Kinetic, mechanistic and model compound studies of the copolymerization of bis-4-substituted-1, 2, 4-triazoline-3, 5-diones

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Title:
Kinetic, mechanistic and model compound studies of the copolymerization of bis-4-substituted-1, 2, 4-triazoline-3, 5-diones
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xiii, 144 leaves : ill. ; 28 cm.
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Lai, Yu-Chin, 1949-
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Polymers   ( lcsh )
Polymerization   ( lcsh )
Triazoline   ( lcsh )
Diels-Alder reaction   ( lcsh )
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theses   ( marcgt )
non-fiction   ( marcgt )

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Thesis:
Thesis--University of Florida.
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Includes bibliographical references (leaves 139-143).
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by Yu-Chin Lai.
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Typescript.
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Vita.

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Full Text











KINETIC, MECHANISTIC AND MODEL COMPOUND STUDIES OF THE
COPOLYMERIZATION OF BIS-4-SUBSTITUTED-1,2,4-TRIAZOLINE-3,5-DIONES








BY

YU-CHIN LAI


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








UNIVERSITY OF FLORIDA


1980




























Copyright 1980

by

Yu-Chin Lai





















This dissertation

is dedicated to my parents,

Mr. Ting Lai and Mrs. Chun Liu Lai

and

my wife, Pi-Ching















ACKNOWLEDGEMENTS

The author wishes to express his sincere thanks to his advisor,

Dr. George B. Butler, for his supervision, encouragement and the

chance he gave the author to develop independent research. Special

thanks are extended to Dr. Thieo E. Hogen-Esch for many useful dis-

cussions.

The author also wishes to show his thanks to Dr. John F. Helling,

Dr. Martin T. Vala and Dr. Eugene P. Goldberg for contributing their

valuable time to serve on the supervisory committee and for their

support in the completion of this project.

Thanks are due to Dr. Chac-Fong Tien, Dr. Koon-Wah Leong,

Dr. Shinichi Ohashi, Dr. John J. Meister and Dr. Huey Pledger for

the stimulating discussions on the research.

Grateful thanks are extended to the fellow laboratory colleagues.

They have generated a pleasant, congenial working environment which

made the author's stay on the 4th floor of SSRB enjoyable.

The author wishes to acknowledge the Department of Chemistry of

the University of Florida, NASA, NSF, ARO, DOE, and The Kerr Manufac-

turing Co. for providing financial support in the form of teaching/

research assistantships and fellowships.

The author is also indebted to Ms. Patty Hickerson for typing

this dissertation.









Finally, completion of the requirements for the degree would

have been extremely difficult without the love and understanding

of the author's parents, Mr. and Mrs. Ting Lai, and wife, Pi-Chinq.















TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS . . iv

LIST OF TABLES . . viii

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

ABSTRACT . . . xi

CHAPTER

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

A. General Background . .. 1
B. Research Objectives . .. 11

II. RESULTS AND DISCUSSION . .. 14

A. Background . . 14
B. Synthesis and Identification of Bis-Triazolinediones. 15
C. Stabilities of Mono- and Bis-4-Substituted-l,2,4-
Triazoline-3,5-diones in Selected Solvent Systems 24
D. Model Compounds Studies .. ......... 37
E. Polymerization Studies of Bis-4-Substituted-l,2,4-
Triazoline-3,5-diones With Selected Substituted
Styrenes . . .51
F. Mechanistic Studies of Formation of Model Compounds 74
G. Kinetics of Formation of Model Compounds and Of
Copclymerization of Substituted Styrenes and Bis-
Triazolinediones . . 86
H. Miscellaneous Polymerization Studies Involving Bis-
Triazolinediones . . 94
I. Conclusion .. .... 99

III. EXPERIMENTAL . . 101

A. General Information . 101
B. Synthesis of 4-Substituted-l,2,4-Triazoline-3,5-
diones ... . . .. 102








Page

C. Synthesis and Identification of Bis-triazolinediones 105
D. Stabilities of PhTD, MeTD and Bis-triazolinediones,
56, 61, 66 in Methylene Chloride, Benzene, DCE, THF
and DMF by Visible Spectroscopy ... 114
E. Synthesis of Model Compounds . .... 115
F. Synthesis of Copolymers Derived From Substituted
Styrenes and 56, 61, 66... .. 120
G. Mechanistic Studies of Formation of Model Compounds 131
H. Kinetic Studies of Formation of Model Compounds and
of Copolymers Derived From 66 and Selected Sub-
stituted Styrenes . . 136
I. Pyridine-Catalyzed Homopolymerization of 56 and 66 .. 137

REFERENCES .. . . 139

BIOGRAPHICAL SKETCH . .... ... 144















LIST OF TABLES


TABLE PAGE

I. Visible Absorption of 4-R-TD in Methylene Chloride,
DCE, Benzene, THF and DMF 28

II. Visible Absorption of Bis-triazolinediones in DCE,
THF and DMF 29

III. Time Variation of Visible Absorbance of PhTD and
MeTD in THF 30

IV. Time Variation of Visible Absorbance of PhTD and
MeTD in DMF 32

V. Time Variation of Visible Absorbance of 56 and 61
in THF 34

VI. Time Variation of Visible Absorbance of 56 and 61
in DMF 35

VII. NMR Data for the Diels-Alder-ene and Double Diels-
Alder Model Compounds 52

VIII. Time Required for Completion of Copolymerization
Between 56, 61, 66 and Substituted Styrenes in DMF,
THF and DCE 57

IX. NMR Data for the Diels-Alder-ene and Double Diels-
Alder Copolymers 70

X. Some Physical Data for Polymers Derived From 56, 61
and 66 With Substituted Styrenes Prepared in DMF,
THF and DCE 75

XI. Weights of Polymers Obtained From Polymerization in
THF 128


viii














LIST OF FIGURES


Figure Page

1 NMR Spectrum of 70 21

2 NMR Spectrum of 68 23

3 NMR Spectrum of 69 25

4 Stabilities of PhTD and MeTD in THF and DMF as Shown
by A/Ao vs t Curve 33

5 Stabilities of 56 and 61 in THF and DMF as Shown by
A/Ao vs t Curve 36

6 IR Spectra of 75 and 76 39

7 NMR Spectrum of 79 40

8 NMR Spectrum of 80 41

9 NMR Spectrum of 77 43

10 NMR Spectrum of 78 44

11 NMR Spectrum of 81 45

12 NMR Spectrum of 82 46

13 NMR Spectrum of 83 47

14 NMR Spectrum of 84 48

15 NMR Spectrum of 85 49

16 NMR Spectrum of 86 50

17 NMR Spectrum of 87A 59

18 NMR Spectrum of 87B 60

19 NMR Spectrum of 87C 61

20 NMR Spectrum of 87D 62










Figure Page

21 NMR Spectrum of 87E 63

22 NMR Spectrum of 87F 65

23 NMR Spectrum of 87G 66

24 NMR Spectrum of 87H 67

25 NMR Spectrum of 871 68

26 NMR Spectrum of 87J 69

27 NMR Spectrum of Products from Dehydration of 90 81

28 NMR Spectrum of Products from Dehydration of 93 82

29 NMR Spectrum of 96 85

30 Second Order Plot of the Copolymerization of 66 and
Selected Substituted Styrenes 93

31 NMR Spectrum of 99 97

32 NMR Spectrum of 100 98















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


KINETIC, MECHANISTIC AND MODEL COMPOUND STUDIES OF THE
COPOLYMERIZATION OF BIS-4-SUBSTITUTED-1,2,4-TRIAZOLINE-3,5-DIONES

By

Yu-Chin Lai

March 1980

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

While the high reactivity of 4-substituted-l,2,4-triazoline-

3,5-dione has been studied extensively as a dienophile, little work

has been done on its role as an enophile, particularly on its use as

a propagating species in polymerization studies. The copolymeriza-

tion between bis-4-substituted-l,2,4-triazoline-3,5-diones (bis-

triazolinedione) and styrene has been studied once, the purpose of

the present work is to try to synthesize new copolymers derived from

substituted styrenes and bis-triazolinediones with potential thermal

stability and to study the mechanism and kinetics of this novel polym-

erization.

Three bis-triazolinediones were prepared: 3,3'-dimethyl-4,4'-

bis[3,5-dioxo-1,2,4-triazoline-4-yl]biphenyl, t-1,4-bis[3,5-dioxo-

1,2,4-triazoline-4-yl]methyl cyclohexane, and 4,4'-bis[3,5-dioxo-

1,2,4-triazoline-4-yl]phenyl ether. Their structures were fully









identified indirectly by their quantitative ene reactions with 2,3-

dimethyl-2-butene.

The stabilities of 4-phenyl-l,2,4-triazoline-3,5-dione (PhTD),

4-methyl-l,2,4-triazoline-3,5-di)ne (MeTD), and bis-triazolinediones

mentioned in the preceding paragraph were checked. It was found

that they are stable in methylene chloride, 1,2-dichloroethane (DCE)

and benzene, and less stable in tetrahydrofuran (THF) and N,N-dimethyl-

formamide (DMF). They decompose faster in DMF.

Model compounds derived from the reactions of PhTD/MeTD with

styrene, p-chlorostyrene, p-t-butylstyrene, a-methylstyrene, and p-

nitrostyrene were prepared for easier identification of structures

of copolymers derived from bis-triazolinediones and substituted

styrenes. It was found that the reactions of styrene and p-chloro-

styrene with MeTD/PhTD gave mixtures of Diels-Alder-ene and double

Diels-Alder adducts, while the reactions involving p-t-butylstyrene,

p-nitrostyrene and a-methylstyrene gave only Diels-Alder-ene adduct.

Copolymerization between bis-triazolinediones and substituted

styrenes was carried out in DMF, THF or DCE. Polymers Formed were

characterized by IR and NMR spectroscopy, differential scanning

calorimetry, gel permeation chromatography, and viscometry. Molecular

weights of polymers range from 5,000-16,000 in most cases. They

were stable up to 2500C and higher. Polymers derived from bis-

triazolinediones and p-t-butylstyrene, a-methylstyrene, p-nitrosty-

rene, and p-acetoxystyrene contained only Diels-Alder-ene repeating

units; whereas polymers derived from the bis-triazolinediones and









styrene, p-chlorostyrene, p-bromostyrene, p-methylstyrene, p-methoxy-

styrene, p-acetoxystyrene and 4-vinylbiphenyl all contained both

Diels-Alder-ene and double Diels-Alder repeating units.

