• TABLE OF CONTENTS
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 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Illustrations
 Introduction
 results and discussion of the methacrylic...
 General mechanism for intra-intermolecular...
 Experimental
 Summary
 Bibliography
 Biographical sketch
 Copyright














Title: Methacrylic anhydride.
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
    List of Tables
        Page v
        Page vi
    List of Illustrations
        Page vii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    results and discussion of the methacrylic anhydride study
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
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        Page 17
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        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
    General mechanism for intra-intermolecular polymerization
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
    Experimental
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
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        Page 98
        Page 99
        Page 100
    Summary
        Page 101
        Page 102
        Page 103
    Bibliography
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
    Biographical sketch
        Page 109
        Page 110
    Copyright
        Copyright
Full Text











METHACRYLIC ANHYDRIDE.
A MODEL STUDY OF THE MECHANISM
AND STEREOCHEMISTRY OF
INTRA-INTERMOLECULAR POLYMERIZATION













By
THEODORE FLINT GRAY, JR.


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


December, 1964













ACKNOWLEDGMMITS


The author wishes to express his deep appreciation

to ;r. G. B. Butler whose guidance and counsel during the

execution of this work were of inestimable value.

The author wishes also to express his gratitude to

the members of his advisory committee and his fellow

graduate students whose advice and direction were a constant

source of encouragement.

The author is indebted to Dr. Wallace Brey and his

associates for the nuclear magnetic resonance spectra

reported in this study.

Special thanks are due Mrs. Thyra Johnston for her

diligence, conscientiousness, and speed in the typing of

this dissertation.

The financial assistance received from a Chemstrand

Fellowship and a Tennessee Eastman Scholarship-Fellowship

is also gratefully acknowledged.













TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS . . . . . . . . . ii

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

LIST OF ILLUSTRATIONS. . . . .. . . vii

Chapter

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

Discovery and Proof of Intra-
Intermolecular Polymerization. . . 1

Development and Expansion. . . . . 3

Statement of the Problem . . . 10

II. RESULTS AND DISCUSSION OF THE METHACRYLIC
ANHYDRIDE STUDY. . .. . . . 11

Kinetics . . . . . . . . 11

Solvent Effects. . . . . . . 27

Conversion Effects . . .. .. 34

Non-Conjugated Chromophoric Interactions 39

Stereochemistry. . . . ...... 46

Summary of Results and Conclusions . . 62

III. GENERAL MECHANISM FOR INTRA-INTERMOLECULAR
POLYMERIZATION . . . . . 65

Mechanistic Driving-Force. . .. 65

Stereochemistry. . . . . . . 78


iii










Chapter Page

IV. EXPERIMENTAL . . . . . . . 80

Equipment and Data . . . . . . 80

Source and Purification of Materials . 81

Kinetic Study. . . . . . . .. 85

Stereochemistry Study. . . . . 94

V. SUMMARY ..... ............ 101

BIBLIOGRAPHY. . . . ..... . . .. 104

BIOGRAPHICAL SKETCH . . . . . . . .. 110













LIST OF TABLES


Table Page

1. Compounds Which Undergo Intra-Intermolecular
.. Polymerization . . . . . . .

2. Cyclization of Methacrylic Anhydride as a
Function of Concentration. . . . . . 15

3. Variation of kll/kc as a Function of Temperature 17

4. Cyclization of Methacrylic Anhydride as a
Function of Temperature. . . . . . . 20

5. Rate of Propagation of Methacrylic Anhydride
Corrected for Fraction of Non-Cyclic Units . 23

6. Solvent Influence on Intra-Intermolecular
Polymerization of Methacrylic Anhydride. . . 28

7. Dependence of Rate and Velocity Coefficients on
the Extent of Reaction for the Heterogeneous
Polymerization of Methyl Methacrylate in 50 Per
Cent Cyclohexane Solution at 22.50C... . .. 33

8. Ultraviolet Spectral Study . . . . .. 41

9. Fractions of Poly(Methyl Methacrylate) in the
Three Stereoconfigurations as Determined by NMR 48

10. Possible Conformations of Poly(Methacrylic
Anhydride) and the Stereochemical Configuration
of the Resultant Poly(Methyl Methacrylate) . 50

11. Tacticity of Poly(Methyl Methacrylate) Derived
From Poly(Methacrylic Anhydride) as Determined
by NMR . . . . . . . 52

12. Tacticity of Poly(Methyl Methacrylate) Derived
From Poly(Methacrylic Anhydride) as Determined
by NMR . . . . . . . . . . 54

13. Structure of Polymers of Methyl Methacrylate
Prepared with Free Radical Initiators. . . 56










Table


Page


14. Probability Treatment of Tacticity in
Poly(Methacrylic Anhydride) . . . . . 59

15. High Conversion Study of the Fraction of Cyclic
Units as a Function of Temperature and Solvent. 87

16. Physical Properties . . . . . . 95

17. X-Ray Diffraction Study of the Degree of
Crystallinity as a Function of Polymerization
Temperature on Poly(Methyl Methacrylate)
Derived From Poly(Methacrylic Anhydride). . 99












LIST OF ILLUSTRATIONS


Figure Page

1. Variation of 1/f as a function of methacrylic
anhydride concentration in dimethylformamide .. 16

2. Variation of 1/fc as a function of methacrylic
anhydride concentration in dimethylformamide
at various temperatures (C.).................. 18

3. Variation of kll/kc as a function of
temperature for methacrylic anhydride in
dimethylformamide ............................ 18

4. Arrhenius plot of logo1 R11/Rc as a function
of 1000/T... ....... .. ............. ....... 21

5. Rate of propagation of methacrylic anhydride
corrected for the fraction of non-cyclic units. 25

6. Variation of 1/fc as a function of anhydride
concentration in cyclohexanone at 0C.
(k1/kc:. 0.26 for methacrylic anhydride; 0.20
for acrylic anhydride.)....................... 30


vii













CHAPTER I


INTRODUCTION

Discovery and Proof of Intra-Intermolecular
Polymerization


Early polymer research with non-conjugated dienes

lead to the hypothesis of Staudingerl that non-conjugated

dienes always yield crosslinked polymers. The hypothesis

was generally accepted although a few exceptions were

observed. Notably, Walling2 found in a study of gel-points

that Stockmayer's equation was violated due to occasional

cyclizations of certain diene crosslinking agents. The

extent of this cyclization was later substantiated both

theoretically45 and experimentally.6,'78

Although it is quite clear now that others had

observed intra-intermolecular polymerization, the generality

as a mechanism for diene polymerization was not recognized

until its discovery by Butler.9 The first step in the

discovery of the alternating intra-intermolecular polymeri-

zation mechanism or cyclopolymerization came in 1951 when

Butler and Ingley9 found that tert-butylhydroperoxide-

initiated diallyl quaternary ammonium salts gave water-

soluble polymers contrary to Staudinger's1 hypothesis.











Further investigation showed little or no unsaturation in

these water-soluble polymers. The mechanism which was

proposed involved a radical attack at one double bond in

the diene followed by an intramolecular radical propagation

at the terminal methylene of the second double bond.

Following the cyclization, the cyclic radical propagated to

another diene resulting in a linear polymer with cyclic

recurring units.


CH2
CH2 CH
Cr I


CH2 H2
SBrG


initiation
or
intermolecular
step


CH2

R-CH2-C Ci

CH 2
N Br @
R R


intermolecular
step


CH2
R-CH2-CH C H.


CH2 N CH2
N/ BrG
R R


III









I +III

CH2
Inter- step /
molecular R-CH2-CH H

CH2 \ /CH2
N^ Br
R -
n

IV

Through degradation studies on the diallyl quaternary

ammonium salts it was shownI1 that cyclic units were present

in the polymer chain thus proving Butler's hypothesis.10

Further substantiating evidence has been reported by

others1213,14 through identification of the cyclic recur-

ring units.

Development and Expansion

Since the preliminary studies and establishment of

the intra-intermolecular polymerization mechanism the

number of monomers and pertinent research reported has

reached the hundreds. Due to this enormous number no

attempt will be made to list the compounds which have ex-

hibited the ability to cyclopolymerize as has previously

been done.15'16'17,18'19 However, it appears from an

examination of the literature that six general types of

monomers have been cyclopolymerized. These general types

and a few representative references are given in Table 1.












TABLE 1

COMPOUNDS WHICH UNDERGO INTRA-INTERMOLECULAR POLYMERIZATION


1. Non-conjugated Dienesl5-19


R
-] ==== R
-jx

^X. -Z


<-u 17


2. Multiunsaturated yielding two or more rings


19 20 N


Y = Z: C=0, 0, (CH2)n

Y # Z: Y=C=O and Z =
CH2 or absent
X: C, 0, N, Si, P, Sn,
S
R: H, alkyl, phenyl,
COOCH3, CN, etc.


21, 22


X = C, N

Y = C, 0














TABLE 1 Continued


3. Non-conjugated Diynesl3


n = 0, 1, 2


CH2 CH2
CH2n


4. Non-conjugated unsaturated other than carbon-carbon


0 0
OCH 'C 23, 24
CH C
CH2. ^CH2
CH2


C


"1 N 25, 26

CH2 CH2
(CH2)n


n = 0, 1













TABLE 1 Continued


5. No mnsaturation


27, 28


6. Cyclocopolymerization15, 29


+2


X: 0, CH2, S, Si










Y = z: /


0,

0


Y 0 Z where Y: H and Z:


Y Z








0/







NR CN


0


0
C-OCH3, CN, etc.


Y Z








7

Examination of Table 1 shows that intra-intermolecular

polymerization is exhibited by quite a wide range of monomers

of varied characteristics. The workers who have reported

these compounds and studied their polymerization have also

shown that cyclopolymerization occurs under the influence of

every type initiator system known. Usually a monomer is

efficiently initiated only by one or two of the initiator

systems; however, in at least one case, 2,6-diphenyl-l,6-

heptadiene, cyclopolymerization was observed under thermal,

free radical, cationic, anionic, and Zeigler conditions.30

The extensive synthetic cyclopolymerization research

has shown that cyclization is most favorable for dienes

capable of forming five- or six-membered rings. Dienes

which result in large ring sizes have been studied by

Marvel.1 He found that the percentages of cyclization for

monomers capable of forming seven- to twenty-one-membered

rings were similar to those observed in common ring closure

reactions; however, the conditions of polymerization play

a large role in the amount of cyclization. Oiwa and Ogata8

have dramatically illustrated this in obtaining 81 per cent

cyclic units in the solution polymerization of diallyl-

phthalate which yields eleven-membered rings. Although

most studies have dealt with conditions favorable to cyclo-

polymerization in the liquid state, Gibbs32 has reported

that irradiation of N,N-diallylmelamine in the solid state










results in intra-intermolecular polymerization thus ex-

tending cyclopolymerization to the solid state.

The largest portion of research concerning intra-

intermolecular polymerization has centered around homo-

cyclopolymerization. Butler has extended his own mechanism

to the unique cyclocopolymerization illustrated in Type 6

of Table 1.15,29 Although the number of references to this

in the literature is small, the mechanism has received

careful study in Butler's laboratory. The results of a

part of this investigation have lead to the derivation of

a general equation for 1,4-dienes and mono-olefins which

undergo cyclocopolymerization.33 The validity of the

equation has been substantiated by experimental cycloco-

polymerizations of divinyl ether and maleic anhydride as

well as other comonomer pairs.3 A less general equation

for the cyclocopolymerization of divinylbenzene and mono-

vinyl monomers has also been published but has not been

checked experimentally.34

Dienes of Type 1 in Table 1 have also been the object
of several copolymerization studies. Most research in the

area of copolymerization of dienes capable of intra-inter-

molecular polymerization with mono-olefins has centered on

conditions necessary to obtain soluble copolymers.29,3538

Recently, copolymerization involving dienes which undergo

cyclopolymerization has been treated quantitatively and the










equations derived tested experimentally to check their.

validity. 39041 From an examination of both the qualita-

tive and quantitative work, especially that of Hwa39 and

Smets,41 a general outline of conditions necessary to

obtain soluble copolymer may be listed. The conditions

which favor soluble copolymer are: (1) comonomer of low

reactivity or similar polarity; (2) low monomer concentra-

tion; (3) low conversion; (4) large differences in the

concentration of the two components.

