibonding orbitals of the

acceptor lower the former and elevate the latter, leading to a net

stabilization with a transfer of negative charge from donor to

acceptor. Interactions of the occupied orbitals of the acceptor with

the unoccupied antibonding orbitals of the donor similarly produce

stabilization with a net charge transfer in the opposite direction.

These interactions are inversely proportional to the energy gap

between the interacting orbitals. The donor is usually recognized as

having the highest energy occupied molecular orbital (HOMO) and the

acceptor is recognized as having the lowest energy unoccupied

molecular orbital (LUMO). The interaction between LUMO and HOMO has

been regarded as an important role in many organic reactions.

The molecular orbital approach arrives at a similar conclusion

to that of the valence bond treatment, but it looks preferable for

two reasons: first, some complexes show more than one new charge-

transfer absorption band. This can be rationalized by the molecular

orbital theory, because there should be a band correlating to the

transition between any of the occupied orbitals of donor and any of

the unoccupied orbitals of the acceptor; secondly, the term "charge-

transfer complex" is misleading in that very little charge is

transferred in the ground states of such complexes, but an

appreciable part of their stability may be due to the back donation

involving interactions between the occupied orbitals of the acceptor








and the unoccupied orbitals of the donor. It is obvious from both

approaches that the charge-transfer forces will influence the

structure of molecular complexes: the maximum amount of charge-

transfer stabilization of the complex is to be expected when the

overlap between these orbitals is greatest. The structure of r-

conjugated donors and acceptors pile parallelly with the planes of

the molecules, but offset slightly to each other.

The fact that charge-transfer absorption bands are observed does

not mean that complexes play any significant role in the reaction.

Conversely, failure to find charge-transfer absorption bands does not

prove that a charge-transfer process is not involved, because in some

cases, the transition energy for the charge-transfer absorption may

be much greater than that required for the thermal charge-transfer

process; the charge-transfer bands may overlap with the absorptions

of the donor and/or the acceptor; the extinction coefficients of

charge-transfer transitions may be much smaller than those of

molecular electronic absorptions.

Kosower6 has reviewed those organic reactions in which charge-

transfer complexes are frequently postulated as intermediates. The

types of reactions discussed involve solvolysis, thermal electron

transfer reactions, and reactions which follow light absorption by a

charge-transfer complex.


Basic Principles of Copolymerization

In 1944 Mayo and Lewis7 successfully developed the first

mathematical analysis of a polymerization system involving a mixture

of two monomers. They considered the four propagation steps outlined








below, and then derived the copolymerization equation as shown below.


Four propagation steps:


- M1




-- M *



-~ M2'



- M2'


--~ M2
2


+ M1



+ M2


Copolymerization equation:


d[M1]
d7 MR 2


[M1] rl[M1] + [M2]
IT1T r2LM2] + LM1J
S2 2 1


Two equations of the propagation reactions are homopolymerizations or

self-propagating steps, and the other two equations are heteropoly-

merizations or cross-propagating steps. MI' and M2' are used as

symbols for the polymer chain end radicals with M1 and M2 terminal

groups, respectively. The copolymerization equation allowed the

copolymerization composition and sequence distribution to be related

to the monomer feed composition through two monomer reactivity

ratios, where r1 = k11/k12, and r2 = k22/k21. This equation has been

proven to be very successful in explaining the experimental results

for many copolymer systems, but there were several systems which


kll


---j
k12
---)


k21



k22
)--


--~ MI


-M M1


-~ 2-








could not be satisfactorily explained. This equation was derived

using several assumptions, i.e., bimolecular propagation mechanism,

absence of the penultimate chain effect and depolymerization, high

degree of polymerization, and identity of overall and effective

concentrations.

Penultimate Chain End Effects

In order to explain some of these deviations, Alfrey and

coworkers8 proposed that the reactivity of a chain end radical

towards a particular monomer molecule could be influenced by the

penultimate group in the growing chain. The mathematical treatment

of this effect in this copolymerization system involves eight

propagating steps and four reactivity ratios. This penultimate model

was able to explain the results of several of those systems which

deviate from the simple copolymerization equation (terminal model).

An example is the styrene-fumaronitrile system.

Charge-transfer Complexes

An alternative approach to explaining deviations from the simple

copolymerization equation was proposed by Bartlett and Nozaki,9 in

1946. They observed that the solution of styrene and maleic

anhydride showed a yellow coloration. This coloration was attributed

to the formation of an electron donor-acceptor complex between this

monomer pair. Therefore, they proposed that the electron donor-

acceptor complex may participate as a monomer in the propagation step

of the polymerization. The mathematical treatment of this complex

model involves eight propagation steps and six reactivity ratios.0








The role of the charge-transfer complex in the polymerization

reaction has usually been classified into two categories: one is so-

called "charge-transfer polymerization," the first proposes that the

interaction between the donor and the acceptor may generate reactive

species to initiate one or the other of the homopolymerization

reactions; the other one proposes that alternating copolymerization

will occur.

Alternating Copolymerization

Alternating copolymerizations are characterized by the fact that

a nearly 1:1 molar ratio of the comonomers is found in copolymers

produced from a wide variety of comonomer mole fractions in the

initial monomer solution. The possible reaction pathways are shown

in Figure 3.11



K
D + A D-A complex




+ -D -A-3- 4-

Alternating copolymer


Fig. 3. The Possible Reaction Pathways Form
Alternating Copolymers.



On the basis of these possible reaction pathways, three

mechanisms have been proposed to explain this strong alternation

tendency between the electron donor and the electron acceptor.








In 1946 Bartlett and Nozaki9 proposed the first mechanism in

which the copolymerization is via a stable monomer complex composed

of the two monomer units. This mechanism has been supported by the

works of Butler and coworkers12-15 maleicc anhydride-divinyl ether

and maleic anhydride-furan copolymers), Caze and Loucheux16 maleicc

anhydride-vinyl acetate copolymer), Goethals and coworkers17 maleicc

anhydride-benzofuran, maleic anhydride-indole, maleic anhydride-

benzothiophene copolymers), Yamashita and coworkers18,19 maleicc

anhydride-p-dioxene, maleic anhydride-1,2-dimethoxyethylene

copolymers), and Gaylord and coworkers20,21 maleicc anhydride-

conjugated diene copolymers). This mechanism is also called the

"complex" mechanism.

Walling22 proposed the second mechanism in which electrostatic

interactions between differently polarized monomers and radicals

decrease the activation energy for the alternating chain propaga-

tion. This mechanism is also called the "free monomer" mechanism.

Price and Alfrey23 have rationalized these reactivities in terms of

resonance and polar effects in a semi-empirical scheme known as the

Q-e scheme. They proposed that the rate constant for a radical-

monomer reaction, for example, for the reaction of Mi" radical with

M2 monomer, can be written as


k2 = PQ2 exp (-e1e2) (10)



where P1 and Q2 are measures of the resonance stabilization of M

radical and M2 monomer, respectively, and el and e2 are measures of








their polar properties. The e value is positive for electron-poor

olefins and negative for electron-rich olefins. The monomer

reactivity ratios may be expressed by the following equations:


Qi
r1 exp [-el(el-e2)] (11)
Q2


r2 = exp [-e2(e2-el)] (12)


The copolymerization tendency, r1r2, is expressed in terms of e-

values:



r1r2 = exp [-(el-e2)2] (13)


From this equation, the combination of two monomers having different

e-values, especially those differing in sign, favors alternating

copolymerization. However, another term, Q, is also important, and

two monomers having very different Q-values fail to produce

alternating copolymers, because of their different reactivities.

The third mechanism was proposed by Shirota24 and Tsuchida,25

respectively. This mechanism involves the participation of both free

monomers and the charge-transfer complex monomer in the propagation

steps. The idea of this mechanism originates from the fact that the

initial copolymerization rate does not necessarily maximize at the

monomer feed ratio of 1:1 where the concentration of the charge-

transfer complex attains maximum, which is inconsistent with the

second mechanism.







Diels-Alder Reaction
The Diels-Alder reaction was discovered about sixty years ago,
because six-membered rings are formed with remarkable stereoselecti-
vity and regioselectivity, this reaction is of great synthetic
utility. Its mechanism has been suggested as either a concerted
reaction or a stepwise reaction. In many cases, it has been regarded
as a reversible reaction. The proposed reaction pathways for this
reaction are shown in Figure 4.26


+ )I


Zwitterions


A
B2 1


I [


Fig. 4. The Reaction Pathways of Diels-Alder Reaction.
The new a bonds between the reactants may be formed simultaneously in
a multicenter mechanism, as shown in reaction pathway A, involving a
one step reaction whose energy profile contains only one activation
barrier. Another possibility is that the two bonds are formed in two
successive reaction steps. The energy profile of this two step


Diene


Biradical








reaction contains two transition states and one intermediate, i.e.,

either a zwitterion or a biradical.

Although the reaction occurs in the unsubstituted diene-

dienophile system, it is most successful when the diene and

dienophile contain substituents of supplementary electronic

influence. Alder found that the reaction rate is often increased by

electron-donating substituents on the diene and by electron-accepting

substituents on the dienophile. This phenomenon has been

rationalized by frontier orbital theory treatment, and is the so-

called "Diels-Alder reaction with normal electron demand." There are

some examples that illustrate inverse electron demand, i.e.,

electron-accepting substituents on the diene and electron-donating

substituents on the dienophile. However, they are unable to find a

suitable model system. The frontier orbital interactions of all

these diene-dienophile systems, i.e., unsubstituted, normal electron

demand, and inverse electron demand, are shown in Figure 5.27 On the

basis of the energy gap of the HOMO-LUMO interactions, the reaction

rates of both "normal electron demand" and "inverse electron demand"

diene-dienophile systems should be faster than those of unsubstituted

diene-dienophile systems.


Copolymerization of Conjugated Diene and Dienophile

In 1970 Butler and coworkers13 studied the copolymerization of

furan and maleic anhydride, and found that a 1:1 copolymer of these

comonomers was produced, regardless of the monomer feed ratios. The








Unsubstituted


Normal electron
demand


LUMO




HOMO


-TII
HOMO




D
's- -J


Inverse electron
demand



LUMO


LUMO



HCMO

HOMO



-+I

A
D


Fig. 5. Frontier OWital Interactions in the Diels-Alder
Reactions.



presence of a donor-acceptor complex between the monomers was

observed by NMR and UV methods. Therefore, they proposed that the

polymerizations proceeded by homopolymerization of this complex to

produce an alternating sequence in the copolymer.

In 197614 and 198115 Butler and Ragab reported further studies

on the mechanism of this copolymerization, and showed the copolymer

was comprised of alternating monomer units as in structure I instead








of structure II, i.e., the homopolymer of the exo form of the Diels-

Alder adduct.




0
-- O T r

oo^ oW
n 0 n
I II




They also studied copolymerization of a number of furan

derivatives with maleic anhydride, comparing the copolymer
microstructures with those of model compounds. They made a

comparative study of various donors and acceptors related to furan

and maleic anhydride and concluded that the trend among the initial

polymerization rates was analogous to that among the equilibrium

constants for complex formation. On the basis of their studies they

suggested that the donor-acceptor complex is the active polymerizing

species.