The reactions between PhTD/MeTD and p-t-butylstyrene are in the

molar ratio 1:10 favoring p-t-butylstyrene and were carried out at

room temperature, and -780C. The reactions were also carried out

with high dilution technique at -780C, where PhTD/MeTD solution was

added slowly into p-t-butylstyrene solution. No 1:1 Diels-Alder

adduct was isolated as a reaction intermediate in all cases, indi-

cating that the relative rate constants for both steps are com-

parable; however, the reaction between MeTD with 2,6-dichlorostyrene

in the 1:1 molar ratio did give 1:1 Diels-Alder adduct.

The kinetic study of formation of model compounds was carried

out, and it was found that the rate constants for the first step are

larger than those for the second step. (kl/k2 = 0.892 4.213 among

reaction systems studied.) This suggested the average rate constants

for the copolymerization between bis-triazolinediones and substituted

styrenes do have some physical meaning. The average polymerization

rate constants are 60.93, 49.87, 8.42, 5.557, 0.838 (1/mole sec) for

the copolymerization of 4,4'-bis-(3,5-dioxo-1,2,4-triazoline-4-yl)

phenyl ether with a-methylstyrene, p-t-butylstyrene, styrene, p-

chlorostyrene and p-nitrostyrene in DCE, respectively.


xiii














CHAPTER I
INTRODUCTION

A. General Background

4-Phenyl-1,2,4-triazoline-3,5-dione, (PhTD), la, a ring system

first prepared in 1894 by Thiele and Stangel possesses an extremely

reactive nitrogen-to-nitrogen double bond capable of a wide variety

of reactions. The compound is synthesized via oxidation of the

0 H

II N-R I N-R
N --/ H
0 0
la R = C6H5 2a R = C6H5
lb R = CH 2b R = CH3

corresponding urazole, 2a, a reaction which may be effected by a number

of oxidizing reagents. Thiele used lead dioxide in dilute cold sul-
1
furic acid; Stolle oxidized heavy metal salts of the urazoles with

iodine;2 Cookson and coworkers used t-butylhypochlorite in acetone;3

Gillis and Hagarty used lead tetraacetate in methylene chloride;4
5 .6
bromine, fuming nitric acid, manganese dioxide, calcium hypochlorite

and N-bromo-succinimide will also effect the oxidation of urazoles.7

Stickler and Pirkle8 reported the most effective oxidation involved

passing nitrogen tetroxide into a suspension of the urazole in cold

methylene chloride which resulted'in rapid formation of the correspond-

ing triazolinedione. Evaporation of solvent followed by sublimation





2

under reduced pressure gave the crystalline triazolinedione. More

recent work by Moore and coworkers accomplishes the oxidation and

subsequent reaction in situ. Oxidation is achieved via an activated
isocyanate such as p-toluenesulfonyl isocyanate in dimethyl sulfoxide.
Conversion is determined spectrophotometrically.
Although a number of 4-substituted-1,2,4-triazoline-3,5-diones
(4-R-TD) have been prepared in this fashion and isolated, the parent
12
compound (R=H) has not been isolated. Stolle first synthesized this

compound in 1912 but did not isolate it. De Amezua, Lora-Tamayo and

Soto10 prepared the compound at low temperature and trapped it in

situ with several dienes via the Diels-Alder reaction. Herweh and

FantazierI prepared the compound by oxidation of urazole, using

nitrogen tetroxide and lead tetraacetate as oxidants, and trapped

the dione with dienes. These authors also studied the decomposition
products by oxidizing urazole with nitrogen tetroxide at room temp-
erature and collecting the gases evolved, such as nitrogen, carbon
dioxide and cyanuric acid.

Investigations into the chemistry of 4-R-TD were begun .in the
early 1960's when Cookson, Gilani and Stevens3 published low temp-

erature 4 + 2 cycloaddition of PhTD with cyclopentadiene, butadiene
and cycloheptatriene to yield 3, 4, and 5, respectively. This led

A N

SN-HC6H I N5- C N CA6H
0N 5 C
0 0 0








to more research concerning the Diels-Alder cycloaddition of 4-R-TD.12-17

Other cycloadditions include the reaction of PhTD with tropone, aze-
pine and diazepine which produced 1:1 adducts 6, 7, and 8, respec-

tively.18


0

//
N
)Ij N C6H5
N
\\
0


CO2Et

- C6H5

fl N C6H5
N


CO2Et
2


-- C6H


19
Ewin and Arnold9 reacted PhTD with isopyrazoles to give 9, which,
on irradiation, loses nitrogen to give 10; this subsequently reacted
with more PhTD to give the 2:1 adduct, 11. Cookson, Gilani and
DRO
R0 R R R
R R
N --C6H5---4 --->C6H5-N I N-C6H5
N R N ).N R
A R
0 0 C6H 0

9 10 11

Stevens20 also reported a 2:1 adduct, 12, of PhTD with styrene,


0


C6H5- N

0


C6H5- IN
0 N
0








presumably the result of a double Diels-Alder reaction. Other 2:1
adducts have been observed, such as 13, the product of PhTD and
benzylidenecyclopropane21 and the 1:1 adduct of PhTD and oxonin,
14, which adds another PhTD to give a 2:1 adduct of unknown struc-
ture.22,23'24 Other investigations of Diels-Alder cycloadditions
include reactions of PhTD with 5-iodocyclopentadiene25 which qave
15, and with polyenic azonines26 that produced compounds structured
as 16.

16H5 1 H C6H5
I H

,Yr-, r o O")-
N N--
I I N -ph

\ x-
0

14 15 16


As stated earlier, 4-R-TD's contain an extremely reactive ring
system. Kinetic studies have shown PhTD to be one of the most power-
ful dienophiles discovered to date.27 PhTD in reaction with 2-
chloro-1,3-butadiene was found to react one thousand times faster
than tetracyanoethylene and some two thousand times faster than
maleic anhydride.
Cycloadditions of triazolinediones are not limited to Diels-
Alder reactions. Pasto and Chen28 observed a [(a + ) + ] cyclo-
addition of alkenylidene cyclopropanes, 17, and PhTD gave 18 and 19.













R' > C C=CH2
H'


0


N-C6H5

0


Dimethylmethylenecyclopropane reacts with PhTD at room temperature21

to yield the 2 + 2 cycloaddition adduct 20. These authors29 have


N s6H


N- C 6H5 NN


also observed cycloaddition reactions of substituted vinyl cyclopro-

panes with PhTD. Van Gustorf and coworkers30 found PhTD to react

with dihydro-1,4-dioxime and indene in a 2 + 2 fashion giving 21 and

22, respectively. The indene reaction pathway was thought to be

polar in nature, as the proposed 1,4-dipole was trapped with water.

Another type of reaction pathway available for triazolinediones

is the ene reaction as shown below. Here triazolinedione reacts as


H3C







R0\ o 2 0
R2 N N
+ I N-R I N -R
R tHN /R f,
3 4 R3 4



an enophile instead of as a dienophile in the case of the Diels-
Alder reaction. Pirkle and Stickler31 first investigated the ene
reaction between 4-methyl-1,2,4-triazoline-3,5-dione (MeTD), and
some monoolefins with allyl hydrogens and found MeTD to be at least
thirty thousand times more reactive toward cyclohexene than is ethyl
azodicarboxylate. Pasto and Chen21 observed the ene product, 23,
in the reaction of (4-phenylbutylidene)-cyclopropane and PhTD.


H

C6H5CH2 H 0

23 C6H5

Saville32 first synthesized a bis-(triazolinedione), bis-(p-
3,5-dioxo-1,2,4-triazoline-4-ylphenyl)methane, 24, which is a highly
reactive bifunctional enophile. The ene reaction of this compound
0 0

CH 2 N
N-7( WO -
0 0
24

with various allylic olefins (e.g. trans-2-butene 2-methylpent-2-ene)
was studied and relatively polar bis-ene-adducts were formed in a
few seconds; addition of this compound into a solution of natural
rubber resulted in instant gelation due to crosslinking.








Recently, the ene reactions between PhTD and MeTD with various
alkenes and polyenes have been studied extensively by Butler and
coworkers. Butler and Williams33 reported the low temperature modi-
fication of dienic polymers such as cis- and trans-polybutadiene,
cis-polyisoprene and random styrene-butadiene copolymer via the ene
reaction with PhTD and/or MeTD. These reactions produced significant
changes in the physical properties of the original polydienes. This
research was also extended to a similar modification of styrene-buta-
diene random and block copolymers, styrene-isoprene block copolymers
and poly(acrylonitrile-co-butadiene) by Leonq and Butler.34 Ohashi,
Ruch and Butler35 studied the ene reactions between allyltrimethyl-
silane, 25, and MeTD/PhTD to give 26, 27 and 28 with strong evidence


Si(CH3)3
H2 N _N ( C CH-Si(CH 3)C CH2
PH r rN
SN--N -+ N--- + N-NH
CH2 1< > < N N'
SR 00 0 N 0 O N 0
Si(CH3)3 I I
R R R
25 26 27 28


in support of a high degree of ionic character in the reaction inter-
mediate. The structures of the products and the kinetics of the ene
reaction between 4-R-TD's and various alkenes have also been studied
by Ohashi, Leong, Matyjaszewski and Butler.36,37 The rates of the
ene reaction between PhTD and various alkenes were reported to follow
the order:









H CH3 H C2H5 H C3H7 CH CH3 H n-H7
c 3 < c
H H H H H H H 'H CH3
29 30 31 32 33

CH3 n-C4H9 CH3 CH3 CH3 CH3
11 H H CH3 C
34 35 36
Cookson and coworkers38 have reported the oxidation of alcohols
to aldehydes and ketones with PhTD. Substituted hydrazines also have
been oxidized by PhTD giving an N-nitrene which reacted with a second
molecule of PhTD39'40 to yield an azimine, 37. Oxidation of benzo-
phenone hydrazone yielded an N-nitrene which reacted with PhTD as
before, but the azimine produced was unstable, evolving nitrogen to
R2N
(C6H5)2C+
+
N-NT N --N:

01 N X O N \ 0 (CH05)2-C =N-N =C -(C6H5)2
0 0 N652 52
C6H5 C6H5

37 38 39

form 38 which reacted further with benzophenone hydrazone41 to give
the azine, 39.
PhTD has been used in the synthesis of prismane by initial reac-
tion with benzvalene, followed by basic hydrolysis and then photoly-
sis.42 PhTD has also been reported to be a useful ligand in iridium
complexes.4








While the high reactivity of the triazolinedione ring system

has been investigated extensively as dienophile, enophile and oxidiz-

ing agent, few studies have been reported on utilizing this high

reactivity as a propagating mode in polymerization. Pirkle and

Stickler44 homopolymerized 4-butyl-l,2,4-triazoline-3,5-dione in

chlorinated solvents by photolyzing the solutions with a visible

light source. The polymer was thought to have a repeating unit, 40,


N -N f

I
n -Bu

40

and a degree of polymerization of twenty. Depolymerization of this

polymer in solution, with regeneration of the monomer in 73% yield,

occurred upon removal of irradiation.