A final illustration of the utility of intra-inter-

molecular polymerization which, in a sense, is related to
42
copolymerization has been pointed out by Hwa. He has

shown that it is possible to obtain alternating copolymers

by using unsymmetrical dienes, such as acrylic methacrylic

anhydride, which in conventional copolymerizations would

not alternate.

If versatility and generality are the measure of the

importance of a mechanism, then Butler's intra-intermolecular

polymerization mechanism must be one of the most important

discoveries in recent years. It has been shown to be

generally applicable: (1) to a wide range of monomers and

ring sizes; (2) under all initiator systems; (3) to polymeri-

zation in bulk, solution, and the solid state; and (4) to

copolymerization as well as homopolymerization.











Statement of the Problem


The literature pertinent to intra-intermolecular

polymerization shows that research in this area has been

approached in a qualitative or synthetic manner largely

ignoring the kinetics, driving-force, and stereochemistry

of the mechanism. The interpretation of the small amount

of work in these three areas is very difficult because the

results are neither conclusive nor in complete agreement

with each other.

It was the purpose of this research to attempt to

clarify the meaning of available literature as well as to

add to its completeness; therefore, to this end, a thorough

study of mechanism and stereochemistry of a model monomer

capable of intra-intermolecular polymerization was under-

taken. The results and understanding gained in the model

study, it was hoped, would be applicable and useful in

clarifying the complex aspects of intra-intermolecular

polymerization.

Methacrylic anhydride was chosen as the model because

it fit the qualifications of: (1) availability; (2) a con-

jugated system which lends itself to an ultraviolet spectral

study; (3) presence of a hydrolyzable group useful in

studying the fraction of non-cyclic units; and (4) allowing

stereochemical configuration to be determined.













CHAPTER II


RESULTS AND DISCUSSION OF THE METHACRYLIC ANHYDRIDE STUDY

Kinetics


In any study aimed at the elucidation of the driving-

force for a mechanism, it is not only desirable but necessary

to understand the important rate and energy factors which

control the reaction. In approaching the problem of

obtaining energy and rate data for intra-intermolecular

polymerization, it was noted that any diene unit which

failed to cyclize would leave a pendent double bond. By

finding the number of these pendent units the calculation

of the number of cyclic units for a given amount of polymer

could easily be made. Since accurate bromometric titration

methods for determining the concentration of methacrylic

acid were known, the number of non-cyclic methacrylic

anhydride units could easily be determined by titrating for

the methacrylic acid produced when a sample of poly(metha-

crylic anhydride) was hydrolyzed. Knowledge of the number

of non-cyclic units can be treated as a function of concen-

tration and temperature. Combining the data obtained in

these treatments with kinetic equations similar to those

used by Mercier,4- the important relationships of the ratio

11










of rates and the difference in energy for intramolecular and

intermolecular propagations may be obtained.

In order for the kinetic equations to be valid two

conditions must be met. First, monomer concentration must

be assumed to be the same before and after polymerization.
Second, any unit which fails to cyclize must not enter

another polymer chain. For these approximations to be

valid, the conversion of monomer to polymer must be as low

as possible. Experimentally it was found that conversions
of 0 to 4 per cent were satisfactory.

The kinetic relationship between intramolecular and
intermolecular propagation can be derived from the following

reaction scheme:


CH3 CH3
SCH2
-CH2-C. C
I I


o0 o


CH3 C H3
I CH 2 I
-CH2- C.*
o o
.C C
0 0" \\0


kcl
intermolecular


CH3 CH3
CH2z CH2 3
jC C

0o^ ^0o


intermolecula
intermolecular


CH3 CH3
CH3
I CH2 |
-CH2-C-CH2-C*
^C ,
o o c o o
C

CH3 CH2


kc
intramolecular








13

The rate of intermolecular propagation (R11) is given by:

R11 = k [M (2[M]) (1)

[M] is given in moles of diene and therefore
must be doubled to account for all double
bonds present.
and similarly for the intramolecular propagation rate (R ):
c

Rc = kcM.] (2)

The ratio of RI, to Rc results in the expression:


R11 2k11 [M
r *--- (3)
Rc kc

The relationship which relates the experimentally deter-
mined fraction of cyclic units (fc) to the rates R11 and
Rc is:
Rc
f C (4a)
c Rll + R,

or
1/f = + (4b)
SRc
Rl
which on substitution of equation (3) for -- gives:

cc
2kll [M]
1/fc = 1 + -T-- (5)
C

A plot of 1/fe versus [M] results in a straight line with
an intercept at infinite dilution corresponding to complete
kll
cyclization and a slope with a value of (2 --) .
c










The experimentally determined values of 1/f as a
function of concentration of methacrylic anhydride in di-
methylformamide are given in Table 2. A plot of 1/fc
versus [M] (Figure 1) results in a slope with a value of
0.85 1./mole; therefore, at 000. the ratio of kll/kc 1 0.42
1./mole. Table 3 and Figures 2 and 5 give the values of
k11/k at various temperatures in the range -200 to + 800.

By substitution of the Arrhenius equation into
equation (3) a relation is obtained which allows the calcu-
lation of the energy difference between an intramolecular
and an intermolecular propagation step. It must be assumed,
however, that the degrees of polymerization are high enough
that the differences in possible termination steps are
negligible.
R11 2kll [M
11 k (3)
Rc kc



-E11
R A -Ell
11= (2M ) 11 RT (6a)
CAce -E C



C C
Rllog(2[M)) All Ec-Ell (6b)


The difference in energy (E -Ell) can be calculated from

the slope of a plot of logloRll/Rc versus 1000/T for a
constant monomer concentration.



















TABLE 2

CYCLIZATION OF METHACRYLIC ANHYDRIDE
AS A FUNCTION OF CONCENTRATIONa


[M]
Mole/i. fc 1/fe

6.0 0.16 6.3

4.0 0.25 4.0

.3.25 0.26 3.8

2.0 0.35 2.9

1.0 0.55 1.8


aSolvent: dimethylformamide; [Benzoin]: 0.25 wt. per cent
based on methacrylic anhydride; temperature: 0.OOC.































1/fc 4-

2-
Slope = 0.83 l./mole
0 1 1 1 1 1 1
0 1 2 3 4 5 6 7
[Methacrylic Anhydride] (mole/l.)

Fig. 1.--Variation of 1/fe as a function of methacrylic
anhydride concentration in dimethylformamide























VARIATION OF kll/kc


TABLE 3

AS A FUNCTION OF TEMPERATUREa


Temperature
oC. fc 1/fc kll/kc


80.0 0.51 2.0 0.16

50.0 0.47 2.1 0.17

35.0 0.38 2.6 0.25

20.0 0.33 3.0 0.31

0.0 0.26 3.8 0.43

-10.0 0.23 4.3 0.50

-20.0 0.20 5.0 0.62


aSolvent: dimethylformamide; [Benzoin]: 0.25 wt. per cent
based on methacrylic anhydride; [Methacrylic anhydride]: 3.25 mole/i.











8


6 0

S20
4- 35
5e 0
80
2


.0 I
0 1 2 3 4 5 6 7
[Methacrylic Anhydride] (mole/l.)
Fig. 2.--Variation of 1/f, as a function of methacrylic
anhydride concentration in dimethylformamide at
various temperatures (OC.)


pO I I I


0.4


-40 -20 0 20 40 60 80 100
Temperature (C.)
Fig. 3.--Variation of kl,/k as a function of temperature
for methacrylic anhydride in dimethylformamide


j I r I i I


v v
g










The experimental results of the variation of cyclic
units as a function of temperature for the polymerization

of methacrylic anhydride at a concentration of 3.25 mole/1.

in dimethylformamide are listed in Table 4. The value of

the slope of a plot of logORll/Rc against 1000/T (Figure 4)'

was found to be 0.563 which corresponds to an energy dif-

ference (E -E11) of 2.6 + 0.3 kcal./mole. The value of

the ratio All/Ac was found to be 0.0039 1./mole.

The results of the kinetic study indicate that the

intramolecular propagation step requires 2.6 + 0.3

kcal./mole greater energy than the intermolecular step.

It is however noted that the rate of cyclization is con-
siderably larger than that for intermolecular propagation.

Furthermore, from the Arrhenius treatment the value of the

ratio All/Ac indicates a very high steric factor favoring
cyclization.
During the pursuit of the above kinetic study,

Gibbs44 reported a rate study on methacrylic anhydride and

its difference from normal vinyl polymerization kinetics.
The results obtained by Gibbs indicated that the rate of

propagation is dependent on the 3/2 power of monomer con-
centration. Since methyl methacrylate exhibits ideal be-

havior in azobisisobutyronitrile initiated polymerizations,
it was expected that the rate for methacrylic anhydride would




















TABLE 4

CYCLIZATION OF METHACRYLIC ANHYDIRDE AS


A FUNCTION OF TEMPERATUREa


Temperature 1000 logl R11
oC. T (OK) fc R11/Rc R,


80.0 2.84 0.51 0.96 -0.0177

50.0 3.10 0.47 1.13 0.0531

20.0 3.42 0.33 2.03 0.3075

0.0 3.67 0.26 2.85 0.4548

-10.0 3.80 0.23 3.35 0.5250

-20.0 3.96 0.20 4.00 0.6021


aSolvent: dimethylformamide; [Benzoin]: 0.25 wt. per cent
based on methacrylic anhydride; [Methacrylic anhydride]: 3.25 mole/i.

















0.6


0.5


0.4
R1l
log10 R
cgO 0.3


0.2


0.1


0.0

2.8 3.0 3.2 3.4 3.6 3.8 4.
1000/T (oK)

Fig. 4.--Arrhenius plot of log10 R1/R as a function of 1000/T










also show first power dependence on monomer concentration.

Though Gibbs seems skeptical of his own explanation for the

3/2 power dependence, he suggests that it is due to low

efficiency of initiation. In light of the results of the

study on the fraction of cyclic units at various concentra-

tions and temperatures, it appears that another explanation

is possible. This new explanation is based on the fact

that even at low concentration, such as Gibbs used, there

are still small numbers of non-cyclic anhydride units

present. Since the rate of polymerization was found by

isolation of polymer over various time intervals, the rate

will be correct in terms of moles of monomer which dis-

appear; however, it will not be correct with respect to the

number of double bonds which have reacted. In order to be

a true measure of the rate of intra-intermolecular polymeri-

zation, the rate Gibbs observed must be corrected for those

double bonds which did not enter the polymer chain. By

using the following equations, the rate data of Gibbs,4

and the fraction of cyclization obtained here, the rate of

propagation can be corrected. The correct rate values

(R' ) are listed in Table 5.

fr = f + /=fn (7)

f = fraction of double bond reacted.

f = fraction of cyclic units, monomer enters
chain through both double bonds.

fn = fraction of non-cyclic units, monomer
enters chain through one double bond.



















TABLE 5

RATE OF PROPAGATION OF METHACRYLIC ANHYDRIDE CORRECTED FOR
FRACTION OF NON-CYCLIC UNITS


[M] a
mole/i. Ra fb fr R


0.72 9.5 0.73 0.87 8.35

0.49 5.8 0.80 0.90 5.20

0.35 3.6 0.85 0.93 3.35

0.14 1.7 0.94 0.97 1.65

0.074 0.9 0.98 0.99 0.89


400C.


400C.


aGibbs' data (44); Solvent: dimethylformamide; temperature:


bData from results here; Solvent: dimethylformamide; temperature:










R'p frRp (8)

R = moles of monomer disappearing per unit
p time.

R' = moles of monomer, corrected for non-cyclic
P units, disappearing per unit time.

The plot of R' versus monomer concentration shows that the

corrected rate is proportional to the first power of monomer

concentration (Figure 5). It appears therefore that there

is nothing unusual in the dependence of rate on monomer

concentration at the low concentrations used.