Gaylord and coworkers have made wide-ranging studies of the free

radical copolymerization of maleic anhydride with conjugated dienes,

i.e., budadiene,20 pentadienes,21 and cyclopentadienes.28 They
postulated that the cyclic adduct and the alternating copolymer arise
from a common intermediate, i.e., the charge-transfer complex as a
result of intramolecular and intermolecular reactions, respec-
tively. The cyclic adduct was proposed to be formed from the complex
in the ground state, and the alternating copolymer from the complex







in the excited state. The general mechanism for reactions of linear
dienes and maleic anhydride proposed by Gaylord and coworkers is
shown below:


0

+ 0 >

0


R //


0


R T
0

0


R


R


R


0

IO

0


0

*0
O








The Research Objectives

In order to gain further insight into the mechanism of the

alternating copolymerizations of diene-dienophile systems and the

relationship between the copolymerization and the Diels-Alder

reactions, the copolymerizations of electron-poor dienes with

electron-rich dienophiles, electron-rich dienes with electron-poor

dienophiles, and electron-rich dienes with electron-poor dienes were

investigated.

The microstructures and sequence distributions of monomers in

the resulting polymers were analyzed by IR, 1H NMR, and recent

developments of 13C NMR techniques.

On the basis of the chemical shift differences between the head-

to-tail and head-to-head monomer sequence distributions, the

mechanisms of these copolymerization systems were suggested.














CHAPTER II
EXPERIMENTAL



General Information

All temperatures are uncorrected and are reported in degrees

centigrade. Melting points were determined in open capillary tubes

using a Thomas-Hoover melting point apparatus. Pressures are

expressed as millimeters of mercury. Elemental analyses were

performed by either Atlantic Microlab. Inc., Altanta, Georgia, or the

University of Florida, Department of Chemistry, Gainesville,

Florida. Infrared spectra were recorded on a Perkin-Elmer Model 281

Infrared Spectrophotometer. Spectra were calibrated by using the

1601 cm-1 line of a polystyrene film. Spectra of liquids were

performed neat as a smear on potassium chloride plates, and those of

solids were obtained by using KBr pellets. Vibrational transition

frequencies are expressed in wavenumber (cm-1) with the intensity of

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

medium (m), strong (s), very strong (vs), and broad (br). Proton

nuclear magnetic resonance (NMR) spectra (60 MHz) were recorded on a

Varian EM-360L Spectrometer. Carbon-13 (25.2 MHz) and proton (100

MHz) NMR spectra were obtained 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 decoupled 13C resonances are designated

as singlet (s), doublet (d), triplet (t), quartet (q), or multiple

(m). Coupling constants (J) are expressed in Hertz (Hz). Ultra-

violet and visible spectra were measured with a Perkin-Elmer 330

Spectrophotometer. Intrinsic viscosities were measured by standard

procedures using a Cannon-Ubbelohde Semimicro Viscometer (dilution

viscometer).


Reagents and Solvents

Reagents were obtained from Fisher Scientific Co., or Aldrich

Chemical Co., unless otherwise noted. Deuterated NMR solvents were

obtained from Merck & Co., Inc., and Aldrich Chemical Co., and were

used without further purification.

All solvents used for general application were of reagent grade

or ACS grade quality. For special purposes, purification of solvents

was carried out by the following procedures reported in the

handbook.29


Monomer Synthesis

Ketene, Diethylacetal(1)30

The reaction was conducted in a 500 ml round-bottomed flask

attached to a reflux condenser, the top of which was connected to a

three-way stopcock leading to a source of nitrogen gas and a mercury

trap, and a water aspirator. The flask and condenser were dried by

warming with a free flame while the system was under reduced

pressure, then dry nitrogen was admitted to the apparatus. The

cooled flask was quickly charged with 205 ml of dry tert-butyl








alcohol and 9.15 g (0.234 mole) of potassium and was then reconnected

to the apparatus. The flow of nitrogen was stopped and the mixture

was boiled under reflux until the potassium was entirely reacted,

hydrogen being liberated through the mercury trap. The solution was

then cooled slightly while nitrogen was admitted to equalize the

pressure. The flask was quickly disconnected just long enough for

the addition of 35.60 g (0.233 mole) of chloroacetaldehyde

diethylacetal. A white precipitate of potassium chloride began to

deposit immediately. The flask was attached at once to a Vigreux

column wrapped with a heating tape, the top of column was connected

to a total-reflux partial take-off still head. The tert-butyl

alcohol was distilled at the ratio of 25 drops per minutes with a

reflux ratio at the still head of about 6:1. This operation required

about 5-6 hours. At the end of this time, the temperature of the oil

bath was raised to 160" and maintained there until no more alcohol

came over. The bath was then allowed to cool while the pressure of

the fractionating system was gradually reduced to 200 mm Hg. The

product was collected; yield: 13.4 g (49.4%); b.p. 83-86" at 200 mm

Hg (lit. rep. 67-75%).

1H NMR (60 MHz, CDC13): 6 1.32 (t, 6H, J = 7.2 Hz), 3.10 (s,

2H), 3.84 (q, 4H, J=7.2 Hz).
13C NMR (CDC13): 6 14.37, 55.46, 63.42, 164.97.

IR (neat): 3148 (w), 2980 (m), 2938 (m), 2890 (s), 1740 (m),

1648 (s), 1480 (m), 1445 (m), 1388 (m), 1372 (m), 1282 (s), 1190 (m),

1162 (m), 1084 (m), 1050 (s), 972 (m), 948 (m), 874 (m), 804 (w), 710

(m) cm .







Ketene, Dimethylacetal (2)31
In a 500 ml three-necked round-bottomed flask equipped with a
thermometer, a mechanical stirrer, and a Vigreux column, which was
fitted with a total-reflux partial take-off still head, were charged
220 ml of anhydrous pinacol and 10.6 g (0.461 mole) of sodium. The
mixture was heated and stirred until all the sodium had reacted. The
solution was cooled to 160" with stirring and 47.5 g (0.381 mole) of
chloroacetaldehyde dimethylacetal was added through the fractionating
head. After the addition of the chloroacetal, the head temperature
dropped rapidly from 130" to 89. The product was collected;
yield: 18.6 g (55.1%); b.p. 89-93" (lit. rep. 50%).
1H NMR (60 MHz, CDC3): 6 3.08 (s, 2H), 3.57 (s, 6H).
13C NMR (CDC13): a 54.14, 55.11, 167.07.
IR (neat): 3144 (w), 3008 (m), 2946 (m), 2840 (m), 2158 (w),
2044 (w), 1900 (w), 1842 (w), 1744 (m), 1648 (s), 1456 (s), 1381 (m),
1295 (s), 1195 (m), 1176 (m), 1128 (m), 1081 (m), 1056 (m), 1030 (s),
970 (w), 918 (w), 890 (m), 872 (m), 840 (w), 828 (w), 720 (m) cm-1.
1,4-Dioxene (3)32




+ C 0
0 0350 nm ni 0


0


OH








In a 400 ml glass cylinder was charged 12.0 g of technical grade

9,10-phenanthrenequinone and 300 ml of dioxane. Nitrogen was bubbled

through this mixture for one hour, then the solution was irradiated

by a 350 nm UV lamp apparatus for 93 hours. The excess dioxane was

removed by a rotatory evaporator, the last traces of dioxane were

removed at 0.5 mm Hg until the odor of dioxane was not detected. The

crude product was collected; yield: 14.6 g.

A 25 ml round-bottomed flask containing all the crude product

was attached to a micro short-path still apparatus and immersed in an

oil bath heated to 250. Within a few minutes, rapid distillation

began. The product was collected; yield: 3.96 g (93.0%); b.p.

90-92.

1H NMR (60 MHz, CDC13): 6 4.05 (s, 4H), 5.94 (s, 2H).

13C NMR (CDC13): 6 64.62, 126.91.

IR (neat): 3090 (w), 2977 (m), 2930 (m), 2878 (m), 2020 (w),

1650 (s), 1456 (m), 1391 (w), 1370 (w), 1328 (w), 1268 (s), 1240 (m),

1122 (s), 1064 (s), 951 (m), 894 (s), 871 (m), 850 (m), 802 (m), 737

(s) cm1.

l-Diethylamino-1,3-butadiene (4)33

In a 250 ml three-necked round-bottomed flask fitted with a

thermometer, an addition funnel, and a mechanical stirrer were placed

45 g (0.615 mole) of diethylamine and 12 g of anhydrous potassium

carbonate. The mixture was stirred and cooled to -10* in an ice-salt

cooling bath. To the mixture was added 21 g (0.300 mole) of

crotonaldehyde in 30 ml of benzene while the reaction mixture was

kept at -5" to -10. Then the mixture was stirred for one hour at 0








and 4 hours at 20; the liquid layer was decanted from the potassium

carbonate; 0.2 g of 9,10-phenanthrenequinone was added and the

solution was fractionally distilled at the reduced pressure. The

product was collected; yield: 21.3 g (56.7%); b.p. 70-74 at 20 mm Hg

(lit. rep. 60.9%).

H NMR (60 MHz, CDC13): 6 1.08 (t, 6H, J = 7.2Hz), 3.05 (q, 4H,

J = 7.2 Hz), 4.30-5.26 (m, 3H), 5.33-6.61 (m, 2H).
13C NMR (CDC13): 6 12.96, 44.93, 98.15, 103.32, 137.39, 141.33.

IR (neat): 3079 (w), 3038 (w), 2962 (m), 2930 (m), 2862 (m),

1630 (s), 1461 (w), 1450 (w), 1420 (m), 1390 (m), 1374 (m), 1360 (m),

1300 (w), 1280 (w), 1250 (m), 1205 (m), 1158 (m), 1110 (m), 990 (m),

951 (w), 922 (m), 843 (m), 814 (w), 770 (w), 646 (m) cm1.

1,1,3-Triethoxy butane (5)34

In a 2000 ml three-necked round-bottomed flask equipped with a

thermometer, a gas inlet tube, and a water-cooled condenser, the top

of which was connected to a mercury trap were placed 600 g (13.02

mole) of absolute alcohol, 300 g (4.28 mole) of crotonaldehyde, and

15 g of concentrated sulfuric acid. The solution was stirred and

heated to 50" for 16 hours under a nitrogen atmosphere. After the

given reaction time, the solution was cooled to room temperature, and

12.2 g of sodium hydroxide was added in as little water as

possible. Then the mixture of ethyl alcohol, crotonaldehyde, and

water was distilled off at 40" and 90 mm Hg. The residue was

fractionated to yield product; yield: 280.9 g (34.5%); b.p. 75-77"

at 10 mm Hg (lit. rep. 31.9-36.9%).








1H NMR (60 MHz, CDC13): 6 1.20 (m, 12H), 1.76 (m, 2H), 3.55 (m,

7H), 4.68 (q, 1H).
13C NMR (CDC13): 6 15.06, 15.30, 19.69, 41.08, 60.82, 61.21,

63.35, 71.49, 100.39.