Saville32 used the bis-triazolinedione, 24, to crosslink natural

rubber. Butler, Guilbault and Turner45 investigated the reaction of

4-R-TD's with vinyl ethers and found low molecular weight copolymers

containing repeating units 41 and 42, formed via a 1,4-dipolar coupling


N-N-N N- N

O N O n 0cN O
I R I
R R

41 42

mechanism. When alkyl ketones were used as solvents for the reaction,46

the 1,4-dipoles, 43, were trapped yielding a new oxadiazole ring

system 44.








0-R R-0 T R
SR"
-RR
N-N -. N


ph 43 ph 44

The existence of a 1,4-dipole was also proved kinetically by Wagener

and Butler.47 Guilbault, Turner and Butler48 also synthesized poly-
mers having backbones of similar molecular structure by reacting PhTD
with N-vinyl carbamates. PhTD has also been observed by Wagener,
Turner and Butler49 to react with vinyl esters to yield 1-formyl-

methyl-2-acyl-4-phenyl-1,2,4-triazoline-3,5-dione, 46, by means of a

1,4-dipole, 45, intramolecular rearrangement, as shown in Scheme I.

Later, Wagener, Matyjaszewski and Butler50,51 employed the 1,4-dipolar

Scheme I


CH2
11
C- R1
+ -I



R2


0 R
0 0
R -C H2 =0
N

0 1 0
C6H5
46


R1 .0


N -N, 2


C6H5

45


R /

0 C I.
N -

0[N 0]

C6 H5


[( -u -i

,U L


' C6H5




12
I
CiR1
N- N

0 N N

C6H5


No N


C6H5
1X)x
C 6 H







rearrangement as a means of propagation in copolymerization of bis-
triazolinediones with divinyl esters and bis-enol esters.

B. Research Objectives
Although Cookson and coworkers20 reported that PhTD spontaneously
reacts with styrene to yield a double Diels-Alder adduct, 20, rein-
vestigation of this reaction by Wagener, Turner and Butler52 revealed
that the Diels-Alder-ene adduct was also found in approximately a 2:1
ratio of 47 to 11 (Scheme II). This is similar to the cases in which
Scheme II

N N.


6J N\N
C6H5 0 0

N-/ 65 6 H5
N-C HC6H
N 5 0

A+ C6H5-N
N ter. 0N 0N N ,N "-0
\ 0
11 C6H 0
0 0 _N
1 C6H5 47 C6H5
maleic anhydride53 reacts with styrene in a Diels-Alder-ene fashion
to give 2:1 adducts 48 and 49. Ethyl azobis formate54 also reacts
with styrene to give products with similar structures. These Diels-
Alder-ene and double Diels-Alder-adducts obviously served as model
compounds for the copolymerization of bis-triazolinediones and styrene.







0
0 0 0


oo ~ N-J

0
48 49 50


Wagener, Turner and Butler observed that when styrene and bis-
triazolinedione 24 or 50 were mixed, a polymer formed spontaneously
and instantly.52 NMR studies showed that structure 51, resulting from
Diels-Alder-ene reactions, accounts for two-thirds of the repeating
units of polymer backbone, while structure 52, resulting from consecu-
tive Diels-Alder reactions, accounts for one-third of the repeating

0

0 H N N-
N R-N\ "
N- N 0,R N 1


0 N


51a R = CH2


51b R = (CH2)6

units. The first purpose of this research was to further this study
by varying the bis-triazolinediones and using different substituted
styrenes in order to correlate the fine structures of polymers with
those of monomers.





13


Although the propagation is believed to go through the Diels-

Alder reaction followed by ene and/or another Diels-Alder reaction,

no reaction intermediate has been isolated; so the second purpose of

this study was to isolate the intermediate in order to study the

reaction mechanism thoroughly.

The polymerization is spontaneous and fast, and no previous

kinetic study has been done. The third purpose of this investigation

was to study the kinetics of the polymerization.














CHAPTER II
RESULTS AND DISCUSSION

A. Background

In the early 70's, Wagener, Turner and Butler52 prepared some

alternating copolymers by reactions of bis-triazolinediones with

styrene (Scheme III). This is the first example of a pronaaating

Scheme III N^ H



r N r O
0 0 0 N


0 1R 0 0
n n

24 R = -)-CH2- 51a R = -CHI- 52a R = CH2-9

48 R = -(CH2)6 51b R = -(CH2)6" 52b R = -(CH2)6



mechanism involving predominantly a Diels-Alder-ene reaction sequence.

A competing double Diels-Alder reaction sequence appears to occur

one-third of the time, leading to polymers containing both structural

units. The fine structures of the copolymers were determined by

comparing their nuclear magnetic resonance (NMR) spectra with those

of model compounds prepared from reaction of styrene with PhTD and

with MeTD in methylene chloride. The polymers are stable up to 250C

and above.









B. Synthesis and Identification of Bis-Triazolinediones

One aim of this study was to synthesize more stable polymers

derived from substituted styrenes and suitable bis-triazolinediones.

So the choice of bis-triazolinediones was based on the premise that

the molecule should contain as few aliphatic hydrogen atoms as

possible. Three new bis-triazolinediones, namely, 3,3'-dimethyl-

4,4'-bis-(3,5-dioxo-1,2,4-triazoline-4-yl)biphenyl, 56, t-1,4-bis-

[3,5-dioxo-1,2,4-triazoline-4-yl]methyl cyclohexane, 61, and 4,4'-

bis-(3,5-dioxo-1,2,4-triazoline-4-yl)phenyl ether, 66, were selected

for this study. Compound 56 was selected because its corresponding

diisocyanate is commercially available; 61 was selected because it

contains a flexible ring system which enhances its usefulness as a

crosslinking agent; 66 was selected for this study because it con-

tains no aliphatic hydrogen, but an oxygen atom which is usually

regarded as a "flexibilizing" link. All three bis-triazolinediones,

56, 61 and 66, were prepared by the modification of a procedure

developed by Saville,3 Turner,5 or Wagener,5 as shown in Scheme IV.

Scheme IV
0

COC12 2H2NNHCOC2H5
H2N R NH2 CO2 > OCN R NCO 2H2NNHCO
57, 62 53, 58, 63
0
1. C2HOH, Na H N\ H
2. H -- I N- R-N
H N-0
0 0


55, 60, 65








Scheme IV (Cont'd.)


N 0
N204 / N
> N-- R--N I
0-50C N N
0 0
56, 61, 663


53, 54, 55, 56 R =




57, 58, 59, 60, 61 R = CH2 CH2




62, 63, 64, 65, 66 R = 0





The bis-triazolinedione 56 was prepared by the following steps:

one mole of the diisocyanate, 53, after purification by recrystalli-

zation from ethyl acetate, was allowed to react with two moles of

ethyl carbazate to give a quantitative yield of the bis-semicarba-

zide, 54. Cyclization of 54 was achieved by refluxina its suspension

in ethyl alcohol/sodium ethoxide, followed by neutralization with

acid and filtration of the bis-urazole, 55. Oxidation with nitrogen

tetroxide of 55 or its salt in methylene chloride in the presence of

sodium sulfate as a drying agent gave the desired his-triazoline-

dione, 56. Unfortunately, 56 is not soluble in methylene chloride,









and there exists no suitable solvent to replace methylene chloride

as a reaction medium; so the reaction procedure leads to some diffi-

culty in the purification of this bis-triazolinedione. A differential

scanning colorimetric thermogram (DSC) of the crude product 56 showed

two peaks; one peak exothermicc) appeared at 208C, indicating the

decomposition of 56, while another peak endothermicc) appeared at

3060C, indicating the melting of sodium nitrate produced from this

oxidation reaction. Nevertheless, the crude product was washed

thoroughly and quickly with water and dried in vacuo. After this

process, the product was believed to be reasonably pure since DSC

thermograms showed only one sharp, large peak at 2080C.

A better procedure for improving the purity of 56 is that the

bis-urazole 55, after recrystallization from methanol, was oxidized

in dry condition, but without a drying agent in the reaction medium.

Purity of the product was greatly improved. Since the bis-triazoline-

dione is soluble in some solvents like acetone, dimethylsulfoxide

(DMSO), N,N-dimethylformamide (DMF) and tetrahydrofuran (THF), all of

which react with it, and is insoluble in other less polar solvents

like benzene, methylene chloride and chloroform, no NMR analysis could

be done on this compound. An indirect structural determination for

this compound was designed and is described later in this section.

t-1,4-Bis-[3,5-dioxo-1,2,4-triazoline-4-yl]methyl cyclohexane,

61, was prepared by a similar procedure except that the corresponding

starting material, the diisocyanate, 58, was synthesized from the








diamine 57 and phosgene. Special care must be taken because of the

toxicity of phosgene. Also, the bis-urazole, 60, had been recrystal-

lized before it was oxidized with nitrogen tetroxide. Since the bis-

triazolinedione, 61, is not soluble in methylene chloride, further

purification is not possible; therefore, its identification can be

accomplished only by indirect methods.

4,4'-Bis-[3,5-dioxo-1,2,4-triazoline-4-yl]phenyl ether, 66, was

prepared in the same manner, starting with the diamine, 62, and going

through the diisocyanate, 63, bis-semicarbazide, 64, bis-urazole, 65,

and finally to the bis-triazolinedione, 66. However, the procedure

for the final oxidation step is somewhat different. During the first

attempt, the bis-urazole, 65, was suspended in methylene chloride with

sodium sulfate added; the system was then treated with nitrogen tetrox-

ide for twenty minutes. The red-colored product went into solution,

after which excess nitrogen tetroxide was removed. The reaction mix-

ture was filtered and the solvent evaporated by using a rotaevaporator,

but once the vacuum was released, the sticky, reddish solid product

decomposed spontaneously to a brown, smoking mass. It was speculated

that excessive oxidation might account for this decomposition; how-

ever, this was evidently not the reason, for when benzene was used

as solvent, after the same type of work-up, the same phenomenon was

observed. It was finally assumed that this bis-triazolinedione, 66,

is very unstable in air or in the presence of moisture, and that it

would be better to keep 66 in solution as long as it is stable in

that condition. The amount of 66 present in solution can be determined









indirectly by its visible absorption and by its quantitative reaction

with some highly reactive, volatile alkene. A study on the stability

of PhTD and MeTD in certain selected solvents (see Section C of this

chapter) revealed that both compounds are very stable in methylene

chloride, 1,2-dichloroethane (DCE), and benzene. Of these three, DCE

was selected, because it is less volatile than methylene chloride

(for better storage of solution) and more polar than benzene (for

faster ene reaction).