Gibbs44 also found the energy of activation for

methacrylic anhydride (E -Et/2) was 8.0 kcal./mole. A

comparison was then made with (Ep-Et/2) for methacrylic

acid which was found to be 9.8 kcal./mole. Gibbs concluded

from the comparison of activation energies that there is

little if any difference between normal vinyl polymerization

energetic and those for intra-intermolecular polymerization

of methacrylic anhydride. The results obtained in the work

here however show that the intramolecular propagation step

requires 2.6 + 0.3 kcal./mole more energy than the inter-

molecular step. With this additional information coupled

with the fact that copolymerization studies have shown that

the non-cyclic and cyclic methacrylic anhydride radicals have

equivalent reactivity,41 it would appear that a comparison

between methyl methacrylate and methacrylic anhydride would

be more reasonable since E -Et/2 equals 5.0 kcal./mole for
p t























U.'
0

10




O 6 e






0 2 Gibbs -,..---


0 0
0.0 0.2 0.4 0.6 0.8
[Methacrylic Anhydride] (mole/1.)

Fig. 5.--Rate of propagation of methacrylic anhydride cor-
rected for the fraction of non-cyclic units










methyl methacrylate.45 Addition of the added energy

necessary for an intramolecular propagation step would give

a value of 7.6 kcal./mole, quite close to the value deter-

mined experimentally. The difference between inter-

intermolecular and intra-intermolecular polymerization

would be readily apparent from the latter comparison.

A second piece of data, which initially appeared to

contradict the kinetic results gathered here, centered

around the interpretation Hwa2 had given volume shrinkage

results. It was found that the polymerization of metha-

crylic anhydride resulted in a volume shrinkage of only

13.7 ml./mole of unsaturation compared to 22-23 ml./mole

observed for methyl, ethyl, and propyl methacrylates. The

low volume shrinkage was interpreted to indicate a pre-

orientation of the methacrylic anhydride in a cyclic

conformation thus requiring little volume change on poly-

merization. The preorientation was also suggested to be

the driving-force for cyclization in the intra-inter-

molecular polymerization of methacrylic anhydride. The

validity of Hwa's interpretation has been opened to question

by the recent report that the volume shrinkage of phenyl,

benzyl, and cyclohexyl methacrylates are all very close to

15 ml./mole.46 In light of this data, it would appear that
the low volume shrinkage observed for methacrylic anhydride

is a characteristic of polymerization systems containing

cyclic units in or near the polymer chain.











Solvent Effects

As has been discussed, the fraction of cyclic units

in methacrylic anhydride polymer is dependent on both

temperature and concentration. In addition it was observed

that solvent plays a role in the determination of the amount

of cyclization. From Table 6 two interesting points are

observed. First, while conversion between 0 to 4 per cent

does not appear to influence cyclization in cyclohexanone

and dimethylformamide, the fraction of cyclic units

continually increases in benzene. Second, it is noted that

cyclohexanone appears to give substantially higher cycli-

zation than dimethylformamide.

Comparison of the value for kll/kc (0.25 1./mole at

350C.) obtained in dimethylformamide with that reported by

Smets 7 for polymerization in cyclohexanone (0.022 1./mole

at 36.60C.) shows that the rate of cyclization is much

larger in the latter solvent, thus adding proof to the

reality of the solvent effect. It must be noted, however,

that the magnitude of the solvent effect may not be as

large as the difference in value of kll/kc indicate. The

reason for this apparent discrepancy is that Smets7 carried

conversion as high as 10 per cent in his study of the

fraction of cyclic units as a function of concentration. In

the research for this paper, it was found that conversions

above 5 per cent, when the methacrylic anhydride


















TABLE 6


SOLVENT INFLUENCE ON INTRA-INTERMOLECULAR
METHACRYLIC ANHYDRIDEa


POLYMERIZATION OF


Benzene Cyclohexanone Dimethylformamide
Conversion (%) fc Conversion (7) fc Conversion (%) fc


0.6 0.18 1.2 0.36 2.1 0.26

2.3 0.26 2.6 0.38 3.9 0.25

3.2 0.33 3.2 0.36 4.3 0.29


aTemperature: 0.0C.; [Benzoin]: 0.25 wt. per cent based on
methacrylic anhydride; [Methacrylic anhydride]: 3.25 mole/i.











concentration was greater than to 2 mole/i., invariably

lead to higher values for the fraction of cyclic units than

obtained in the 0 to 4 per cent range. Further indication

that the magnitude of the value may be in error is given

in a comparison of kll/kc for methacrylic anhydride in

cyclohexanone obtained here and that reported by Mercier-

for acrylic anhydride under identical conditions. This

comparison (Figure 6) shows that at 00C., both monomers

have approximately the same value of kll/kc. Smets47

makes a similar comparison and finds that the value for

kll/kc is 0.022 1./mole at 36.60C. for methacrylic anhydride

while acrylic anhydride has a value of 0.17 1./mole at

350C. Though the relative difference between k11/kc values
for methacrylic and acrylic anhydrides may change with

temperature, it is not believed that the large change

observed above will occur over a 350. range. However,

even though there may be some question of the actual magni-

tude of the solvent effect in going from cyclohexanone to

dimethylformamide the direction of the results is the same

in both sets of data.

Having established the presence of a solvent effect

in the cyclopolymerization of methacrylic anhydride it is

necessary to give a reasonable explanation for its occur-

rence. In approaching this problem it is immediately

recognized that in some manner the solvent must influence





























1/f 42


Acrylic Anhydride

1 2 3 4 5 6
[Anhydride] (mole/I.)

Fig. 6.--Variation of 1/fc as a function of anhydride
concentration in cyclohexanone at OOC. (k,/k :
0.26 for methacrylic anhydride; 0.20 for
acrylic anhydride.)











the magnitude of k11 relative to kc. On examination of the

data, it is noted that poly(methacrylic anhydride) is in-

soluble in both cyclohexanone and benzene, but soluble in

dimethylformamide. This tends to indicate that precipita-

tion of the growing polymer chain favors cyclization. The

reason cyclization may be enhanced by precipitation is

that the lower the solvation of a polymer chain the tighter

it will coil.48 By being both heterogeneous with respect

to monomer and solvent and tightly coiled, it seems logical

that the radical would be sterically hindered to such an

extent that very exacting orientation of incoming monomer

molecules would be necessary for reaction to occur. Due

to this increased orientation requirement and slower dif-

fusion of monomer in the heterogeneous medium, kc would

become more and more favorable with respect to kll as the

system becomes increasingly heterogeneous.49
The fact that the system such as methacrylic anhydrid(

in benzene or cyclohexanone could be heterogeneous enough

at low conversion to cause increased coiling and thereby

favor kc is substantiated by research with both acrylic and

methacrylic anhydride. Acrylic anhydride polymerized in

cyclohexanone has been found to exhibit kinetics typical of

a heterogeneous system at low concentrations and conversions.

Also, a tremendous rise in the heterogeneous nature of the

system was observed by light scattering at conversions lower










than 2 per cent.50 In addition it has been found that the

rates of polymerization, even at low concentrations, for

acrylic50 and methacrylic lL'47 anhydrides are much faster

in cyclohexanone than in dimethylformamide. This is

probably due to the early operation of the Trommsdorff

effect resulting from the heterogeneous cyclohexanone

system.

Added weight is obtained for the argument that the

rate of cyclization may be favored by precipitation from

the kinetic data obtained in the heterogeneous polymeriza-

tion of methyl methacrylate.51 It was shown in this study

that although the overall rate of polymerization increased

over the first few percent conversion, the value of k

continually decreased (Table 7). The decrease in the size

of k shows that bimolecular reaction is slowed considerably

due to the heterogeneous medium. The implication for

intra-intermolecular polymerization is that heterogeneous

conditions lead to a marked decrease in k1l, and probably

influence kc to only a small extent since it is a uni-

molecular reaction, thus resulting in a higher value for

kc /kl which is observed as a higher fraction of cycliza-
tion.



















TABLE 7

DEPENDENCE'OF RATE AND VELOCITY COEFFICIENTS ON THE EXTENT OF
REACTION FOR THE HETEROGENEOUS POLYMERIZATION OF
METHYL METACRYLATE IN 50 PER CENT
CYCLOHEXANE SOLUTION AT 22.50C.

Conversion Rate kp kt
% % hr."- l.mole-lsec-1 1.mole-lsec-l

0 .1.69 167 3.54 x 107

1 1.91 133 1.78 x 107

2 2.31 134 1.25 x 107

3 3.13 76 2.16 x 106

4 4.46 61 6.84 x 105

5 5.22 44 2.67 x 105

6 5.36 30 1.18 x 105

12 3.3 --











Conversion Effects

In expanding the study of intra-intermolecular

polymerization of methacrylic anhydride, it was noted that

polymers obtained from conversion of 50 to 80 per cent

(prepared from equal weights of monomer and benzene,

cyclohexanone, or dimethylformamide, using ultraviolet

light and 0.25 weight per cent of benzoin, and a .tempera-

ture range of -600C. to +10000.) always gave values for

the fraction of cyclization between 0.85 and 0.95 (see

Table 15 in Chapter IV). In comparing these results with

those obtained at low conversion (Table 3) under similar

conditions, (3.25 mole/1. and a temperature range of -20C.

to +80C.) it is obvious that the value of fc has increased
tremendously from low to high conversion. The explanation

for this apparent increase in cyclization is difficult and

may involve as many as four factors.

First, it is quite obvious that increasing conversion

favors cyclization due to depletion of available monomer.

This, however, does not account for the complete difference

in the fraction of cyclization observed, but does explain

a part of it.
Second, some of the unsaturation present at low

conversion probably disappears at higher conversion due to

crosslinking reactions. This factor has been established

by Gibbs4 in a study of intrinsic viscosity as a function











of conversion at various methacrylic anhydride concentra-

tions. He found evidence for gel at all conversions if the

methacrylic anhydride concentration was greater than 34 per

cent by weight. Below this concentration the conversion

could be taken to at least 20 per cent before gel appeared.

At higher conversions than 20 to 30 per cent it would seem

that the poly methacrylicc anhydride) would become totally

insoluble. It was observed, however, that all samples

would dissolve in dimethylformamide to give at least a 1

per cent solution. The time necessary for complete solu-

tion to occur was generally one to two days. This time

period required to dissolve poly methacrylicc anhydride)

may be either a characteristic of the polymer due to its

molecular weight and rigidity or the result of a slow

catalytic effect of dimethylformamide which breaks inter-

molecular crosslinks.
The possibility that the time for solution is

characteristic of poly methacrylicc anhydride) seems

reasonable since it was found here that the poly (methyl

methacrylate) prepared from poly methacrylicc anhydride) had

a viscosity average molecular weight of 200,000 to 350,000
when benzene and dimethylformamide were the polymerization

solvent and 50,000 to 100,000 when cyclohexanone was present.

The molecular weight added to the known rigidity of the

methacrylic anhydride polymer chain could easily result in










difficult solubility. Also, adding weight to this argument
is the fact that repeatedly dissolving and isolating the
polymer does not substantially change its infrared spectrum
or the time required for it to dissolve.
Since Gibbs 4 has shown that above a concentration
of 34 per cent that some gel is present at all conversions,
there must be at least a few crosslinks present in the
polymers studied here. Therefore, in order for these
polymers to dissolve at least some of the crosslinks must
be broken. This would probably be a time consuming process
which may be the reason for the time required for poly
methacrylicc anhydride) to dissolve. This process may be
illustrated as follows:
CH3 CH3

CH CH2\C -C-CC C--
-0H2-C C- -C2

0= C C= 0 1-, C O

0, 0 0
I I I I

-CH C-C--
1-CH C 1H | CH2 |

CH3 CH3 CH3 CH3

It was found that only six to twelve hours are required to
dissolve polymers obtained from polymerization of methacrylic











anhydride at a concentration of 0.2 mole/l. This seems to

support the possibility of some type of catalytic effect.

Hwa39'42 has also noted the possibility of this catalytic

effect. He found that while methacrylic anhydride gives

soluble polymer, many copolymers of methacrylic anhydride

are highly insoluble indicating that non-cyclic anhydride

units when flanked by a different monomer cannot undergo

the interchange illustrated above.