IR (neat): 2978 (s), 2930 (m), 2878 (m), 1481 (w), 1443 (m),
1374 (m), 1342 (m), 1298 (w), 1278 (w), 1239 (w), 1120 (s), 1100 (s),

1060 (s), 1002 (m), 974 (m), 944 (w), 848 (w), 796 (w) cm1.

l-Ethoxy-1,3-butadiene (6)35


OEt OEt
H I I
CH3 CH = CH CHO + 3 EtOH CH3 CH CH CH
-H20 1E


OEt


In a 300 ml three-necked round-bottomed flask equipped with a

dropping funnel, a thermometer, and a 1.8 cm diameter, 15 cm length

glass tube wrapped with a heating tape, the top of which was
connected to a distillation apparatus was placed 76.6 g of 1,1,3-

triethoxybutane. To the liquid, heated to boiling, was added

dropwise a 38.4 g portion of the triether containing 0.07 g of
phosphoric acid. During this period, the 1-ethoxy-1,3-butadiene
formed was allowed to distill constantly with the ethanol vapor as
carrier. When the addition of this solution was over, an additional
38.4 g of triether was supplied, and the whole system was subjected
to distillation. The rate of removal of the 1-ethoxy-1,3-butadiene
and ethanol vapors was adjusted so that the vapor phase maintained








its temperature at 110-120. Several drops of triethanolamine was

added to the receiver as an inhibitor. The distillate collected was

extracted twice with an equal volume of water, followed by drying

over anhydrous sodium sulfate. Distillation of this layer under

reduced pressure gave pure trans-l-ethoxy-1,3-butadiene, 27.1 g

(34.3%); b.p. 58-60* at 105 mm Hg.

1H NMR (60 MHz, CDC13): 6 1.26 (t, 3H, J = 7.2 Hz), 3.76 (q,

2H, J = 7.2 Hz), 4.64-6.73 (m, 5H).

13C NMR (CDC13): 6 14.52, 65.06, 107.02, 111.02, 133.44,

150.69.

IR (neat): 3079 (w), 3041 (w), 2970 (m), 2921 (m), 2868 (m),

1688 (w), 1636 (s), 1598 (m), 1472 (w), 1434 (w), 1412 (w), 1388 (m),

1330 (m), 1295 (w), 1242 (w), 1188 (s), 1162 (m), 1124 (m), 1103 (m),

1018 (m), 988 (m), 910 (m), 874 (m), 850 (w), 812 (w), 650 (w), 630

(m) cm-1.

Ethyl Sorbate (7)

In a 1000 ml three-necked round-bottomed flask equipped with a

mechanical stirrer and a distillation apparatus were placed 112.1 g

(1.0 mole) of sorbic acid, 180 ml of absolute alcohol, 90 ml of

toluene, and 2 ml of concentrated sulfuric acid. The mixture was

stirred and heated on an oil bath. An azetropic mixture of alcohol,

toluene, and water began to distill at 75. Distillation was

continued until the thermometer in the neck of the flask rose to 78,

when further heating was suspended. The distillate was collected in

a 500 ml flask containing 75 g of anhydrous potassium carbonate. It

was well shaken, filtered, and returned to the distilling flask. The








flask was again heated until the temperature rose to 78-80". When

distillation was discontinued, the residual liquid was poured into a

500 ml round-bottomed flask, and distilled under vacuum. The product

was collected; yield: 110.8 g (79.1%); b.p. 85 at 20 mm Hg.

1H NMR (60 MHz, CDC13): 6 1.27 (t, 3H, J = 7.2 Hz), 1.85 (d,

3H, J = 5.4 Hz), 4.18 (q, 2H, J=7.2 Hz), 5.61-6.52 (m, 3H), 7.03-7.53

(m, 1H).

13C NMR (CDC13): 6 14.3, 18.6, 60.1, 119.1, 129.8, 139.1,

144.8, 167.3.

IR (neat): 3200 (m), 2980 (m), 2940 (m), 2910 (m), 2876 (w),

1710 (s), 1642 (s), 1618 (s), 1446 (m), 1390 (m), 1368 (s), 1327 (s),

1303 (s), 1260 (s), 1240 (s), 1218 (m), 1188 (s), 1138 (s), 1086 (m),

1036 (s), 998 (s), 948 (w), 922 (m), 868 (m), 798 (m), 740 (w), 710

(w), 690 (w) cm-1.

Ethyl Muconate (8)36

In a 100 ml round-bottomed flask fitted with a reflux condenser

attached to a drying tube containing calcium chloride were placed 4.0

g of muconic acid, 40 ml of absolute alcohol, and 1 ml of

concentrated sulfuric acid. The solution was refluxed for 24

hours. After the given reaction time, the reaction mixture was

evaporated by a rotatory evaporator, and the crude residue was

extracted with ether. The ether solution was washed with the 3%

potassium carbonate solution to remove the unreacted muconic acid,

the extract was dried, filtered, and evaporated. Recrystallization

from methanol yielded 2.17 g (38.9%) of pure product, m.p. 61-63*

(lit. rep. 63-64*).








1H NMR (100 MHz, CDC13): 6 1.32 (t, 6H, J = 7.2 Hz), 4.24 (q,

4H, J = 7.2 Hz), 6.19 (dd, 2H, J = 11.6, 3.0 Hz), 7.31 (dd, 2H, J =

11.6, 3.0 Hz).

13C NMR (CDC13): 6 14.17, 60.80, 128.37, 140.71, 165.87.

IR (neat): 3064 (w), 2979 (m), 2938 (w), 2908 (w), 1696 (s),

1610 (s), 1475 (w), 1465 (w), 1441 (w), 1386 (w), 1367 (m), 1310 (s),

1250 (s), 1158 (s), 1088 (m), 1020 (s), 858 (s), 810 (w), 740 (m),

714 (m), 690 (m) cm-1.

2,4-Pentadienoic Acid (9)37,38

Procedure A. In a 500 ml three-necked round-bottomed flask

equipped with a constant pressure dropping funnel, a mechanical

stirrer, and a thermometer were placed 90 g (0.865 mole) of malonic

acid and 200 g (2.528 mole) of pyridine. The solution was stirred

and cooled in an ice-salt bath. To the solution was added dropwise

60 g (1.070 mole) of acrolein. The mixture became yellow and

deposited a very viscous oil. After 3 hours, the temperature was

raised to 35-40" where it was kept for 5 hours during which the oil

dissolved with evolution of carbon dioxide. The solution was

acidified and extracted with ether. Upon removal of the ether, the

acid was recovered as pale yellow crystals, 18.7 g (22.1%) (lit. rep.

30%). Pure acid was obtained by recrystallization from petroleum

ether, m.p. 67-69" (lit. rep. 72*).

Procedure B. In a 500 ml four-necked round-bottomed flask

equipped with a mechanical stirrer, an addition funnel, a

thermometer, and a water-cooled condenser attached to a drying tube

containing calcium chloride were placed 75 g (0.721 mole) of malonic








acid, 105 ml (1.298 mole) of pyridine, and 0.3 g of hydroquinone.

The solution was heated to 50, then 45.3 g (0.808 mole) of acrolein

was added dropwise with stirring, and the temperature was maintained

at 50 for 2 hours, and then at 80* for further 2 hours. The

reaction mixture was poured on to ice, acidified, and the acid was

extracted into dichloromethane. Upon removal of the solvent, the

acid was recovered as pale yellow crystals, 34.3 g (48.5%) (lit. rep.

56%). The pure acid was obtained by recrystallization from the

petroleum ether, m.p. 68-70" (lit. rep. 72).
H NMR (60 MHz, CC14-TMS): 6 5.44-7.66 (m, 5H), 12.26 (s, 1H).

13C NMR (DMSO-d6): 6 123.13, 125.81, 134.88, 144.29, 167.34.

IR (KBr): 3300-2500 (m, br), 1700 (s), 1630 (m), 1598 (m), 1430

(m), 1402 (m), 1308 (m), 1278 (s), 1216 (m), 1158 (m), 1007 (m), 964

(w), 928 (m), 864 (w) cm-1.

Methyl 2,4-pentadienoate (10)38,39

Procedure A. In a 50 ml beaker equipped with a mechanical

stirrer was placed 5.0 g (0.051 mole) of 2,4-pentadienoic acid in

14.2 ml of 3.5 N aqueous ammonia solution. To this solution was

added a solution of 9.5 g of silver nitrate in 9.0 ml of water. The

precipitated silver salt was filtered, washed by deionized water, and

dried in a vacuum oven at 45. The yield was 8.48 g.

In a 100 ml round-bottomed flask equipped with an ice-water

cooled condenser were placed all the silver salt, 5.88 g of methyl

iodide, and 60 ml of dry ether. The solution was refluxed for 3

hours. The filtrate was fractionally distilled to give the product,

1.0 g (17.5%); b.p. 50* at 20 mm Hg.








Procedure B. In a 250 ml round-bottomed flask were placed 66.5

g (0.678 mole) of 2,4-pentadienoic acid, 110 ml of methanol, and 1.35

g of concentrated sulfuric acid. The mixture was allowed to stand

overnight, and was then refluxed for 3 hours. The mixture was

treated with water and extracted with ether. The extract was dried

over anhydrous sodium sulfate. Finally, the ether was removed and

the ester was purified by fractional distillation, 24.7 g (32.5%)

(lit. rep. 70%); b.p. 50-52* at 20 mm Hg.

1H NMR (60 MHz, CDC13); 6 3.76 (s, 3H), 5.40-7.56 (m, 5H).

13C NMR (CDC13): 6 51.13, 121.55, 125.15, 134.51, 144.50,

166.77.

IR (neat): 3088 (w), 3050 (w), 3000 (m), 2950 (m), 2900 (w),

2840 (w), 1850 (w, br), 1716 (s), 1642 (s), 1600 (s), 1490 (w), 1435

(s), 1417 (m), 1370 (w, br), 1310 (s), 1268 (s), 1205 (s), 1146 (s),

1035 (m), 1008 (s), 961 (m), 928 (m), 868 (m), 742 (w), 720 (m), 705

(w) cm-1.

l-Cyano-1,3-butadiene (11)38,40

Procedure A.


OCO2H + C1SO2NCO-4 -C- NHSO2C1
-CO
2 0



N

CH3


CN + SO3 + HC1









In a 300 ml three-necked round-bottomed flask equipped with a

mechanical stirrer, a thermometer, and an addition funnel were placed

25.0 g (0.255 mole) of 2,4-pentadienoic acid and 100 ml of

dichloromethane. The solution was stirred and cooled to 0 after

which 30 g of chlorosulfonylisocyanate was added dropwise through the

addition funnel with the temperature being kept below 20. The

intermediate separated overnight as pale brown crystals which were

removed and dried under vacuum, 18.7 g (75.0%).

In a 25 ml three-necked round-bottomed flask equipped with a

teflon-sealed mechanical stirrer, a micro short-path distillation

apparatus, and an addition funnel was placed 17.0 g of the

intermediate. N-Methyl pyrrolidone was added to these crystals under

vacuum, at such a rate that the heat of reaction was just sufficient

to maintain the mixture at the boiling point of the product. Since

the rate of addition was too high, most of the monomer polymerized in

the reaction vessel. The yield of the product was only 0.2 g (2.9%);

b.p. 57-58* at 32 mm Hg.

Procedure B.



0

0 H20 0
1 21
CH3 CH = CH CHO + C C1 + KCN--- CH3 CH = CH CH
CN

5750
CN









Pyrolysis of crotonaldehyde cyanohydrine benzoate at 575 1 10",

was conducted by dropping the ester at a rate of one drop per 1.4

second through a vertical 2.4 cm diameter, 31 cm length quartz tube

packed with a ceramic beads. To minimize dimerization of the trans-

l-cyano-l,3-butadiene, the volatile components of the pyrolysate were

distilled at 1 mm Hg in a distillation apparatus with a dry ice

condenser with the receiver immersed in a dry ice-acetone cooling

bath. Utilizing 56.5 g of the ester, the yield of the crude mixed

dienes was 12.7 g (57.2%); b.p. 57-60" at 32 mm Hg (lit. rep. 70%).