4,4'-Bis-[3,5-dioxo-1,2,4-triazoline-4-yl]phenyl sulfone, 67,

was synthesized in exactly the same manner as 66; again, this compound
0 0

11 N so 2

N 0
0 67


is not stable in air. Also, as only a small amount of this his-

triazolinedione was obtained, it was not studied further.

Since the above-named bis-triazolinediones, 56, 61, and 66,

are either not capable of being purified or isolated without decomoo-

sition, the purity and amount of bis-triazolinediones must be deter-

mined indirectly. Triazolinediones are the most reactive enophiles

known; they react with alkenes both rapidly and quantitatively.

Ohashi and Butler37 reported that 2,3-dimethyl-2-butene reacts with

PhTD and MeTD much faster than other alkenes; actually this ene

reaction is too fast to measure its rate spectroscopically. The ene

product is unique as can be seen from the symmetrical nature of









2,3-dimethyl-2-butene; therefore, that compound was selected as a
reactant for the triazolinediones 56, 61 and 66, as shown in Eq. 1,
in order to determine the bis-triazolinediones qualitatively and
quantitatively.

CH3 CH3
9 CH3 CH I il
N 0-N CH3 CH3 C-- CI- -
N- R--N | --- C A C N N fR
N N--R- 2 23 N
%0 Ci CH3 CH3 H 0

'CHn CH
C "CH3 (Eq. 1)

56 R 68



61 R- CH 69


66 R =-0 70


Thus, bis-triazolinedione 66 solution in DCE was allowed to
react with 2,3-dimethyl-2-butene; the characteristic red color of
66 disappeared immediately, resulting in a yellowish solution. After
removal of solvent and drying, constant weights (for 2 measurements)
were obtained indicating a quantitative reaction to give the ene
product 70. The NMR spectrum in CDC13 of the product as shown in
Fig. 1 indicates no detectable impurity other than the ene product,
and the assignments of peaks are quite straightforward. The peak at
6 = 1.60 ppm was assigned to methyl protons from methyl groups












































_



.41


E
re


C,
S-

4-













-Q








,)
LL-










CD
co
s:









attached to carbon next to the urazole rings; the peak at 1.82 ppm

was assigned to the methyl protons from the methyl groups attached

to vinyl carbons; the peak at 4.97 was assigned to vinyl protons;

the peaks around 7.05 ppm and 7.47 ppm were assigned to aromatic

protons; and the broad peak around 8.97 ppm was assigned to N-H

protons. The elemental analysis for this compound was also in good

agreement with calculated values. Infrared (IR) spectra also gave

strong support for the assigned structure. From the weight of ene

product, the weight of bis-triazolinedione 66, in solution, can be

calculated. The molar extinction coefficient of 66 at max = 544nm
max
in DCE is 358. There is no apparent loss in absorbance at max even

after three days, indicating that 66 is very stable in DCE.

The identification and purity of the bis-triazolinedione, 56,

was determined by its quantitative reaction with 2,3-dimethyl-2-

butene to give 68. Although 56 is not soluble in methylene chloride,

68 is soluble in methylene chloride. The NMR of the crude product

in acetone (see Fig. 2) gave the following peaks: 6 = 1.64 ppm was

assigned for the methyl protons from methyl groups attached to C next

to the urazole rings; the peak at 1.89 ppm was assigned to the methyl

protons from the methyl group attached to the vinyl carbons; the peak

at 2.29 ppm was assigned to the three methyl protons from methyl

groups attached to the aromatic rings; the peaks around 4.97 ppm were

assigned to vinyl protons; the peaks from 7.14 ppm to 7.66 ppm were

assigned to three aromatic protons and the broad peak around 8.35 ppm

was assigned to N-H protons. Results from elemental analysis were in





23















-.










oo
--

E
0;
--

0
4,

o v0



00













o o





e--
.<0 o- *,









good agreement with calculated values. The IR spectrum also gave

strong support for the assigned structure and the purity of 61 can

be calculated in this way.

The identification and purity of the bis-triazolinedione, 61,

were determined similarly. The NMR spectrum in chloroform, as shown

in Fig. 3, gave peaks between 6 = 0.65 ppm to 2.10 ppm which were

assigned to the protons of the aliphatic ring; a peak at 1.58 ppm

was assigned to the methyl protons from the methyl groups attached

to the C next to the urazole rings; a peak at 1.81 ppm was assigned

to methyl protons from the methyl groups attached to vinyl carbons;

the peaks around 3.34 ppm were assigned to methylene protons; the

peak at 4.98 ppm was assigned to vinyl protons; and the broad peak

around 9 ppm was assigned to N-H protons. Elemental analysis and IR

absorbances also gave strong support for the ene product structural

assignment.

Because the amount of bis-triazolinedione can be determined quan-

titatively, this overcomes some difficulties in the purification of

these reactive ring systems. Thus, quantitative reactions of bis-

triazolinediones with other species can be studied without ambiguity.


C. Stabilities of Mono- and Bis-4-Substituted-l,2,4-Triazoline-3,5-
Diones in Selected Solvent Systems

Generally speaking, triazolinedione ring systems are stable in

solvent systems of low polarity, less stable in more polar solvent

systems. Although triazolinediones had been reported to be unstable

qualitatively by some authors, quantitative studies have not been





25






























_0
0-



O








o 0

E


0
0)




oo c






o .
--


oo













.o 0
o*O








done. For example, Cookson et al.20 and Ruch,57 in separate studies,

reported the slow reaction of PhTD with acetone to form l-hydro-2-

acetomethyl-4-phenyl-1,2,4-triazoline-3,5-dione, 71, the reaction

possibly going through the extremely low concentration of enol form.
0
H CH2 C CH3


0 N 0
I
C6H5
71

Wamhoff and Wald58 reported that PhTD reacts with ethers containing

a-hydrogens, e.g. dioxane 72a, THF 72b, diethyl ether 72c and others,

thermally or photochemically, to give various products, 73, 74, in

different proportions as shown in Eq. 2. Obviously hydrogen attached

R R


A or 1 (Eq. 2)
0 H

H H
C6H5 C6H5
73

72a R-R = -CH -O-CH2- 74a

72b R-R = -CH -CH2- 74b

72c R=R = CH3 74c



to a-C of ethers serves as a proton donor. Herweh and Fantazier1

reported the stability of 1,2,4-triazoline-3,5-dione solution in

various solvents, e.g. DMF, DMSO, diglyme, at different temperature









and, as expected, it decomposed faster at higher temperatures. From

the above statements, it is evident that the stabilities of mono- and

bis-triazolinediones must be carefully examined before any chemistry

involving the triazolinediones can be studied. Thus the stabilities

of PhTD, MeTD, 56, 61, 66, in various commonly used solvents like

methylene chloride, DCE, THF, benzene, and DMF were examined by

following the change with time of visible absorbances at Xmax (unit =

nm, resulted from n -* transition), for a certain period. Table I

shows the visible absorption maxima and extinction coefficients of

PhTD and MeTD in these selected solvents. As can be expected, PhTD

always has higher max than MeTD because of higher delocalization of

the T-electrons through the aromatic ring. Both PhTD and MeTD show

hypsochromic shifts in polar solvents because of lowering of nonbond-

ing orbitals by the solvents. The extinction coefficients for PhTD

and MeTD in DMF are estimated values because of higher decomposition

rates. Table II shows the visible absorption maxima and extinction

coefficients for bis-triazolinediones 56, 61, 66, in DCE (for 66

only), THF (for 56, 61 only), and DMF (for 56, 61 only). Needless

to say, the extinction coefficients for bis-triazolinediones are

about twice those of similar mono-triazolinediones.

Both PhTD and MeTD are quite stable in methylene chloride, DCE

and benzene. Within experimental error, there is no significant

change in absorbance, even after two days, but they are less stable

in THF and DMF. Table III shows the variation of absorbances (A =

absorbance at time, t, Ao = initial absorbance) of PhTD and MeTD in




























U-








z
0





LL







LU



UJ
m



0









I--
0:

-I-



La
.J La








CC>









C-
I-










00
I-




th
>-
I-





a-
a
a-






o
>-J

'-4


to r-.




n i
LA LA

en

LOCM



Sao
0O Cm
LA LA









N. 0




tO o-
NCO






- r-



0 C)






r- r-




! !
r en





Sro
Ln LO





LD
-r, m

) 0
I I


0
C,




4-.
r






*r-



0
N




C
0 ,-


r
r- OL
MX




4->C
0 *t







*a 0
+-o

*r--

O
-aC
- *
O re





4-)



E .0
t- 0



II
0)

r4- v





(A .0
*r- 0
In
La m

*Xl

















TABLE II

VISIBLE ABSORPTION OF BIS-TRIAZOLINEDIONES
IN DCE, THF AND DMF
lent DCE THF DMF
bis- X
triazo- max max max
linediones

56 -537 300 527 300

61 530 312 520 300

66 544 358 -


* Estimated values.













TABLE III

TIME VARIATION OF VISIBLE ABSORBANCE OF PhTD AND MeTD IN THF
dione dione
PhTD MeTD PhTD MeTD
A/Ao A/Ao
t(min At(min)

0 1.0000 1.0000 65 0.9794 0.9874

5 0.9972 0.9961 70 0.9766 0.9874

10 0.9957 0.9942 75 0.9752 0.9864

15 0.9945 0.9942 80 0.9739 0.9855

20 0.9931 0.9942 85 0.9697 0.9845

25 0.9931 0.9932 90 0.9656 0.9826

30 0.9917 0.9923 95 0.9642 0.9826

35 0.9904 0.9913 100 0.9629 0.9826

40 0.9876 0.9903 105 0.9615 0.9826

45 0.9849 0.9884 110 0.9601 0.9826

50 0.9821 0.9874 115 0.9587 0.9826

55 0.9807 0.9874 120 0.9587 0.9816

60 0.9794 0.9874









THF. PhTD decomposes 4.13% and MeTD decomposes 1.84% in 2 hours.

Table IV shows the time variation of absorbance of PhTD and MeTD

in DMF. PhTD decomposes 16.67%, MeTD decomposes 12.75% in 25 minutes,

and 6.19% and 1.94%, respectively, in 2 minutes. Thus, 4-R-TD's are

much less stable in DMF than they are in THF. Interestingly enough,

PhTD is always less stable than MeTD no matter how polar the solvent,

probably due to the higher reactivity of PhTD as an enoDhile. In-

formation on stabilities of PhTD and MeTD in selected solvents is

given in Fig. 4 for comparison.