In brief, it appears that crosslinking may account

for some of the apparent increase in cyclization with

conversion, but the exact extent that can be attributed to

crosslinking becomes clouded due to the difficulty in

interpreting solubility data. In this connection, however,

it may be noted49 that pendent double bonds do not cross-

link as readily as might be imagined due to the necessity

of two bulky chains diffusing together; thus, the number of

crosslinks which may result from the high number of non-

cyclic units at low conversion is probably much less than

the difference in the apparent value of cyclization indicates.

Third, perhaps one of the more important reasons for

increased cyclization at high conversion is due to precipi-

tation of the polymer chain. Even when dimethylformamide

is used as a solvent precipitation occurs since, at

conversions of 20 to 30 per cent, there is insufficient

solvent to keep all of the polymer in solution. The











importance of precipitation, if the data has been interpreted
correctly, has already been discussed in connection with the
solvent effect and could be equally important in the con-
version effect.
Finally, it appears that pendent anhydride units
may interchange with each other giving a monomeric unit and
an intramolecular anhydride unit in the polymer chain.


CH3 CH3
I CH2I |
-CH2-C C---
I I


O= C

,-


CH2
CH3


0
I

CH2
CH3


CH3 CH3

CH2-C C



c=-
-CH2-C






CH3 CH3


This interchange has been noted by Hwa 2 and is probably
due to the instability of unsymmetrical anhydrides. Hwa's
work shows that the bulk polymerization of acrylic propionic
anhydride gives soluble poly (acrylic anhydride) and a
liquid which was assumed to be propionic anhydride. In
order to verify the nature of this liquid, a similar study
was undertaken here in which methacrylic-propionic anhydride











was prepared. By polymerization in bulk at 355C. and sub-

sequent gas liquid chromatography on the liquid left, it

was found that approximately 10 per cent of the propionic

anhydride units had undergone interchange during the

polymerization. At 800C., 20 to 30 per cent of the anhydride

units had interchanged. These results prove Hwa's assumption

to be correct and add the possibility that methacrylic

anhydride pendent units may undergo similar interchanges.

Since the interchange is temperature dependent it would be

more important in polymerizations at high temperature.

To summarize, it appears that the increase in the

observed value of cyclization with conversion is in fact

due only in part to actual cyclization during polymeriza-

tion. Decreasing monomer concentration and increasing

heterogeneity actually cause increased cyclization; but,

crosslinking, and pendent anhydride interchange increase

the observed value of cyclization due to their ability to

remove unsaturated units from the polymer chain.

Non-Conjugated Chromophoric Interactions

Brooks17'52 in a study of the ultraviolet spectra of

non-conjugated dienes observed that the absorption maxima

for methacrylic anhydride is shifted bathochromically from

ethyl, allyl, and methallyl methacrylate. It was suggested

that the bathochromic shift was in the direction expected











if interaction of non-conjugated double bonds in the excited

state existed. If indeed this shift was due to double bond

interaction it would be evidence in support of a lower

activation energy for the intramolecular propagation step

in methacrylic anhydride.* If this initial study and the

suggested explanation are correct, there would be direct

contradiction between the kinetic study (which indicates a

higher activation energy for the cyclic step in methacrylic

anhydride) and the ultraviolet study. In order to resolve

the apparent discrepancy between these studies a thorough

ultraviolet spectral investigation of acrylate and

methacrylate esters and anhydrides was undertaken here.

A comparison of the values for the wavelength maxima

and extinction coefficient obtained here (Table 8) with

those given by Brooks17,52 show considerable differences.

On investigation it was found that the differences were due

to instrumental failure of the Bausch and Lomb Spectronic

505 used by Brooks. The accuracy failure is quite pro-

nounced below 210 mu. and appears to be due to excess stray

light, quartz optics, and partial photomultiplier failure.

Even though the values are in error, both this work and

Brooks' show that the bathochromic shift for methacrylic

anhydride relative to its esters is real.


For a discussion of the proposal that non-conjugated
interactions may be the driving-force for cyclopolymeriza-
tion see Chapter III.



















TABLE 8

ULTRAVIOLET SPECTRAL STUDYa


Wavelength Maxima Extinction
Compound A-max, mu. Coefficient


Methyl Methacrylate 201.5 8600 (10350)53

Allyl Methacrylate 201.5 10100

Vinyl Methacrylate 205.7 12200

Methacrylic Anhydride 209.0 19100

Methacrylic Propionic Anhydride 209.0 9700

Acrylic Methacrylic Anhydride 201.5 18300

Acrylic Anhydride 199.5 20400

Methyl Acrylate 191.0 10700

Ethyl Acrylate53 192.3 14200


silica; [M]:
U. V. ratio


aSolvent: iso-octane; Cell: 0.01 cm. far U. V.
1 x 10-2M 1 x 10-3M; Instrument: Beckman DK 2A far
recording spectrophotometer under nitrogen flush.











In an attempt to substantiate Brooks' explanation

for the bathochromic shift, the unsymmetrical anhydride,

methacrylic-propionic anhydride, was prepared and its

structure proved. This anhydride is similar to methacrylic

anhydride but has only one double bond; therefore, if

Brooks' explanation is correct the unsymmetrical anhydride

should have a wavelength maximum similar to the methacrylate

esters. However, as is seen in Table 8, methacrylic and

methacrylic-propionic anhydrides have the same absorption

maxima and as would be expected the extinction coefficient

for methacrylic anhydride is twice that of its unsymmetrical

counterpart. These results indicate that the bathochromic

shift is not due to excited state non-conjugated interaction

between double bonds; therefore, there apparently is no

contradiction between ultraviolet and kinetic data concern-

ing the activation energy of the intramolecular propagation

step relative to the intermolecular step. Further exami-

nation of the available data tends to indicate that the

bathochromic shift is due to electronic stabilization

through partial resonance of the non-bonded electrons on

the anhydride oxygen with the carbonyl group. To add

support to this suggestion the ultraviolet spectra of vinyl

methacrylate was obtained. Since this compound has an

unsaturated group attached to the ester oxygen, a stabili-

zation similar to that observed for methacrylic anhydride











should result in a bathochromic shift compared to methyl

methacrylate. Table 8 shows that vinyl methacrylate is

bathochromically shifted by 4 mu., about one-half the shift

observed for the anhydrides. To gain a clearer overall

picture of the reason for the bathochromic shift when an

unsaturated group is attached to the acrylate and metha-

crylate ester or anhydride oxygens, it is useful to look

at the reasonable resonance forms that may be involved in

the electronic transition from ground to excited state.

The two most important resonance forms involved in

a XC* transition of an a,P-unsaturated system are:

CH3 + CH3
o3 + 3
CH2=C-C=0 ---- CH2-C-C-0O
R R

I II

In the ground state, structure I is undoubtedly the most

important resonance form with a small contribution from II.

In the excited state, however, form II becomes most impor-

tant.54,55,56 Although these two resonance forms are basic

to the nn* transition, other resonance forms involving the

R group can influence the relative energy of the ground and

excited states which would shift the absorption maximum.

Some of the resonance structures which may be important in

altering the relative difference in energy from the ground

to the excited states are:











CH3 CH3

CHf==C--C=0 ------ CH2=C--C--O0

o lo

Rl Ro
R' R'

III IIIA

R' = alkyl or allyl


CH3 CH3

CH2= C--C=0 CH2= C--C--0
0 0+
/ /
CH2= CH CH2= CH

IV IVA


CH3

0
+CH2--C= C-O


CH2=CH

IVC


CH3
+ I
SCH2-C=C--o

0

R/

IIIB




CH3
1
(->.- 3 CH2=C--C==0O



"CH2-CH

IVB


CH3

+CH2-C=C -0"
\o+

CH2- CH

IVD


CH3

CH ==C-C==0
0

R'L-Co,


CH3
I -
CH2 ==C-C-0



R"--Co


CH3
I




0-


CH3

CH2- =--O0



R"--C
VD
VD


CH3

---- CH-- C=C-0"


R" = CH3-CH2-
or
rH3
CH2=C-


0

Bn-%0











As discussed above, III, IV, and V are probably the most

representative ground state structures that can.be drawn

for saturated or allyl methacrylate esters, vinyl metha-

crylate, and methacrylic or methacrylic-propionic

anhydrides. If III, IV, and V are the largest contributors

to the ground state, then except for small inductive dif-

ferences through the anhydride and ester oxygens the

electrons in the a,3-unsaturated systems must be of similar

energy. In the excited state, however, it will be noted

that there are only two resonance forms of similar energy

for III whereas there are four for both IV and V. Evi-

dently the added delocalization present when an unsaturated

group is attached to the methacrylate acyl oxygen stabilizes

the excited state of the molecule which is observed in the

ultraviolet spectra as a bathochromic shift. This explains

why vinyl methacrylate (IV) and methacrylic anhydride (V)

show bathochromic shifts when compared to methyl or allyl

methacrylate (III).

To explain the reason for the larger shift (8 mu.)

of methacrylic anhydride compared to vinyl methacrylate

(4 mu.), another examination of the resonance structures is

necessary. While it is noted that both IV and V have four

important excited state resonance forms and that structures

IVB and IVD-are similar to VB and VD, it is immediately

recognized that the relative contribution to the energy of











their respective systems must be quite different. The

reason for this difference is that a negative charge is

developed on carbon in IVB and IVD while in VB and VD it

develops on oxygen. Since oxygen is more electronegative

than carbon the negative charge is more stable and resonance

forms VB and VD gain added importance. Apparently, it is

this added stabilization and subsequent increased importance

of VB and VD that results in the larger bathochromic shift

for methacrylic anhydride.

Stereochemistry

Soon after proving the validity of the mechanism of

intra-intermolecular polymerization, Crawshaw and Butler57

noted that poly (acrylic acid) derived from the cyclo-

polymerization of acrylic anhydride had substantially

higher degrees of crystallinity than that obtained from

acrylic acid monomer. Recently, the discovery of stereo-

chemical control in the cyclopolymerization of acrylic

anhydride has received further support. Mercier43 has

shown in an infrared study using model compounds, meso and

racemic c,ac-dimethyl glutaric anhydrides, that acrylic

anhydride polymerized in dimethylformamide at low tempera-

ture or cyclohexanone at high temperature is predominately

isotactic; while, at low temperature in cyclohexanone

syndiotactic polymer was obtained. It was also noted that










the syndiotactic polymer could be converted, presumably

through a-hydrogen-carbonyl enolization, to the more stable

isotactic form by heating the polymer in cyclohexanone.

This tends to indicate that the kinetic or syndiotactic

product is always formed but that it can be isomerized to

the-thermodynamic or isotactic product through either the

catalytic influence of a solvent such as dimethylformamide

or high temperature polymerization in cyclohexanone.

In order to study the extent of the stereoregulating

control, which had been exhibited in the intra-intermolecular

polymerization of acrylic anhydride, Miller58'59 and

Butler59'60 studied the tacticity of poly(methyl metha-

crylate) derived from poly(methacrylic anhydride) as a

function of polymerization temperature. The methacrylic

anhydride system was chosen in this study due to: (1) the

ease with which poly(methacrylic anhydride) can be converted

to poly(methyl methacrylate); (2) the availability of a

quantitative method using nuclear magnetic resonance to

ascertain the stereochemical configuration of the poly-

(methyl methacrylate).61'62 Table 9 lists the results of

Miller's study.58'59 The first important factor which is

noticed is that the isotactic character has increased tre-

mendously over the.790C. range. Miller in studying the

change noted that the a values62'63 based on the isotactic

peak represent a "non-sigma" system62 which means the














TABLE 9

FRACTIONS OF POLY(METHYL METHACRYLATE) IN THE THREE STEREOCONFIGURATIONS
AS DETERMINED BY NMRa


Polymerization Conversion cX, based
Temperature, C. % i, % h, % s, % on i peak


1 78 17.9 43.5 38.6 0.420

20 96 31.3 38.5 30.1 0.557

30 68 24.2 40.7 33.9 0.560b

30 33 39.0 31.5 29.2 0.560b

40 45 34.0 35.7 30.2 0.583

50 37 35.8 36.3 28.0 0.597

60 70 42.4 32.2 25.2 0.655

70 75 49.3 29.2 21.5 0.705

80 88 66.7 20.3 13.0 0.815


aSolvent: benzene; [Methacrylic Anhydride]:
[AIBN]: 1.0 per cent by wt.

bAverage of the two 30C. samples.