1H NMR (60 MHz, CDC13): 6 5.27-7.33 (m, 5H).

13C NMR (CDC13): 6 99.42, 117.35, 126.27, 133.73, 150.20

(trans-isomer).

13C NMR (CDC13); 6 97.95, 115.70, 126.42, 132.41, 149.23 (cis-

isomer).

IR (neat): 3220 (w), 3092 (w), 3048 (w), 3010 (w), 2218 (m),

1860 (w, br), 1622 (m), 1588 (m), 1418 (w), 1290 (w), 1258 (w), 1002

(m), 955 (m), 930 (m), 832 (m) cm-1 (trans-isomer only).

IR (neat): 3220 (w), 3092 (w), 3048 (w), 3010 (w), 2218 (m),

1860 (w, br), 1622 (m), 1588 (m), 1572 (m), 1428 (w), 1418 (w), 1358

(w), 1290 (w), 1258 (w), 1228 (w), 1002 (m), 955 (m), 930 (m), 832

(m), 774 (m), 665 (m) cm-1 (mixture of both isomers).

Crotonaldehyde Cyanohydrin Benzoate (12)40

In a 1000 ml three-necked round-bottomed flask equipped with a

thermometer, an addition funnel, and a magnetic stirring bar were

placed 50 g of crotonaldehyde and 150 ml of benzene. The solution

was cooled to -10* in an ice-salt bath. To the solution was slowly








added 100 g of benzoyl chloride, then added dropwise was 61.9 g of

potassium cyanide while the reaction mixture was kept at the same

temperature. After the cyanide had been added the mixture was

stirred for 2 hours at -10" and then was allowed to warm to room

temperature. The organic layer was separated, washed with two 25 ml

portions of 5% sodium carbonate solution, and dried over anhydrous

magnesium sulfate. After distillation of the benzene, the residue

was fractionated through a Vigreux column. The product was

collected, 110.9 g (77.3%); b.p. 123-125" at 1 mm Hg.
1H NMR (60 MHz, CDC13): 6 1.84 (d, 3H, J = 6.0 Hz), 5.44-6.62

(m, 3H), 7.24-7.71 (m, 3H), 7.93-8.20 (m, 2H).

13C NMR (CDC13): 6 17.50, 61.75, 115.65, 121.30, 128.17,

128.42, 129.78, 133.78, 135.53, 164.39.

IR (neat): 3060 (w), 3038 (w), 2972 (w), 2942 (m), 2920 (m),

2858 (w), 1730 (s), 1670 (m), 1598 (m), 1572 (m), 1490 (w), 1450 (s),

1379 (m), 1316 (s), 1300 (s), 1255 (s), 1178 (s), 1142 (m), 1088 (s),

1065 (s), 1023 (s), 962 (s), 930 (m), 802 (w), 710 (s), 682 (m) cm-1.

l-Carbethoxy-l-cyano-1,3-butadiene (13)41

In a 300 ml round-bottomed flask equipped with a magnetic

stirring bar and an addition funnel were placed 25.0 g of zinc

chloride, 100 ml of dioxane, and 33.9 g (0.30 mole) of ethyl

cyanoacetate. To the solution was added dropwise 25 ml (0.375 mole)

of acrolein at room temperature. After 3 hours, the reaction

solution was diluted with 250 ml petroleum ether, extracted three

times with 500 ml portions of cold dilute hydrochloric acid, then








dried and concentrated. The product was collected, 28.2 g (62.3%),

m.p. 37-380 (lit. rep. 68%, m.p. 39-40").

1H NMR (60 MHz, CDC13): 6 1.37 (t, 3H, J = 7.2 Hz), 4.35 (q,

2H, J = 7.2 Hz), 6.07 (m, 2H), 6.97 (m, 1H), 7.86 (d, 1H, J = 5.5

Hz).

13C NMR (CDC13): 6 13.79, 62.18, 106.73, 113.36, 131.68,

133.83, 154.93, 161.36.

IR (thin film): 3049 (m), 2262 (m), 1946 (w), 1709 (s), 1629

(s), 1592 (s), 1473 (m), 1443 (m), 1428 (w), 1401 (w), 1374 (m), 1348

(m), 1321 (m), 1297 (s), 1250 (s), 1188 (m), 1068 (s), 1015 (m), 993

(m), 960 (m), 859 (w), 833 (w), 761 (m), 733 (w) cm-1.

1,3-Butadienyl trimethyl ammonium chloride (14)42

In a 450 ml autoclave were placed 24.7 g of trimethylamine, 18.9

g of trans-1,4-dichloro-2-butene, and 180 ml of benzene. The

solution was heated to 100" for one hour in the closed system. After

the given reaction time, the solution was cooled to room

temperature. The product was filtered, washed, then dried in a

vacuum oven at 50* to yield 25.9 g, 1,4-bis(trimethylammonium)-2-

butene chloride. This salt was added with 52 ml 10% NaOH and 105 ml

water, then the mixture was distilled until the condensate was

neutral. The residual solution was neutralized with 10% hydrochloric

acid, decolorized, filtered, and evaporated in a rotatory evaporator

under reduced pressure. The residue was extracted with chloroform.

The extract was dried over anhydrous sodium sulfate. Finally, the

chloroform was removed and product was obtained 3.54 g (15.9%).








1H NMR (60 MHz, CDC13): 6 3.67 (s, 9H), 5.37-7.45 (m, 5H).
1C NMR (CDC13): 6 53.95, 123.84, 125.79, 129.05, 137.04.


Copolymer Synthesis

All copolymers were synthesized by roughly the same method.

Azobisisobutyronitrile (AIBN) was used as the initiator in the

organic phase reactions; azobis(2-amidinopropane)hydrochloride (V-50)

was used as the initiator in the aqueous phase reactions.

Pyrex polymerization tubes were charged with the prescribed

quantities of freshly purified monomers, initiators, and solvents.

The tubes were connected to a high vacuum line, degassed by several

freeze-pump-thaw cycles, and sealed off under vacuum.

The monomers were polymerized by heating the sealed tubes at the

prescribed temperature in a shaking water bath for a fixed period.

At the end of the reaction time, the tubes were removed from the

bath, cooled to -78* in a dry ice-isopropanol cooling bath in order

to stop the reaction, and opened. The solution was then slowly added

to a large excess of rapidly stirred precipitation solvent (petroleum

ether was used unless otherwise noted). The polymers were purified

by dissolving them in acetone and then precipitating from petroleum

ether. After having been dried overnight in vacuum, the copolymers

were weighed and analyzed.

The copolymerization conditions, yields and analysis data for

the polymerizations of both diene-dienophile and diene-diene systems

are shown in Tables 1-11.








TABLE 1

Conditions for the Polymerizations of Methyl 2,4-Pentadienoate
(MPD) with Electron-Rich Dienophiles


b d
Sample Electro-richa TX102 fAc mAIBMX104 Vol.e Time Temp.
No. dienophile (ml) (Hr.) (0C)


1 DOE 1.33 0.504 1.04(0.77%) 4 63 50
2 BVE 5.90 0.502 1.47(0.25%) 5 66 60
3 BVE 1.52 0.499 4 68 60
4 CEVE 1.11 0.495 0.43(0.39%) 2 64 50
5 1.64 1.000 0.82(0.50%) 3 66 60


aAbbreviations used:
AN, acrylonitrile
ATBD, 1-acetoxy-1,3-butadiene
BTAC, 1,3-butadienyl trimethyl ammonium chloride
BVE, n-butyl vinyl ether
CBD, 1-cyano-1,3-butadiene
CCB, 1-carbethoxy-l-cyano-1,3-butadiene
CEVE, 2-chloroethyl vinyl ether
DABD, 1-diethylamino-1,3-butadiene
DEM, diethyl muconate
DHP, 2,3-dihydropyran
DOE, 1,4-dioxene
EA, ethyl acrylate
EBD, 1-ethoxy-1,3-butadiene
ECA, ethyl a-cyanoacrylate
ESB, ethyl sorbate
EVE, ethyl vinyl ether
FN, fumaronitrile
KEA, ketene, diethylacetal
KMA, ketene, dimethylacetal
MPD, methyl 2,4-pentadienoate
PA, potassium acrylate
PPD, potassium 2,4-pentadienoate
TSBO, 1-trimethylsilyloxy-1,3-butadiene
TVAB, trimethyl vinyl ammonium bromide
bTotal moles of monomers.

CMole fraction of acceptor in the initial feed.

dMoles of AIBN (mole % AIBN based on mT).


eVolume of benzene that was polymerized.












TABLE 2

Yields and Analysis Data for Polymers in Table 1


Sample Yield Analysis [n]
No. Grams % C, % H, % dl/g


1 0.150 20.0

2 1.698 51.3 64.03 7.30

3 0 0

4 0.222 35.9

5 0.802 43.6 0.24a


alntrinsic viscosity was measured in tetrahydrofuran at 25C.


















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TABLE 4

Data for Polymers in Table 3


Sample Yield Analysis 1n]
No. Grams % C, % H, % N, % dl/g


6 0.54 74.9

7 2.21 81.5 63.66 6.19 9.06 0.38a

8 1.24 87.9

9 0.50 26.5

10 0.74 76.1

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12 0.36 19.7 63.72 6.23 9.11

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14 1.48 73.6

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16 0.52 77.3

17 0.67 86.4


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TABLE 5

Conditions for the Copolymerizations of Acrylonitrile (AN)
with Electron-Rich Dienes


b d
Sample Electro-richa TX102 fA mAIBMX104 Vol.e Time Temp.
No. diene (ml) (Hr.) (C)


18 EBD 2.75 0.500 0.99(0.30%) 4 71 60

19 DABD 1.46 0.500 1.40(0.96%) 5 65 60

20 ATBD 3.08 0.500 0.66(0.22%) 4 67 60

21 TSBD 2.99 0.499 0.60(0.20%) 4 67 60

22 EBD 4.25 0.502 8 70 60

23 DABD 3.66 0.500 4 69 60

24 ATBD 1.82 0.503 4 67 60

25 TSBD 1.49 0.502 4 67 60


a-eSee Table 1 for footnote descriptions.













Yields and Ana


TABLE 6

lysis Data for Copolymers


in Table 5


Yield Analysis
Sample [n]
No. Grams % C, % H, % N, % FAa dl/g


18 0.95 37.9 71.6 8.7 9.2 0.498 0.155b

19 0.10 7.7 73.9 10.2 15.5 0.485 0.459C

20 1.00 39.3 64.3 7.0 6.4 0.405 0.347c

21 0.70 24.0 61.4 9.0 6.9 0.488 0.254b

22 0.40 12.5 70.6 8.6 8.7 0.477

23 0 0

24 0.20 13.3 64.8 6.8 6.1 0.391

25 0.10 6.9


aMole fraction of acceptor in the
of elemental analysis.

bIntrinsic viscosity was measured

CIntrinsic viscosity was measured


copolymer calculated from results


in toluene at 25*C.

in tetrahydrofuran at 25*C.




















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TABLE 8

Yields and Analysis Data for Copolymers in Table 7


Yield Analysis
Sample [n]
No. Grams % C, % H, % N, % FAa dl/g


0.24

0.10

0.04

1.30

0.70

0.60

0.30

0.49

0.60

0.37

0.79

0

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7.8


0.648

0.694


0.84b

1. 03b


0.873

0.769

0.621

0.819


aMole fraction of acceptor in the copolymer calculated from results
of elemental analysis.

bIntrinsic viscosity was measured in tetrahydrofuran at 250C.