From this study, it is evident that both PhTD and MeTD are more

stable in less polar solvents, and less stable in more polar solvents.

Thus, it is better to use methylene chloride, DCE or benzene as reac-

tion solvents for mono- and bis-triazolinediones as long as solubility

permits. This is the case for 66. Stability of this compound in DCE

was checked, and there is no detectable change in absorbance after

three days. However, bis-triazolinediones like 56 and 61 are not

soluble in the above-named less-polar solvents, but soluble only in

the more-polar solvents like THF and DMF. Accordingly, there is no

other choice but to use DMF or THF for polymerization studies involv-

ing 56 and 61. The stabilities of 56 and 61 are shown in Table V and

VI and Fig. 5. Thus, 56 and 61 decompose 11.7% and 7.1%, respectively,

in THF in one hour and decompose 5.25% and 4.02%, respectively, in

DMF in 3 minutes. Since the polymerizations for 56, 61 and substi-

tuted styrenes are spontaneous and fast in these two solvents, it is

still suitable to use them.













TABLE IV

TIME VARIATION OF VISIBLE ABSORBANCE OF PhTD AND MeTD IN DMF


PhTD MeTD ne PhTD MeTD
A/A A/
t(min) t(min)

0 1.0000 1.0000 13 0.8702 0.9100

1 0.9619 0.9931 14 0.8643 0.9044

2 0.9381 0.9806 15 0.8607 0.9037

3 0.9286 0.9668 16 0.8571 0.9002

4 0.9167 0.9571 17 0.8548 0.8975

5 0.9071 0.9529 18 0.8523 0.8934

6 0.9024 0.9418 19 0.8500 0.8906

7 0.8976 0.9371 20 0.8476 0.8864

8 0.8880 0.9307 21 0.8452 0.8843

9 0.8833 0.9280 22 0.8405 0.8823

10 0.8786 0.9224 23 0.8381 0.8795

11 0.8762 0.9169 24 0.8357 0.8767

12 0.8738 0.9141 25 0.8333 0.8726








33

















CO 5--
i- Ui U-
> 0

C 3:
r .OLL



,0 E:








0* *
4- >-





C,


C) LLn












uU -
0) 0 L

C,


4 I-


S.0
CO L.O -





I-
C



I-
1 CCO
*r-








CCt
0 *r-




.-1-
LL-






(*r
N tr- C
a .^-


Olc


O CO O0 o
c1 Co CO Co










TABLE V
TIME VARIATION OF VISIBLE ABSORBANCE OF 56 AND 61 IN THF


Bis-dione Bis-dione
56 61
A/ o A/ o
t(min) t(min)

0 1.0000 0 1.0000
a 0.9884 5 0.9913
13 0.9620 10 0.9844
17 0.9488 15 0.9685
20 0.9405 20 0.9551
25 0.9306 25 0.9495
30 0.9190 30 0.9430
36 0.9107 35 0.9393
40 0.9074 40 0.9355
46 0.8992 45 0.9336
50 0.8909 50 0.9336
56 0.8860 55 0.9308
61 0.8826 60 0.9290
66 0.8810 65 0.9262
72 0.8760 70 0.9243
75 0.8727 75 0.9206
80 0.8678 80 0.9187
85 0.8612 85 0.9150
90 0.8595 90 0.9121
95 0.8579 95 0.9121
101 0.8512 100 0.9112
105 0.8496 105 0.9075
109 0.8496 110 0.9037











TABLE VI
TIME VARIATION OF VISIBLE ABSORBANCE OF 56 AND 61 in DMF

done t done

A/A 56 61 A/Ao 56 61
t(min) t(min)


1.0000

0.9694

0.9572

0.9475

0.9450

0.9358

0.9266

0.9190

0.9113

0.9037

0.8976

0.8899

0.8853


1.0000

0..9836

0.9672

0.9598

0.9507

0.9453

0.9380

0.9288

0.9215

0.9161

0.9142

0.9106

0.9051


0.8807

0.8761

0.8716

0.8654

0.8609

0.8578

0.8547

0.8502

0.8456

0.8410

0.8364

0.8318

0.8272


0.9015

0.8942

0.8905

0.8850

0.8796

0.8777

0.8759

0.8741

0.8723

0.8704

0.8668

0.8631

0.8613

























































































O Co C4 01
oCD \ cn m\ cn


1)

U




*

O ,C






CU 3
o- in



co o

aO c-"


th LL.
CO




0 10 Lo

*r- -o
E

.-' r-

*r-
it-
C "
r-r-
0 LO I
o r--







01:

m w
T ko
CC






O I Ln
*r- r
4^-'





I-, i |

- -
]o







4-
L.


O CO CO C
CD CO CO CO








D. Model Compounds Studies


Except for a few polymers with simple structure, the NMR spectra

of polymers are generally broad, making the determination of struc-

ture difficult. However, with the studies of model compounds, struc-

ture determination for polymers becomes easier.

The model compounds derived from styrene and PhTD, 47 and 11,

styrene and MeTD, 75 and 76, as shown in Scheme V, were prepared by

Wagener, Turner and Butler.51 The reactions were repeated in this

work. Similar results were obtained, except that the pure double

Diels-Alder adduct, 76, which had not been isolated previously from

-the Diels-Alder-ene adduct, 75, has now been isolated by column

chromatography. The IR spectra of 75 and 76 are shown in Fig. 6

for comparison.

The reaction between MelD and p-chlorostyrene gave a mixture

of Diels-Alder-ene adduct, 79, and double Diels-Alder adduct, 80,

in the ratio of 3:1, favoring 79, as can be expected because re-

aromatization leads to the more thermally stable adduct, 79.

Separation of 80 from 79 was achieved by column chromatography.

The assignments of NMR peaks for 79 (see Fig. 7) are seen to be quite

straightforward by comparing this spectrum with the spectrum of 75.

Thus, peaks around 3.91 ppm (d,d) and 4.23 ppm (d,d) were assigned

to two non-equivalent methylene protons; peaks around 5.54 ppm

(pseudo triplet) were assigned to methine protons; peaks around

8.26 ppm were assigned to aromatic proton attached to C next to the

fused ring and to the carbon with C1 atom attached. The assignments







Scheme V


x




O
0


1--+
0 R
R


X



S /N
\Y N\
I 0 R


Y


R-N
SN
0


S R
R = C6H5 R = CH3
Y=H 47 75
Y=C1 77 79
Y=tBu 81 82
Y=H -3 84
Y=NO2 85 86


R = C6H5
.11
78


of other peaks are trivial and not necessary to be discussed. The
assignments for peaks of the NMR spectrum of 80 (Fig. 8) presented
some difficulty; however, with the help of double resonance (shown
in Fig. 8), this difficulty was overcome. The peaks around 5.37 ppm
(d,J = 6 cps) were radiated, and peaks around 6.51 ppm (d,d,J1 =
6 cps, J2 = 2 cps) were changed to a doublet. Thus, the peaks around
5.37 ppm were assigned to vinyl proton cis to Cl; the assignments of
other peaks are shown on the Table VII.


0

/


X=H,
X=H,
X=H,
X=CH3,
X=H,


R = CH3
76
80










40











C!



VO
















-9>
0


S 0
I,-

a)



z

C
C-.
0 CV)
















































o
S 4-
0
E
4-)
U
0 0
Si
t ^



o



cr.


LL-









Similarly, the reaction between PhTD and p-chlorostyrene gave a

mixture of the Diels-Alder-ene adduct, 77, and the double Diels-Alder

adduct, 78, in the ratio of 2:1, favoring 77. The assignments of NMR

peaks of 77 (Fig. 9) and 78 (Fig. 10) are recorded on Table VII.

The reaction between PhTD and p-t-butylstyrene gives only Diels-

Alder-ene adduct 81. Possibly, the presence of this bulky t-butyl

group on the styrene will cause too much steric hindrance for the

second Diels-Alder reaction to occur across the hexadiene ring.59 The

reaction between MeTD and p-t-butylstyrene also gives Diels-Alder-ene

adduct 82 as the sole product. The assignments of NMR spectra of 81

(Fig. 11) and 82 (Fig. 12) are given on Table VII.

a-Methylstyrene reacts with both PhTD and MeTD to give the Diels-

Alder-ene adducts 83 and 84, respectively. Again, no double Diels-

Alder adduct forms which is possibly due to the enhancement of the

ene reaction by the methyl group present on the vinyl C where the ene

reaction occurs. The NMR spectra of 83 and 84 are shown in Fig. 13

and Fig. 14, respectively.

p-Nitrostyrene reacts with PhTD and MeTD to give the Diels-Alder-

ene adducts 85 and 86, respectively. The presence of the nitro group

lowers the highly occupied molecular orbital (HOMO) of the Diels-Alder

intermediate. This increases the energy gap between frontier orbit-

als,60 i.e. the HOMO of diene and the LUMO (lowest unoccupied molecular

orbital) of dienophile for Diels-Alder reaction, makes the second

Diels-Alder reaction less favorable, and leaves the ene reaction as

the only course of reaction for the initial Diels-Alder reaction inter-

mediate. The NMR spectra of 85 and 86 are shown in Fig. 15 and Fig.

16, respectively.









































.0
---= 1























o n E
0(







0
ro
_o .. ".
E
>-


Q)





























o>-<




-Q 0~































































p 7.








































I
col
t-
-0 c
rn E






*-
S -I
U


-o


I-
n
*,

*
-s r


0






-o

-Q







-0


I a -



CO
CD"






































co







47





ft











-I+
.0.






_0





o -



J
e
%o



S-
+J
0)
0
..
0
r-




o c*



o 0









-Q
0-.
















2

a.
-LC O


0







49



















0








-2





o
Lo






0
a-
Ca
S o




S-



LO
U






r-




LL


















































*.
to






c-
0

E



r-


4-L
0-










0r


I .









From the model compound studies, it is clear that the substituent

of N of PhTD or MeTD has no effect on the structure of the reaction

products between PhTD, MeTD and substituted styrenes. However, the

substituents on styrene do affect the ratio of Diels-Alder-ene to

double Diels-Alder adducts. In general, the presence of bulky or

strong electron-withdrawing groups on the para position of styrene

inhibit the second Diels-Alder reaction. Alkyl groups with hydrogen

atoms attached to the C next to the carbon being substituted on the

alpha position of styrene will enhance the ene reaction. NMR spectra

of model compounds are summarized in Table VII for comparison.

