Study of cyclocopolymerization

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Title:
Study of cyclocopolymerization
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Cyclocopolymerization, Study of
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xii, 127 leaves : ill. ; 28 cm.
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English
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Chu, Yuan Chieh, 1943-
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Polymers   ( lcsh )
Polymerization   ( lcsh )
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Thesis:
Thesis--University of Florida.
Bibliography:
Includes bibliographical references (leaves 123-126).
Statement of Responsibility:
by Yuan Chieh Chu.
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Typescript.
General Note:
Vita.

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University of Florida
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STUDY OF CYCLOCOPOLYMERIZATION


by

YUAN CHIEH CHU















A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF

THE UII'.VEF::ITY OF FLORIDA IN PARTIAL FULFILLtIF1T OF THE

PE..UiIF rlENTS FOR THE r,'EFFEE OF DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA

1977
































Dedicated to

the mother of Lawrence Chu


















ACKNOWLEDGEMENTS

The author would like to express his special gratefulness to

Professor George B. Butler for his encouragement and invaluable

guidance during the execution of this work.

The author also would like to express his appreciation to his

advisory committee and other faculty members in the Department of

Chemistry whose assistance and suggestions contributed much to this work.

He wishes to thank Mrs. Carol Albert for typing this thesis, Professor

G.B. Butler for checking the English composition, Dr. S.F. Tien for

his suggestions on the theoretical aspects, and T. Baugh for his work
13
on C nmr spectroscopy.

Finally, the author wishes to express great appreciation to his

wife, Rolan, whose forbearance and understanding made this work

possible.

The financial support for this work from the Department of

Chemistry and Professor G.B. -Butler's National Institutes of Health

grant is gratefully acknowledged.
















TABLE OF CONTENTS


ACKNOWLE ME1 T . .

LIST OF TABLES . .

LIST OF FIGURES . .


ABSTRACT

CHAPTER


I. INTRODUCTION . .


History of Cyclopolymerization and
Cyclocopolymerization . .. 1

Mechanism of Cyclopolymerization .. 11

Mechanism of Cyclocopolymerization ... 16

Statement of Problem . ... 22

II. THE STRUCTURE OF COPOLYMER OF DIVINYL ETHER-
MALEIC ANHi'L. FIDE SYSTEM . 24

Introduction . ... 24

Results and Discussion . ... 25

The Mechanism of Cyclization ... 47

III. THE COPOLYMERIZATION OF DIVINYL ETHER-
FUMARONITRILE . ... 52

Introduction . ... 52

Results and Discussion . ... 53

IV. EXPERIMENTAL . . 100


Materials . .

Equipment and Data . .

Synthesis Related to Monomer Preparation

Copolymerization . .


. 100

. 101

. 103

. 110


Page

. ii

. vi

. viii







Page

APPENDIX TEF E.LIHEMISTRY BACKGROUND FOR 5,5- AND
5,6-BICYCLIC SYSTEM IN THE COPOLYMER OF DVE-MAH ... .119

BIBLIOGRAPHY. . . ... 123

BIOGRAPHICAL SKETCH . . ... .. .127














LIST OF TABLES


Page

I. The Relation Between Concentration and Cyclization. 12

II. The Energetical Parameters for Cyclopolymerization. 15

III. The Reactivity Ratio of Copolymerization .. 18

IV. The Comparison Between JHD and JHH .. 28

V. The Chi-mi:cal Shifts for the Methine Protons of
DVE-MAH Copolymer . .. 33

VI. Chemical Shift Differences Between cis and trans
Disubstituted Vicinyl Carbons in 13C nmr Spectra. 44

VII. Determination of Equilibrium Constant of FN-DVE in
Acetonitrile with Constant FN Concentration
(0.00101 m/l) . .... 57

VIII. Comparison of Copolymer Initiated by Different Methods
in Acetonitrile. ... . 61

IX. The Compositions of Copolymers Prepared in Aceto-
nitrile at Room Temperature within 10% Conversion 64

X. The Limiting Yield of Copolymerization with Excess
DVE in Feed Composition. . 67
13
XI. Comparison of 1C nmr Spectra between Homopolymer of
DVE and the Copolymer of-DVE and FN ... 70

XII. The Light Intensity Dependence on Quantum Yield and
Rate in Acetonitrile at Room Temperature .. 73

XIII. The Linear Relations of Intensity (I) to the Quantum
Yields (4) and Rates . 74

XIV. Comparison of Quantum Yield and Rate at 236 nm and
300 nm . . ... 75

XV. The Rate of Copolymerization of DVE-FN System in
Acetonitrile at 300 nm, at I = 1.52 x 1016
Photons/Sec. . . .. 82









Page

XVI. The Rate of Copolymerization of DVE-FN System in
Acetonitrile at 236 nm, at I = 6.4 x 1014
Photons/Sec. . . .. 84

XVII. The Dependence of Total Concentration on Rate. .. 90

XVIII. The Determination of Reactivity Ratio rl ..... 97

XIX. The Copolymerization of DVE-FN System with Additives 111

XX. The Copolymerization of DVE-MAH System at Different
Temperature . .... 116


vii















LIST OF FIC'FE[


Figure Page

1 IR spectrum of the copolymer of DVE-MAH prepared in
xylene at 1300C . .... 29

2 60 MHz nuclear magnetic resonance spectra of (a) DVE-MAH
copolymer, (b) DDVE-MAH copolymer in acetone d 32

3 100 MHz nuclear magnetic resonance spectrum of DDVE-MAH
copolymer ....... ... ..... .35

4 300 MHz nuclear magnetic resonance spectra of (a) DVE-MAH
copolymer, (b) DVE-MAH [r ".H copolymer in acetone-d6 .. 36
13
5 C nuclear magnetic resonance spectra of (a) DVE-MAH
copolymer, (b) poly(maleic anhydride), (c) hydrolized
DVE-MAH copolymer . . ... .40
13
6 C nuclear magnetic resonance spectrum of 2,3-dimethyl
succinic acid . . ... 42
13
7 C nuclear magnetic resonance spectra of DVE-MAH
copolymer prepared at (a) 130, (b) 100, (c) 72, (d) 250C 46

8 The absorption of the complex of DVE-FN in acetonitrile
(a) 0.6 m/l of DVE, (b) 0.6 m/l of FN, (c) (DVE) =
(FN) = 0.6 m/1. . . .. 54

9 The determination of the stoichiometry of the DVE-FN
complex in acetonitrile by continuous variation method
at 300 nm (DVE) + (FN) = 0.60 0.03 m/1. ... 55

10 Charge transfer absorption of DVE-FN complex in aceto-
nitrile. . . ... ..... 58

11 IR spectra of the DVE-FN copolymer initiated (a) at
300 nm, (b) at 236 nm, (c) by Alb!:. . ... 63

12 60 MHz nuclear magnetic resonance spectra of the DVE-FN
copolymer initiated (a) at 300 nm, (b) at 236 nm,
(c) by AIBN. . . ... .. ... 63

13 The compositions of the DVE-FN copolymer initiated at
(a) 236 nm, (b) 300 nm. . ..... 65


viii











13
14 1C nuclear magnetic resonance spectra of the copolymer
initiated (a) at 236 nm, (b) by AIBN, (c) at 300 nm. 69

15 The dependence f feed composition on rate at 300 nm
(I 1.52 x 10 photons/sec) for total concentration
(a) 2.40 m/l, (b) 1.20 m/l, (c) 0.60 m/1. ... 83

16 The depencenc4 of feed composition on rate at 236 nm
(I 6.4 x 10 photons/sec) for total concentration
(a) 2.0 m/l, (b) 0.6 m/1. . ... 85

17 The dependence of total concentration on rate (x) at 300 nm,
fd = 0.5, (A) at 300 nm, fd = 0.6, (o) at 236 nm,
fd = 0.5, (*) at 236 nm, fd = 0.8. ... .' ..91

18 The determination of reactivity ratios -- (T) = 2.0 m/l,
at 300 nm ---- (T) = 2.0 m/l, at 236 nm, -- (T) =
1.1-4.5 m/l, with AIBN. . . ... 98

19 60 IH:: nuclear magnetic resonance spectra of (a) DVE,
(b) DDVE with 250 ppm sweep width, (c) DDVE with 100 ppm
sweep width. . . ... ... 105

20 60 MHz nucelar magnetic resonance spectra of (a) 2,2,2',2'-
tetradetueriodiethylene glycol, (b) diethylene glycol. 107

21 60 MHz nuclear magnetic resonance spectra of (a) bis-
(2-bromo-2,2-dideuterioethyl)ether, (b) bis(2-bromoethyl)-
ether. . . ... ....... 109

22 The viscosities of the DVE-MAH copolymer in DMSO prepared
in (a) benzene at 76-780C with 77% conversion, (b) in
benzene at 51-540C with 25% conversion, (c) in benzene
at 61-640C with 47% conversion, (d) in CH.i at 60-610C
with 43% conversion, (e) in benzene at 28-2AOC with 31%
conversion initiated by light. . .... .. 118


Figure


Page














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

STUDY OF CYCLOCOPOLYMERIZATION

By

Yuan Chieh Chu

June, 1977

Chairman: George B. Butler
Major Department: Chemistry

The well-known alternating 1:2 cyclocopolymer of divinyl ether

(DVE) and maleic anhydride (MAH) has been found to possess interest-

ing anti-tumor and biological activities. Recent research on the

structure of the cyclopolymer has raised a question about the ring

size of this cyclocopolymer. In this research program the structure

of this copolymer was reexamined by use of spectroscopic methods.

A linear, soluble copolymer was obtained by the copolymerization in

solvents with active hydrogens, such'as chloroform and xylene. The

ir spectra showed the existence of both monomers in the copolymer
-i
based on the strong bands at 1775, 1855, 1230 cm1 (cyclic anhydride),
-i
and 1090 cm- (cyclic ether).

By use of deuterated copolymers, the H-nmr peaks at 6 2.31, 3.47,

4.06, and 4.49 ppm with an area ratio of 2:1:1:1 were assigned for

the hydrogens of methylenes, methines on the backbone anhydride unit,

methines on the ring anhydride unit, and methines adjacent to oxygen

on the cyclic ether ring, respectively. Through the examination of








the possible isomeric structures of the bicyclic ring, the splitting

of each peak group was further assigned for cis and trans di-substi-

tutions on the anhydride unit.

The splitting pattern on the 300 MHz nmr spectrum of divinyl

ether 2,3-dideuteriomaleic anhydride copolymer confirmed the unsym-

metrical six-membered ring structure. 1C nmr spectra was discussed

and was consistent with the conclusion from the H-nmr spectra.

A chair-form six-membered ring with trans isomer next to each

side of the ring oxygen with a small portion of cis isomer was assigned

for the structure of DVE-MAH copolymer.
13
Based on little or no change of the 1C nmr spectra of the

copolymers prepared at different temperatures, it was concluded that

there was no significant change of structure caused by temperature

effect. This led to the sole assignment of the six-membered ring

structure of the copolymer as an energetically favored product.

A mechanism for the cyclization was proposed based on the HOMO-

LUMO interaction of the comonomers and the radical intramolecular

addition on the preoriented double bond. This mechanism led to the

formation of six-membered ring structure of the copolymerization as

the sole product.

The participation of the charge transfer complex in the cyclo-

copolymerization was investigated with the divinyl ether-fumaronitrile

system by light initiation. The evidence and the composition of the

complex were obtained by the UV spectroscopic method. The structure

of the copolymer was proposed on the basis of elemental analysis and
13
C nmr spectrum, as a mixture of 1:1 cyclocopolymer and 1:2 cyclo-

copolymer structures, both with six-membered rings. The initiation






mechanism involving polar deactivation of excited molecules and the

propagating mechanism were proposed to explain the rate maximum

phenomena and the relation between copolymerization rate and total

concentration of the comonomers at 236 nm and 300 nm irradiation.

A consistent result was obtained by the proposal of the participation

of the CTC in both the initiation and propagation processes.














CHAPTER I
INTRODUCTION

History of Cyclopolymerization and Cyclocopolymerization

It is well known that multifunctional monomers such as unconjugated

divinyl monomers are crosslinking agents in vinyl polymerizations.

However, certain compounds, such as diallyl phthalate and ethylene
2
diacrylate, undergo cyclization during polymerization, with the result

that 40-75% of the divinyl compound used is incapable of crosslinking.

Butler and coworkers3 found that several diallyl quarternary ammonium

salts polymerized to yield soluble and hence linear polymers containing

little or no residual unsaturation. Under the same conditions monoallyl

ammonium salts failed to polymerize. To explain the unusual results,

Butler and Ai4.1 o proposed an alternating intramolecular intermolecular

chain propagation mechanism to form a cyclic structure in the chain

(eq. 1). This type of process is now commonly termed cyclopolymerization.

Since these initial investigations, a large number of 1-6 non-

conjugated dienes of type I have been cyclopolymerized using appropriate

catalysis to yield soluble, most-ly saturated polymers with cyclic struc-

tures in the main chain.