50/50 by wt.;











penultimate unit influences the placement of succeeding

monomer units.

Butler60 has given very detailed consideration to

the results and implications of Miller's work.58,59 After

a thorough examination of the types of propagating steps

which are possible (Table 10), he suggests that a tendency

of the cyclized radical to remain non-planar at low

temperatures, due to ring strain required by planarity,

favors axial propagation which-leads to predominate

syndiotactic or heterotactic sequences. As the polymeri-

zation temperature rises the energy necessary for a planar

cyclized radical is available and results in increasing

numbers of equatorial propagations leading to isotactic

placements.

It is interesting to note that factors other than

temperature may be important in stereoregular control.

through intra-intermolecular polymerization. Tiers64 found

very little if any difference in poly methacrylicc anhydride)

prepared at 1000C. using benzoyl peroxide and toluene

solvent, and that obtained at -450C. using gamma irradiation

and bulk solution. Since so many variables (solvent,

temperature, concentration, and initiator) are involved the

real significance of these results is questionable.

Since there is very little literature dealing with

the possible stereochemical significance of intra-inter-














TABLE 10

POSSIBLE CONFORMATIONS OF POLY(METHACRYLIC ANHYDRIDE) AND THE
STEREOCHEMICAL CONFIGURATION OF THE RESULTANT
POLY (METHYL METHACRYLATE) a

Ring I Ring II Ring III Stereoregular
(1) (2) (3) (4) (5) (6) Form

A e(d) (d)e e(d) (d)e e(d) (d)e Isotactic

A' a(1) (1)a a () (1)a a(1) () a Isotactic


B e(d) (1)a e(d) (1)a -e(d) (1)a Syndiotactic

B' a(1) (d)e a(1) (d)e a(1) (d)e Syndiotactic


C e(d) (d)e a(l) (l)a e(d) (d)e Duosyndiotactic

C' a () (1)a e(d) (d)e a(l) (1)a Duosyndiotactic


D e(d) (1)a a(1) (d)e e(d) (1)a Duosyndiotactic

D' a () (d)e e(d) (1)a (1) (d)e Duosyndiotactic

aConformations: a = axial; e = equatorial; Configurations: d -
dextrorotatory; 1 = laevorotatory.











molecular polymerization, and that which is available lacks

consistency in results, a systematic study of the influence

of temperature, solvent, monomer concentration, and con-

version on the tacticity of poly methacrylicc anhydride)

was undertaken to complete the study of methacrylic

anhydride for this paper.

The first objective of this new study of methacrylic

anhydride was to extend Miller's work to other solvent

systems. Using equal weights of methacrylic anhydride and

cyclohexanone or dimethylformamide, polymer was obtained at

various temperatures, hydrolyzed, methylated, and submitted

for nuclear magnetic resonance analysis. Table 11 shows

the results of this analysis. Examination of this data

indicates that within experimental error there is neither a

temperature nor solvent effect on the tacticity. Further

understanding of the data in Table 11 may be obtained

through a study of the a values. If the system is "sigma"

then the end-unit of the methacrylic anhydride polymer chain

will control the configuration of the next monomer unit

added. The probability that the new unit will have the

same configuration as the end-unit is a. If the probability

treatment is valid: P = a2; Ps (1 a)2; and Ph

(a a )62,63 Taking a representative value for a from

Table 11 of 0.4, it is found that Pi = 0.16, Ps = 0.36,

and Ph = 0.48 if the system is "sigma." As can be seen,

















TABLE 11

TACTICITY OF POLY(METHYL METHACRYLATE) DERIVED FROM
POLY(METHACRYLIC ANHYDRIDE) AS DETERMINED BY NMRa


0('*
Polymerization Conversion Based on
Solventb Temp., OC. % i, % h, % s, 7 i peak


C -40 40 15 32 53 0.39

C 0 45 15 42 43 0.39

C 20 43 11 38 51 0.33

C 80 46 13 41 46 0.36


D 20 45 19 37 44 0.43

D 40 48 16 38 46 0.40

D 60 35 20 40 40 0.45

D 90 51 16 39 45 0.40


a [Methacrylic Anhydride]: 50/50 by wt.; [Benzoin]:
per cent based on methacrylic anhydride.

Solvent: C = Cyclohexanone;.D Dimethylformamide.


0.25 wt. -











these values correspond very closely to those obtained

experimentally indicating that the polymerizations of equal

weights of methacrylic anhydride and cyclohexanone or di-

methylformamide are "sigma" systems. These results are in

accord with those of Tiers,64 but completely out-of-line

with those reported by Miller.58'59

The meaning of the data on the stereochemical con-

figuration of methacrylic anhydride as it relates to intra-

intermolecular polymerization was clouded further when the

kinetic study described previously indicated that at low

conversion large numbers of non-cyclic methacrylic anhydride

units would be present when equal weights of monomer and

solvent were polymerized. In order to eliminate the

possibility of complicating results due to non-cyclic units,

a second study was undertaken using 0.2 mole/,. of metha-

crylic anhydride. This low monomer concentration insures

that the fraction of cyclic units, even at low conversion,

will be 0.9 or better. The results of this low concentration

study in benzene, cyclohexanone, and dimethylformamide are

given in Table 12. Analysis of the data in Table 12 indi-

cates that there is no solvent effect on tacticity. The

influence of conversion appears to be small though, as is

seen in the three benzene samples prepared at 500C. (Table

12), there is a small increase in heterotacticity with a

corresponding decrease in syndiotactic character as the













TABLE 12

TACTICITY OF POLY(METHYL METHACRYLATE) DERIVED FROM
POLY(METHACRYLIC ANHYDRIDE) AS DETERMINED BY NMRa


oc(
Polymerization Conversion Based on
Solventb Temp., oC. % i, % h, % s, % i peak


B 10 54 21 44 35 0.46

B 50 32 17 42 41 0.41

B 50 42 18 46 36 0.43

B 50 88 19 48 33 0.44

B 80 63. 19 45 36 0.44


C 10 99 19 42 39 0.44

C 50 98 21 42 37 0.46

C 80 72 19 47 34 0.44


D 10 77 18 42 40 0.43

D 50 73 19 42 39 0.44

D 80 35 19 48 33 0.44


a
[Methacrylic Anhydride]: 0.2 mole/1.;
per cent based on methacrylic anhydride.


[Benzoin]:


0.25 wt. -


bSolvent: B = Benzene; C = Cyclohexanone; D = Dimethylformamide.










conversion is increased. There does not appear to be a

temperature effect for samples polymerized in benzene;

whereas, in cyclohexanone there is a slight increase in

heterotactic character and parallel decrease in syndio-

tacticity with increasing temperature. Taking a representa-

tive value of a equal to 0.44, it is found that Pi = 0.19,

Ph = 0.31, and Ps = 0.50 from the probability treatment.
In comparing these values with those obtained experimentally

it is recognized that polymerization at low monomer concen-

tration gives "non-sigma" results. This indicates that the

end-group is not the only factor contributing to the con-

figuration of the unit being added and corresponds in this

respect to the results Miller58'59 obtained.

It is interesting to compare the tacticities of poly

methacrylicc anhydride) obtained at high monomer concentra-

tions (Table 11) and those at low concentrations (Table 12),

This comparison shows that there is only a slight difference

in isotactic sequences; but, it is noted that the polymeri-

zations at low concentration give 5 to 10 per cent higher

values for heterotactic character and 5 to 10 per cent

lower value for syndiotacticity than is obtained at high

concentration. The explanation for these differences appear

to be due to the incorporation of some non-cyclic units in

the poly methacrylicc anhydride) prepared at high monomer

concentration. The non-cyclic units would be expected to











enter the polymer chain in stereochemical configurations

similar to those observed in the free radical polymerization

of methyl methacrylate (Table 13). -Since poly (methyl


TABLE 15

STRUCTURE OF POLYMERS OF METHYL METHACRYLTE
PREPARED WITH FREE RADICAL INITIATORS


Polymerization
conditions i,% h,% s,%

Irradiation in bulk, OOC. 7.5 30.0 62.5

Benzoyl peroxide in bulk,
1000C. 8.9 37.5 55.9


methacrylate) gives large amounts of syndiotactic character

it might be concluded that non-cyclic methacrylic anhydride

units should increase the amount of syndiotacticity and

decrease the heterotacticity. This is exactly what is

observed when Tables 11 and 12 are compared.

In analyzing the data in Table 12, which presumably

represents the stereochemical configuration of a completely

cyclic polymer, two factors are noticed. First, as has

been discussed, the system is "non-sigma." Second, the
heterotactic or duosyndiotactic character predominates over

a slightly smaller percentage of syndiotactic character,

which in turn is roughly twice as large as the isotacticity.

These two factors, coupled with the fact that non-cyclic











units increase the syndiotactic character, tend to indicate

that the cyclization step in intra-intermolecular polymeri-

zation is completely random with respect to the configu-

ration.

CH3 CH3 CH3 CH3


C-CH2-C C-
-c-,2-c C.
(1) I Random (1)
Scyclization j

SC o/ C C o C 0


Probability of e(d) = a(l) at carbon (1).


In the intermolecular propagation step, however, there is

stereospecific placement of the monomer unit. The stereo-

specific process is split in two parts. First, if the

cyclization step resulted in an axial conformation then,

due to steric restrictions which eliminate axial-axial

propagations in one ring, the intermolecular propagation
step will be equatorial.



0

(e)(
(e) CH3
o-s* CH3 stereospecific \ (e)
equatorial (e)
propagation ,


CH3


CH3
(a)











Second, if the cyclization step results in an

equatorial conformation, there will be competition between

equatorial and axial propagation in the intermolecular step.

If it is accepted that the cyclization step is completely

random and the intermolecular propagation is stereospecifi-

cally equatorial when the cycylization step resulted in an

axial conformation, it can be shown (Table 14) that a

random intermolecular propagation, when cyclization resulted

in an equatorial conformation, will lead to the following

probabilities for each type sequence: Pi = 0.22; Ph =

0.45; and Ps = 0.53.

A comparison of the probabilities obtained in this

theoretical treatment (Table 14) with those observed

experimentally (Table 12) shows that the theoretical value

for the isotactic probability is slightly high while that

for the syndiotactic sequence is low by a similar amount.

This tends to support Butler's60 suggestion that con-

siderable ring strain would result if the cyclized radical

was planar; therefore, axial propagation is favored since

the a-methyl at the radical-carbon tends to occupy an

equatorial position. Since the axial propagation is

favored, there will be a slight increase in the amount of

syndiotactic and heterotactic character with corresponding

decrease in isotactic sequences.















PROBABILITY TREATMENT


TABLE 14

OF TACTICITY IN


POLY(METHACRYLIC ANHYDRIDE)


Ring Ib Ring II Possiblee Stereoregular Total
(1) (2) (1)c (2)d Configuration Form i h s

e.(d) (d)e lddd b- i 4 8 6

(l)a Iddl h h
a(1) (d)e
a(1) (d)e Idld s s

Probabilities

(d)e dldd s h Pi Ph Ps
e(d)
(1)a dldl s s

e(d) (d)e
a(l) (d)e dlld h h 0.22 0.45 0.33


(ed) (d)e dddd i i

e(d) (d)e (l)a dddl i h

a(l) (d)e ddld h s

aConformations: a = axial; e = equatorial. Configurations: d
dextrorotatory; 1 = laevoratatory. Tacticities: i = isotactic; s =
syndiotactic; h = heterotactic.

bRing I: All possible starting ring conformations.

CRing II (1): Random a(l) or e(d) cyclization.

dRing II (a): Intermolecular step random e(d) or a(1) if
Ring II (1) is e(d); but, stereospecific e(d)if Ring II (1) is a(l).

elll or ddd: isotactic; Idl or dld: syndiotactic; lld or ddl:
heterotactic or duosyndiotactic.
