E. Polymerization Studies of Bis-4-Substituted-l,2,4-
Triazoline-3,5-diones With Selected Substituted Styrenes


One aim of this work was to synthesize copolymers derived from

substituted styrenes and bis-triazolinediones and to correlate the

microstructures of the copolymers as well as their thermal stabili-

ties with those of the starting comonomers. The substituted styrenes

selected for study range from those with electron-donating groups to

those with electron-withdrawing groups, as well as bulky groups, halo-

gens, and those with substituents on the alpha position. Specifically,

styrene, D-chlorostyrene, p-butylstyrene, a-methylstyrene, p-nitro-

styrene, p-methylstyrene, p-bromostyrene, p-methoxystyrene, p-acetoxy-

styrene, and 4-vinylbiphenyl were studied. Of these, styrene was

purified by distillation at low pressure under nitrogen; p-acetoxy-

styrene was purified by distillation under reduced pressure;6 and

p-nitrostyrene was purified by recrystallization from methanol at




























V/)




0 3= -r -r Y- r
0.

-I



-lJ



a L

a0 0 n -y CM N- L

m-i I
aw




r' o

-j 0
V-4 =3
i- 0





&-j

I 0









I--
w
ULJ






C)
-i3 -> -


CM
)


)
J


a a a a a a a


* *







O CY qU -0 O


0 0 0 0! M 0







E E EE -j E E
C- i CM LO- 0a C% Cr rC






4- .* CM C C* CM
S a ; r
min cc n irm con n






C C O r CO %i m





4- (o LOOc- -:dcl C-O m ) r)-C
LAD ID rA-n r- r t" < LA r C(iY C(V



- r -. r,- r r -. r-. (i (~ M(n


n F- ln


I-. to LA
LA LO LO


cc LA LO
LA LA LA


XI XI X X X X X X



F"j c. C ---r-







Co co










c- -o o -o co r- rc


It


























-~ r- C
,a E
m LO -












c'J LC C'.
I- r F-


a* C
1-o X> -o

SCM r- o


CO CO OC




C) Cj i- -U-

4 -; E 1 X












Ktv
r- I -. r .r~C









o orno cr>

c %c c) e' cM cz
















-C C
co- 00


Cn i


,-o- Io -o-






co a n '^ D d


n n c






*n *













00 CO CO


tj,
C.
U

d



I!










X
C-
U )
*





co












I)








0.
F->

c'J

II >

'3 0'


Q.
U
CO)




II

'3


a L O









SII
E 11
o














C


0 C o

S: Q C% (
o 0 0 U








LA Ln t L
EE E



i- eC c cc




















CM r- CO 0
1 *-


- a C M










E -O E -

C- C- -l C-

ms ~ n Cl-



coha aon a n a C


























C C C
E) t E CE
O CM r- c
*- *C;r LA C*











-- I-









SE oto ES> oo


-o

cr
C

C-)
t-E
UJ



-J

C-
?









about -400C followed by drying in vacuo at OOC.62 All other substi-

tuted styrenes were used as received. The solvents used for polym-

erization studies were also carefully purified. DMF was purified

first by stirring with KOH, then distilling from CaO at low pressure

under nitrogen; DCE was purified by storing over sodium hydroxide

followed by distillation from P205; THF was purified by refluxing

with a 0.5% suspension of cuprous chloride for 1/2 hour, followed by

distillation, drying the distillate with KOH, redistillation, and

finally refluxing over and distilling from lithium aluminum hydride.

The copolymerizations of 56 and 61 with selected substituted

styrenes were carried out by mixing equal moles of substituted sty-

rene solution in DMF and suspensions of 56 or 61 in DMF at room

temperature. The reactions are spontaneous, fast, and highly exo-

thermic with color change from red (or pink) to yellow. The poly-

mers formed were soluble in DMF. Purifications were done by twice

repeated dissolution-precipitation using DMF/ether. The final pre-

cipitated products were washed thoroughly with ether by stirring at

low temperature and finally dried in high vacuum at high temperature

(110C) for 48 hours to make sure of complete removal of DMF. The

polymers derived from 56 and substituted styrenes are yellowish;

those derived from 61 and substituted styrenes are white, except

those from p-nitrostyrene and 4-vinylbiphenyl, which are yellow.

Copolymerization of 56 and 61 with substituted styrenes in THF

was done by first dissolving the monomers in THF, then mixing the

two comonomer solutions at once with stirring. Color change was









steady, indicating polymerization was proceeding. The polymerization

in THF is much slower than that in DMF. The reactions are complete,

except in a few cases, in less than one hour. Polymers formed were

not always completely soluble in the solvent. Polymers derived from

61 and substituted styrenes are almost completely soluble in THF,

whereas polymers derived from 56 and substituted styrenes are much

less soluble in this solvent. The soluble portions were purified

by repeated dissolution/precipitation from THF/hexane, and the in-

soluble portions were purified by extraction with hot methanol from

a Soxhlet apparatus'(because of the solubility of bis-urazole in hot

methanol). The quantities of each fraction are shown in the Experi-

mental Section.

From these polymerization studies, it is clear that there is not

much difference in using either THF or DMF as solvent in view of the

stabilities of bis-triazolinediones 56 and 61 in the respective

solvents. Compounds 56 and 61 decompose faster in DMF (about 5% in

3 minutes) but they also react faster with substituted styrenes in

this solvent. Compounds 56 and 61 decompose much slower in THF (about

10% in 60 minutes), but they also react much slower with substituted

styrenes; in addition, there is a solubility problem in using THF,

but there is also a problem in removal of DMF as solvent. An evalua-

tion of these factors leads to the conclusion that DMF is a better

solvent for these polymerization studies.

Copolymerizations of bis-triazolinedione 66 with substituted

styrenes were done by mixing equal moles of substituted styrene










solution in DCE and 66 in the same solvent prepared via the oxida-

tion step at room temperature. The reaction is spontaneous, slightly

exothermic, and completed in less than an hour in most cases. The

yellowish polymers formed are not soluble in the solvent, and puri-

fication was accomplished by extraction with hot methanol, usinq a

Soxhlet apparatus, followed by drying in vacuo.

The times required for completion of copolymerization between

bis-triazolinediones 56, 61, and 66 in DMF, THF, or DCE are shown in

Table VIII for comparison. Copolymerization was fast in DMF and

slower in DCE and THF.

p-Fluorostyrene, prepared in low yield by a modification of

procedures published by Overberger and Saunders,63 Bachma and

Lewis,6 and Brooks,65 was copolymerized with 61 to give a cross-

linked polymer with a swelling ratio of 19.4 in DMF. No other

characterization was done on this polymer; copolymerization between

p-fluorostyrene and 56 and 66 was not studied.

The copolymers derived from bis-triazolinediones 56, 61 and 66

with selected substituted styrenes were characterized by IR, NMR,

viscometry, gel permeation chromatography (GPC), vapor pressure osmo-

metry (VPO), and DSC in order to determine the microstructures,

molecular weights and thermostabilities of the polymers. It must be

pointed out: (1) because the polymers are insoluble in more volatile

solvents like acetone, chloroform, methanol, and toluene, and high

temperature operation of the VPO apparatus was not possible, these

measurements were not done. The molecular weights, therefore, were































0 0 0 0 0 0 0
A A


4-)
C
o C

in A


S00U C 0 C C C
Ca CM


SE

In V
r-


4- 4-P
C c

0 <
C C
*r- *r*


C LA VD r, CD CM)
M Ln d- LO
C')


2E L.
W C
3:



ZLL





LZ
-I-
CD m





u-
0(f0
LU




0 -

0C

F- F-








(II





U-


a)
a CA


C 00


a) 4-'
S.. 0 >


I I
CL MI


Sr-0-


3- -
4-' 4-'
~cc
C C
10I fl0

C C
*, *3


0)
Ca 0
0) C




r U
=. S-
4-' 4-'

E CL
I I
bS 0


x 0
co
E) C
C a) 0)

E E
I 4-I I
0. CL CL


()
C

SL

ca

x C

0 C
U *r
vo >
I I
CL at


- r-
4-) 4-'


0 41

C C
*r *3r









determinated indirectly by fitting the characteristic elution volumes

and intrinsic viscosities of polymers from GPC operation into the

universal calibration curve log [n] M v.s. Ve, where [n] is intrinsic

viscosity, M is molecular weight, Ve is elution volume. This curve

is prepared from the elution volumes and intrinsic viscosities of

standard mono dispersed polystyrene samples manufactured by Pressure

Chemicals, Pittsburgh, PA. All the measurements were carried out in

DMF. (2) Although elemental analyses for model compounds are in good

agreement with the calculated values, this is not true for polymers

for the reason that 'polymers contain heteroatoms in a big molecule,

and many side reactions occur during the combustion process; there-

fore, the combustion may not be complete; also, the high thermosta-

bility of the polymers may account for this.

Since IR spectra of polymers do not give much information about

their microstructures because of overlap of infrared absorption peaks,

the microstructures of the copolymers were determined mainly by NMR

spectroscopy. The assignments of NMR peaks of polymers were made

possible by comparing the spectra with those of appropriate model

compounds prepared in this study. For example the spectrum of the

polymer derived from 56 and styrene (87A) is shown in Fig. 17. The

assignments of peaks were made by comparing the positions of peaks

with those of model compounds 47 and 11 (see Table VII). The assign-

ments of spectral peaks of polymers derived from 56 and p-chloro-

styrene (87B), Fig. 18; p-t-butylstyrene (87C), Fig. 19; a-methyl-

styrene (87D), Fig. 20; p-nitrostyrene (87E), Fig. 21, were made by

































4-
o
E
5-
u





r-:
Q -






-Q r-
4cr
LL


-8


-0 -0
i


0D





-0







60







-o



















4-
-Q
O
E

C)









LL



S-Q
8-





-Q







61







I





-i









-o




0
o

E









I I-
U-

*rQ
00















































- 0
4-
0
E
4.i



V)
ar
rj







o o
zO







*rq







63









o






9













co
4-
0
E
43
-s





o




0


0 --

40









comparing with those of model compounds 77 and 78, 81, 83, 85,

respectively. (See Table VII or the figures for those compounds.)

Similar assignments were made for polymers derived from p-methyl-

styrene (87F), Fig. 22; p-bromostyrene (87G), Fig. 23; p-methoxy-

styrene (87H), Fig. 24; p-acetoxystyrene (871), Fig. 25; and 4-

vinylbiphenyl (87J), Fig. 26, using 47 and 11, 77 and 78 as model

compounds. The assignments for spectra of polymers derived from 61

and 66 with these selected substituted styrenes were done similarly.