In cyclocopolymerization, the comonomer contributes to formation of

the cyclic structure along with the nonconjugated diene. Butler reported

the first example of cyclocopolymerization. By copolymerizing divinyl

ether (DVE) and maleic anhydride (MAH), using a free radical initiator,

a soluble polymer was obtained. A mechanism similar to the cyclopolymer-

ization was proposed which is shown in equation 2.








This cyclocopolymer has been found to possess interesting


biological activity.


R


X


(Eq. 1)


X n+1


CH
X CH Si
2' /)
CH3



0
\ /
P 0 :S
/\ 0 / '
R


CH3
Ge

CH3





/So 2


S/R
/N










0 i"~


+ R* Initiation>
+ R -------;


0

o//
0


Intermolecular
propagation





Intramolecular
Cyclization







0



Intermolecular \t agation'





- Alte > >r
Alternate repetition


0


(Eq. 2)








The proposed mechanism was based on the following facts:6

(a) a soluble copolymer was formed, (b) little or no residual unsaturation

was detected in the copolymer and characteristic absorption bands for

cyclic anhydride and ether were observed in infrared spectra, (c) the

composition of the copolymer was close to a diene-olefin molar ratio

of 1:2 over a wide range of comonomer feed composition, (d) quantitative

conversion to copolymer was obtained, (e) the cleavage by hydriodic acid

and the incorporation of iodine into the copolymer indicated the pres-

ence of cyclic ether groups, and (f) neither monomer homopolymerizes

readily under the same condition as copolymerization.

Following Butler's discovery, the copolymerization reactions for

a wide variety of 1,4-dienes and olefins have been reported. Butler

and coworkers further studied some mono-olefin-1,4-diene systems to

produce 1:2 (1,4-diene:monoolefin) copolymer with generalized structure II.


Y CH
X X = 0, SO, Si

/ /2 / oCH3
Y n O0

y Y = -CN or Y-Y = 0

(II) "0


Stille and Thomson prepared, with a variety of free radical initia-

tors, a soluble copolymer of a nonconjugated diene, 1,5-hexadiene, and

sulfur dioxide. Elemental analysis of the copolymer samples substantiated

the existence of a material containing exactly two sulfur dioxide portions

to one of diolefin. The six-membered ring structure was confirmed by

comparing the ir spectra of the copolymer sample with pentamethylene

sulfone.





5





02 0

III



Price and coworker prepared the copolymers of N,N-divinyl

aniline with diethyl fumarate in bulk and solution with azobis-isobutyro-

nitrile (AIBN) at 600C. Diethyl fumarate, having widely different

polarity from that of divinyl aniline, and being reluctant to homo-

polymerize, polymerized with divinyl aniline in widely different monomer

concentration ratios to give copolymers of nearly constant 2:1 molar

ratio composition. The colubility of this copolymer and the negative

results of analysis for residual double bond by infrared absorption in

the 6.0-6.2 p region, supported the cyclic copolymer structure IV.


C 6H COOEt



S COOEt.
COOEt
COOEt

IV

The copolymerization of divinylphenylphosphine with acrylonitrile

was studied by Butler, et al. The copolymer produced was soluble in

DMF and showed no residual unsaturation. Elemental analysis indicated

the copolymer contained 0.265 mole fraction of divinylphenylphosphine

and 0.732 mole fraction of acrylonitrile. The structure of this

copolymer and the reaction for its formation are as follows (eq. 3):









CN
+C R-
+ nCH 2=CH -->


6H5

R-CH
'p ---------CH -CH --


.27 CN 0.73
S\CCN


CH
.6 5


CH2CH

CN
0.73


Rigid or multicyclic systems have been reported. Meyersen and

Wang0 prepared several copolymers of fused ring systems such as bicyclo-

pentene with sulfur dioxide or maleic anhydride in solution by free

radical initiation. Copolymer was obtained in the ratio of 1:2 as in

structure V in equation 4.


X = SO or
X :SO2 or


/.- /x

+ 2X~)

V n


K1>0


Eq. 4


Yamaguchi and Onoll reported the copolymerization of sulfur dioxide

and dicyclopentadiene (DCPD) in liquid sulfur dioxide with AIBN or other

radical initiators at o or 200C. Soluble copolymer was obtained with a

composition ratio of DCPD to sulfur dioxide of 1:2, and containing


C H5
6 5

^/ \ ^


0
2








virtually no residual double bond.

was proposed as VI.


The structure of this polysulphone


\ >-so,----

VI n
12
Butler and Pledger2 proposed 1:1 alternating copolymer of maleic anhydride

with 5-ethylidene-, 5-methylene-, and 5-vinyl-bicyclo(2,2,l)-2-heptene.

Evidence supported a tricyclic structure which incorporated maleic

anhydride as part of a six-membered ring repeating unit, for example

structure VII.


CHR


0 -0
Cx


The essential structure of the cyclocopolymers were proposed based

on the following methods.

1. Elementary analysis Most of the copolymers which have been studied

have a 1:1 or 1:2 comonomer composition in the copolymer regardless of

the wide range of feed composition, solvent, or initiator concentration.

2. Little or no residual absorption in carbon carbon double bond -

This indicates that all the double bonds in the diene were incorporated








into the copolymer. Only high degree of cyclization and crosslinking

can explain this observation. The residual unsaturation can be

detected by the absence of, or little ir absorption in the 6.0 to 6.2 p

region and nmr. Negative results of catalytic hydrogenation has been

used to show the absence of residual carbon carbon double bond in the

copolymer.

3. The solubility of copolymer and the absence of gelation at high

conversion rule out the crosslinked structure.

4. Existence of both monomers in the resulting polymer This can be

shown by the characteristic absorption bands of the comonomers in the
~--1
infrared spectra. For example, the 1100-1085 cm strong, broad band

for cyclic ether and the 1860, 1795 cm- bands for cyclic anhydride in

the ir spectra of DVE-MAH copolymers indicating the existence of both

comonomers in the copolymer.

5. The alternating ratios are always supported by elementary analysis.

Chemical method may support the proposed structure. Butler and

Guilbaultl3 hydrolyzed and dehydrohalogenated the copolymer of DVE-

chloromaleic anhydride, followed by the treatment with KMnO to get the

vic-diol copolymer. The degradation result of this vic-diol copolymer

upon periodic acid cleavage supported the 1:1 structure with only DVE

units on the backbone.



i. KOH 1. KMnO


SC1n 2. HC L H n 2.
V ---0 I
SCOOH

0
HIO
Eq. 5
H
COOH n C=O C=0
'H n COOH
COOH COOH








Both five- and six-membered rings can be formed during the cycliza-

tion step. Unfortunately not much work has been done along this line

to distinguish between these possibilities.

Stille and Thomson7 used the ir absorption spectra of model compounds,

VIII and IX, to compare with the 1,5-hexadiene-sulfur dioxide copolymer.

They concluded that the six-membered ring structure (III) was present in

the copolymer.








VIII IX



This method has also been used by Meyersen and Wang0 in their

fused ring system-sulfur dioxide copolymer as mentioned in the last

section.

Butler and Fujimori14 studied'ring size by the readiness of the dehy-

drohalogenation of the cyclocopolymer. The quantitative elimination

of only half the chlorine content of dichloro-maleic anhydride-DVE

cyclocopolymer provided the first support for the proposed six-membered

cyclic repeating unit. There would have been no such elimination if the

repeating unit were five-membered. If both the halogens and the

hydrogens at the 2-position to the oxygen were eliminated, the product

would be a furan derivative which should be detectable due to its

aromatic character.









aq. NaoH

O7 _-- -HC
Cl Cl n / n Eq. 6

O '\0 0 CO CO
Na Na




0

aq. NaOH i

0 0 n -.2HC I nN Eq. 7
COONa COONa




On the other hand, the ring structure of the cyclopolymer has been

intensively investigated by chemical and spectroscopic methods. Butler,

CrawshaS and Miller5 conclusively proved the existence of cyclic struc-

ture of cyclopolymer prepared by free radical initiation for diallyl

quaternary ammonium salts. A nondegraded polymer was obtained by

treatment with KMnO4. However, the ring size was not determined by

these authors. Later, by 13C nmr spectroscopy,6 both the five- and

six-membered rings were found in these cyclopolymers by comparing with

model compounds. Dehydrogenation of the cyclopolymer followed by the

identification of the resulting aromatic rings enabled Marvel and Vest17

to confirm the six-membered ring structure in the cyclopolymer of

2,6-dicarbomethoxy-l,6-heptadiene prepared by free radical initiation.
Me OMe Me
C OO 0e
C r R- KC10 Eq. 8
'n n








Spectroscopic methods have been applied to studying the ring
18
size for the cyclopolymer. Butler and Myers8 used both ir and nmr

spectroscopy to analyze the cyclopolymer obtained from dimethacrylamide

and its N-methyl and N-phenyl derivatives. They found that the polymers

were composed of both five- and six-membered rings. Electron spin
19 20
resonance studies have shown that the radicals from N-substituted

N,N-diallylamine in the presence of TiCl /H 02 or TiCl /N2NOH initiation

are five-membered ring cyclic species. It is possible that the radicals

involved in polymer formation have very short lifetimes (thereby not

detectable by ESR) and those radicals which are detectable are stable

but non-propagating species.

The extended chemical shift range, the absence of the simplicity
13
of proton decoupled 1C nmr spectra, in which each carbon resonates as a
13
singlet, makes the 13C nmr spectroscopy extensively useful for study of

polymer structures. Johns, Willing, Middleton,and Ong21 used the 13C

natural abundance pulsed Fourier transform nmr spectroscopy to distin-

guish the different structure features of the polymers formed by radical

induced cyclopolymerization of a series of N,N-diallyl amines by

comparing with the model compounds. The polymers of N,N-diallylamines

all contained cis and trans substituted pyrrolidine rings with the ratio

5:1. The polymers of N,N-bis(2-allyl)amine gave complex spectra due to

the presence of both cis and trans pyrrolidine and piperidiene rings.

Mechanisms of Cyclopolymerization

Since the discovery of cyclization in the cyclopolymerization, many

studies have been made on the nature of the cyclization step by theoreti-

cal consideration and experimental methods.








A statistical approach to cyclopolymerization was taken by Butler
22
and Raymond.22 They concluded that to explain the high degree of cycliza-

tion at high monomer concentration (Table I), a more favorable pathway

from 1,6-diene to cyclic polymer might exist than would be predicted

on a purely statistical basis.

Table I
The Relation Between Cyclization
and Concentration
Assumed
Monomer Cone. m/l Cyclization % Conc. m/1 Cyclization %

Diallyl quaternary pure
ammonium salts >5.0 96-100 monomer <50

Diallyl silanes 1.2-2.3 >95 1.00 70

Acrylic anhydride %8.0 9P-100 0.10 96

Diallyl phosphine bulk 100 0.001 100




Gibbs and Barton23 explained this by considering the presence of the

large pendant group which would tend to prevent intermolecular reaction

and will frequently be presented to the reactive species in a conforma-

tion which is favorable for polymerization (cyclization). Butler
24
et al. studied the effect of the stability of the cyclized radical on

the rate of cyclopolymerization. The overall rates of divinyl monomers

were considerably greater than that of the corresponding monovinyl

monomers, the ratios varying from 2 to 10. They estimated the effective

concentration of the intramolecular double bond with respect to the

radical propagation, and values greater than 20 M at 500C were obtained.

This incredible effective concentration indicated that a considerable

preorientation prior to reaction exists. This favorable preorientation

may be related to an electronic interaction between the developing








radical site and the intramolecular double bond or in the ground state

before the initiation as proposed by Butler.25

In an effort to explain the strong polymerization of 1,6-heptadienes

relative to their monoolefinic counterparts, Butler25 proposed that

an electronic interaction between the unconjugated double bonds of

1,6-dienes or between the intramolecular double bonds and the reactive

species after initiation might exist.




R *R





These interactions would reduce the entropy change in going from the

ground state to the activated state required for the intramolecular

pr.1.: .tion. The ground and activated state energies both would be

reduced. Mikulasova and Hvirik26 calculated the total activation energy

for radical polymerization of diallyldimethylsilane and found it to

be ca. 9 Kcal/(mole double bond) less than that for allyltrimethylsilane.

The electronic interaction is supported by UV absorption evidence,27

but it is not necessary for cyclopolymerization as shown by Gibbs.28

They found that in the case of methacrylic anhydride versus methacrylic

acid, there was essentially no difference in total activation energies

in the polymerizations. Marvel and Stille29 obtained a cyclic polymer

from 2,5-dimethyl-l,5-hexadiene, and suggested an unusual driving

force from diene monomer to cyclic polymer.

The activation energy for cyclization is not necessarily smaller

than the intermolecular addition for same radical as shown by several

authors based on the kinetic scheme developed by Mercier and Smets.30





14


They derived the kinetic relationships between intramolecular and

intermolecular propagation for the free radical polymerization of

acrylic anhydride.