(e)
CH2-


pseudo \
C(e) H CH3 (a)3 (a)
H3 -CH2
(a)
axial attack
preferred


The explanation of the experimental results shows

that Hwa's65.conclusion that the cyclic propagation step

is random and the intermolecular step always result in

trans (ae or ea) propagation is partially correct. However,

the evidence gathered shows that, although the trans (ae or

ea) propagation is highly favored, there are significant
numbers of cis (ee), but no (aa), propagations. Further,

probably due to the stereospecific intermolecular

propagation, when the cyclic step resulted in an axial
chain conformation, the methacrylic anhydride system

exhibits "non-sigma" behavior.
To summarize, it appears that intra-intermolecular

polymerization of methacrylic anhydride does result in at

least one stereospecific propagation step which explains

the reason for the "non-sigma" relationship and the high










degrees of heterotactic and syndiotactic character. Actually,

since the high degree of heterotacticity results from a

partially stereospecific process it is probably better to

term this sequence duosyndiotactic to avoid the connotation

that it developed through a random process. The importance

of recognizing that intra-intermolecular polymerization

gives a unique'and different stereochemical configuration

has been emphasized by the discovery66 that poly (methyl

methacrylate) derived of poly methacrylicc anhydride) has a

higher monolayer collapse pressure (33 dynes/cm.) than poly

(methyl methacrylate) prepared by conventional polymeriza-

tion processes. This high collapse pressure indicates that

cyclopolymerization results in the tightest packing and

toughest film possible. Butler's60 explanation for the

observed tacticities in Miller's58'59 work seems to be

applicable to both the results obtained here and those re-

ported by Hwa66; not only this, the results of both this and

Hwa's work substantiate Butler's suggestion that the stereo-

chemical configuration obtained in intra-intermolecular

polymerization is a result of a minimization of ring strain

and steric interaction of neighboring rings.

The results of the stereochemical study also show

that there is little or no solvent effect on the stereo-

regular configuration, but that there is apparently a small

increase in heterotacticity and a corresponding decrease in










syndiotacticity with increasing conversion and temperature.

Further, it was found that polymerization at high monomer

concentration results in an increase in syndiotactic

character at the expense of isotactic and heterotactic

sequences. This appears to result from incorporation of

non-cyclic anhydride units along the polymer chain which,

like methyl methacrylate, give predominantly syndiotactic

sequences.

Summary of Results and Conclusions

As a result of the experimental study which has

been carried out, it appears that a reasonably consistent

picture of the energetic and behavior of methacrylic

anhydride in intra-intermolecular polymerization can now

be drawn.

The kinetic study of the fraction of cyclic units

as a function of temperature and concentration indicates

that the intramolecular propagation has a higher energy of

activation than the intermolecular step (E -E1l = 2.6 + 0.3

kcal./mole). The energetically favorable intermolecular

step, however, is largely counterbalanced by a large steric

factor favoring the cyclic step (All/Ac = 0.0039 1./mole).

Since there is a competition between an intra-

molecular and an intermolecular propagation, it has been

found that the conditions which favor high degrees of

cyclization are: (1) high temperature; (2) low monomer










concentration; (3) poor solvent system; and (4) high con-

version. Soluble poly methacrylicc anhydride) may, however,

be obtained even under conditions that lead to large numbers

of non-cyclic units. This is possibly due to the inter-

change of pendent and crosslinked anhydride units. It is

interesting to note that methacrylic anhydride copolymers

will be insoluble if crosslinked since the anhydride inter-

change cannot occur when foreign monomer units are between

the methacrylic units.

The bathochromic shift observed for methacrylic

anhydride in a comparison of its ultraviolet spectrum and

those for the methacrylate esters was found not to be due

to non-conjugated interaction. Rather, a study of metha-

crylic-propionic anhydride and vinyl methacrylate, which

also exhibit bathochromic shifts, indicate that the shift

is due to added electronic stabilization through resonance

of the non-bonded electrons on the acyl oxygen with the

unsaturated unit attached to it.

It was found in the study of the stereochemistry of

the intra-intermolecular polymerization of methacrylic

anhydride that the cyclization step is completely random

while the intermolecular step involves a stereospecific

placement of the incoming monomer unit. There apparently

is no solvent effect on the stereochemical configuration;

but, it was found that increasing conversion and temperature











result in a small increase in heterotacticity and a

corresponding decrease in syndiotacticity. Polymerization

at concentrations which give large numbers of non-cyclic

units complicates the interpretation of the data, but it

appears that the non-cyclic units generally result in

syndiotactic sequences thereby making these polymers higher

in syndiotactic character than completely cyclic polymers.

As can be seen the intra-intermolecular polymeri-

zation of methacrylic anhydride is a very complex process.

Due to the number and the inter-related nature of the

variables, it has been very difficult to interpret the

importance and the meaning of these variables independently;

however, an attempt has been made to point out each variable

and its particular function. It is hoped that the interpre-

tations given are at least partially correct and, if not,

will provide the necessary impetus to those who follow to

find the correct explanations.













CHAPTER III


GENERAL MECHANISM FOR INTRA-INTERMOLECULAR POLYMERIZATION

Mechanistic Driving-Force


Although the discovery and proof of the existence of
intra-intermolecular polymerization was made some time ago,

the development and understanding of the underlying factors
which constitute the driving-force for cyclopolymerization

have not been possible due to a lack of data. Recently,

however, the amount of data concerning the mechanism has

more than doubled. From the new evidence now available it

is possible to gain a partial understanding of the
mechanistic driving-force for intra-intermolecular

polymerization.

In approaching the problem of understanding the

driving-force, two unique and characteristic traits of

intra-intermolecular polymerization must be recognized.
First, experimental evidence shows that the intramolecular

propagation step is highly favored over the intermolecular
step.13,143,2,67 Second, the degree of polymerization of

diene monomers is higher than that for the corresponding
mono-unsaturated derivatives.10'13'14,67 The explanation

for these facts is complex and involves several inter-











related conditions some of which are inherent in the molecule

and others which depend on the polymerization system.

Two factors which have been found to be important in

all reactions involving cyclization are the statistical

probability of the reacting groups coming together and the

thermodynamic stability of the product. From the available

literature, it appears that these two factors explain the

degrees of cyclization obtained in intra-intermolecular

polymerization of dienes capable of forming seven-membered

or larger rings.',5,6,7,8,31 These factors also are un-

doubtedly important in the cyclopolymerization of 1,5-and

1,6-dienes; however, as Raymondl8 has shown, at high

concentration, the probability of a double bond from another

molecule being in a volume element equal to a radius of one

bond length around the reaction site is greater than for

the other end of the same molecule to lie in the same

volume element. It might be pointed out that Raymond com-

pared the results of his statistical calculation, which

assumed a freely rotating molecule, with experimental

results from the polymerization of dienes on heterogeneous

catalysts surfaces. This comparison is not strictly correct

since in one case rotation is free and in the other res-

tricted; but, his conclusions are correct since the

literature shows that experimentally observed values for

cyclization in freely rotating systems are higher than the











statistical calculation indicates.10,12,30,67 It is

interesting to note that the failure of the statistical and

thermodynamic stability treatment to explain the high degree

of cyclization in intra-intermolecular polymerization has a

parallel in condensation polymerization. Flory68 points

out that the competition between ring formation and chain

polymerization is readily accounted for in bifunctional

monomers with less than five and more than six members

through application of statistical probability and ring

stability considerations. But, as in the case of intra-

inter.olecular polymerization, these factors do not

completely account for the large tendency of monomers

capable of forming five-and six-membered rings to cyclize.

The probability argument also fails to explain the higher

degree of polymerization observed in cyclopolymerization.

Other considerations which may help explain the

difference between statistical and observed values of

cyclization are entropy and steric factors. It seems

reasonable that any steric restriction placed on a diene,

such as the addition of bulky groups, that would decrease

the degrees of freedom and at the same time force the double

bonds closer together would favor cyclization. Cyclization

would not only be favored by the added statistical proba-

bility of the bonds coming together, but the loss in degrees

of freedom from steric factors would mean that the additional










loss of freedom due to cyclization would be less than if

the steric factor was absent. This would result in a

smaller negative entropy term and thereby favor the cycli-

zation. At unit concentration, a unimolecular process is

generally favored by the frequency factor over a bimolecular

process in the same system by a factor of about 100.69

This favorability can be enhanced further by the entropy and

steric factors increasing the frequency factor for the uni-

molecular process.

The suggestion that steric factors may be important

in intramolecular polymerization was recognized by Butler10

in his original work on diallyl quaternary ammonium bromide

polymerizations. He noted that soluble polymer could be

obtained under all conditions of polymerization for dimethyl-

diallylammonium bromide, but that diallylammonium bromide

gave insoluble polymer under some conditions. Additional

evidence that steric and entropy factors aid cyclization is

obtained from the iodoperfluoroalkane free radical cycliza-

tion of 1,6-heptadiene, diallyl ether, diallyl cyanamide,

and 1,6-heptadiene-4,4-dicarboxylate.70 The first two

dienes gave both cyclic and non-cyclic adducts with the

iodoperfluoroalkane while the latter two dienes, which have

added steric requirements due to the substituted groups,

gave only the cyclic monoadducts.










Kinetic studies of the fraction of cyclic units in

acrylic anhydride43 and the study here on methacrylic
anhydride also support the steric and entropy favoritism of

the cyclic propagation over the intermolecular step. These

results not only indicate that steric and entropy factors

favor cyclization over those cases where these factors are

absent, but also tend to indicate that the decrease in

entropy for a cyclization step is smaller than the decrease

that results from adding an entirely new monomer unit.

This seems plausible since in the intramolecular propagation

step the molecule is already in the polymer chain and only

rotational motion will be lost in the cyclization. However,

in adding a new monomer molecule to the chain, the process

results in a loss of translational and rotational degrees

of freedom. Since it is known that the order of importance

of the contributions of degrees of freedom to entropy is

translation > free rotation > hindered rotation > vibration>

electronic transition,71 the intermolecular propagation

step must have a much larger negative entropy term than the

cyclization step; therefore, the cyclic propagation step

must be highly favored over the intermolecular step as far

as entropy is important.

Steric factors may also be important in explaining

the high degrees of polymerization observed in intra-

intermolecular polymerization. As has been discussed above,










steric factors may be an important part of the driving-force

for cyclization; it also may, in a different manner, result

in a more favorable propagation step from the cyclic radical

to the next monomer molecule. This reasoning is based on

the belief that the cyclic radical would be less sterically

hindered by neighboring atoms and the polymer chain than

its non-cyclic counterpart.


.CH21 /CH2X
-CH2-CH CH. -CH2-CH CH.

i I I

I R R
II
The steric favoritism of the intermolecular step depends on

two factors. First, the radical is not as hindered in I as

in II; and second, II has twice as many X groups as I thus

increasing the steric crowding of groups in the polymer.

The reduction in steric hindrance would thereby facilitate

the approach and reaction of the next monomer unit. It

must be noted however, that even though this effect may be

important, it will probably be small and therefore only be

noticeable in difficult polymerizable systems; in fact, the

higher degree of polymerization through intra-intermolecular

polymerization has only been noticed in these

systems.10,13'14,67 This steric argument seems to parallel

that by Brown for "front strain."72 The studies on "front











strain" have shown that while the progressive substitution

of alkyl groups for hydrogen on ammonia increases the base

strength, it decreases the ease of reaction with a Lewis

acid due to steric repulsion between groups in the acid and

base. However, if the alkyl groups are part of a ring

system and therefore tied-back, such as in quinuclidine,

there is no "front strain" and the increased basicity due

to the alkyl groups increases the reactivity of the amine

toward Lewis acids. As has been stated, steric and entropy

factors are important in both the cyclization and inter-

molecular propagation steps but the exact significance of

each cannot be determined until more research has been

reported in these areas.

One additional factor which is inherent in the diene

molecule which appears to be important in the effective

competition of cyclic over bimolecular propagations is non-

conjugated interaction of the reacting double bonds. The

concept of non-conjugated interaction was proposed by

Butler15'73 in an effort to explain both the amount of

cyclization and the high degrees of polymerization observed

in intra-intermolecular polymerization. It is thought that

this type interaction would result in a lower energy of

activation for the cyclic propagation step and therefore

favor this step with respect to the intermolecular one.