CIntrinsic viscosity was measured in toluene at 25*C.



















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TABLE 10

Yields and Analysis Data for Polymers in Table 9


FAa
Sample Yields Analysis
No. Grams % C, % H, % N, % mole-%


41 0.63 28.3

42 0.12 15.2

43 0

44 0

45 0

46 0

47 0

48 0.22 10.0 58.4 6.0 10.2 88.3

49 1.24 67.5 67.5 6.9 15.6 49.3

50 0

51 0

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aMole fraction of acceptor in the copolymer calculated from the
results of elemental analysis.








Copolymerizations in Aqueous Phase

Acetone was used as precipitation solvent for those

copolymerizations which were carried out in aqueous phase. The

conditions and results of polymerizations of water-soluble monomers

are shown in Table 11.








TABLE 11

Conditions and Results of Polymerizations
of Water-Soluble Monomers



Sample Acceptora Donora mTXlO2b fAc mV-50XO4d Vole Time Yield
No. (ml) (Hr.) (%)


53 TVAB PA 0.848 0.494 0.57(0.49%) 2 20 48.8

54 TVAB PA 0.627 0.493 0.30(0.47%) 3 22 60.8

55 TVAB PPD 1.426 0.500 0.63(0.44%) 4 22 67.7

56 BTAC PA 0.163 0.500 0.08(0.50%) 2 40 0

a-cSee Table 1 for footnote descriptions.

dMoles of V-50 (mole % V-50 based on mT).

eVolume of water that was polymerized.








Monomer Reactivity Ratios

In order to determine the monomer reactivity ratios of

acrylonitrile and 1-ethoxy-1,3-butadiene, radial copolymerizations

were carried out at 60C with the use of AIBN as initiator; total

monomer and initiator concentrations were kept constant at 5.5 M and

1.30X10-2 M, respectively (Table 12).




TABLE 12

Conditions, Yields and Analysis Data for the Copolymerizations
of Acrylonitrile (AN) with 1-Ethoxy-1,3-butadiene (EBD)


EBD Copolymer Produced
in feed Time Yield Analysis EBD
(mole-%) (Hr.) % C, % H, % N, % (mole-%)


9.0 20 86.3 68.1 6.4 20.9 12.6

16.7 62 76.1 68.5 6.7 20.0 14.9

27.7 13 21.4

27.7 4 7.3 9.4 49.6

37.6 16 19.2

37.9 7 10.0 9.2 50.2

50.3 32 18.2 71.5 8.7 9.1 50.6

63.1 40 10.4 8.6 52.7

73.3 52 9.4 8.3 54.0

83.5 90 5.6 71.1 8.8 7.5 57.5








In order to determine the monomer reactivity ratios of

acrylonitrile and l-diethylamino-1,3-butadiene, radical

copolymerizations were carried out at 60*C with the use of AIBN as

initiator; total monomer and initiator concentrations were kept

constant at 5.8 M and 1.4X10-2 M, respectively (Table 13).


TABLE 13

Conditions, Yields and Analysis Data for the Copolymerizations
of Acrylonitrile (AN) with l-Diethylamino-1,3-butadiene (DABD)


DABD Copolymer Produced
in feed Time Yield Analysis DABD
(mole-%) (Hr.) % C, % H, % N, % (mole-%)


23.3 9 6.1 72.1 9.0 18.3 32.4

27.9 15 6.0 71.7 9.0 18.2 33.0

34.3 20 5.9 72.6 9.2 17.8 35.9

41.2 22 5.3 71.9 9.8 16.6 43.5

49.9 45 7.4 73.4 10.0 15.7 50.2

59.0 62 2.7 73.1 10.6 15.1 55.6

68.5 72 0

75.2 146 0








Copolymer Characterization

The resulting polymers were analyzed by IR, 1H NMR and 13C NMR

methods.

NMR Techniques

Since the greater spectral simplicity resulting from the lacking

of coupling and greater spectral width, the 13C NMR technique has

been regarded as a more powerful tool than the 1H NMR technique in

analyses of copolymers.

The Jeol-FX-100 instrument has been used for taking the 13C NMR

spectra of the resulting copolymers. However, this instrument has

limited space in the computer memory system for data storage; the

computer word length would overflow before an adequate signal-to-

noise ratio was attained. This problem was overcome by using the

frequency domain (or block) averaging technique.43 According to this

method, the free induction decay is averaged for a certain number of

scans such that Fourier transformed, phase corrected, stored in a

separate area of memory, and acquisition repeated after zeroing the

data area. After a second block of data is Fourier transformed, this

is added to the first result and the process is repeated until a

sufficient signal-to-noise ratio is obtained.

The INEPT (Insensitive Nuclei Enhanced by Polarization Transfer)

technique provides an alternative to the off-resonance experiment for

assignment of quaternary, methine, methylene and methyl carbons.

This approach was proposed by Ernst44 and Doddrell,45 respectively.

It overcomes two of the disadvantages of the off-resonance

experiment, i.e., overlap of resonance lines and decreased








sensitivity. In the case of delay time (A) is 1/4J, all of the

protonated carbons exhibit a positive signal intensity in the

spectrum, while at A = 2/4J, only methine carbons show maximum

intensity with methyl and methylene carbons at minimum intensity and

A = 3/4J, methyl and methine carbons show positive intensity with

methylene carbons 180" out of phase.

IR Spectroscopy

IR spectra were obtained either by using the KBr pellet

technique or by coating a thin film on KBr plates. The abbreviations

used below for the various monomer and comonomer pairs used to

synthesize the polymers are the same as those used in Tables 1-11.

MPD-CEVE, 2983 (m), 2940 (m), 2907 (w), 2838 (w), 1730 (s), 1650

(m), 1430 (m), 1360 (m), 1330 (m), 1308 (m), 1262 (m), 1220

(m), 1190 (m), 1156 (s), 1020 (m), 964 (s), 910 (w), 850

(w), 722 (w) cm-1

MPD, 2988 (m), 2942 (m), 2840 (m), 1725 (s), 1650 (m), 1432 (s),

1355 (m), 1330 (m), 1310 (m), 1262 (s), 1220 (m), 968 (s),

912 (m), 850 (w), 730 (s), 640 (w) cm1.

CCB, 2980 (m), 2930 (m), 2866 (w), 2226 (w), 1733 (s), 1622 (m),

1464 (m), 1442 (m), 1390 (m), 1368 (m), 1250 (s), 1156 (m),

1090 (m), 1070 (m), 1015 (m), 970 (m), 890 (w), 852 (m), 760

(m) cm-.

CCB-CEVE, 2979 (m), 2938 (m), 2900 (w), 2864 (w), 2350 (w), 2320

(w), 2241 (w), 2198 (w), 1738 (s), 1624 (m), 1465 (m), 1442

(m), 1388 (m), 1368 (m), 1295 (m), 1235 (s), 1158 (m), 1092







(m), 1019 (m), 968 (m), 912 (m), 854 (m), 760 (w), 730 (m),
668 (w), 645 (w) cm-1.
CCB-BVE, 2979 (m), 2938 (m), 2902 (m), 2866 (m), 2242 (m), 2198

(w), 1735 (s), 1722 (m), 1622 (m), 1463 (m), 1442 (m), 1388
(m), 1368 (m), 1297 (m), 1235 (s), 1158 (m), 1092 (m), 1019
(m), 968 (m), 912 (m), 853 (m), 760 (w), 730 (m), 668 (w),
645 (w), 620 (w) cm-1.
AN-EBD, 2978 (m), 2924 (m), 2868 (m), 2238 (m), 1648 (m), 1478 (w),
1442 (m), 1380 (m), 1348 (w), 1302 (m), 1245 (w), 1216 (w),
1168 (m), 1104 (s), 1040 (w), 972 (m), 938 (w), 850 (w), 806

(w), 754 (w), 729 (w) cm-1.
AN-DABD, 3044 (w), 2962 (m), 2924 (m), 2862 (m), 2232 (m), 1722

(w), 1646 (s), 1448 (m), 1400 (m), 1374 (m), 1345 (m), 1295
(m), 1250 (m), 1214 (m), 1180 (m), 1169 (m), 1098 (m), 990

(w), 940 (m), 915 (w), 810 (w), 778 (m), 730 (m) cm-1.
AN-ATBD, 3018 (m), 2926 (m), 2850 (w), 2238 (m), 1735 (s), 1670

(m), 1432 (m), 1370 (s), 1230 (s), 1085 (m), 1040 (m), 1020
(s), 970 (s), 936 (m), 754 (m), 662 (w) cm-1.
AN-TSBD, 3100 (w), 2952 (m), 2857 (w), 2237 (w), 1651 (m), 1448

(m), 1406 (m), 1365 (w), 1251 (s), 1210 (m), 1165 (m), 1122
(m), 1075 (s), 970 (m), 930 (m), 850 (s), 751 (m), 688 (w),
642 (w) cm-1.
CBD (mixtures of trans and cis isomers)-ATBD, 3020 (w), 2921 (m),
2859 (w), 2241 (m), 2221 (m), 1732 (s), 1673 (w), 1632 (w),
1438 (m), 1372 (m), 1237 (s), 1045 (m), 1020 (m), 969 (s),

913 (m), 758 (m), 731 (m), 645 (w) cm-1.







CBD (trans isomer only)-ATBD, 3020 (w), 2920 (m), 2855 (w), 2239

(m), 2219 (m), 1732 (s), 1670 (m), 1629 (w), 1435 (m), 1370

(m), 1239 (s), 1038 (m), 968 (m), 759 (w) cm-.

CBD-EBD, 3040 (w), 2979 (m), 2928 (m), 2240 (w), 2221 (w), 1669

(w), 1649 (m), 1441 (m), 1372 (w), 1304 (w), 1204 (w), 1162

(m), 1104 (m), 1085 (m), 970 (s), 937 (w), 915 (w), 853 (w),

805 (w), 750 (w), 730 (m) cm-1.

MPD-ATBD, 3000 (m), 2952 (m), 2842 (w), 1730 (s), 1652 (m), 1436

(s), 1372 (m), 1235 (s), 1160 (s), 1021 (m), 970 (s), 915

(m), 852 (w), 731 (m), 647 (w) cm1.

MPD-EBD, 3010 (w), 2962 (m), 2942 (m), 2840 (w), 1730 (s), 1646

(m), 1432 (m), 1355 (w), 1260 (m), 1218 (m), 1189 (m), 1155

(s), 1100 (m), 1076 (m), 1020 (m), 965 (s), 930 (w), 848

(w), 742 (w) cm-1.

CCB-ATBD, 2980 (m), 2938 (m), 2845 (w), 2350 (w), 2228 (w), 1736

(s), 1670 (w), 1645 (w), 1622 (m), 1465 (m), 1442 (m), 1335

(m), 1270 (m), 1233 (s), 1154 (w), 1092 (m), 1020 (m), 968

(m), 935 (w), 916 (w), 854 (w), 762 (w), 728 (m), 645 (w)

cm1.