(CH2=CHCO) 0
k0 1


(CH 2CHCO) 0

k.
1


0-


Eq. 9


The rate ratio of the intermolecular propagation (R.) to the intra-
1

molecular propagation (R ) was derived;
c


-E./RT
A.e i
R./R = 2 [monomer] l -
i c -E /RT
Ae c


where the difference in activation energies (E -E.) can be calculated.
c 1
Several E -E. values are listed in Table II. These results indicated
c i

that the intramolecular propagation step requires greater energies









than the intermolecular step (E >E.). However, the rate of cyclization
C i1

is considerably larger than for intermolecular propagation (k /k.>l).
C 1
The values for the ratio A /A. indicated a high entropy factor favoring
c 1

cyclization. The decrease in entropy for a cyclization step would

perhaps be expected to be smaller than that for addition of a new

monomer unit. Only rotational motion will be lost in cyclization; on

adding a new monomer molecule to the chain, the loss of translational

and rotational degrees of freedom will result. Therefore, as far as

entropy is important, cyclization would be favored over intermolecular

propagation.


Table II
The Energetic Parameters for Cyclopolymerization

Monomers E -E. Kcal/mole A /A. mole/l k /k. mole/l
C 1 c 1 c i

Acrylic anhydride 2.4 167 5.9

o-Divinyl benzene 1.9 50 2.8

Diallyl phthalate 0.3

Methacrylic anhydride 2.6 256 2.4




Guaita31 has studied the temperature independent factor of

cyclization parameters for the free radical copolymerization of acrylic

anhydride and divinyl ether. The results indicated that the high frac-

tions of cyclization in cyclopolymers from symmetrical unconjugated

dienes can be thermodynamically accounted for by an entropic effect

largely exceeding the energetical one. The entropy decrease was smaller

in the intramolecular reaction than in the intermolecular reactions.
25
These entropic effects are consistent with Butler's25 postulation of

the preorientation of two double bond by electronic interaction in both








ground and activated states. The nature of this preorientation between

the double bonds has been though to be due to a charge transfer complexa-

tion in the copolymerization, especially in the cyclocopolymerization to

produce alternating copolymers.

Mechanism of Cyclocopolymerization


Barton and Butler32 described a general

equation of 1,4-dienes and monoolefins where

is bimolecular in construction. The kinetic


in equation 10.

mi + M


m + M2




m3 M


kll
k11 .
-- m1
k12
-----> m3
m3
k
c
C
k33
---- il


copolymerization composition

the cyclic repeating unit

scheme considered is shown


k32
m + M ---2
3 2
k
kcl
m + M -----
c 1

k
Sc2
me + M2 -2

k21

m2 + M1 ---j
mS + M2


(Eq. 10)


M is the diene CH 2=CH-X-CH=CH2 where X is CH2, O, SO2, etc. M2 is

the monoolefin, CHY=CHZ. The m' is the radical,-QCH CHCHHCH2, m2 is the

radical --CHYCHZ, m3 is the uncyclized radical
3

Y/



Z

and m" is the cyclized radical
c


Y *




A five-membered ring structure for m" is possible.
c









The derived equation which related copolymer composition to monomer

feed composition in terms of five reactivity ratio parameters was given

as equation 11.
1 1 x
(1 + rx) + ( -)]
1 M a r
2 2


n = (E
1 x 3 1 r2 -
S[ + + 2] + + ( 1 + + )(1 + r x)
a r x M2 x c


where x = M /M2 is the mole fractional ratio of monomers in the feed,

n = m /m2 is the mole fractional ratio of monomers in the copolymer at

low conversion, rI = kll/kl2' r2 = k22/k21' r3 = k32/k31' rc = kcl/kc2'

and a = k /k32. The equation may be approximated to simpler forms in

the following cases.

a. If kc>>k32 so that a is very large and cyclization is the predominan

reaction of the radical, m3, the equation (11) gives
3'


n = (1 + rlx)(l + r x)/[r x + (r2/x) + 2]
1 c 2


q. 11)


t


(Eq. 12)


This is equivalent to considering the addition of monoolefin to diene

radicals to be a concerted bimolecular step proceeding through a cyclic

transition state and producing the cyclic repeating units.

b. If in addition there is a strong alternating tendency so that

r lr2,r =0 then equation (11) reduces in the limit to n= 1/2. This

predicts an alternating copolymer composition of 2:1 molar in contrast

to 1:1 for the similar limiting case of the classical binary copolymer
33, 34
composition equation and that for the cyclopolymer composition equation.3 34

c. If the diene has a negligible tendency to add to its own radicals and

rl=r c0 and there is also predominant cyclization, then equation (12)

gives


n = 1/[r,/x) + 2]


(Eq. 13)







32
All three cases have been found as in Table III.3



Table III
The Reactivity Ratio of Copolymerization

Case a Case b Case c

System r r2 r3 System System r2

DVE-AN 0.024 0.938 0.017 1,4-PD-MAH 1,4-PD-AN 1.13

DVS-AN 0.364 0.067 0.067 DVE-MAH DM-1,4-PD-AN 3.31

DVE-PMI DVE-4-VP 32.0

DVE = Divinyl ether; AN = Acrylonitrile; 1,4-PD = Dimethyl-l,4-penta-
diene; MAH = Maleic anhydride; PMI = N-Phenyl maleic imide;
4-VP = 4-Vinyl pyridine: DVS = Divinyl sulfone; DM-1,4-PD =
Dimethyl-1,4-pentadiene.


In cases (b) and (c) very low values for r have been reported.

This low value is remarkable in the case of monomers such as acryl-

nitrile, and indicates that almost all the AN radicals in m3 react

to form a ring. The actual ring formation may be either a stepwise

reaction or a concerted reaction to form the product. Orientation

of monomers via a charge transfer complex (CTC) prior to free radical

reaction explains this unusual cyclic structure and also accommodates

the kinetic data (eq. 14).



O R R "
.--- Concerted __

/ \0 n, (Eq. 14)


Stepwise


7








Evidence for the participation of a CTC in the copolymerization
35
between styrene and MAH was presented by Tsuchida and Tomono.3 They

concluded that the CTC and uncomplexed MAH took part in the copolymer-

zation. Evidence for participation of a CTC in the cyclocopolymeriza-

tion of 1,4-dienes with monoolefin was presented by Butler and Joyce36

on the comonomer pairs, DVE-MAH, DVE-MI, DVE-FN and dihydropyran

(DHP)-MAH. Butler and his group have intensively studied the partici-

pation of CTC in cyclocopolymerization. The evidence of the existence

of the CTC was confirmed by both UV and nmr spectroscopies. The

equilibrium constant of the complexation can be obtained by these

spectroscopic methods. The complex is formed by interaction of an

electron-rich donor (D) and an electron -deficient acceptor (A).


D + A ----- [D, A--]


The composition of all the complexes formed by 1,4-diene and monoolefins

were 1:1 complexes. The alternating copolymer compositions found were

2:1 in olefin to 1,4-diene ratio for most of the 1,4-dienes with MAH or

FN. This is consistent with the postulation that the CTC undergoes a

1:1 alternating copolymerization with the electron acceptors such as

MAH and FN, which can thus account for the structure of the copolymer.

Some 1:1 copolymer has been obtained which can be considered as the

product of the homopolymerization of the 1:1 complex.

One necessary requirement for these alternating copolymerizations

is that neither of the comonomers should be homopolymerizable to a

significant extent under the same condition of the copolymerization. If

the acceptor is homopolymerizable such as AN, MMA and 4-VP, acceptor will









be incorporated in the copolymer to a greater extent than the expected

value for 2:1 copolymer, i.e. 67%.

The contribution of complex can be further demonstrated by

terpolymerizations. The terpolymerization of styrene, MAH, and

2-chloroethyl vinyl ether (ChEVE) studied by Tsuchida and Tomono35

can be explained by treating the system as a copolymerization of two

complexes, styrene-MAH and ChEVE-MAH. Butler and Campus studied the

terpolymerization of DVE-MAH-AN system. The DVE-MAH ratio in the

terpolymer was always less than 1:1 and had a lower limit of 1:2

regardless of the feed ratio of the termonomers. These results were

interpreted in terms of the participation of the CTC of DVE-MAH in the

copolymerization process with either MAH or AN.

The MAH reacted with DVE in the absence of normal radical initia-
38
tion to form cyclic 2:1 copolymer.3 It was postulated that initiation

via a molecular complex occurred (eq. 15).



D A

D + A --- [D!, A7] D + A7 (Eq. 15)

D A

Active forms


The initiation of CTC can be demonstrated by photo-initiation of this
39 '
system and the DVE-FN system. Zeegers and Butler3 photo-initiated the

DVE-FN system with different wavelengths. They showed that both the

complex formed between DVE and FN and the noncomplexed species were

able to initiate the polymerization by light initiation.

Miller and Gilbert40 observed that vinylidine cyanide spontaneously

copolymerized with vinyl ethers when the two comonomers were mixed at








room temperature. Yang and Gaoni41 observed that 2,4,6-trinitrostyrene

as the acceptor monomer spontaneously copolymerized with 4-VP as the

donor monomer. Butler and Sharp42 reported the spontaneous copolymeriza-

tion of DVE and DVS.

The concerted cyclization has been argued by Butler and
13
Guilbault. They found that chloromaleic anhydride copolymerized

with DVE to form soluble copolymers of 1:1 composition with no residual

unsaturation. The ease with which the copolymer underwent dehydro-

halogenation indicated that the'hydrogen and chlorine atoms on the

anhydride unit are in a trans configuration as a result of a stepwise

cyclization process.

The steric effect of highly substituted acceptors, tetrahydro-

naphthoquinone (THNQ) and dimethyltetrahydronaphthoquinone (DMTHNQ) on

the copolymerization with DVE was studied by Fujimori and Butler.43

They found that the copolymers was in constant 1:1 composition regard-

less of the feed composition. A terpolymerization of these two acceptors

with DVE was studied. Both the copolymerization and terpolymerization

and the composition can be explained by assuming that competition

between an acceptor monomer and the CTC towards the cyclized DVE radical

in the propagation step appears to favor the CTC in CTC mechanism.

These authors4 studied the steric effect of substituted MAH on the

copolymerization with DVE. They found that (i) a strong complex gave

1:1 cyclocopolymer having a copolymer backbone consisting of only DVE

units, (ii) a sterically hindered acceptor would produce 1:1 cyclocopolvmer,

and (iii) a weak CTC and reactive acceptor would produce 1:2 cyclocopolymer.

They did not mention the reactivity change of the acceptor due to the

substitution. The alternating tendency and the rate increased by using









a large amount of ZnCl2 with the DVE-FN system. A 1:2 alternating

copolymer was obtained spontaneously. This system studied by Butler
44
and Fujimori was consistent with the participation of a CTC in the

copolymerization mechanism.
38
Solvent effects have been studied by Butler's group. The K

value (equilibrium constant of CTC formation) decreased with increase

of the dielectric constant of the solvent for MAH-DVE system. The

rate of the copolymerization and number average molecular weights

decreased in more polar solvents. In all cases, 2:1 copolymer resulted.
45
The study of the initial rate as a function of the feed composition

made it possible to determine the relative value of the different pro-

pagation reaction rate constants consistent with a mechanism by successive

and selective addition. However, participation of the CTC in a competing

mechanism with the above cannot be completely excluded.

In conclusion, a large portion of the evidence favors the partic-

ipation of CTC in both the initiation and the propagation steps in the

alternating cyclocopolymerization. A complete explanation or mechanism

to fit all known data has not been reported. It is reasonable to say

that the reactivity, the complexation and the steric hindrance of the

comonomers all take part in the alternating tendency, rate, and the ring

size in cyclocopolymerization. The solvent and initiator may also

determine the rate profile of this copolymerization.
Statement of Problem

The objective of the present research has been to study cyclo-

polymerization of donor 1,4-dienes with acceptor monoolefins and hope-

fully learn more about the role of charge transfer complex (CTC) formed

between the comonomers in the cyclocopolymerization mechanism and to








develop a method to elucidate the structure of the cyclocopolymer by

various nuclear megnetic resonance spectroscopic methods. The following

research was conducted with this purpose in mind.

The Structure Analysis of Cyclopolymer of Divinyl Ether-Maleic Anhydride
(DVE-MAH) Comonomer Pair.
13
The ir, H-nmr, and C nmr spectroscopies are employed for this well

known 1:2 alternating copolymer. The 100 MHz and 300 MHz H-nmr spectra

were investigated in order to analyze the ring size and hopefully the
13
cis and trans content of the bicyclic ring. The 1C nmr spectrometer

should give simpler spectra and by comparing with literature values,

it should be possible to determine the ring size of the copolymer.

A partially deuterated divinyl ether (DDVE) was prepared which should

simplify the H-nmr spectral analysis. The 100 MHz and 300 MHz H-nmr

spectra of this DDVE-MAH copolymer should give more information on the

copolymer structure and help in the assignment of the respective signals

of the spectra which has been shown to be informative based on the liter-

ature.16, 21
ature.

Rate Maximum Analysis

The study of the copolymer rate copolymerization rate as a function

of the feed composition made it possible to determine the participation

of CTC in the cyclocopolymerization. An irradiation at the wavelength

where only complex absorbed should confirm the initiation through CTC.