The NMR data for all polymers studied thus far are summarized in

Table IX for comparison. No NMR spectrum for polymer derived from

4-vinylbiphenyl and 66 was taken because of its low solubility in

DMF, or other suitable solvent.

From the analyses of NMR spectra, it is quite clear that poly-

mers derived from 56, 61 and 66 with p-t-butylstyrene, a-methylstyrene,

p-nitrostyrene and p-acetoxystyrene contain only the Diels-Alder-ene

reaction product as the sole repeating unit. These results are in

parallel with the structures of model compounds; all other polymers

contain both Diels-Alder-ene and double Diels-Alder reaction products

as repeating units in the approximate ratio of 2:1 or larger, favor-

ing the former. It is interesting that p-acetoxystyrene gives poly-

mers which contain only Diels-Alder-ene repeating units. The acetoxy

group, behaving as an electron-withdrawing unit; also 4-vinylbiphenyl,

gives polymers which contain both types of repeating units indicating

that this group is not bulky enough to completely inhibit the second

Diels-Alder reaction. It can be predicted that p-isopropylstyrene

would give polymers containing both repeating units.







65















-Q

















co
4-
0
E


'a
r-










LL-









































C4-
0


4--
o




C-






cJ
/V)



i "



*r-


-8 -







67










C-


















-4
0
-9







4-8
Co


E






-



Q to

*r








PL. #1







68













0






i4
-o








0










E
S-

V)
cc









9 CO
r











oo
L2







0 0
C-










0
o o
fE







69















-Q
0












-0







-0 4-
0O
o
E

C-
U


oc





0%
*r-
Lt




-Q -o







o 1 -





.9 -0
-8 /-D





















o


So*





aC



4-+
Z:


:,0AC


Clf


-J
C)



-..1



I

-J
-I
Li




Li
-J


C)
=C)
DL,




C)
c2 :












-I







M:
-l
0
I-








I-


M =

C)M N 0L I
0 0 m
O 0 0 I0 1
X: Cm O O
II II 11 II II
>- >- >- >- >-


II II II II II



UI

N
-0 II
=3 >- CM%
r- c) 0
I 0 1- Z
II II II i-- II
> >- >- .0 >-

3 3 3:: 0 2:
II II II II II

X X X X X


02 /'-\
\ -

/ oC


*r-







+


-c


.X


-K
5-


9-
0
0-


r- r-

0 00


0- CN







O LD
U0 LO
r- r*


r- CM

C* *)



00 C

to tz



LO LA
* *

0 o

U- UC
00

*A LA


C*-
* *4







C.J CM


*
















Sco 0 co co Io
00 CO CO C


9-



C..-



LA)


ci-
N-



N-

ehL


I I I



I I I




I I I



I I I
1 1


0
I *

LO


d- fb


CO I


I
N











m O0

3 0
.9- C















CM C)

r- a-
OOC


r- a-

Cccc


-cc
+

3-
+


* *



0 C

ro aO

C0 C
NO CO


C. cN


to LO
r-. r.



r : 9





CM CM
*








ON
0.0 ko




o rC)
LN to



CO
* .

LA LA

CU) U


CF) (%

'a .


CO C

7 r--


LA CM 0
S AO CO
I *
Lo LO LO


* O


(0 0C
0 CO
O CO


CO N.
Un U)

co0 r



LO LO

\- -
td~- 't


CON
00
* *
N-co


I I I


00C-00
r- WCOD r-

r- r- a- r-




CO CO CO CO
co ~~co % o0


O C
0




CM




r%- r-.
o CM
o0.a-
LAN. *


CMO 0

I I I *
us r^


LOL
0 0



) LA O

n LOn L)
oo

*'


Ol CM
CM N-

NN
* *


CM
0
I


N
rr


CM
* I




LA
r-

* |





a- i-


a- CM



- o


CM





CM


a- CM a- CM
m C.) w
CO LA 1 0 CO
CM CM r- CO CM

CM CM "O CM CM


CM CM CM


I I I
CM CO CM


Cs C14 CsC\
a- CM r- CM


ICO CO C CM a- CM t)
C') c') CM C) c> n c

(' C) a- Cm i- Cn C')


* II
* I


I I
I I


r-. o Ln

a- a- r-




000


,LL Cc I c* cm> co o LL LL o 0 co -co
r coi CI o co 0 co 00 Co co co co
CO 00 00 CO CO CO CO CO CO CO L0 CO CO CO 00


r. LCM L

. N. rN. N.
**** VV


N. 0
Lr CM
r%. N.
..
Lnc


i
I)
E

0


CO CNO 0
co co d C)



O CO CO
N CCLCO




O, CM0C

000













.- r LA ID 4** CC 0
*



*- 0 O O O O CO O" C d
"
Oa






0 a 0; N3 00
r, LO a, oo o m o Co co Mr to



SF C) N CD CO r-






N. r- N- N N

i- Us. -^ N -- r-- -"- ^. *.
CM










+ M j ( OL O C (
'. *
CM NC) o o)





.* .
Ln CM C CM Cn



r^ i q:o Len f
o -
i l l I


u CO 0
S* r- Co CO OC
(U 19 U 1 90 in


LA U-LOO L LA OO LO
C- ) UC CO (. C("O L L
( In L n An Ln An in Ln L L




Co L



















0N N









0.
S- N- CoCdC- C- ( C
C..) CM








a\ Q a a a

.0


















C-

















I C I

'-- +-Q)


aU 4-
V (-)r- 4-




0)
C di* 0




4 JC .0 4-)


U )-
4i 0-0-- -










S- -0 S-'
-- UOC

2 0 U C


( n.- =
4-' 0 4-)











(a 0 c"
C- {C 0O o
(. 9I 0
-- C Ci < 4- .
U 4Jc n o *

S 4 3--,- J-
0 .)
r5 (l4-5 .- -
S-4-.)




0 Qi L-
I--"

*0 3(




U4 4- -" 4-
U cO C)
c- 0 O 0
C>
0 0 ( AI *)
to a 'a C C 3

oX S 00 0
U 4 -' '-C -

.-- -0 L- )
LU 4.) U)C *-4-) C

_E 0 4-0 II a 0D
'a C C( 01 -)
*s-O O 20. (
,.- 1 V, 0 r- "C 0 4--
E 0z 0 0 0 *-C S
*re *i- CS-C 4L
S0 4- 4- 0.-Lr$.I 0
*D *'- + *r 0 0a C
Si U 0 4-0) E =
S0 0 (a.C -E- I0
u 0 C4-)L- L-
3 in i D t 4-)
C *r 4- 0 VI U
S 0 0 v) 0 5 0)

0 *r- r 0 *e V

> 0C 0

to C !- C1 0 -C0 0
S 0 0 4 3 C
oL n 0
>a d 0 0- 04- L L C*r 0
S0> 0) CO 0CC SL
0 3 1 3Ir-
o 3 3 U
0 0) dO V) *-
40 0 4-' 5 S- X) 4i

> 0 0> C 4- C
SU U O I 'OX CD
0, X X VI0 (0 f
0) 0i 4-'a- Q0 0 E
vi vi 01 -01 d

E U 4- LS0 0
>, 4- (U)i i-
$- I. 01 X r- U

SL U- L 3i C- Z

4*C -K

*@ *
45O 45 45









The molecular weights of the polymers obtained range from 5,000

to 16,000 for most, with few exceptions. The stoichiometric factor

controls the molecular weights, as can be expected. In general, the

molecular weights of those polymers obtained for polymerization in

THF are about 30-70% of those obtained for polymerization in DMF.

Surely, decomposition of 56 and 61 in THF is more serious for these

polymerization reactions. It seems easier to get higher molecular

weight polymers if polymerizations are carried out in DCE, like the

polymers obtained from copolymerization of 66 and the substituted

styrenes.

There are no reliable criteria to judge the thermal stabilities

of the polymers. Thermostability depends more on the structure of

the polymer than on the molecular weight. It would be predicted

that copolymers derived from the aromatic bis-triazolinedione 66

would possess the highest thermostability. Some physical data for

the copolymers prepared are summarized in Table X for comparison.

F. Mechanistic Studies of Formation of Model Compounds

In the reaction of styrene and maleic anhydride53 (see Scheme VI),

the initial Diels-Alder adduct, which apparently cannot be isolated,

is first formed. It possesses a carbon-hydrogen bond weakened by

both allyl and pentadienyl resonance,66 and reaction with a second

molecule of maleic anhydride yields the ene product and the 4 + 2

adduct in a ratio of about 8:1. Similarly, the reaction between PhTD/

MeTD with styrene to give 1:2 adducts would pass through the 1:1

Diels-Alder adduct intermediate which is also difficult to isolate.










TABLE X

SOME PHYSICAL DATA FOR COPOLYMERS DERIVED FROM 56, 61 AND 66
WITH SUBSTITUTED STYRENES PREPARED IN DMF, THF AND DCE

Polymer Solvent* Molecular Weight** Tm(decompn) Polymer Structure***


226
225
295
293
272
260
275
260
271
267
264
265
269
258
257
257
288
287


87A

87B

87C

87D

87E

87F

87G

87H

871

87J

88A

88B

88C

88D

88E

88F


DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF
DMF
THF


7400
8230
8700
5600
6700
3640
4900
2460
9800
4810
10400
7310
5700
3160
10100
6350
8400
3770
10200
9140
1000
1000
10200
4800
15400
12200
9300
3650
8700
2610
10200
5400


D-A-E > D-D-A

D-A-E > D-D-A

D-A-E

D-A-E

D-A-E

D-A-E > D-D-A

D-A-E > D-D-A

D-A-E > D-D-A

D-A-E

D-A-E > D-D-A

D-A-E > D-D-A

D-A-E > D-D-A

D-A-E

D-A-E

D-A-E

D-A-E > D-D-A










TABLE X (Cont'd.)


Polymer Solvent Molecular Weight Tm(decompn) Polymer Structure

88G DMF 9600 254 D-A-E > D-D-A
THF 4550 257
88H DMF 11200 250 D-A-E > D-D-A
THF 6830 240
881 DMF 7900 258 D-A-E
THF 3860 257
88J DMF 9500 280 D-A-E > D-D-A
THF 3500 269
89A DCE 1950 282 D-A-E > D-D-A
89B DCE 5120 282 D-A-E > D-D-A
89C DCE 2080 269 D-A-E
89D DCE 8400 246 D-A-E
89E DCE 14420 311 D-A-E
89F DCE 36700 304 D-A-E > D-D-A
89G DCE 4160 258 D-A-E
89H DCE 7620 250 D-A-E > D-D-A
891 DCE 36230 260 D-A-E
89J DCE 18490 292 D-A-E > D-D-A


Solvent used for polymerization.
** Molecular weights for polymers prepared in THF
numerical average of the soluble and insoluble
*** D-A-E = Diels-Alder-ene repeating unit. D-D-A
Alder repeating unit.


were recorded as
portions.
= double Diels-









Scheme VI



+ .0


0 0

0
0 /0 \



O --

0 0 0
48 (89%) 49 (11%) 0
The purpose of this mechanistic study was to isolate the reaction

intermediate for the formation of model compounds in order to verify

the mechanism for this polymerization study and to determine the

absolute and/or the relative reaction rates for both steps of the

reaction.