ESB-ATBD, 2973 (m), 2928 (m), 2340 (w), 1732 (s), 1695 (m), 1670

(m), 1650 (w), 1434 (m), 1370 (m), 1234 (s), 1172 (m), 1155

(m), 1090 (m), 1020 (m), 969 (m), 934 (w), 852 (w), 762 (w)
-1
cm
CCB-EBD, 2978 (m), 2928 (m), 2898 (w), 2862 (w), 2223 (w), 1736

(s), 1620 (m), 1462 (m), 1442 (m), 1386 (m), 1366 (m), 1240







(s), 1156 (m), 1090 (m), 1019 (m), 969 (m), 910 (w), 852

(m), 760 (m), 728 (w), 645 (w) cm-1.

CBD-BVE, 3041 (w), 2980 (w), 2920 (m), 2848 (w), 2238 (w), 2220

(m), 1628 (w), 1438 (m), 1355 (w), 1080 (w), 969 (s), 912

(m), 753 (w), 728 (m), 643 (w) cm-1.
FN-EBD, 2979 (m), 2938 (m), 2880 (m), 2242 (m), 1669 (m), 1648 (m),

1480 (w), 1442 (m), 1398 (w), 1373 (m), 1330 (w, br), 1178

(m), 1105 (s), 1018 (w), 979 (m), 945 (w), 885 (w), 848 (w),

810 (w) cm-1.

ECA-EBD, 2978 (m), 2930 (m), 2900 (m), 2862 (w), 2239 (w), 1745

(s), 1660 (w), 1465 (m), 1438 (m), 1380 (m), 1365 (m), 1250
(s), 1158 (m), 1100 (m), 1008 (m), 850 (m), 740 (w) cm-1.

Several Diels-Alder adducts have been isolated from the

copolymerizations of electron-rich dienes with electron-poor

dienophiles. The spectral data of these compounds are shown below.

4-Cyano-3-ethoxycyclohexene

1H NMR (60 MHz, CDC13): 6 1.22 (t, 3H, J=7.2 Hz), 2.70 (m, 4H),

2.82 (m, 1H), 3.63 (q, 2H, J=7.2 Hz), 4.00 (m, 1H), 5.53-6.10 (t,

2H).
13C NMR (CDC13): 6 15.16 (t), 22.03 (t), 22.41 (t), 22.71 (t),

23.00 (t), 30.75 (d), 30.89 (d), 64.77 (t), 64.86 (t), 73.25 (d),

119.50 (s), 120.52 (s), 125.15 (d), 125.69 (d), 129.39 (d), 129.83

(d).

IR (neat): 3028 (m), 2968 (s), 2938 (s), 2882 (s), 2238 (m),
1742 (m), 1685 (w), 1648 (m), 1618 (w), 1480 (m), 1445 (m), 1432 (m),

1389 (m), 1369 (m), 1324 (m), 1290 (m), 1270 (m), 1227 (w), 1171 (m),








1090 (s), 1058 (m), 1020 (m), 980 (m), 940 (w), 915 (m), 890 (m), 868

(m), 835 (w), 814 (w), 795 (w), 768 (w), 756 (w), 722 (m), 679 (m),

652 (m) cm-1.

4-Cyano-3-diethylaminocyclohexene

1H NMR (60 MHz, CDC13): 6 1.07 (t, 6H, J=7.2 Hz), 2.09 (m, 4H),

2.60 (m, 5H), 3.60 (m, 1H), 5.46-6.10 (m, 2H).
13C NMR (CDC13): 6 14.13, 14.28, 21.88, 23.49, 24.56, 25.53,

29.53, 30.26, 43.96, 44.40, 57.26, 54.48 120.91, 122.08, 126.57,

127.05, 128.52, 128.86.

IR (neat): 3022 (m), 2962 (s), 2928 (s), 2864 (m), 2840 (m),

2238 (m), 1642 (m), 1463 (m), 1449 (m), 1431 (m), 1379 (m), 1335 (m),

1300 (m), 1285 (m), 1262 (m), 1204 (m), 1180 (m), 1144 (m), 1110 (m),

1062 (s), 1032 (m), 980 (w), 959 (w), 931 (w), 902 (w), 870 (w),778

(w), 764 (w),720 (m), 668 (m) cm-1.

4-Carbethoxy-3-diethylaminocyclohexene

1H NMR (60 MHz, CDC13): 6 0.95 (t, 3H, J=7.2 Hz), 0.98 (t, 3H,

J=7.2 Hz), 1.25 (t, 3H, J=7.2 Hz), 1.98 (m, 4H), 2.53 (m, 5H), 3.63

(m, 1H), 4.13 (q, 2H, J=7.2 Hz), 5.45-6.08 (m, 2H).

IR (neat): 3018 (m), 2964 (s), 2928 (s), 2900 (s), 2865 (m),

2810 (m), 2718 (m), 1732 (s), 1674 (m), 1643 (m), 1463 (m), 1447 (m),

1370 (s), 1335 (m), 1298 (s), 1259 (m), 1220 (s), 1202 (s), 1160 (s),
1100 (m), 1055 (s), 1035 (s), 978 (m), 962 (m), 932 (s), 910 (s), 882

(m), 863 (m), 842 (s), 794 (m), 766 (w), 752 (w), 732 (m), 689 (m),

645 (w) cm-.








4-Cyano-4-carbethoxy-3-ethoxycyclohexene

1H NMR (60 MHz, CDC13): 6 1.12 (t, 3H, J=7.2 Hz), 1.33 (t, 3H,

J=7.2 Hz), 2.23 (m, 4H), 3.58 (m, 2H), 4.30 (m, 4H), 5.73-6.27 (m,

2H).

13C NMR (CDC13): 6 13.69 (q), 15.06 (q), 21.93 (t), 22.08 (t),

22.32 (t), 28.94 (t), 46.49 (s), 49.47 (s), 62.04 (t), 62.53 (t),

65.25 (t), 65.45 (t), 72.96 (d), 116.38 (s), 117.69 (s), 122.62 (d),

125.49 (d), 127.69 (d), 131.63 (d), 166.04 (s), 168.43 (s).

IR (neat): 3038 (w), 2978 (s), 2937 (m), 2898 (m), 2240 (w),

1750 (s), 1648 (w), 1464 (m), 1442 (m), 1431 (m), 1391 (m), 1368 (m),

1329 (m), 1312 (m), 1294 (m), 1240 (s), 1200 (s), 1170 (m), 1090 (s),

1062 (s), 1048 (s), 1020 (m), 969 (m), 934 (w), 880 (m), 853 (m), 803

(w), 769 (w), 733 (m), 721 (m), 632 (w) cm-1.

4-Ethoxy-4,7,8,9-tetrahydro-, 3-i sobenzofurandione

1H NMR (60 MHz, CDC13): 6 0.87 (t, 3H, J=7.2 Hz), 2.05 (m, 1H),

2.50 (m, 3H), 3.13 (q, 2H, J=7.2 Hz), 3.86 (m, 1H), 5.60 (m, 2H).
13C NMR (CDC13): 6 15.08 (q), 21.41 (t), 36.28 (d), 45.78 (d),

64.16 (t), 68.54 (d), 127.03 (d), 131.12 (d), 171.13 (s), 174.34 (s).

Complexation Studies

1H NMR Determination of the Formation Constants

AN-EBD system. The 1H NMR chemical shift variations, A6,

between completed and free states of the 1-ethoxy-1,3-butadiene in

this diene-dienophile system were studied in benzene-d6 solution with

tetramethylsilane as internal reference at 25*C and 60C. The

results are given in Tables 14 and 15, respectively.











CH2 6
3


TABLE 14

1H NMR Data for Determination of Formation Constant of
Complexation of AN-EBD System at 25C


[EBD]o

(mole/l)


[AN]o H(1) H(3) H(5) H(6)
6 obs., A 6 obs., A 6 obs., A 6 obs., A
(mole/1) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz)


0.116 0 642.8 0 608.3 0 334.2 0 93.4 0

0.116 0.975 643.9 1.1 608.3 0 339.7 5.5 96.6 2.8

0.116 2.045 645.3 2.5 608.4 0.1 344.2 10.0 99.2 5.8

0.116 2.949 646.1 3.3 608.3 0 347.4 13.2 101.2 7.8

0.116 4.336 648.6 5.8 608.5 0.2 352.3 18.1 104.0 10.6








TABLE 15

1H NMR Data for Determination of Formation Constant of
Complexation of AN-EBD System at 60C


[EBD]o [AN]o H(1) H(3) H(5) H(6)
6 obs., A 6 obs., 6 obs., A 6 obs., A
(mole/1) (mole/1) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz)


0.116 0 641.7 0 608.1 0 339.7 0 95.8 0

0.116 0.975 642.7 1.0 607.8 -0.3 344.0 4.3 98.4 2.6

0.116 2.045 643.9 2.2 607.8 -0.3 348.4 8.7 101.0 5.2

0.116 2.949 645.1 3.4 607.9 -0.2 351.8 12.1 103.1 7.3

0.116 4.336 647.0 5.3 356.0 16.3 105.6 9.8


AN-DABD system. The 1H NMR chemical shift variations, A6,

between completed and free states of the 1-diethylamino-l,3-butadiene

in this diene-dienophile system were studied in benzene-d6 solution

with tetramethylsilane as internal reference at 25"C. The results

are given in Table 16.


3 1
CH2 6

2
CH
3CH








TABLE 16

1H NMR Data for Determination of Formation Constant of
Complexation of AN-DABD System at 25C


[DABD]o [AN]o H(1) H(5) H(6)
6 obs., A 6 obs., A 6 obs., A
(mole/1) (mole/1) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz)


0.086 0 592.3 0 264.4 0 75.4 0
0.086 0.894 594.2 1.9 268.3 3.9 78.2 2.8
0.086 1.806 595.7 3.4 271.7 7.3 80.3 4.9
0.086 2.843 597.4 5.1 275.4 11.0 83.0 7.6
0.086 4.274 600.1 7.8 280.2 15.8 86.2 10.8


13C NMR Chemical Shift Variations


AN-EBD system. The 13C NMR chemical shifts of free and

completed states of l-ethoxy-1,3-butadiene in AN-EBD system are shown

in Table 17.





TABLE 17

13C NMR Data for the Complexed and Uncomplexed EBD Molecules


[EBD]o [AN]o C(1) C(3) C(4) C(2) C(5) C(6)

(mole/l) (mole/l) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz)


0.116 0 3788.3 3359.8 2783.7 2693.3 1628.8 366.6
0.116 0.975 3789.5 3359.8 2782.4 2693.3 1632.5 366.6
0.116 2.045 3789.5 3359.8 2781.2 2693.3 1633.7 366.6
0.116 2.949 3790.7 3359.8 2781.2 -- 1635.0 366.6
0.116 4.336 3789.5 3359.8 2781.2 -- 1636.2 --







AN-DABD system. The 13C NMR chemical shifts of free and

completed states of l-diethylamino-1,3-butadiene in AN-DABD system

are shown in Table 18.


1C NMR Data for


TABLE 18

the Complexed and Uncomplexed


DABD Molecules


[DABD]o [AN]o C(1) C(3) C(4) C(2) C(5) C(6)

(mole/1) (mole/1) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz)


0.086 0 3539.3 3459.9 2610.3 2499.2 1127.1 326.3
0.086 0.894 3542.9 3461.1 2603.0 2493.1 1127.1 326.4
0.086 1.806 3545.4 3462.4 2598.1 2488.2 1128.4 326.4
0.086 2.843 3546.6 3462.4 2594.4 2484.6 1128.4 326.4
0.086 4.274 3547.8 -- -- 2480.9 1128.4 --


Diels-Alder Reactions with Inverse Electron Demand

This author has studied Diels-Alder reactions with inverse

electron demand. These reactions were carried out in organic

solvents for 2 days with 0.5% by weight of 2,6-Di-t-butyl-4-methyl

phenol as a free radical inhibitor.