The participation of CTC in propagation can be supported by an analysis

of the proposed kinetic scheme. In order to compare the rate at the same

light intensity, the quantum yield was measured right after each irradia-

tion. The structure of the cyclocopolymer of divinyl ether-fumaronitrile
monomer pair was determined by elemental analysis and 13C nmr spectroscopy.
monomer pair was determined by elemental analysis and C nmr spectroscopy.














CHAPTER II
THE STRUCTURE OF COPOLYMER OF DIVINYL ETHER-MALEIC ANHYDRIDE SYSTEM

Introduction

The field of cyclopolymerization has been explored extensively. A

variety of monomers containing two isolated double bonds have been found

to polymerize to form linear polymers containing cyclic units and little

or no residual unsaturation. -High degrees of cyclization are obtained

when five- or six-membered rings can form and when all double bonds have
16
the same reactivity such as in diallylquaternary ammonium salts and
21
N-substituted diallylamines.21 The polymers of N,N-diallyl amines all

contained cis and trans-substituted pyrrolidine rings with ratio 5:1.

With a substituent on the 2-position such as N-methyl-N,N-bis(2-alkylallyl)-

amines, a complex spectra showed the presence of both pyrrolidine and
13
piperidine rings. The 1C nmr spectra of poly(diallyldimethylammonium)

chloride showed a predominant content of five-membered ring linked

mainly in a 3,4-cis configuration. Several works have studied the polymers

obtained from N-substituted dimethacrylamides.1' 4 In most cases five-

membered ring was found predominant with a small amount or no six-

membered ring.

The radical cyclization reaction involved in the polymerization has

been studied by means of model compounds. Julia reviewed the works

on the cyclization of the 5-unsaturated radicals.47 Without substitution

on the radical carbon, only five-membered ring product was obtained.

With electronegative substituents on the radical carbon, the six-

membered ring product predominated.

24








Smith studied the cyclization of several 2-(allyloxy)ethyl radicals
48
with tributyltin hydride. The 2-allyloxy ethyl radical gave the tetra-

hydrofuran derivative as the only cyclic product. The 2-methyl- and

2-phenyl-allyloxyethyl radicals cyclized to give both five- and six-

membered ring products; in the latter radical the pyran derivative was

the predominant product.

Smith also found that with higher temperature the percentage of the

unfavored product increased; this indicated that the ring formation is

temperature dependent. It can be concluded that a five-membered ring is

energetically favored in the case of symmetrical non-conjugated dienes.

A steric effect would change the direction for radical attack on the

double bond. For unsymmetrical non-conjugated dienes with opposite

polarization on each double bond, the six-membered ring is predominant

as explained later. A head to tail cross-propagation has been found for

several oppositely polarized vinyl monomer pairs, such as maleic anhydride-
49
vinyl ether pairs, which introduced an alternating copolymer. The

cyclocopolymerization of DVE-MAH is similar to unsymmetrical non-conjugated

dienes, in which the cyclization step involves a favorable cross-propaga-

tion reaction of oppositely polarized units.

It seemed worthwhile, therefore, to investigate the structure of the

copolymer of DVE-MAH and to study the temperature dependence of the five-

and six-membered ring distribution in the copolymer.

Results and Discussion

Synthesis and Copolymerization of Bis(2,2-dideuteriovinyl)ether

Due to the small amount of materials available, the structures of

the products in each synthesis step were determined by ir and nmr spectro-

scopy. A comparison of these spectra with spectra reported in the








literature and the spectra of the corresponding non-deuterated products

prepared by the same procedure confirmed the structures of the deuterated

compounds. In all cases the ir and nmr spectra of the non-deuterated

products were exactly the same as reported in the literature. Therefore,

the procedure for preparation of the non-deuterated ompounds were

applicable for the deuterated analogues.

A reaction scheme is shown in the following route:



SD H

O LiAlD /

THF AOH


DD


P D\ Br
/' \D KOH -D PBr3
0 -- 0 D 3
S D Triethanol ,D Pyridine
amine
D NBr
D





The 2,2,2',2'-tetradeuteriodiethylene glycol was prepared essentially

according to the method given by Bloomfield and Lee with only minor

modification.50 For complete reduction of anhydride, a prolonged reflux

period was required. In order to take the most advantage of lithium

aluminum tetradeuteride (LiAlD ), only a little excess of the deuteride

was used. The resulting glycol was soluble in water to a large extent,

hence, to isolate it from water solution was difficult. Even a salting

out process did not succeed. The reduction in ether solution was not








successful because of the low solubility of the anhydride. The reaction

seemed not to go at all. The best result was by using tetrahydrofuran

(THF) as solvent, with a small amount of water to destroy the aluminum

salt and release the glycol. The addition of 9 N sulfuric acid to dissolve

the aluminum salt did not improve the yield significantly. Therefore,

the complete dissolution of aluminum salt was not necessary. Water, fol-

lowed by dilute acid was used to bring the glycol into THF solution.

The addition of excess anhydrous potassium carbonate, K2C02, neutralized

the acid by evolution of carbon dioxide and absorbed water present in

the THF solution.

The diethylene glycol prepared by the same procedure showed exactly

the same ir and nmr spectra as reported in the literature. The ir

spectrum of 2,2,2',2'-tetradeuteriodiethylene glycol showeJ two
--1
absorptions at 2220 and 2110 cm of C-D stretching. The structure was

further confirmed by the nmr spectrum, in which a singlet was observed

instead of the multiple in the spectrum of non-deuterated diethylene

glycol. The peak ratio of 1:2 instead of 1:4 (for diethylene glycol) also

indicated that the product obtained was tetradeuteriodiethylene glycol.

The bromination of deuterated ethylene glycol was straightforward.51

The same method when applied to non-deuterated ethylene glycol gave a

product with exactly the same nmr and ir spectra as reported in the

literature. The ir spectrum of the resulting liquid for bis(2-bromo-
-I
2,2-dideuterioethyl)ether showed an absorption at 2170 cm which was

assigned to the C-D stretching. The nmr spectrum clearly confirmed the

structure with a singlet at 6 3.80 ppm. On the contrary, non-deuterated

dibromoethyl ether showed an AA'BB' multiple at 6 3.70 ppm.

Finally the synthesis of bis(2,2-dideuteriovinyl)ether was prepared

by dehydrobromination from the corresponding dibromo compound. Only








the nmr spectrum was analyzed. The disappearance of ABX system which

showed up in the spectrum of divinyl ether, was evidence of the replace-

ment of the four terminal hydrogens by deuteriums. A clear spectrum

was obtained by using larger sweepwidth. The constants for the hydrogen-

deuterium coupling (JHD) was obtained by analyzing this spectrum.

By multiplying JHD by 6.5, the corresponding hydrogen coupling constants
52
(JHH) were obtained and were found to be close to the reported value.
(Table IV).


Table(Table I).

Table IV

The Comparison Between JHD and JHH

Coupling J (Hz) Multiplied Reported
by 6.5 JHH (Hz)


trans 2 13.0 13.8

cis 1 6.5 6.2




The synthesized terminal deuterated divinyl ether (DDVE) was

copolymerized with MAH at 720C in cyclohexanone by AIBN initiation.

The polymeric product was isolated and purified as a white powdery

solid which was soluble in acetone and dimethyl sulfoxide.

A series of copolymers of DVE and MAH were prepared at different

temperatures. The ir and nmr spectra were obtained and are discussed in

the next section.

The Structure of Copolymer

Infrared (ir) spectra. The ir spectra were shown in Fig. 1. The
-i
two strong peaks at 1775 and 1855 cm1 correspond to the reported
-1 53
absorption of succinic anhydride at 1782 and 1865 cm for symmetric









































O
CO
Ln
-1




o















CD
C)
0o
-
0u








and antisymmetric carbonyl stretching, respectively. The strong peaks
-l
at 1230 and 950-920 cm were assigned for the C-O-C absorptions for
-i
cyclic anhydride unit. The strong peak at 1090 cm-1 with a shoulder
-l
between 1060-1020 cm was assigned for the C-O-C stretching for pyran

structure. The five-membered ring structure was ruled out by the fact
-1 54
that the C-O-C stretching absorption for tetrahydrofuran is at 1062 cm

The structure of the copolymer shown as structure X, with a 2,6-disubsti-

tuted tetrahydropyran ring and an anhydride unit on the 3,4-positions.






H H

H H
S H



0

X


The 1:2 composition of DVE to MAH has been reported by Butler based on

the facts discussed in Chapter I. The spectra for 2,5-disubstituted

tetrahydrofuran has been reported by Mihailovic,et al.5 They observed
-l
strong absorption at 1100 cm .for both cis and trans-2,5-dimethyl-

and diethyltetrahydrofuran.

The structure of the copolymer supported by ir spectra is likely

to have a six-membered ring. A conclusive result cannot be reached

because a suitable model compound for the comparison of ir spectra is

not available.

Hydrogen nuclear magnetic resonance (H-nmr) spectra.

The H-nmr spectra of polymers are usually broad. Therefore,








structure determination by H-nmr spectra is difficult. With the help

of the spectra of deuterated compounds and high resolution nmr spectro-

scopy, it is possible to simplify the spectra and separate the overlapping

peaks. The 60 MHz nmr spectrum for DVE-MAH system copolymer was shown

in Fig. 2a. A four peak pattern was observed at 6 4.49, 4.06, 3.47 and

2.31 ppm with an area ratio of 1:1:1:2. The H-nmr spectrum of the

copolymer prepared with DDVE and MAH under the same polymerization

conditions exhibited the disappearance of the strong peak at 6 2.31 ppm

(Fig. 2b). Only the weak peaks corresponding to the residual solvent

were observed. Hence, the peak in the spectrum of nondeuterated copolymer

at 6 2.31 ppm was assigned for methylene protons which were B to the

ring oxygen. It has been reported that in the spectrum of the copolymer

prepared with DVE-3,4-dideuteromaleic anhydride (DMAH), the two peaks

centered at 6 3.47 and 6 4.06 ppm disappeared.5 Hence, these two

peaks are due to the four methine protons linked on the anhydride forms.

The peak at lower field was assigned to the proton on the rir., based on

the fact that the proton in a fixed position within a bicyclic ring will

experience a downfield shift caused by the electronegative oxygen nearby.

The methine protons next to oxygen are expected to experience a

deshielding effect to shift tb lower field at 6 4.49 ppm. The methine

protons next to oxygen have been reported to absorb between 6 4.00 and
57
6 3.30 ppm.57 Strong electron withdrawing effect of the two succinic

anhydride groups apparently shifts the methine proton to even lower field.

According to this analysis based on peak assignment and area inter-

gration, it can be concluded that the repeating unit of the copolymer has

two to one ratio of maleic anhydride to DVE which are arranged in an

exactly alternating manner. A random distribution of bicyclic and succinic





32










I-w




w3






r0
00



0 0
E Qu

0D >










C+-
0
CT3
C, TJ
o0












0

0 c)
a~)

CD 0
Cd



Q) (












cr-

0
CD














br3



-H0
kO,-
0
S t
(\J
.0
-r1
















Table V

The Chemical Shifts for the Methine Protons of DVE-MAH Copolymer

Spectraa Next to 0 On the Ring On the Backbone
Anhydride Anhydride

60 MHzb 4.49 4.06 3.47

60 MHzc 4.38-4.44 4.08 3.50

100 MHzc 4.18-4.44 3.88 2.96, 3.30

300 MHzb 4.29, 4.57 3.92, 4.14 3.01, 3.30

300 MHzd 4.34, 4.46
4.67, 4.84

A6e 0.22 0.29-0.34

Af 0.28-0.47

All chemical shifts (6) are in terms of ppm relative to the
standard, TMS.
Non-deuterated copolymer.
cDeuterated copolymer of DDVE and MAH.
Deuterated copolymer of DVE and DMAH.


The chemical shift differences between the assigned cis and
trans methine protons.
See reference 59.








anhydride units would give a more complex spectrum than the one reported

here.

The 60 MHz H-nmr spectrum is not able to distinguish between the

five- and six-membered ring due to the broad peaks caused by vicinal

protons and the different conformations and configurations.

For the purpose of distinguishing the cis and trans disubstitutions

and the five- and six-membered ring structures, a high resolution 100 MHz

H-nmr spectrum was performed for the copolymer of DDVE-MAH in acetone-d6

at 500C (Fig. 3). The broad peak at 6 3.50 ppm with a shoulder at 6 3.16

ppm in 60 MHz spectrum was separated into peaks at 6 3.30 and 2.96 ppm.

The shoulder between 6 4.38 and 4.44 ppm was still unseparated and broad.

A 300 MHz nmr spectrum of DVE-MAH copolymer (Fig 4a) was performed by

Butler's group, in which a further separated pattern was observed.58

The three peaks for methine proton groups are summarized in Table V.