In order to obtain experimental evidence for this proposal











CH2 H
*CH2-CH CH-

C CH2
x:


C


+CH2-CH CH

CH2 CH2


0CH2

H2-CH CH


CH2 CH2
"X


CH2- H CH

CH /CH2










CH2\.
-CH2-CH CI

CH, x CH2


an extensive ultraviolet spectral comparison of dienes and

their mono-unsaturated derivatives was undertaken. The

interaction was expected to stabilize the diene system

similar to the delocalization in butadiene and thereby

exhibit a bathochromic shift in the ultraviolet spectrum of

the diene. Brooks17'52 and Raymond18 have observed small

bathochromic shifts; however, the size of the shift and

complex number of factors which must be eliminated before

the shifts can be attributed to interactions has made these

results suggestive of, but not conclusive proof for, the

existence of the proposed interaction. Brooks and Raymond

have interpreted their observed bathochromic shifts in

different ways. Brooks explains his results in terms of an










excited state interaction while Raymond suggests that his

results indicate interaction in both the ground and excited

states. Miles19 has considered both arguments and points

out that in the ground state the only type ux interaction

that can occur without hydrogen-electron repulsions results

in the formation of a five membered ring which is not

observed. It is further noted that a ira interaction is

possible and would lead to the observed six-membered ring.

However, as Dewar74 has pointed out, the ground state

stabilization in butadiene is only partially due to de-

localization (maybe a minor part). If this is the case

then the nfr interaction and resultant stabilization would

be expected to be insignificant compared to the rotational

energy it must overcome to exist. It would appear therefore

that non-conjugation interactions will be an excited state

phenomena except perhaps in a few special cases.

A study of the literature shows that evidence other

than that from ultraviolet studies is available to help

substantiate Butler's proposal. Mikulasova75 has shown

that the overall activation energy in the free radical

polymerization of diallyldimethylsilane is about 9 kcal./mole

lower than that for allyltrimethylsilane. Smets0 has found

a slightly lower or equal energy of activation for the cyclic

propagation step compared to the intermolecular step in the

free radical polymerization of vinyl-trans-cinnamate. From











a combination of kinetic and copolymer data on this monomer

Smets suggests a pseudocyclic benzyl stabilized radical to

explain the results. This is the same as the excited state

interaction proposed earlier by Butler.15'73

Recent reports of monomeric free radical cycliza-

tions also appear to support an excited state interaction

theory. Brace7 has found that iodoperfluoroalkane free

radical cyclizations of 1,6-heptadiene leads to non-cyclic

mono and diadducts and cyclopentane monoadducts. The

failure to find any cyclohexane adducts lead Brace to

explain his results on steric grounds; but, he fails to

completely justify the primary radical which develops during

the formation of the cyclopentane adduct. A similar study
76
was reported by Cadogan76 using ethyl diallylacetate,

benzoyl peroxide initiator, and various thiols as chain

transfer agents. The results of this study showed the

presence of acylic mono and diadducts, a cyclopentane mono-

adduct, and also, a cyclohexane monoadduct. It was shown

that dilution gave larger amounts of cyclic monoadducts but

the ratio of the two cyclic adducts remained constant. It

was further stated that no general rationalization could be

made to explain the results of both Brace and Cadogan.

However, in light of Butler's excited state interaction

proposal an apparently plausible explanation can be sug-

gested. Consider the following reaction step:









(2)

R (3)
R. 4+ -. (1)



x x

III IV

In the transition state, the free radical at 0(1) interacts

with the second double bond in the diene (IV). The ensuing

chain transfer step can occur at either 0(2) or C(3) but

the choice will be governed by the steric requirements of

diene IV and the incoming chain transfer agent. This

explanation seems plausible and avoids the necessity of

developing a very unstable primary free radical during the

formation of the cyclopentane adduct.

From the standpoint of cationic initiated intra-

intermolecular polymerization, evidence is also available

in support of the excited state interaction theory. This

support stems from the increased rate of solvolysis observed

in unsaturated p-nitrobenzenesulfonates, such as the 5-

hexenyl ester, over their saturated analogs.7778 Addi-

tional supporting evidence has recently been reported in

the cationic cyclization of dienes and trienes.79,80'81'82

This work shows from the stereochemistry of the products

that concerted ring closures occur in some cases and in

others an allylic type cation is apparently present as an

intermediate.










As has been seen the concept of non-conjugated

excited state interaction is quite important in explaining

the results observed in intra-intermolecular polymerization

as well as in other systems. It has also been shown that

there is quite good evidence for the validity of Butler's

proposal. In some systems, however, it appears that the

interaction is not important; in fact, it is found that the

cyclic propagation step is of higher rather than lower

energy relative to the intermolecular step. The systems

which undergo intra-intermolecular polymerization without

the benefit of the energy lowering interaction are acrylic43

and methacrylic anhydrides, diallyl ether,83 and N,N-

diallylmelamine.32 In the cases of the two anhydrides it

was found that the activation energy of the cyclic step

exceeded that of the intermolecular step by about 2 kcal./

mole. Breslow8 has reported that the rate of reaction of

bromotrichloromethane is slower with diallyl ether, wherein

the allyl groups cyclize, than with allylethyl ether. He

concludes that this indicates a lack of assistance on the

part of the second allyl group during the reaction and thus

the cyclization must result from a step-wise reaction.

Thus far the factors which have been discussed and

found to be important in the overall driving-force for

intra-intermolecular polymerization are those which are

inherent in the diene molecules. From the experimental











results obtained for this paper, it becomes obvious that

conditions of polymerization are very important in obtain-

ing high degrees of cyclization. Although it had been

recognized before this study that dilution would favor

cyclization, it had not been recognized that temperature,

solvent, and conversion could also be made favorable or

unfavorable to cyclization. It appears that any time the

energy for cyclization is higher than that for the inter-

molecular propagation step a higher temperature will lead

to increased cyclization. The opposite would be true if

the cyclic step was the lower energy one. As far as solvent

and conversion are concerned it would appear that selection

of heterogeneous conditions are preferable if high degrees

of cyclization are desired. It might be inferred from this

that heterogeneous catalyst systems would also favor

cyclization; however, there is no experimental evidence to

substantiate this, though it is known that the Zeigler

catalyst systems do give large amounts of cyclic polymer

through operation of the intra-intermolecular mechanism.

In summary, it appears that statistical probability,

thermodynamic stability, steric and entropy effects, and

polymerization conditions are important in the driving-force

of every intra-intermolecular polymerization. In addition,

non-conjugated excited state interactions are important in

the driving-force of many, but not all, dienes which undergo










cyclopolymerization. These factors and an understanding of

each allow for a clearer picture of the mechanism of intra-

intermolecular polymerization, but the exact extent to
which each of these factors is important individually still
remains unclear. Perhaps when data is made available and

analyzed by the recently reported84 general kinetic equation

for cyclopolymerization a better understanding of the

quantitative aspects of these factors will be possible.

Stereochemistry

Very little can be said concerning the general

mechanism involved in the stereochemical configuration

observed in intra-intermolecular polymerization since only
one paper has considered this area extensively and a few

other papers have even remotely considered it. From this

small number of papers, however, it appears that three
generalities may be made.
First, it appears that due to the ring formation in

intra-intermolecular polymerization there is higher degree

of order in the polymer chain than is obtained in normal
vinyl polymerization. This increased order appears to be
responsible for higher crystallinity57 and tighter packing66
in the resulting polymer.

Second, the results of the stereoregular studies on

acrylic43 and methacrylic58'59'64'65 anhydrides indicate










that the kinetic product is formed in free radical intra-

intermolecular polymerizations rather than the thermodynamic

one. In acrylic anhydride, due to the possibility of a-

hydrogen-carbonyl-enolization, the kinetic product (chain

axial-equatorial) isomerizes to the thermodynamic product

(chain equatorial-equatorial) under the conditions of a

catalytic solvent or high polymerization temperature." Since

the enolization is not possible for methacrylic anhydride,
the high percentages of heterotactic and syndiotactic

character indicate that the polymer chain is in predomi-

nately the 1,3-axial-equatorial conformation meaning that

the kinetic product has been formed.

Finally, in contrast to free radical intra-inter-

molecular polymerization, the alkyl-metal coordination

catalysts apparently give the thermodynamic product in the

cases of 1,6-heptadiene and 1,5-hexadiene.60 This would
mean that the heptadiene would have a 1,3-diequatorial con-

formation while the hexadiene would give the 1,3-cis-

isomer, which is more stable than the trans due to ring-

pickering.85












CHAPTER IV


EXPERIMENTAL

Equipment and Data


Temperatures reported are uncorrected and in degrees

centigrade. Pressures are expressed in millimeters of

mercury as determined by means of either a Zimmerli or

McLeod gauge.

Refractive indices were determined with a Bausch
and Lomb Abbe 34 Refractometer equipped with an achromatic

compensating prism.

Intrinsic viscosities were calculated from efflux

times of benzene solutions of poly (methyl methacrylate)

through a Cannon-Ubbelohde Semi-micro Dilution Viscometer

set at 25C. in a constant temperature bath.

Gas-liquid chromatographic (GLC) analyses were made

with a Wilkens Aerograph Model A-110-C Gas Chromatographic

Instrument using helium for eluent gas and a five-foot

column packed with 20 per cent Silicone GE SF-96 on fire-

brick.

Infrared spectra were obtained with a Perkin-Elmer

Infracord Double-beam Infrared Recording Spectrophotometer

or a Perkin-Elmer Model 21 Double-beam Infrared Recording

80










Spectrophotometer. Both were equipped with sodium chloride

optics and calibrated with polystyrene film.

All ultraviolet spectra were obtained with a nitrogen
flushed Beckman Model DK-2A Ratio Recording Spectrophoto-

meter equipped with far ultraviolet silica optics and cells.

Wavelengths were calibrated with the emission lines of

mercury.

Nuclear magnetic resonance (NMR) spectra were ob-

tained with a Varian V-4302 High Resolution Nuclear Magnetic

Resonance Spectrometer, operating at 56.4 megacycles.

Sample temperature was maintained at 90-1000C. during the

measurements.

X-ray diffraction spectra were obtained with a

Norelco X-ray Diffractometer Model 12045 using a pro-

portional counter.

Elemental analyses were performed by Galbraith

Laboratories, Knoxville, Tennessee.

Source and Purification of Materials

Methacrylic anhydride, acrylic anhydride, metha-

crylic acid, methyl methacrylate, allyl methacrylate, vinyl

methacrylate, sodium methacrylate, methyl acrylate, and

acrylyl chloride were obtained from Borden Chemical Company,

Monomer Polymer Laboratories. The esters and anhydrides

were purified by fractional distillation until refractive










indices, infrared spectra, and GLO indicated a purity of

99+ per cent. The other reagents were used as received.

Propionic anhydride, propionyl chloride, and cyclo-

hexanone were obtained from Eastman Organic Chemicals. The

anhydride and chloride were redistilled before use. The

cyclohexanone was dried 48 hours over anhydrous sodium

sulfate and distilled shortly before use.

Diazomethane was prepared from N,N -dinitroso-N,N'

dimethyl terephthalamide (DuPont EXR-101) which was obtained

from the Explosives Department of the DuPont Company.

Diisopropyl ether and lithium aluminum hydride were

obtained from Peninsular ChemResearch, Inc. The ether was

dried 24 hours and distilled from lithium aluminum hydride

shortly before use.

Acculutes of 1/10 N sodium thiosulfate and 1/10 N

bromine were obtained from Anachemia Chemicals Ltd. and

diluted to the desired concentration.

Hydroquinone was obtained from Matheson, Coleman,

and Bell Company and used as received.

The following reagent-grade chemicals were obtained

from Fisher Scientific Company and/or J. T. Baker Chemical

Company: benzene, hexane, diethyl ether, spectro-analyzed

iso-octane, chloroform, soluble starch, benzoin, sodium

hydroxide, sodium hydrogen carbonate, sodium chloride,

anhydrous sodium sulfate, anhydrous calcium sulfate, dri-Na,










potassium iodide, potassium iodate, mercuric sulfate, and

cuprous chloride. Benzene and hexane were dried 48 hours

over dri-Na and distilled before use. Chloroform was

washed with sulfuric acid and water to remove the ethanol

preservative and distilled for use in NMR. The other

reagent grade chemicals were used as received.