The diene-dienophile pairs of these reactions, reaction

conditions and results are shown in Table 19.








TABLE 19

Conditions and Results for Diels-Alder
with Inverse Electron Demand


Reactions


Dienea Dienophilea Solvent Temp. ("C) Result


DEM KEA Toluene 110 No Cycloadduct

DEM KMA Toluene 110 No Cycloadduct

DEM EVE Ether 25 No Cycloadduct

ESB KEA Toluene 110 No Cycloadduct

ESB KMA Toluene 110 No Cycloadduct

ESB EVE Ether 25 No Cycloadduct

CCB KEA Toluene 110 Polymer

CCB KMA Toluene 110 Polymer

CCB DOE Toluene 110 Polymer

CCB EVE Ether 25 Polymer

MPD KEA Toluene 110 No Cycloadduct


aSee Table 1 for footnote description.













CHAPTER III
RESULTS AND DISCUSSION



Those polymerizations carried out in benzene solutions may be

classified into three categories: 1) the polymerizations of

electron-poor dienes with electron-rich dienophiles; 2) the

copolymerizations of electron-rich dienes with electron-poor

dienophiles; 3) the copolymerizations of electron-rich dienes with

electron-poor dienes.



Polymerizations of Electron-Poor Dienes with
Electron-Rich Dienophiles

Polymerization of Methyl 2,4-Pentadienoate

The polymerization and copolymerization of methyl 2,4-

pentadienoate (MPD) were studied in benzene solution with

azobisisobutyronitrile (AIBN) as initiator. The reaction conditions

and results are summarized in Tables 1 and 2.

On the basis of the results of elemental analysis and spectral

data, the resulting polymers are composed of the diene monomer units

only.

The MPD monomer which has two different double bonds, may in

principle form polymers of five different types of microstructure,

i.e., the 1,2; cis-1,4; trans-1,4; cis-3,4; and trans-3,4 types. The

selection of these microstructures should be influenced by the








reaction conditions to be adopted and possible geometrical structures

of the monomers. The five possible types of microstructure are shown

below:


X



x



1,2 cis-3,4 cis-1,4



n


X



trans-3,4 trans-1,4



where X = CO2CH3.

The 1-substituted 1,3-butadiene monomers may consist of two

geometrical structures, i.e., the cis-isomer and the trans-isomer.




x


trans-isomer


cis-isomer








The 1H NMR and 13C NMR spectra of MPD monomer are shown in

Figures 6 and 7, respectively. Because of the steric factor, the

olefinic carbons of these geometrical isomers should appear at

different chemical shifts in the 13C spectra. But in Figure 7, there

are only four peaks corresponding to the olefinic carbons. In the

infrared spectrum, an absorption was seen at 961 cm-1 which is

characteristic of the trans-1,4 structure. Therefore, the MPD

monomer synthesized was proven to have the trans geometrical

structure only.

Microstructure of Poly(Methyl 2,4-Pentadienoate)

Infrared spectroscopy is very useful to distinguish the

microstructure of diene polymers. The most characteristic

vibrational modes of olefins are out-of-plane C-H bending vibrations

between 1000 and 650 cm-1. In the infrared spectra of the resulting

polymers, absorptions were seen at 722, 910 and 968 cm-1 which are

characteristic of cis-1,4, trans-3,4 and trans-1,4 structures,

individually.

The 1H NMR and 13C NMR spectra of the resulting polymers are

shown in Figures 8 and 9, respectively. In Figure 8, the peaks at 6

5.43 and 5.50 are assigned to the olefinic protons of the trans-1,4

structure and the peaks at 6 5.87 and 6.60 are assigned to those of

the trans-3,4 structure. A broad peak at 6 2.33 is attributable to

the methylene protons. The broad peak at 6 3.00 is attributable to

the methine proton, and a peak at 6 3.64 is attributable to the

protons of methyl group. The integration of 'H NMR spectrum shows





63




















0i
(o
LA



















C\






0
E
c\





















a)
4-

0
E

L








to



=
-4


U)






1-






LL

















0



4J



o
4-




0
r-






C
4r-
T"







0 0
dr










S-
4-g





0
_ E


L
+->





N
-r

C0
o


c-,










-4-
u



















00





o 0
CoC

S I-
i-4
s "








co
1-1




































































8


c,


65














0




C-)
4J













C~C
o 0,



C

r_






G,

0,


~Ix







0
a-







4-

0

E
CL
U














CD
coo
















K
0,



LL



















































/



8,


N
8


0















o
\O

So


a






*r-




Cr-
c-











I-




0

C)








4-.
0

E







N
CO




r-






















U
Q)-

















-I


O
- C\J
1-1








that the polymers consist of 90% of trans-1,4 and cis-1,4 structures

and 10% of trans-3,4 structure.

In Figure 9, the peaks at 6 173.45 and 166.29 are assigned to

the carbonyl carbons of the trans-1,4 and the trans-3,4 structures,

individually. The peaks at 6 150.74 and 121.64 are assigned to the

olefinic carbons of the trans-3,4 structure, the peaks at 6 132.32

and 129.39 are assigned to those of the trans-1,4 structure. The

peak at 6 51.46 is attributable to the carbon of the methyl group

(-C02CH3) of the trans-1,4 structure. The peaks at 6 48.73 and 35.23

are assigned to the methine carbon and methylene carbon,

respectively, of the trans-1,4 structure.

On the basis of all spectral results, poly(methyl 2,4-

pentadienoate) obtained with radical initiation was mainly composed

of trans-1,4 units.

The trans-positioned electron clouds of the propagating radical,

conjugated with the allyl group and the carbonyl group in the same

plane seems to be most stable; this could be the reason why trans-1,4

units constitute the main structure of the polymers.




C-?=0O
CH308 G








The MPD is a monomer which was readily polymerized with the use

of the radical initiator. In some cases, the electron donor-acceptor

complex can be activated thermally or photochemically to generate the

free radical necessary for initiation of polymerization. In the

copolymerization of MPD and n-butyl vinyl ether without free radical

initiator added, there was no polymer isolated. This result shows

the donor-acceptor interaction of this monomer pair is probably too

weak to form a reactive intermediate of free radical nature.

Polymerization of l-Carbethoxy-l-cyano-1,3-butadiene

The polymerization and copolymerization of 1-carbethoxy-l-cyano-

1,3-butadiene (CCB) were carried out in benzene solution with and

without AIBN as initiator. The reaction conditions and results are

summarized in Tables 3 and 4.

On the basis of the results of elemental analysis and spectral

data, the resulting polymers are composed of the diene monomer units

only.

The chemical properties of CCB are very similar to ethyl a-cyano

acrylate which is the important component in "super glue." These

monomers have two strong electron-withdrawing groups on one olefinic

carbon, so they are polymerized very easily by anionic initiation.

Therefore, to this polymerization system, about 1% by weight of

benzoic acid was added as anionic inhibitor.

Microstructure of Poly(1-Carbethoxy-l-cyano-1,3-butadiene)

In the region of C-H out-of-plane vibration in the infrared

spectra of the resulting polymers, a strong absorption band at 970

cm-1 ascribable to the trans-1,4 structure was observed.








The H NMR and 1C NMR spectra of the resulting polymers are

shown in Figures 10 and 11, individually. In Figure 10, the peaks at

6 5.66 and 5.88 are assigned to the olefinic protons. The peaks

centered at 6 4.30 correspond to methylene protons (-C02CH2-), and

the peaks centered at 6 1.32 correspond to the protons of methyl

group. A broad peak at 6 2.78 is assigned to the methylene protons

of the polymer backbone.

In Figure 11, the peak at 6 166.09 is assigned to the carbonyl

carbon. The peaks at 6 130.37 and 127.25 are assigned to the

olefinic carbons. The peak at 6 116.23 corresponds to the nitrile

carbon. The peaks at 6 63.60 and 39.75 are assigned to the methylene

carbon (-C02CH2-) and the methylene carbon (-CH2-CH=CH-),

individually. The peak at 6 51.66 is assigned to the quarternary

carbon on the polymer backbone. One peak at 6 13.89 corresponds to

the carbon of the methyl group. Based on the spectral data, it was

found that poly(l-carbethoxy-l-cyano-1,3-butadiene) is composed of

the trans-1,4 microstructure only. This result can be rationalized

by the same explanation given for poly(methyl 2,4-pentadienoate),

i.e., the trans-positioned electron clouds of the propagating

radical, conjugated with the allyl group, the carbonyl group and the

nitrile group in the same plane seems to be most stable.

The CCB is a monomer which is readily polymerized by free

radical or anionic initiation. In Tables 3 and 4, sample 13 shows

that with benzoic acid as anionic inhibitor, CCB could not be poly-

merized thermally in benzene solution without free radical initia-

tion. Sample 14 shows that with benzoic acid as anionic inhibitor,



































-0









_ '-


- U'





71








or-



-o









I
0













0
cJ















o















-\1-
r--



0
cE













r-
0)
fU









r-1

cL
'-
















o


0





,-

'-4
00


O






o






S0
-o








CCB could be polymerized in benzene solution with free radical

initiation. Sample 8 shows that spontaneous polymerization of a 1:1

monomer feed ratio of CCB and n-butyl vinyl ether (BVE) produced a

high yield of poly(CCB). Sample 9 shows that when polymerization

under similar conditions to sample 8, except that a large amount of

benzoic acid was added, the yield of poly(CCB) was much lower than

that of sample 8. Sample 10 shows that when polymerization under

similar conditions to sample 8 except that only a small amount of

benzoic acid was added, the yield of poly(CCB) was similar to that of

sample 8. Sample 11 shows that under similar polymerization

conditions to sample 8, except a large amount of radical inhibitor

was added, the yield of poly(CCB) was zero.

On the basis of these investigations, the interaction of CCB

with electron-rich dienophiles probably forms a reactive intermediate

of free radical nature to initiate polymerization.

Polymerization of l-Cyano-1,3-butadiene

The polymerization and copolymerization of 1-cyano-l,3-butadiene

(CBD) were studied in benzene solution with AIBN as initiator. The

reaction conditions and results are shown in Tables 9 and 10.

The mixture of cis and trans CBD isomers was used for these

polymerizations. On the basis of spectral data, the resulting

polymers were composed of the diene monomer units exclusively.

In the infrared spectra of the resulting polymers, two

absorption bands in the nitrile group stretching region were
-1
observed: an absorption at 2238 cm- which may be due to the nitrile

group attached to a saturated carbon atom, and one at 2220 cm1








possible originated by a nitrile group attached to an unsaturated

carbon atom.

Mechanism of Polymerization of Electron-Poor Dienes and
Electron-Rich Dienophiles

Frontier orbital theory has successfully explained many free

radical reactions. For a radical, the frontier orbital is the

singlet occupied molecular orbital (SOMO). This orbital interacts

with both the HOMO and LUMO of the closed shell substrates and the

perturbation energy is in inverse ratio to the energy difference

between frontier orbitals.

Radicals with a higher energy SOMO (nucleophilic radicals)

should react fast with substrates with a low energy LUMO, and

radicals with lower energy SOMO (electrophilic radicals) should react

fast with substrates with a high energy HOMO. Figure 1246 shows the

frontier orbital energies and coefficients for 1-substituted

dienophile donors and 1-substituted diene acceptors.