Bode and Brockmann reported that the cis- and trans-2,3-disubsti-

tuted succinic anhydride showed 0.47-0.28 ppm difference in chemical
59
shift and the difference decreased with larger substitution.59 Therefore,

we can assign the methine groups of highest field with 0.34-0.29 ppm

splitting as the anhydride unit in the copolymer backbone. The one at

the lower field with less splitting (0.22 ppm) is then assigned as the

anhydride unit on the ring, which is deshielded by the neighboring pyran-

oxygen as discussed in the last section. In disubstituted succinic

anhydride, the chemical shift for the trans form is less than that for

cis form, 6 >6 t thus the four peaks in the MHz spectra for anhydride
Scis trans'

protons can be assigned as: 3.01, 3.20, 3.92 and 4.14 for the protons on

trans-backbone, cis-backbone, trans-ring and cis-ring anhydride units,

respectively. On the backbone, the population of cis anhydride units



























0)

















0
o3 c a



















C))f


U
w0










S
2u5:













r r)
0 a
















C) U
0
oS u




a a
a










0









cn
rif
0~ 1/
0)
Sc)
25
0O
0~ 0 N

0L









bC













K-


OC
0
rC









O











0
'.r
E
a



o
m









o











o
mn


.0
a
0
C)




I
rcl







0


4-)







C)
a
o










Q)
()
n3













o '.
10
C4-)









E
CC





o










SC)
cd
00






.H H


SO
a
o0
o ct)





rW





a
E




0IR
Sl~
*3- Sr


9~~7-~:








and the trans anhydride units are more or less the same. In contrast, more

trans form was present in the ring. The latter can be explained by the

possible bicyclic ring conformation, where a trans configuration is more

favorable. Butler and Guilbault prepared the copolymer of chloromaleic

anhydride with DVE having cyclized 1:1 composition with only DVE units
13
in the backbone.3 They investigated dehydrohalogenation of the copolymer.

From the ease with which the copolymer underwent dehydrohalogenation, they

suggested that the hydrogen and chlorine atoms on the anhydride unit in

the ring were in a trans configuration. However, H-nmr spectra showed

the presence of both cis and trans conf1,irations with the latter in

favor.

By examination of the model of the bicyclic ring with large

substitutions on the carbons next to the oxygen, the six-membered ring

with chair form and trans junction is more favorable (trans isomer). In

this structure (XI), the two protons at the junction are in trans configura-

tion. A chair form with cis junction is another alternative configuration

(cis isomer). However, the latter configuration (XII) experiences more

ring strain. On the contrary, a bicyclic ring with two five-membered

rings experiences much strain and only cis junction is possible, especially

when one of the rings is an anhydride unit (XIII). The heat of combustion

of trans bicyclo(3.3.0)octane is greater than the cis isomer by ca.

6 Kcal/mole.6 [hu:., a trans junction pyran bicyclic structure with the

presence of cis isomer explains the analysis of 300 MHz nmr spectrum of

the DVE-MAH copolymer, based on the analysis of methine protons on the

anhydride units.

For a disbustituted cyclic ether, the chemical shift difference

between the cis and trans of the methine protons next to oxygen in the








literature have been reported to be between 0.11 and 0.51 ppm.6 62,

In the case of the DVE-MAH copolymer, the methine proton signal was

split into two peaks by 0.28 ppm as shown on the 300 MHz spectrum. It

is reasonable to assign this group of peaks as a mixture of the two

configurations with more trans-isomer present because of the larger

area in the higher field corresponding to the cis form which was more

populated for a favorable trans isomer.



H


0O


0

cis isomer 0 0
XII
H H
XIII






trans isomer
XI

This splitting pattern was more clearly observed in the 300 MHz

spectrum for the copolymer of DVE and DMAH (Fig. 4b). The two separated

methine proton (next to oxygen) peaks were further split into doublets.

The doublet indicated the nonequivalency of the two protons on each side

of the oxygen in the pyran ring. In contrast, the two protons for the

five-membered ring structure are more or less equivalent.

The methylene peaks on the higher field can be analyzed as a

mixture of two doublets; the larger doublet is assigned for trans isomer








which if further split by the fact that the methylene proton groups are not

equivalent. The splitting peak at the lower field with less intensity can

be assigned to the less populated cis isomer. In fused five-membered ring

structure, it is possible that the two methylene groups are linked in

either cis or trans configurations.63 However, a trans configuration

would introduce some strain in the bicyclic system with the two bulky sub-

stitutions on the pseudo equatorial positions of the half-chair conforma-
64
tion.6 A cis configuration with the possible conformation is shown in
64
structure XIII.64 In this structure both the two methine hydrogens and

the two methylene groups on the 2- and 5-position are equivalent. There-

fore, the splitting on Fig. 4b is most likely due to a chair form six-

membered ring with trans junction (trans isomer) with some cis isomer.

Further confirmation could be obtained by using bicyclic model compounds

and/or studying copolymers of additional monomers, e.g., CH2=CDOCD=CH2.
13
C3 Nmr Spectra

The line broadening inherent in H-nmr has severely limited the poten-

tial of this technique for polymer structure analysis. In contrast, the

extended chemical shift range, the absence of significant dipolar line
13
broadening and the simplicity of proton decoupled 1C nmr spectra, in

which each carbon resonates as a singlet, makes these spectra extremely

useful for the study of polymers.

The spectrum of the copolymer of DVE-MAH was shown in Fig. 5a.

The spectrum consists of five major peak groups. From comparison with

published data the following general assignments can be made: the broad

peaks centered at 6 31.4 ppm with a shoulder at 6 35.8 ppm for methylene

carbon, the broad peak centered at 6 44.2 and 51.5 ppm with a shoulder

at 6 53.7 ppm for the carbon adjacent to the carbonyl groups, broad peak















I,



/_~


3/











/703


o
C" ~


-------------
; 1 ^


(I)


CM

- C1
CM




-r


LC










co







E
a
&.


r:
\I/

Y
g,
u
/1\
r:


,0



r-l

0
o

o
0





>






00

0)

- )





o N
n3 >

O r-
0) 0

0






c0
4-)




icS
c I










bCm

*m 0
O0









centered at 6 78.7 ppm for methine carbon adjacent to the oxygen, the peaks

at 6 171.7 and 174.3 ppm for carbonyl carbons (Fig. 5a). The spectrum for

the copolymer hydrolyzed in D 0 does not change the pattern, but shifts

the peak to lower field (Fig. 5c). A comparison between the hydrolyzed

copolymer and the diacid model compound can be used for the assignment

of spectrum.

In a large series of compounds containing carbonyl groups, the

shielding is mainly influenced by the local electrons on the carbons.

The two carbonyl peaks Lui,.~-t that two types of carbonyl groups are

present corresponding to the two anhydride carbonyls proposed by H-nmr

apectra, where one of the anhydride units is in the backbone and the other

forms the bicyclic ring. The two carbonyl carbons in each anhydride unit

are not expected to be greatly different from each other as far as the local

electron density is concerned. Therefore, the broadening of the peaks can

be explained either by the two different carbonyl carbons in each anhydride

unit or by the mixing of both cis and trans anhydride forms. A broader

peak is observed at the lower field, which may indicate the equal mixing

of both the cis and trans forms.

The assignment of each carbonyl peak can be made by considering the

chemical shift difference between cis and trans configurations (A cis a),

which would broaden the carbonyl peaks. The carbonyl carbon absorptions

of succinic anhydrides have been reported to be between 6 171.7 and 175.3
65 13
ppm. The C nmr spectrum for a dl-meso mixture of 2,3-dimethyl succinic

acid is shown in Fig. 6. The chemical shift differences between the

two carbonyl carbons, the two methine carbons and the two methyl carbons

are 0.7, 0.9 and 1.4 ppm respectively. This small chemical shift differ-

ence for carbonyl carbons between the isomers of dimethyl succinic anhydride























CM








(J
C\J

OCM





r-3-


v


E-
0,
a




























co

t--


* '0
hCOr-A

bC *j
U~


cn~ 0
~d 0
C)








is expected for the carbonyl carbon peaks for the copolymer where only

a broadening effect is observed. The peak at the lowest field can be

thus assigned for the carbonyl carbons on the backbone because it is

broader than the other carbonyl carbon peak. This is reasonable because

the sharper peak then assigned for the anhydride on the ring, can be

explained by the less population of cis form. This sharper peak is

broadened by the hydrolysis of the copolymer as expected by the loss

of the rigidity of the bicyclic structure.

A comparison between the spectrum of the copolymer and poly(maleic

anhydride)(Fig. 5b)8 showed clearly that the broader carbonyl carbon peak

can be assigned to the anhydride unit on the backbone, and also, the methine

carbon peak at the higher field is for the anhydride unit on the backbone.

On the other hand, the two peaks at 51.5 and 53.7 ppm with a difference of

2.2 ppm can be assigned for the two non-equivalent methine carbons on the

six membered ring by comparing with the $- and y-carbons on the tetra-

hydropyran which has a difference of 2.8 ppm.

The peaks at the lower field of the methine carbon region (6 51.5-

55.5 ppm) are then assigned to the methine carbons on the ring anhydride

unit; the larger peak from trans isomer and the weak peak from the smaller

contribution of cis isomer. The methylene carbon peak is assigned to

the trans isomer which is broadened by the non-equivalency of the two

methylene groups in the copolymer. The shoulder at 6 35.8 ppm can be

assigned for the methylene carbons of the less populated cis isomer.

By comparing the methine carbons of the copolymer with poly-

(diallyldimethylammonium)chloride, (XIV), 1,1,3,5-tetramethylpiperidinium

iodide, (XV), and 1,1,3,4-tetramethylpyrrolidinium iodide, (XVI), in

Table VI, the chemical shift difference between the cis- and trans-

methine carbons in the copolymer is closer to the six-membered ring







structure than the five-membered ring structure.


P:
U &


Table VI

Chemical Shits Differences Between cis and trans Disubstituted
Vincinal Carbons in 13C nmr Spectra

Structure A6cis-trans (ppm)
On the Backbone On the Ring


Hydrolized
Copolymer
of DVE-MAH

2,3-Dimethyl
Succinic Acid

XIV

XV

XVI


0.9


4.5-5.0


1.8

6.2


66


Kunitake and Tsukino66 suggested an all five-membered ring structure

for the copolymer of DVE-MAH system by the fact that a highly symmetric

structure is involved, the two singlets observed for the carbonyl carbons


-'i


, b4










and the comparison of the estimated chemical shift values to the

experimental values. This suggestion can be argued against by (1)

in the spectrum of the copolymer, the difference between the two

carbonyl carbons in each anhydride unit is so small that a splitting

causes only the broadening of the peaks. Hence, the absence of the

doublet for each peak cannot be explained as the absence of the non-

equivalent carbonyl carbons, such as those in the six-membered ring

in the copolymer. (2) The analysis of H-nmr spectra was best represent-

ed by six-membered ring copolymer structure, although the unlikely

mixing of both five- and six-membered ring structures cannot be ruled

out completely.

The Temperature Dependence on the Copolymer Structure

Due to the possibility of the mixing of both six- and five-

membered ring structures in the copolymer, temperature effect experi-

ments were carried out to investigate the temperature dependence on the

contribution of these two structures.

The copolymers were prepared at different temperatures, 250, 720,

1000, and 1300C. The results are shown in the experimental section. The

spectra for each copolymer are shown in Fig. 7. No major change was

observed. The small side peak a.t 6 35.8 and 51.5 ppm both gradually

disappeared or flattened with the decreasing of temperature. This small

change cannot be considered to be real because of the accidental experi-

mental errors such as lower resolution and the different concentrations of

the samples. Even the different solvents used for preparation should be

considered.

It is reasonable to conclude that no significant change of structure

caused by the temperature effect is obtained. This fact can be explained











-co o---/- 0
H. H
A
/ H-CH CH

r\ 2









(b)











I






(d)


171.7 78.7 51.544.2 29.2
ppm (6)
Fig. 7 1C nuclear magnetic resonance spectra of DVE
MAH copolymer prepared at (a) 130, (b) 100, (c) 72,
(d) 25 OC









by the production of only one energetically favored product which is

the six-membered ring structure as revealed by all the spectroscopic

analysis.

The Mechanism of Cyclization

The structure and temperature analysis concluded that a highly

energetically favored six-membered ring copolymer was the product of

the copolymerization of DVE-MAH system. In cyclization of the sym-

metric non-conjugated dienes, the ring size is controlled by the

entropy effect of the two ring formation processes. A five-membered

ring product is favored because of the less entropy change involved.

With substitution, a sterically favored six-membered ring formation

is able to compete with the former process. Also, the substitution on

the radical carbon of the uncyclized radical makes both the processes

higher activiation energies and hence, less selective. At the extreme,

with two electronegative and steric substituents on the radical carbon,

a six-membered ring formation will be highly favored.47

The energetical factor is much different for a cyclization involving

non-symmetric non-conjugated dienes such as the cyclization in the

cyclocopolymerization of DVE-MAH system. During the cyclization step,

the vinyloxy double bond is attacked by a radical on the anhydride unit:


0.



0O
0 0



XVII / N'/-



0









This process can be shown to be highly enthalpy-controlled by

considering the closer energy gap between the HOMO of vinyloxy double

bond and the singly occupied molecular orbital (SOMO) of the anhydride

radical than that for the corresponding symmetrical diene cyclization.