In order to make this possible, careful examination of the choice

of substituted styrene must be made. The substituted styrene chosen

for study must meet the following requirements: it must speed up the

reaction of the first step while exerting no effect on the second

step in order to make isolation of the intermediate possible; it must

give a simple reaction in order to afford easier separation of the

reaction intermediate and products; also, it must be available in
reasonable amounts for study, The first choice of a compound among

all substituted styrenes which may meet these criteria is p-t-butyl-

styrene, since it gives only the Diels-Alder adduct, and the substi-

tuent group enhances the reaction of the first step.








p-t-Butylstyrene was allowed to react with PhTD/MeTD in methylene
chloride at a molar ratio of 10:1 favoring p-t-butylstyrene at room
temperature and at low temperature (-780C). Simply by mixing these
two solutions (see Scheme VII), the product was isolated from p-t-
butylstyrene by adding hexanes as non-solvent. Both product and
recovered p-t-butylstyrene were identified by NMR spectroscopy. The
Diels-Alder-ene adduct was isolated as the sole product. Hiqh dilu-
tion techniques were then applied by adding a dilute solution of
Scheme VII

xY




0 R+ ) N= N / /N
0 1 0 Y N 0
Y R\
R0 R
N xoel

0 NN/NH 0 Y X
x
X r N

Y NN 0 N N


R R
(1) X=H, Y=t-Bu A: R.T. molar ratio (sty/4-R-TD = 10/1)
B: -78C molar ratio (sty/4-R-TD = 10/1)
C: -780C high dilution technique
molar ratio (sty/4-R-TD = 10/1)
(2) X=t-Bu, Y=H
(3) X=Y=tBu









PhTD (0.038M PhTD in CH2C12, 150 ml) to a dilute solution of p-t-

butylstyrene (0.19M in CH2C12, 300 ml) at -780C slowly over a period

of 8 hours. Again, no Diels-Alder intermediate could be isolated,

leading to the conclusion that the reaction rates of both steps for

the formation of these model compounds are comparable over a wide

temperature range.

a-t-Butylstyrene and a-p-di-t-butylstyrene were then synthesized

in an effort to overcome the difficulty met in the above case.

Because of steric hindrance, it was expected that only the double

Diels-Alder adduct would form in the reaction of a-t-butylstyrene,

with MeTD/PhTD, and only the Diels-Alder adduct would form in the

reaction of a-p-di-t-butylstyrene with MeTD/PhTD. Syntheses of these

substituted styrenes were accomplished by a modified procedure

developed by Corson, Tiefenthal, Atwood, Heintzelman and Reilly,67

as shown in Scheme VIII. Thus, bromobenzene was treated with

Scheme VIII

Br

Br2,Fe 12. nBuLi
2. tBu-CCH3

R 3. H CH
CH3 CH //,H2
$ +tB
HO tBu H3C CH
CH3




R R
R = H:90 91 92
R = tBu:93 9-5









n-butyllithium to give phenyllithium, which was treated with pina-

colone which, after hydrolysis, gave 2-phenyl-3,3-dimethyl-2-buta-

nol, 90. Dehydration was carried out by refluxing 90 with amberlite

(Malinckrodt, prepared by acidification of the salt, mesh 100-200)

to give a mixture of products with NMR spectrum shown in Fig. 27.

Further expansion of the spectrum for the methyl region (6 1.0-2.0)

and vinyl region (6 4.5-5.5) gave a fine spectrum which clearly showed

allylic coupling (vinyl proton and methyl proton) (see Fig. 27).

Apparently, there were two components in the product mixture, one

being the desired product 91, the other its structural isomer, 2,3-

dimethyl-3-phenyl-l-butene, 92. The outcome is trivial, because the

dehydration goes through a carbonium ion intermediate, this rearrange-

ment giving product 92. The ratio of 91 to 92 is about 20:17. Both

compounds have similar melting points and polarity which make isola-

tion difficult. a-p-Di-t-butylstyrene was synthesized similarly,

starting from t-butylbenzene, going through t-butyl-bromobenzene,

followed by a Grignard type reaction to give carbinol 93. Dehydra-

tion of this carbinol using Amberlite gave a mixture of the desired

compound 94 and its structural isomer, 2,3-dimethyl-3-p-t-butylphenyl-

1-butene, 95, in the ratio of 4.3:1, favoring the desired product.

The NMR spectrum of the mixture is shown in Fig. 28 (with expansion

of the regions 6 1.3-1.7, 6 4.8-5.1).

The separations of the desired products 91 and 94 from their

respective structural isomers, 92 and 95, can be carried out theoretic-

ally, although they are very similar in polarity and boiling point/







81

















0
-Q






oo








4-
O





0 0








cc
0




*-













L .
j o
E












U-








82













O.
C-^
o-







4-
0
o
.O. c



-0





L.

SU-


Q 0



4-
0




co










0r-
L.
1' a




ci j









melting point. High performance liquid chromatography was used for

this purpose. However, although the operation has been repeated

several times, no purified substituted styrenes have been obtained,

and no further work was done because of time limitations. Neverthe-

less, preliminary tests on the reactions with PhTD do give promising

results, as predicted.

A plausibly better method for the preparation of these substi-

tuted styrenes is conversion of their respective carbinols to bromides

followed by base catalyzed elimination of hydrobromide. Again,

because of the time limit, no progress was achieved here.

An alternative attack on the mechanistic problem would be to

use 2,6-disubstituted styrenes (e.g., dihalo-substituted styrenes)

to react with MeTD/PhTD in which the ene reaction could be excluded

completely because no allylic hydrogen would be present in the initial

Diels-Alder product and also because of the high bonding energy of the

C-X (e.g. X = Br, C1, or atoms other than H) bond which would be ex-

pected to cleave only by a thermal process. So the reaction should

lead to formation of Diels-Alder and/or double Diels-Alder adduct only.

2,6-Dichlorostyrene, a commercially available substituted styrene,

was chosen for this study. It was allowed to react with an equal

moler of MeTD (both were dissolved in methylenechloride) slowly by

adding MeTD solution into the 2,6-dichlorostyrene solution in ten

portions, each portion being added only after the characteristic

color of MeTD had disappeared from the reaction mixture completely,

in order to minimize the undesirable side reactions (decomposition










of MeTD). After the reaction was complete, the product was precipi-

tated by adding nonsolvent hexane; no residual 2,6-dichlorostyrene

remained. An NMR spectrum of the crude product as shown in Fig. 29

indicated that only the 1:1 Diels-Alder adduct, 96, had formed and

no double Diels-Alder adduct was present.
C1 H
Hi
*' /'. CH2


H C1 L-N
H \
96 CH3
96 3

Although PhTD would be expected to react faster with 2,6-

dichlorostyrene, no study was done with this compound as it could

produce a product which would be more difficult to identify because

of overlapping NMR peaks.

From these studies, it is quite clear that the reactions between

PhTD/MeTD and substituted styrenes go through an initial 1:1.Diels-

Alder adduct and that this adduct undergoes further reactions to give

the double Diels-Alder and Diels-Alder-ene adducts, which serve as

model compounds for the polymerization reactions of bis-triazoline-

diones and substituted styrenes.








85












-o






















r ) 0
0
-9







-.
Ch







-.I
*






LL






-
O:

ad e









G. Kinetics of Formation of Model Compounds And Of
Copolymerizat of Substituted Styrenes and Bis-Triazolinediones

The copolymerizations of substituted styrenes with bis-triazoline-

diones proceed in a stepwise manner through Diels-Alder-ene and

double Diels-Alder reaction schemes; so this process can be classified

as an example of step growth polymerization. The rate of a step

growth polymerization is the sum of the rates of reaction between

molecules of various sizes. A characteristic of step growth polymeri-

zation is that any two species in the reaction mixtures can react with

each other. The kinetic analysis for this kind of polymerization can

be greatly simplified if one assumes that the reactivities of both

functional groups of a bifunctional monomer are the same, i.e. that

the reactivity of one functional group of a bifunctional reactant is

the same, irrespective of whether or not the other functional group

has reacted and the reactivity of a functional group is independent

of the size of the molecule to which it is attached.68 These simpli-

fying assumptions make the kinetics of step growth nolymerization

identical to those for the analogous small molecule reaction. Thus,

for the copolymerization of 2 monomers of A-A, B-B types

A-A + B-B k A-A-B-B

dCal (Eq. 3)
d[Ca = k[Ca][Cb]
dt

If-the concentrations of A-A, Ca and B-B, Cb are very nearly stoi-

chiometric after several mathematical manipulations, one obtains

P = kt (Eq. 4)










in which P is percentage of conversion, Co is the initial concentra-

tion of monomers. A plot of P vs t gives k (as the slope),
69 Co[l-p]
the rate constant.

However, the kinetics of the polymerization studies in this work

are not so simple, but are much more complicated than those of

simple condensation polymerization reactions. First, it may not be

reliable to assume that the reactivity of both functional qrouos are

equal, because one dione unit in a bis-triazolinedione can act as a

dienophile to give the Diels-Alder adduct with substituted styrene

or with the 1:1 adduct, while the other dione unit in the same mole-

cule can act as an enophile to give the Diels-Alder-ene adduct;

besides, both may act as either a dienophile or an enophile. Also,

even though both dione units in a bis-triazolinedione molecule act

as dienophiles, they still may show big differences since one could

react with styrene while the other could react with the 1:1 Diels-

Alder adduct. Similarly, the 1:1 adduct could react either as an

ene or as a diene, the reaction rates for these two being different.

(Actually, the ene reaction is favored over the Diels-Alder reaction.)

So, to make the kinetic treatment easier, one more assumption must be

added to the basic assumptions for a kinetic treatment of general

condensation (step growth) polymerization. That is, the reactivity

of a substituted styrene is not too greatly different from that of

the Diels-Alder adduct, i.e. the reaction rates of the reaction

between a substituted styrene and bis-triazolinedione and of the

reaction between the 1:1 adduct and the bis-triazolinedione are about