3.0 T D


-0.5





E(ev) D |
-9.0 HMO -9.5
HMO f-9.5
SHCMO4 --H



Figure 12. Frontier Orbital Energies and Coefficients for
1-Substituted Dienophile Donors and 1-Substituted Diene
Acceptors.









The SOMO-LUMO interaction is always stabilizing, but the SOMO-

HOMO interaction (two orbitals, three electrons) is not always

stabilizing. Bernardi et al.47 have shown this phenomena by

inclusion of overlap in the theoretical analysis. Their method may

lead to a better understanding of the nature of the two orbitals-

three electrons interaction.

For the polymerization system of electron-poor dienes and

electron-rich dienophiles, the difference of HOMO energies between

diene and dienophile is only 0.5 ev (shown in Fig. 12). So the SOMO-

HOMO interaction may not be a decisive factor to these reactions. On

the other hand, the difference of LUMO energies between them is 3.5

ev, and also this interaction is always stabilizing. The interaction

of SOMO-LUMO should play a more significant role than that of SOMO-

HOMO.

Not only the energies of the frontier orbitals but also the

coefficients of the corresponding atomic orbitals are of importance

in the interaction. In Figure 12, for 1-substituted electron-rich

dienophile, the substituted LUMO coefficient is larger than the

unsubstituted LUMO coefficient. With the consideration of orbital

overlap factor, a free radical would attack at the substituted

position of this type monomer. However, another factor, the steric

a-effect, should destabilize this interaction. For a 1-substituted

electron-poor diene, the unsubstituted LUMO coefficient is larger,

and free radical attack at this position would not cause steric

repulsion. Based on these factors, we can successfully explain why

the resulting polymers are composed of diene monomer only.








Copolymerizations of Electron-Rich Dienes with
Electron-Poor Dienophiles

Copolymerization of l-Ethoxy-1,3-butadiene and Acrylonitrile

The copolymerizations of l-ethoxy-l,3-butadiene (EBD) with

acrylonitrile (AN) were carried out by free radical or spontaneous

initiation in benzene at 60. In addition to the resulting

copolymers, an appreciable amount of Diels-Alder adducts were formed

as by-product. The reaction conditions and results are shown in

Tables 5, 6, 9 and 10.

A structural study of AN-EBD copolymer was undertaken to confirm

its alternating nature and to determine its microstructure.

Monomer Reactivity Ratio of EBD and AN

In order to determine the monomer reactivity ratios of EBD and

AN, the copolymerizations were performed by radical initiation with

various monomer feed ratios in benzene at 60", where the

concentrations of the total monomer and free radical initiator (AIBN)

were kept constant at 5.5 M and 1.3X10-2 M, respectively.

The compositions of the resulting copolymers with low conversion

(about 10%) were determined by elemental analysis. The results and

conditions are shown in Table 12. It was found that the copolymers

have a highly alternating structure, even with varying feed ratios of

monomers, as judged on the basis of nitrogen analysis and NMR

measurement.

Figure 13 shows the EBD content of copolymers obtained in the

presence of the AIBN initiator system gives an almost constant value

of 49-57% irrespective of a wide range of variations of monomer feed

ratios.









100

















0
o





S
0
0





o 50 100

EBD in Monomer(mole-%)





Figure 13. Monomer Feed--Copolymer Composition Curve for
Copolymerization System of EBD and AN.



The IH NMR and 13C NMR spectra of the resulting copolymers are

shown in Figures 14 and 15.

According to the copolymer composition equation, many methods

have been developed since 1944 to determine the monomer reactivity

ratios rI and r2. The most accurate method may be the nonlinear

least-square method that was developed by Tidwell and Mortimer.48

However, this method is most tedious because of the computer














































I I I I I I I I I
8 7 6 5 4 3 2 1 0


Figure 14.


1H NMR Spectra of AN-EBD Copolymers, Except D
(Spontaneous Initiation), the Others Prepared with Free
Radical Catalysts. Copolymer Compositions of EBD(%):
(A) 14.9; (B) 49.6; (C) 50.6; (D) 52.3; (E) 54.0; (F)
57.5.












A



-ju~3Jt

-ui~L1'j


jULLKLUD


ii


mw6Yk*i


I I 1 1
160 140 120 100


Figure 15.


1H Decoupled 13C NMR Spectra of AN-EBD Copolymers, Except
D (Spontaneous Initiation), the Others Prepared with Free
Radical Catalysts. Copolymer Compositions of EBD(%):
(A) 14.9; (B) 49.6; (C) 50.6; (D) 52.3; (E) 54.0; (F)
57.5.


i K


i_.i


I 1
80 60


I I
40 20








iteration that is required. For this work, the monomer reactivity

ratios rI and r2 were determined by Fineman-Ross method49 and Kelen-

Tudos method,50 individually.


Fineman-Ross equation:


(1/F 2) (1/F1 1)
r -1r 2 (14)
(1/f 1) 2 1 (1/f1 1)2
1 (1/fl 1)


where F1 = mole fraction of monomer 1 in copolymer,

fl = mole fraction of monomer 1 in feed.

Figure 16 shows the plot according to the Fineman-Ross equation.


Kelen-Tudos equation:


G r2 F r2
G (r + -) (15)
a + F 1 a a + F


where G = x(1 1/y); x = [M1]/[M2] in monomer feed; F = x2/y; and y

= d[M1]/d[M2] in the copolymer; a is an arbitrary constant,

preferably equal to (FMFm )05, FM and Fm being the highest and the

lowest values of F; (1 and 2 represent the monomers EBD and AN). The

plot according to the Kelen-Tudos equation is shown in Figure 17.

The monomer reactivity ratios rl and r2, were calculated by both

methods, then the Alfrey-Price Q and e values were calculated from

them. The results are summarized in Table 20.


































































0




U LJ1


C.-


o


I






































































Lr\
O 0
0


S+/ 0








TABLE 20

Monomer Reactivity Ratios and Alfrey-Price Q and e Values
for the Free Radical Initiated Copolymerization of EBD and AN


Calculation Method r1 r2 e Q


Fineman-Ross 0.071 0.029 -1.287 1.046

Kelen-Tudos 0.069 0.022 -1.348 1.284


Judging from the fact that the product of the monomer reactivity

ratios is close to zero, the copolymer should have a high degree of

alternation of EBD and AN units in the chain.

Microstructure of AN-EBD Copolymers

In the infrared spectra of AN-EBD copolymers, absorptions were

seen at 729, 754, 938 and 972 cm-1 which are characteristic of cis-

3,4, cis-1,4, trans-3,4 and trans-1,4 structures, respectively.

The 1H NMR spectrum of 1:1 molar ratio AN-EBD copolymer is shown

in Figure 18. On the basis of integration of olefinic protons, the

copolymers are composed of 51% trans and cis-1,4 addition and 49%

trans and cis-3,4 addition. Table 21 shows the assignments of

chemical shifts in 1H NMR spectrum of AN-EBD copolymer, based on two

polymer sequence units I and II.

The 1H decoupled 13C NMR spectrum of 1:1 molar ratio AN-EBD

copolymer is shown in Figure 19. Along with off-resonance and INEPT

spectra, the assignments of chemical shifts in Figure 19 are shown in

Table 22, based on polymer sequence units I and II.





83






















0
Ln
c,,



0
C.)
41















0
o-





H 0
co




Lr


L.
coo






C1
u











C:)
(c


m co









CNN
-4
~ ('~C
TU -4

HU





CNN


-4-
C:L ..










TABLE 21

Assignments of Chemical Shifts in 1H NMR Spectrum
of AN-EBD Copolymer


Proton Chemical Shifts Chemical Shifts Number
Assignments 5 (observed) 6 (calculated)52 of Protons


12 6.20 6.20 0.5

1, 2 5.53 5.46 1.0

11 4.27 4.66 0.5

3, 7, 7' 3.13-4.03 3.55, 3.75 2.5

5, 5' 2.70 2.60 1.0

6, 10 2.36 2.39 1.5

4, 9 1.43-2.06 1.61, 1.76 3.0

8, 8' 1.23 1.22 3.0




























0














"-3-









C
C)






CD


0
o






L-n

c,





C-

O






0
o

C-)









s-




























O
0










N

Cz-
+-o



















0


rm
rI p











TABLE 22

Assignments of Chemical Shifts in 13C NMR Spectrum
of AN-EBD Copolymer


Carbon Chemical Shifts Chemical Shifts5
Assignments 6 (observed) 6 (calculated)-3


1' 148.06 144, 142.9

1, 2 133.88, 128.76, 127.78 133.6, 132.5, 130.6, 129.5

3, 3' 121.69, 121.01

2' 105.46, 103.22 106.5, 105.4

4 76.61, 71.59 80.9, 75.6

5, 5' 67.59, 64.43, 63.70

6 37.77, 36.70 36.1

7, 8 34.55 34.1, 33.0

9' 30.75, 29.53, 28.70 30.0

9 27.87, 27.58 26.1

10 26.17, 25.87, 25.34 24.0

11, 11' 14.86, 14.78







Determination of Formation Constant of Charge-Transfer Complex

The formation constant (Kf) of the charge-transfer complex (C)

between a donor (D) and an acceptor (A) is characterized as follows:


Kf
D + A C (16)



K =[C] (17)


Evidence for the formation of a weak charge-transfer complex is

the appearance of a new absorption band in the ultraviolet-visible

region of the spectrum and occasional appearance of color on mixing

the two components. However, in some cases, a new band fails to be

distinguished in the electronic spectrum because of overlap of the

absorptions of the donor and/or acceptor. Other techniques must be

used to identify the presence of a complex. For example, proton

chemical shifts in the NMR spectra may provide evidence for complex

formation in many cases.

In order to study complex participation in copolymerization, it

is necessary to establish that a molecular complex is formed between

the monomers. The UV and NMR methods were utilized to study the

formation constant of charge-transfer complex in the AN-EBD system.

The UV method was performed in n-hexane solution at room temperature,

but no charge-transfer bands could be detected

spectrophotometri call.








The formation constants of AN-EBD system were determined by the

NMR method using the equation that was developed by Foster and

Fyfe.54



T = AKf + oKf (18)
0


where A = 6D 6 is the difference between the chemical shift of
obsd o
D
the donor protons in completing media (6 bsd) and the shift of the

donor in uncomplexed form (6 ), = 6D o is the shift for the
o AD o
pure complex relative to the shift for the pure donor, [A]o is the

concentration of the acceptor, in this case, the concentration of

acceptor in large excess so that the experimental data can be

utilized in a linear plot according to equation 18. The proton

chemical shifts of EBD were measured with various concentrations of

AN in benzene-d6 solution. Tables 14 and 15 summarize the results

that were measured at 25" and 60, respectively.

By plotting A/[A]o vs A, straight lines were obtained, the slope

and intersection with the ordinate permit the calculation of the

formation constant. Based on the chemical shifts of methylene

protons (-OCH2-), the values of Kf calculated are 0.12 at 25" and

0.05 at 60. However, it was found that the chemical shift of the

TMS peak was affected by the composition of the mixture, so the

spectra were calibrated via a characteristic signal of the deuterated

benzene. Based on these corrected chemical shift values, the values

of Kf calculated are 0.19 at 25" and 0.10 at 60". Due to the complex

formation, the chemical shifts of the protons in the EBD monomer