LUMO


LUMO


SOMO
alkyl
radical SOMO
stabilized H':'lD
HOMO radical destablized
double double bond
bond


0




X- O




The HOMO of the vinyloxy double bond is polarized to have higher

orbital density on the terminal position.6 Therefore, a fast radical

addition on the terminal carbon of the double bond leads to a six-

membered ring radical. A copolymer with six-membered ring structure X

is thus obtained.

As discussed in chapter I, a charge transfer complex was proposed to

explain the fast cyclization. The charge transfer complex can be applied

here with the help of HOMO-LUMO concept to predict the ring structure

of the cyclization step.

The Milliken theory of overlapping and orientation principle predicts

that stabilization in the molecular complex formation should essentially








be determined by the overlap of the donor HOMO and the acceptor LUMO.68

In the examination of ir and Raman spectra of DVE, Claugue and Danti
69
proposed the presence of two rotational isomers.9 The more stable isomer

has C symmetry, in which the two vinyl groups, although coplanar are
s
non-equivalent. Hirose and Curl examined the microwave spectrum and
70
assigned the C conformer. They found a small nonplanarity caused

by H-H repulsion between the 3-hydrogen of the cis vinyl group and the

a-hydrogen of the trans vinyl group-(XVIII).


H






H
XVIII

cis-trans


The charge distributions in vinyl ether and vinyl methyl ether were

calculated by CNDO/2 method by Fueno, et al.67 It was found that a large

electron density was on the terminal position as in sturctures XIX and

XX.







O CH


XIX









This charge density of orbital actually describes the orbital density of

the HOMO of DVE. The LUMO of MAH has been described by Fukui as

structure XXI with higher orbital densities on the double bond carbons,

but antisymmetrical to the plane of symmetry of this compound.71

Therefore the most stable conformation for a DVE-MAH complex can

be expected as XXII, based on the conformer structure of DVE and the

molecular densities of both.comonomers.


XXI
0 path a


R, 0


R* path b



R


XXII


(Eq. 16)




XVII


.ii-n this complex is initiated by a radical, a six-membered ring

radical will be formed concerted (Path a) or stepwise through an anhydride

radical addition on the terminal carbon of the vinyloxy unit (path b).

This complexation would reduce the energy gap between the complex and

the propagating anhydride radical, thus, a radical addition on the

complex occurred and the reaction is supposed to be fast. This special









complexation and/or interaction would significantly reduce the activa-

tion enthalpy for the formation of six-membered ring. In the range

of the temperature sutdied, a five-membered ring formation cannot compete

with it at all, which explains the temperature independence on the

structure of the cyclocopolymerization.

In conclusion, on the mechanism of the cyclization and copolymer-

ization of DVE-MAH system, it is reasonable to be stated as follows.

(1) The intramolecular cyclization is favored over the intermolecular

addition due to the lower entropy change of the former process than the

latter one. This explains the high degree of cyclization.

(2) The entropy preference cannot be explained on the base of activation

energies and the statistical probability. A preorientation either

through the delocalization of the radical with the intramolecular double

bond or the formation of complex is proposed.

(3) This preorientation would lead to a six-membered ring structure

by a favorable energy factor based on the !IlH',) orbital density of DVE.

For a symmetrical nonconjugated diene the five-membered ring cyclization

is favored by the entropy factor.

(4) A faster rate of this cyclocopolymerization than the copolymerization

of the corresponding monoolefin -pairs can be explained by the closer

energy of the anhydride radical to the complex.

The proposed cyclization mechanism can be applied on other comonomer

pairs and is worthy of further investigation.















CHAPTER III
THE COPOLYMERIZATION OF DIVINYL ETHER-FUMARONITRILE

Introduction

It was pointed out in Chapter 1 that a donor-acceptor pair of

comonomers could produce alternating copolymer through a charge transfer

complex (CTC). In the cyclocopolymerization of donor 1,4-dienes with

acceptor monoolefins, alternating cyclocopolymers having 1:2 composi-

tion were obtained for several systems. The participation of CTC formed

between the donor and acceptor was proposed to explain the alternating

copolymerization. However, it has been known for sometime that the

compositions for the copolymers are 1:2 while the stoichiometry of the

CTC are always 1:1. An alternating copolymerization of a CTC and a free

monoolefin was proposed as an explanation. It has been shown that

when an acceptor monoolefin is highly sterically hindered and hence much

less reactive, according to the above explanation, a 1:1 cyclocopolymer
14, 43
was obtained apparently through the homopolymerization of CTC., 43

With a less sterically hindered monoolefin and less reactive monoolefin

it is possible to form a cyclocopolymer with composition between 1:1

and 1:2. The cyclocopolymer of DVE-FN has been reported having the FN

content between 0.55 and 0.63 mole fraction which is in the range of
32
0.50-0.67 for the 1:1 and 1:2 composition.32 With dilution, less FN

content was reported and a contribution of either homopolymer structure

of DVE and/or 1:1 comonomer unit in addition to the regular 1:2

comnomer unit was proposed as an explanation.37
comonomer unit was proposed as an explanation.









A further structural analysis and the study of the participation of

CTC in the copolymerization are discussed in this chapter

Results and Discussion

Study of the DVE-FN complex in Acetonitrile

On the basis that the complex formed between DVE and FN may

participate in the mechanism of initiation of the photocopolymerization

in acetonitrile solution, the characteristics of the complex were

studied in the same solvent. The existence of the complex was estab-

lished by UV spectrophotometry. A mixture of 0.6 m/l of DVE and 0.6 m/1

of FN showed a large absorption between 250 nm and 350 nm (Fig. 8)

although a distinguishable new absorption band was not observed.

This large enhancement of absorption indicated the presence of complex.

A 1:1 stoichiometry was determined by the continuous variation method
72
at 300 nm- (Fig. 9). The maximum of the absorption for different

compositions of DVE and FN, while their total concentration was kept

constant was found for equimolar composition.

The charge transfer complex of an acceptor-donor pair is in

equilibrium with the free components. The charge transfer complex exists

in resonance between the no-bond state and the dative state; thus the

wave function of the charge'transfer complex (TCT) can be expressed as a

linear combination of wave functions of the no bond state [Y(D,A)] and

the dative [W(A*, DT)] (Equation 1 and 2).


K
c (
A + D --- [(A,D) + (A*, D.)] (Eq. 17)


CT = a'-(A,D) + b.'(A7 DI)


(Eq. 18)
























o c

oyr,






S0 o
m 00


oo


C)
O 11











4 0
*H r










N *H-





0 *r-Q





-0 0
-P



















CDM
0o o
- O >J o
xC D










oo


So Qo




CM O


CD;


a









I -IA0























































































i O O o 0
aoueqjosqv


0*





C+
C X II










o 4-











-H 4 -)
Eo











,r-i
,O







4-) 0
0
co
0 a
O










0 --


a)
S0o3


0 4

*H 4.o
m r'- o

o o
-o CD









C *H)


0
o oO











4) C
u








F Iol





p-i (ti








For a regular loose complex, a2>>b2 in the ground state of the com-

plex. The dative structure corresponds to an ionic-radical-like pair.

There must be also an excited state (41CT) which can be called a charge
73
transfer state given by


CT = b o'(A,D) + a Y,(AD,D*) (Eq. 19)

;':2 '2
The excited state is mostly dative (a 2>>b ); excitation of an electron

from TCT to 'CT essentially amounts to the transfer of an electron from

donor to acceptor. Spectroscopic absorption would occur with this excita-

tion (charge transfer absorption). A charge transfer absorption is

possible for any pair of molecules if in contact, even if they do not

form a stable complex.

A complete absorption spectrum of a complex consists of absorption

to (1) locally excited state (states of donor or of acceptor, more or

less but usually not greatly modified in the complex.) (2) charge

transfer states [(YCT in Eq. 19, and other charge transfer states includ-

ing the excited dative structures, for example 4(D* ,A*)].

The equilibrium constant (K ) of the complex can be measured by

using Merrifield and Phillips method.74

Ac
(D) -K A + K (A)c (Eq. 20)
(D)o c Ac c ( Ac

(D)o = The initial donor concentration

(A)o = The initial acceptor concentration

Ac = Absorbance of complex at certain wavelength

K = The equilibrium constant for the formation of weak complex

=(Complex)/(D)(A)










hc = The extinction coefficient of the complex at wavelength.


For a series of solutions containing different concentrations of

DVE but with constant concentration of FN, with condition (DVE)>>(FN),

a plot Ac/(DVE) against Ac should be linear. From the gradient of the

line, K may be evaluated directly without recourse to an extrapolated

intercept. The absorption of DVE-FN complex and the resulting plot in

acetonitrile are shown in Fig. 10 and Table VII. The equilibrium con-

stant was small (K = 0.10) and cannot be evaluated exactly, but it is

compatible with the equilibrium constant measured in methanol solution
39
(K = 0.12 to 0.20).
c



Table VII

Determination of Equilibrium Constant of rEN-DVE in
Acetonitrile with Constant FN Concentration (0.00101 m/1)

(D)0 280 nm 300 nm

m/c A A/(D)0 A A/(D)0


0.846 0.031 0.0520 0.013 0.0154

1.69 0.081 0.0479 0.029 0.0172

2.12 0.100 0.0472 0.031 0.0146

2.96 0.137 0.0463 0.042 0.0142

3.81 0.152 0.0399 0.040 0.0105

K 0.09 0.11
c




The equilibrium constant of complexation can be determined by nmr
75
spectroscopy using the Hanna-Ashbaugh equation.75 The attempted nmr

method failed because one of the quartet absorptions of the a-vinyl






















































































L_ (NJ CH

0 C C C) C

ao-qoq


()
H


4-)
rl

0
cj C)
Q)
0 0










0




4-)





0)

0 ) 0




0
co









(,0








Ct



C')
Q 0)









*rl









proton of DVE covered the peak of the protons of FN, whose chemical shift

was to be used to determine the equilibrium constant in acetonitrile.

The Structure of the Complex

The spectroscopic determination of stoichiometry and the equilibrium

constant of the charge transfer complexes of monoolefins with 1,4-dienes
37
have been thoroughly discussed previously.37 'i lr ly, in all cases

studied the stoichiometry is 1:1. The structure of the complex has not

been established. Either one or both of the double bonds of the 1,4-diene

can be completed with acceptor. Take DVE and FN as an example:


0 0


A, / 1:1 complex
CN CN
C-N, CN CN -- -CN






The first structure is not likely because with a free double bond

available, a second acceptor would be completed more or less as easily

as the first acceptor molecule to form a 1:2 complex.


S70 CN
CN 1:2 complex


CNCN

As pointed out in Chapter II, considering the conformation of DVE

and the orbital densities of both HOMO of DVE and LUMO of acceptor, the

most stable conformation of the complex can be predicted as structure X:III.

The proposed relation between no bond state and the dative state of this

complex is shown in equation 21.











NC



t N

9 XXIII





NC
NC

.--/-N "(Eq. 21)

+ 0 __
Dative state No bond state


At ground state the complex can be represented by the no bond state,

the excited state (CTC)* after the absorption of appropriate light energy,

can be represented by dative state. In general an excited state would be

radiationlessly deactivated without associating with external environment.

In the case of (CTC)*, the state is so polar that the environmental polar

molecules (acceptor, donor and ground state complex) would participate in

its deactivation processes.

At 236 nm, while most of the light is absorbed by the free monomers

to form excited monomers, the excited state of DVE would interact with

the ground state of FN to form an exciplex which possesses higher energy

than the previously mentioned c rge transfer state [(CTC)* formed by

irradiation at 300 nm where only the complex absorbs].76 The exciplex is

polar enough to be deactivated with the participation of ground state

molecules. (Scheme I)











300 nm environmental
(DVE -- FN) -- -- (DVE -- FN)* en DVE + FN
molecules


236 nm FN environmental
DVE n DVE* -F-- (DVE**FN) Dr -ome DVE + FN
molecules


environmental
molecules



DVE



Scheme I



The Structure of the Copolymer of DVE-FN System
13
Ir and H-nmr spectra. The ir, H-nmr and 1C nmr spectra were record-

ed for the copolymers prepared by irradiation at 300 nm, 236 nm and with

AIBN, in acetonitrile with feed composition fd = 0.5 (Table VIII).



Table VIII

Comparison of Copolymers Initiated by Different
Methods in Acetonitrile

Feed Composition Initiation Conversion md'

(FN) (DVE)

0.6 m/1 0.6 m/1 AIBN 44% 0.408

0.6 m/1 0.6 m/l 236 nm 40% 0.402

0.6 m/1 0.6 m/1 300 nm 55% 0.486
*Molar fraction of DVE in copolymer calculated from nitrogen
and carbon content





62


All the copolymers showed the same characteristics in ir and H-nmr

spectra, thus indicating that the same propagation processes are employed

for all methods of initiation.
-I
The copolymers absorbed in the infrared region: 2250 cm- (s)

(CN stretching) and near 1100 cm-1 (broad)(ether group), showing the

existence of the comonomer units. There was also the presence of
-1 3
vinyloxy double bond absorption at 1630 cm It has been observed32

that only a small amount of residual unsaturation (from 2.0 to 3.5%) was

in the copolymer prepared by the initiation of AIBN in dimethylformamide.

The infrared spectra of copolymers initiated by light at both 236 nm

and 300 nm had the same characteristics as the one initiated by AIBN in

acetonitrile (Fig. 11). It is reasonable to assume that the same small

amount of unsaturation was in the photocopolymers. This conclusion was

also shown in the H-nmr spectra (Fig. 12) where no absorption contributed

by vinyloxy double bond was observed. Therefore, there is no significant

contribution of the structures with the pendant vinyl group in the copoly-

mer.





0

/ XXIV

\ CN / n

CN

The composition of the copolymer. The composition of the copolymers

has been determined over a wide range of monomer feed compositions. The

copolymers of DVE-FN are quite hygroscopic. The elemental analysis showed

higher hydrogen and oxygen weight p-r>c:nrtjr, than calculated from nitrogen





























Wave number (cm- )
Fig. 11 IR spectra of the DVE-FN copolymer initiated
(a) at 300 nm, (b) at 236 nm, (c) by AIBN.


ZY VdN
CN
CN

a








7.0 6.0 5.0 4.0 3.0 2.0 l.O 0
ppm (6)
Fig. 12 60 MHz nuclear magnetic resonance
spectra of the DVE-FN copolymer initiated
(a) at 300 nm, (b) at 236 nm, (c) by AIBN


~ I







and carbon. The nitrogen content is only from FN monomer, the calculation

of the number of nitrogen atoms permitted the determination of the

copolymer composition.



no. of moles of FN = no. of moles of nitrogen atoms/2



Sno. of moles of carbon atoms no. of moles
no. of moles of DVE = o F
of FN x 4






md = the molar fraction of DVE in the copolymer



no. of moles of FN
no. of moles of DVE + no. of moles of FN


The results are shown in Table IX and Fig. 13.


Table IX

The Compositions of Copolymers Prepared in Acetonitrile at
Room Temperature within 10% Conversion

Concentration (m/l) 300 mn 236 nm
b c
(FN) (DVE) fd md m

0.4 1.6 0.80 0.410 0.408

0.8 1.2 0.60 0.372 0.436

0.6 0.6 0.50 0.486a 0.402a

1.2 0.8 0.40 0.412 0.400

1.6 0.4 0.20 0.351 0.436

Average 0.406 0.416

More than 40% conversion.
Molar fraction of DVE in feed.
Molar fraction of DVE in copolymer calculated from
nitrogen and carbon weight percentage.








































ol x


0


K
\ \
Ctd\ *0\


\\ \


I I I


-= --


I I

o o
0 0


0 0 0 0


io od
-P
4.)


0

4()
co 4
Or





0o
E)
4-1

o 0
0
o












o
0 ,(


















C
oo


o o
o
E ^








c'3
bt )'>








There was no apparent trend for compositions of copolymer. The

copolymers irradiated at different wavelengths have similar compositions

(average md = 0.406-0.416). It indicated that the same propagation process

was employed for both wavelengths. For a typical 1:2 copolymer and a 1:1

copolymer, md is 0.33 and 0.50 respectively. The compositions of both

copolymers fell in the range from 0.351 to 0.486 within a wide range of

feed compositions. Together with the spectroscopic data this is the basis

of assuming a copolymer containing both the 1:1 and 1:2 copolymer structures

XXIV. Note that is is not necessarily a block copolymer in the sense of

1:1 and 1:2 monomer combinations. The 1:1 repeating unit has been found
77
in the copolymerization of p-dioxene-MAH,77 DVE-DMTHNQ and DVE-THNQ
43
systems, in which the homopolymerization of a 1:1 CTC was considered.

CN

0 "0


CN XXV
S CN x
CN CN



When the reaction time of copolymerization was long enough so that

the reaction was almost completed, it was observed that the yield at 236 nm

for large excess of DVE in feed composition was more than the corresponding

theoretical maximum of conversion of a perfect 1:2 copolymer but less than

or close to the 1:1 copolymer (Table X). At 300 nm the yield was less

than the theoretical 1:2 copolymer.

The excess yield at 236 nm can be explained by the involvement of

either the homopolymerized DVE or the 1:1 copolymer structure in the 1:2

overall copolymer structure. When FN is about used up at the end of the










reaction, homopolymerization of DVE has a chance to compete with the

copolymerization. The fraction of DVE in copolymer (md) supports the

involvement of homopolymerization of DVE. What is important is that the

close value of nd at both 300 nm and 236 nm (md = 0.560.03) indicating

that the involvement of homopolymerization is in the propagation process

instead of the initiation process, in other words, in the early stage

of the copolymerization, the homopolymerization is not involved.



Table X

The Limiting Yield of Copolymerization with
Excess DVE in Feed Composition


Wavelength
(nm)

300






236


Feed
Composition


2

5

10

1

2

5

10


Yield
(mg)

24.8

40.1

115.7

25.7

45.1

78.9

16&.0


Theoretical Yield
1:2 Copolymer 1:1

32.5

49.7

135.1

24.8

32.5

57.3

143.7 1


The fraction of DVE in copolymer calculated from nitrogen and carbon
content.
Based on the reacted amount of FN.
Average = 0.56.





The different initiating wavelength would finally form the same

intermediate or intermediates which initiates the same propagating radicals.

13
The structure of this copolymer can be further confirmed by 1C nmr spectro-

scopy.


b
(mg)b
Copolymer


a, c
md


32.5

42.5

75.0

.88.2


0.54

0.59



0.52

0.57








13 13
The 1C nmr spectra. The 1C nmr spectrum of the copolymer is

shown in Fig. 14. The four peaks at 6 118.5, 117.9, 116.6, and 116.1

ppm from TMS in the CN region supports the six-membered ring structure

where two of them correspond to the two unsymmetrical CN's on the ring

and the other two correspond to the CN's on the skeleton.

It was pointed out in Chapter II that the small difference between

the two carbonyl carbons would only cause a broadening of the peak

instead of splitting it. This assumption can be applied here that the

doublet of each CN peak does not indicate two non-equivalent CN's in

the ring or on the backbone. The chemical shift difference (0.5-0.6 ppm)

between each peak in the doublet is close to the difference of the carbonyl

peaks of dl-meso mixture of 2,3-dimethyl succinic acid (0.9 ppm). We

can assign the doublet as the consequence of the mixture of cis- and trans-

dicyano substitutions on each fumaronitrile unit. These assignments will

lead to a reasonable conclusion that in backbone, cis- and trans-disubstitu-

tions are more or less equally populated, by considering the equal

intensities of the doublets as shown on the peaks at 6 117.9 and 118.5 ppm.

The CN's at 6 116.6 and 116.1 ppm indicated the different populations of

cis- and trans-disubstitutions, whichare possible during the ring formation.

It is difficult to assign the chemical chifts of the CN groups

without comparing with model compounds, but at least a copolymer with

the 1:1 and 1:2 copolymer composition is consistent with the spectra.

The two C-O-C peaks in the C-O-C region indicated the existence of
13
two different C-O-C linkages in the copolymer. Comparing the 1C nmr

spectra of homopolymers of DVE with the copolymers enabled us to clarify

e exclusion of homopolymer structure in the copolyr.78 (Table XI)
the exclusion of homopolymer structure in the copolymer. (Table XI)















































Fig. 14 13C nuclear magnetic resonance
spectra of the copolymer initiated (a) at
236 nm, (b) by AIBN, (c) at 300 nm.









Table XI


Comparison


13
of 1C nmr Spectra Between
the Copolymer of DVE


Homopolymer of DVE and
and FN


Chemical Shift
(ppm from TMS)
of C*'s


No. of CN Substitutions
on C*'s


Calculated
total shift
(ppm)


Homopolymer


a, 0; B, 1; Y, 2

a, 0; l, 1; Y, 1


*The special carbon in consideration.


XXIX


XXVI


CN CN
CN CN


Material


XXVIII

XXIX

XXX


82.3, 83.4, 151.1

84.2

77.8


Copolymer


XXVI

XXVII


79.6

76.7


XXVIII


XXVII








Comparing the C*'s in trimethyleneglycol (two oxygens are three carbons

apart) with pentamethyleneglycol (two oxygens are five carbons apart),

there is a 2.9 ppm difference in chemical shift due to the distance of
79
the two oxygens.79 The 2.9 ppm difference of the two C-O-C absorption

in the copolymer can then be explained by comparison between the C*'s

in structure XXVII and then XXVI.




HO OH HO OH



59.2 ppm 62.1 ppm







In conclusion, at low conversion, the copolymer contained a mixture

of structures XXVI and XXVII, a small amount of residual unsaturation and

probably some homopolymer structure which can be neglected for kinetic

consideration. The average md = 0.41 corresponding to a %". of structure

XXVII. This ratio of structure XXVI to structure X'".'11 was reflected
13
by the almost equal intensity of the two C-O-C absorption in 1C nmr

spectra.

To distinguish between pure five- and six-membered ring structures

is very difficult because of the lack of information. As discussed

in Chapter II, it is unlikely to have a mixture of both six- and five-

membered rings structures in the copolymer because of the simplicity of

the spectrum. Furthermore, a favorable conformation of the complex and

the orientation of the cyclization makes the six-membered ring structure

more possible.









Quantum Yield Study

Quantum yields for formation of copolymer were measured in aceto-

nitrile and at different wavelengths. The intensities are different at

different wavelengths for monochromatic light source. It will be pos-

sible to compare the quantum yields at different wavelengths by knowing

the dependence of intensity on quantum yield.

The data obtained for 0.6 m/l FN and 0.6 m/l DVE in acetonitrile

at-300 nm showed small dependence on light intensities. The intensity

was altered by using different slits.

The quantum yields were not exactly independent of the intensity

for nonequal molar solutions with 0.47 m/l of FN and 0.71 m/l of DVE

in acetonitrile at 300 nm. The intensities were altered either by

the different slits or with a copper screen in front of the sample tube

in this case. Also, the quantum yields were changed with different

intensities at 236 nm, with 0.6 m/l of DVE and 0.6 m/l of FN. The data

of the light intensity dependence on qauntum yeild and rate are listed

in Table XII.

The linear dependence of intensity on quantum yield are shown in

Table XIII. The linear correlation coefficients were close to one

indicating that the equations can be used for comparing the quantum

yields at the same intensity for different wavelengths. The results are

shown in Table XIV. Apparently the quantum yield at 236 nm is larger

than at 300 nm.

Ferree and Butler observed that the quantum yield was constant or

declined slightly as the wavelengths decreased, until part of the divinyl

ether band is excited at 236 nm, at which point the quantum yield in-

58
creased drastically. This fact suggests that only excitation in either



























CO r-H LO C0 D m D CO
Cm =f r-C H D CO t- @l in N ln m El- Cc m H
o n C c- oc ri o N H C o Co o o

C) 0 CD H-, C CD C) C) C) C) C) C) C) C) CI








rI-









4o O O 4 CO -o cO c O LO O on o4 O
0 C) C) C) 0 0 0 C0 0 CD CD 0) 0 -0 0H

C) C) C) C) C) C C) C) C) C) 0D C) C) C) C)


4










O
0









H O
O

















0

UO
0 -
C,



4 4

cn
HO
CO








C M
0

0
0
*r


'0






q) (U
c




0a
r0










Q) Ix
HH









C
orro



05
4 00



H C)

O E
0 0
0<


M C E
O H





C0


4H


C0

l-l


in co 4-

co CO in N N co










L10 r
0o oC (D CD C04

o co C CO CD CO

+1 +1 +I +1 +1 +1
LO CDO O LO LO LD
CO CO CO CO CO CO
C@ CM @4 @4 @4 @4


0 4
S0


0 C

(o

O

E



0 0
0
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*4
0 44
r C
O 0




40 '4I
r4-



0 0
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044





0 0
*H 4-i

U u

C) C)


0 0


OD (




0.0


,--i ,-D LO -" (D (D --) I ,--t
I H r-i H H H- H H
C-lD C) C C) CD C) C) C)D


0 0 0 0 0 0 0 0 0



SH H
roo CM CO Ln .d- ilL


0 CO 4--


+1 +1 +1
0 0 0
C 0 0C
CO .CO CO


















0C
.,-1 (

H *H


0 0
rO


00
U














0
*H




r-
r m
'o
















CY 0

(0
0
-)
H O c

1 0




O I--t 0


.0 0



O


SO )
0-







c0






0 O*>
0 H




















S 0
S 0

-P



















ro
M, r0
C 0)
*H *H




C 0-!
0
0 0

r0


co 0 C)n C

cm; O O


-- I H-
I 0 I
O r-4 CO O
-I C, r-i-
00o L
x H
-H + I-I
I + b
bj D O M O
In 0 rH 0
r r-1 r I H
I I H 0
O O C r-1 <
--I n -i co c-
x C; x
o o o



0 ) O C o

IH 4 r- H

0 I + r- I C- I

I II 0 II 0 II


11 CN I1 C II C1
o o o
0 0 0

0( CO C\N


- r- r-H r
0t f0 0

S00 0 00 0

H-1 H-I H H-- i H r-H


0
Co)


U
0

()

0

0
44
C



'H



r-i



C








M





0T









the charge transfer complex absorption band or the divinyl ether

absorption band leads to initiation of copolymerization.



Table XIV

Comparison of Quantum Yield and Rate at 236 nm and 300 nm

Compound Concentration Wavelength Intensity Quantum Rate
(nm) Photons/sec Yield mg/min.
14
FN 0.47 m/l 236 8.86 x 1014 0.118 0.479

DVE 0.71 m/1 300 8.86 x 1014 0.076a 0.304a

aCalculated from equations in Table XIII.





It has been suggested that an exciplex was responsible for the

copolymerization while no ground state charge transfer complex was

observed,76 such as the photocopolymerization of vinylcarbazol and

acrylonitrile. Since at 236 nm the only effective photoabsorbing

species was DVE, the initiation process must proceed via the excited

state of DVE. Although there was no evidence of exciplex of DVE and FN,

no significant homopolymerization was obtained with DVE alone, this

fact indicating that the excited DVE initiated copolymerization possibly

through the interaction with the ground state of FN.



236 nm
DVE -236 > (DVE)*


(DVE)* + FN (DVE* -> FN)

exciplex









At 300 nm the photoabsorbing species was complex, therefore the

initiation process proceeded via the excited state of the complex.



DVE + FN ---< (DVE FN) ---- (DVE-FN)*
<---- 300 nm



At both wavelengths, the excited species dissociated into initia-

ting radicals. Although the initiating radicals have not been identified

they could be a paired cationic radical and anionic radical.


kd
(DVE+FM)* -- 2R*


(1 d
(DVE*-*FN)


The ionic radicals initiated the copolymerization through free radical

processes because both air and a small amount of diphenylpicryl-

hydrazyl free radical (DPPH) retarded the reaction.


R O
R* + (DVE -- FN) --

CN



N CN


A small amount of FN (1%) did not initiate

excess DVE (99%) to a significant extent.

ether radical formation can be excluded at

the copolymerization.

R* + =-0-= -- R-


the homopolymerization of large

This indicated that the divinyl

least in the early stages of


_0"









The initiation through free fumaronitrile cannot be excluded but probably

is not able to compete with the low energy pathway of the complex

initiation process.

At 300 nm the light was totally absorbed by the complex for the

solution of 1.2 m/1 and of FN and 1.2 m/1 of DVE.


FN + DVE -- (DVE -- FN)


(DVE -- FN)* is the excited complex.



(DVE FN)* (DVE)
(FN)

(DVE-- FN)


300 nm d
30 nm (DVE -- FN)* 2R*
cc


Ground state molecules


Scheme II

I = The light intensity absorbed by the complex.

=I (light intensity absorbed by actinometer).

c = The quantum yield with only radiation deactivation considered.

The excited complex may be deactivated by collision processes.

As discussed before the exact structure of the excited state is not

known, but it may still be very polar and very likely to be deactivated

by the polar monomers and the ground state complex. The radiationless

deactivation process may be proposed as in Scheme II.

The rate of formation of the primary radicals (R*) can be derived by

applying the steady state assumption and assuming that the radiationless

rates of the deactivation of excited complex is proportional to the total

concentration of monomers, (T).









-d(DVE -- FN)* (T)DE
( dt )rl = kr(T)(DVE --, TN)*
dt rl rl



Therefore,



d(DVE -- FN)*
d(D I-c Fc (DVE -> FN)"(kd + k r(T)) 0
dt cc d rl



From Scheme II



R. = k (DVE -P FN) =. (kdI c )/(kd + K ,(T))
i d dcc d rl



At 236 nm the complex absorbed insignificantly but DVE absorbed part

of the light, Id = absd(DVE), and is responsible for the initiation

through the following equation.


k'
236 nm FN d
DVE I DVE* ---) (DVE* -> FN) 2R*
d d df

rl
radiationless deactivation

Dd is the quantum yield with only radiation deactivation considered.

In the same way as proposed at 300 nm, the rate of formation of the

primary radicals (R-) can be derived by assuming the rate of the
d(DVE* --> FN)
deactivation of exciplex, (- d( ----) is proportional
dt rl
to the total concentration of monomers (T).



d(DVE* > FN)
dtV- = k (DVE*)(FN)-(DVE*-- FN)(k' + k' (T)) = 0
dt df d rl



k'dIabs d d(DVE)
R. = k' (DVE* --: FN) = d abs d d
i d k' + k'rl (T)
d rl









Dependence of Feed Composition on Rates

It was of considerable interest to measure the rate of copolymeriza-

tion obtained for different feed compositions. As explained later, the

study of the rate as a function of the feed composition when the total

monomer concentration is kept constant should give information on the

role of the charge transfer complex in the mechanism of copolymeriza-

tion.

The effect of the variation of the concentration of the reactants

on the rate of a photochemical reaction is difficult to determine

unless the rates are corrected to a constant absorbed light intensity

from known variation of rate with the absorbed light intensity.

The rate of copolymerization was measured in acetonitrile. The

samples were prepared as indicated in the experimental section. The

solutions were irradiated at room temperature for a measured period

of time and the reaction was stopped by immediately opening and roto-

vapping to dryness. Methanol was added, and the insoluble polymer was

filtered and washed with methanol, and dried in an oven at 500C at least

for 4 hours. The actinometer solution was irradiated in the same tube

right after the reaction. The rate was obtained by measuring the

weight of the polymer after drying. The dependence of the light

intensity on rate is reported in Table XII. The linear relation is

shown in Table XIII.

Rates of products formed in secondary reactions (including the

polymerization) usually show some other than first order dependence

on intensity. In general, bimolecular termination by a reaction

involving active chain carrying species results in rates proportional

to the square-root of intensity. Termination which occurs from a first









order reaction leads to a rate which is dependent on the first power

of intensity. It was observed that the rates were dependent on an

order between 0.72 1 of intensity. It was close to first order for

the equal molar solution at 300 nm. Possibly both the bimolecular and

unimolecular termination are operating in photocopolymerization. The

first order termination is more possible because the propagating radical

may be terminated by chain transferring to solvent and the polar monomers.

The dependence of feed composition on corrected rate was listed in

Table XV and XVI and Fig. 15 and 16.
.16
The rates were compared at I = 1.52 x 10 photons/sec and
14
6.4 x 1014 photons/sec for irradiation at 300 nm and 236 nm respectively.

It was observed that at 300 nm, the maximum rate was at fd = 0.5

(equal molar solution), but at fd > 0.5 at 236 nm for both total

concentration [(T) = 2.40 m/l and 0.60 m/l]. The composition of copoly-

mers were in the same range (md = 0.35-0.48), and not much different

from each other for both wavelengths. Interestingly, at 236 nm, the

rate maximum fell on fd = 0.66 and 0.80 for higher total concentration,

(T) = 2.00 m/l, but on fd = 0.55-0.80 for lower total concentration,

(T) = 0.60 m/l. The ir and nmr spectra were almost identical. These

facts indicated that the same propagation process was employed. The

different positions of rate maxima were then due to the different

initiation porcesses.

Mechanisms

The kinetical derivation of the overall rate of copolymerization

can be done by assuming the simplest propagation as follows.





















\ CN k
\ k12
/ \ \CN
CN
CN M2
CN m2







CN



I + (DVE F N) k -2
CN


CN m


(Cq. 22)


0

+ (DVE-> FN) -


CN CN
CN
CN

M m*
1 1


(Eq. 23)














Table XV

The Rate of Copolymerization of DVE-FN System in Acetonitrile
at 300 nm, at I = 1.52 x 10 Photons/Sec.

Total Ratea Total Ratea
Concentration fd (mg/min) Concentration fd (mg/min)
(m/1) (m/l)

0.60 1.00 nil 1.20 0.80 0.179

0.60 0.90 0.051 1.20 0.60 0.313

0.60 0.82 0.117 1.20 0.50 0.376

0.60 0.80 0.098 1.20

0.60 0.70 0.131 2.40 0.98 0.087

0.60 0.67 0.154 2.40 0.70 0.475

0.60 0.60 0.150c 2.40 0.60 0.604

0.60 0.55 0.154 2.40 0.50 0.749

0.60 0.52 0.185 2.40 0.33 0.580

0.60 0.50 0.198 2.40

0.60 0.45 0.161 2.40

0.60 0.40 0.190 2.40

0.60 0.40b 0.053 2.40

0.60 0.30 0.167 2.40

0.60 0.20 0.147 2.40

0.60 0.00 --- 2.40
aThe rates were corrected to I = 1.52 x 106 photons/se with equation

log rate a /rate = log 1.52/I x 10.
b cal exp exp
Sample was open to air.
CAverage values.






83











(\] *
LnH






o E-'-
F
o
0 H II 0






o
Co

o po

OC






O *rl *H
LA CO+
Y / ", P 4r-



S\ 0 0
\ X 0
0




o--T--
; C

Sko



\ \ ,C-
S 0 4 -




o o 4-Co







(o
ac
0 0 I 000 0 4 -1


(~uI/rEC) uoT 4- ) ( q-











Table XVI

The Rate of Copolymerization of DVE-FN System in Acetonitrile
14
at 236 nm, at I = 6.4 x 10 Photons/Sec.

Total Ratea Total Ratea
Concentration fd (mg/min) Concentration fd (mg/min)
(m/l) (m/1)

0.60 1.00 nil 2.00 0.90 0.0413

0.60 0.90 0.0217c 2.00 0.80 0.0692

0.60 0.80 0.0274c 2.00 0.80b 0.0267

0.60 0.70 0.0231c 2.00 0.66 0.0686

0.60 0.60 0.0229c 2.00 0.50 0.0644

0.60 0.55 0.0303 2.00 0.40 0.0448

0.60 0.50 0.0246c 2.00

0.60 0.48 0.0235 2.00

0.60 0.45 0.0170c 2.00

0.60 0.41 0.0197 2.00

0.60 0.40 0.0179 2.00

0.60 0.31 0.0209 2.00

0.60 0.00 --- 2.00

The rates were corrected to I- 6.4 x 101 photons/sec with the equation
log rate /rate = 0.72 log 6.4/I x 10
b cal exp exp
Sample was open to air.
CAverage value.























































































0 0 0 0 0 0 0

0 0 0 0 0 0 0

(uyTm/S) uoTqezTjGwa m odoo jo Ga'H


-zr

\O *


H


Eo



L(\




4-)O
C\l


cd






0



-H 0

-r 4-)
cHO


4D, 4-)

a0 0)
u 0
O o




00







- 0
oC







r-t _

aip
E >








E0
O0









4->r

(Dr









In this copolymerization, the cyclized DVE radical (XXXI)

attacked complex and monomers to produce polymers with 1:1 and 1:2

compositions, respectively. The 1:1 composition cannot be explained

by the polarity of the radical and complex, because the negatively

polarized radical (XXXI) would attack the positively polarized carbon

carbon double bond of an acceptor monomer since polymerization of DVE

under the same condition is negligible. The propagation of the copoly-

merization can be interpreted as a competition between the acceptor

monomer FN and the CTC toward the cyclized DVE radical (XXXI).

Although the cyclization of the DVE radical (XXXI) could react

preferably with the acceptor such as MAH because the reaction of a

radical and a monomer of opposite polarities would stabilize the

transition state,0 the FN may not be so preferable because of the

less polarization then MAH. Thus, the reactivities of FN and the complex

are compatible. As a result, a competition between FN and CTC control

the structure of the copolymer of DVE-FN system. On the other hand,

the complexation of the HOMO of DVE and LUMO of FN would increase the

energy of HOMO of DVE71 and make the CTC more reactive toward the

destabilized cyclized radical (XXXI) than the uncomplexed DVE.

In equations 22 and 23; the cyclization may proceed by both

concerted and stepwise processes. A fast cyclization has been observed

for this cyclocopolymerization, which indicated a concerted mechanism.

But some results showed the stepwise mechanism, especially for the

fact that both cis and trans disubstituted ring units were obtained in

the analysis of spectra. A stepwise cyclization cannot be ruled out.

However, by assuming a fast stepwise cyclization (probably just a little

slower than the cis-trans rotation around the disubstituted single bond)










of radical XXXII, the same result will be concluded as with the

concerted process as far as rate is concerned.







CN

CN

XXXII



By a;zuinir, only the cross-termination



t12
mi + m2 -- dead polymer



and the steady state:



kl2(ml')(M2) = k21(m2.)(M)


k (M )
Ri = R = 2k 2(ml.)(m ) = 2k 21(M (m.)2
21 1


Then, by assuming (DVE --- FN) = K (FN)(DVE)
c


R.k
i 21 1/2 1/2 1/2
Rate = ( )/2(DVE) /2(FN)K [2k2 + k lK (DVE)]
2k k c 12 11 c
12 t12

By definition (FN) = (1 fd)(T), (DVE) = fd(T)

where (T) = total concentration= (FN)+(DVE), f = (DVE)/(T)
The rate maximum is a function of (T) and will be at fd = 0.5 by keeping
The rate maximum is a function of (T) and will be at f = 0.5 by keeping