Dimethylformamide was obtained from DuPont Company.

It was dried over anhydrous calcium sulfate for 48 hours

and fractionally distilled before use.

Sulfuric and hydrochloric acids were obtained from

Allied Chemical Company.

Kinetic Study

Polymer preparation.-Methacrylic anhydride of the

desired concentration in benzene, cyclohexanone, or di-

methylformamide was prepared in volumetric flasks of the

appropriate size. These solutions were added, by means of

a funnel, to cleaned and dried Kimble Neutraglas 20 or 50

ml. ampuls containing 0.25 wt. per cent of benzoin based

on the methacrylic anhydride concentration. While under

dry nitrogen gas flush, the sample ampul was cooled in a

dry-ice and acetone bath and sealed with a natural gas-

oxygen torch. After sealing, the ampuls were placed just

beneath the surface of a constant temperature bath (+100 to

-60 0.10C.). When at constant temperature the samples










were irradiated with a Blak-Ray XX-15 long wavelength ultra-

violet lamp from a distance of four to eight inches. The

time necessary to obtain a desired conversion was determined

by trial-and-error. The sample was isolated by breaking

open the ampul and pouring its contents into rapidly

stirred diisopropyl ether. Approximately 10 parts ether

to one part sample were used. It must be emphasized that

the ether must be exceedingly dry and not contain any

traces of base (such as from drying with sodium) if results

are to be accurate and reproducible. The ether precipitated

polymer is filtered off with a sintered glass filter and

dried 24 hours in vacuo at 50 to 6000.

The amount of poly methacrylicc anhydride) necessary

to give 0.002 equivalents of unsaturation was weighed

accurately and hydrolyzed. Hydrolysis was obtained by re-

fluxing two pellets of reagent-grade sodium hydroxide in

100 ml. of distilled water for each 0.5 g. of sample present.

When hydrolysis was complete, as evidenced by the sample

dissolving, the solution was cooled, one drop of phenol-

phthalein added, and neutralized by dropwise addition of 6N

sulfuric acid.

Bromometric titration.-The method described by

Siggia86 for bromination of unsaturated compounds was used

to determine the fraction of cyclic units in poly (metha-

crylic anhydride) samples. An estimated 10-15 per cent










excess of 0.1N potassium bromate-bromide solution (25-30
ml.) was placed in a 250 ml. Erlenmeyer flask with ground-
glass neck. A 50 ml. separatory funnel with ground-glass
joint was inserted into the flask and, with the stop-cock

open, the flask was evacuated through the top of the funnel.
After evacuation, the stop-cock was closed and 5 ml. of 6N
sulfuric acid placed in the funnel. The acid was slowly
added to the flask to avoid excess air from entering.
Three minutes were allowed for the evolution of bromine and
then 10-20 ml. of 0.2N mercuric sulfate was added. The
sample containing approximately 0.002 equivalents of un-
saturation was added and the funnel rinsed once with 10 ml.
of distilled water. The flask was placed in a black cloth

and swirled from time to time over a ten minute period.
After ten minutes, 15-20 ml. of 2N sodium chloride was
added followed by 15 ml. of 20 per cent potassium iodide.
After shaking the flask thoroughly the vacuum was released,
funnel removed, and walls of the flask washed down. A
magnetic stirring bar was added to the flask and the solu-
tion titrated with standard sodium thiosulfate solution
(about 0.05N). When the solution changed from deep red to
pale yellow, titration was stopped and 2 ml. of a one per
cent starch solution was added. The titration was resumed
and continued until the violet to colorless end-point was
obtained.








86

For comparison with the sample, a blank was run
using the same procedure except that a neutralized hydrolysis
solution without polymer was used as the sample.

The equation used for the calculation of the fraction
of cyclic units (f.) was:

(Vb-V )(N)(MW)
f =1 -
c (wt.)(2000)(B)
Vb milliliters of thiosulfate for blank.

Vs milliliters of thiosulfate for sample.

N normality of sodium thiosulfate.
MW molecular weight of sample.

wt. weight of sample used.

B number of moles of bromine being absorbed.

The reproducibility of the above procedure was
checked for the poly methacrylicc anhydride) system. It
was found that various concentrations of standard methacrylic
acid poly methacrylicc acid) solutions could be determined

accurately (+l to 2%) if 0.002 equivalents of unsaturation
were present. The accuracy appeared to be as good as +2 to
4 per cent down to 0.001 equivalents.
The results of the low conversion study of the
fraction of cyclic units as a function of concentration,

temperature, and solvent have been listed earlier (Chapter
II, Tables 2, 3, and 6, respectively). The results of the
study at high conversions are shown in Table 15.















TABLE 15

HIGH CONVERSION STUDY OF THE FRACTION OF CYCLIC UNITS AS A
FUNCTION OF TEMPERATURE AND SOLVENTa


Polymerization Conversion
Solventb Temperature, oC. % fc


B 0 37 0.88

B 80 73 0.94

C -60 45 0.85

C 40 49 0.90

C 100 57 0.87

D 10 33 0.92

D 30 43 0.95

D 50 47 0.87

D 80 35 0.89

D 100 43 0.95

a
[Methacrylic Anhydride]: 50/50 by wt.; [Benzoin]: 0.25 wt.
per cent based on methacrylic anhydride.

bSolvent: B "Benzene; C = Cyclohexanone; D Dimethylformamide.










In order to avoid errors in accuracy several

variables were checked. First, by using standard solutions

of methacrylic acid poly methacrylicc acid) the hydrolysis

procedure was checked and found not to influence the re-

sults. Second, several samples of poly methacrylicc
anhydride) were dissolved, reisolated, and dried to check

for trapped monomer. The results showed that the first

isolation was sufficient to remove all monomer.

Preparation of methacrylic-propionic anhydride.-The
procedure described by Yakubovich87 was used for the prepa-

ration of this mixed anhydride. Into a one-liter, three

necked flask, equipped with a mechanical stirrer,

thermometer, and a 150 ml. addition funnel, was placed a

solution of 90 g. (1.05 mole) of methacrylic acid in 250
ml. of dry diethyl ether. This solution was cooled, by

means of an ice-salt bath, to 00 to 50 C. and treated
slowly with 0.1 g. of cuprous chloride and 95 g. of pyridine.

While still at 0 to 50 C. and maintaining this temperature,

92.5 g. (1 mole) of propionyl chloride was added dropwise.
Following this addition, the reaction mixture was allowed

to warm to room temperature. After stirring at this
temperature for one hour, the mixture was cooled to 0C. and
washed with a cold 1:4 solution of hydrochloric acid. The
layers were separated and the organic layer repeatedly










washed with cold sodium hydrogen carbonate solution. The
crude product was fractionally distilled through a semi-

micro distillation set-up at reduced pressure. During the
distillation the pot liquid was stirred and the pot tempera-
ture never allowed above 3505. The distillation gave 72 g.
20
of a pure colorless liquid, b.p. 28-29 C./0.5 mm., n2
20
1.4300, d2 1.023.

The structure of the product was proved by infrared
and elemental analyses. The infrared spectra of the
distillate showed the following absorption bands: 1806 and

1751 cm.-" (C=O); 1638 cm.- (C=0). For comparison a
solution (1:1 mole ratio) of methacrylic and propionic
anhydrides was prepared. The mixture showed four absorption
bands in the carbonyl region: two for methacrylic anhydride

1787 and 1730 cm.-1 (C=0); two for propionic anhydride 1818
and 1752 cm.-1 (0=0). The comparison of the liquid obtained
in the reaction compared to the known mixture shows that
the mixed anhydride has been made and is not a mixture of
the two symmetrical anhydrides. Elemental analysis also
corresponds to the proposed structure.
Anal. Calcd. for C7H1003:. C, 59.14; H, 7.09.
Found: C, 58.95; H, 7.04.

Polymerization of methacrylic-propionic anhydride.-A
20 ml. Kimble Neutraglas ampul was charged with 5.10 g. of











methacrylic-propionic anhydride and 0.0154 g. of benzoin,

flushed with dry nitrogen gas, cooled in dry-ice and

acetone, and sealed. The sealed ampul was placed in a

constant temperature bath set at 30 C. and irradiated with

a Blak-Ray XX-15 long wavelength ultraviolet lamp for 30

minutes. The sample was broken open and liquid decanted

into a screw-top vial. The weight of the liquid indicated

a conversion of 60 per cent. Similar irradiation of a

second ampul for 20 minutes at 800C. gave 65 per cent

conversion.

The liquid decantate was analyzed by infrared spectra

and GLC. Both samples showed the presence of extra carbonyl

peaks in the carbonyl region showing that some symmetrical

propionic anhydride was present.

GLC on the pure methacrylic-propionic anhydride shows

that it isomerizes in the injector block to give the two

peaks corresponding to the symmetrical anhydrides. However,

by taking the increase in size of the peak corresponding to

propionic anhydride relative to that for methacrylic

anhydride it was found that at 300C. approximately 10 per

cent of the propionic pendent groups had interchanged to

give symmetrical propionic anhydride and presumably an

intramolecular anhydride unit in the polymer. At 800C.,

approximately 20 to 30 per cent had undergone the inter-

change reaction (see Chapter II for a discussion of the

significance of the interchange).










Preparation of acrylic-methacrylic anhydride.-This
compound was prepared by the procedure described by Hwa.42
In a one-liter, three necked flask, equipped with a mechani-
cal stirrer, addition funnel, thermometer, and reflux

condenser was placed a mixture of 108 g. (1 mole) of sodium
methacrylate, 0.1 g. cuprous chloride, and 500 ml. of
reagent-grade benzene. While the contents were stirred,

115 g. (1.27 mole) of acryryl chloride was added over a
period of 30 minutes followed by a 3 hour reflux. The
precipitate was filtered off and the filter-cake washed
with benzene. The benzene was removed at reduced pressure
and the crude product fractionally distilled through a
semi-micro distillation set-up. Using an oil-bath to avoid
superheating and never letting the pot temperature rise
above 400C., 26.5 g. of a colorless liquid, b.p. 33C./0.7
mm., n20 1.4517 (1.4516 Hwa2), and d40 1.056 was obtained.
Infrared showed absorption bands at: 1790 and 1730 cm.-1
(C=O); 1633 cm.-1 (C=C). Since the carbonyl absorption
bands for methacrylic (1787 and 1730 cm.-1) and acrylic
(1797 and 1734 cm.- ) anhydrides were not sufficiently
separated to give four carbonyl peaks when a 1:1 mole
mixture of the anhydrides was made, the structure proof for
acrylic-methacrylic anhydride could not be made complete.
However, its structure was partially substantiated by GLO
which showed equal amounts of acrylic and methacrylic











anhydrides present and the properties were the same as those

described by Hwa.42

Ultraviolet spectral investigation.-All compounds

studied (see Table 8 in Chapter II) were fractionally dis-

tilled until their properties coincided with values in the

literature, where available, and, in addition, showed a

purity of 99+ per cent by GLC and infrared spectra (Table

16). The absorption curve for each compound was taken at

three or more concentrations in the range 1 x 10-2 to
1 x 10 M. In each case Beer's Law was obeyed within the

concentration range used. The absorptivity value, a, was

calculated from the equation: A = abc. A was the ab-

sorption of the sample corrected for the solvent blank; a

was the absorptivity; b was the cell thickness, which was

0.01 cm. in each case; c was the concentration given in

mole/liter of compound.

Preparation of diazomethane.-Use no ground-glass

joints! All connections are rubber and set-up was made in

an efficient hood. In a one-liter, round-bottom, distilling

flask was placed a large magnetic stirrer, 200 ml. of re-

agent-grade benzene, and 240 ml. of 40 per cent aqueous

sodium hydroxide. The side-arm of the flask was connected

to a condenser, which was connected to a one-liter Erlen-

meyer flask in series with a 250 ml. Erlenmeyer flask.

Both receiver flasks were cooled to 50C. and this temperature















TABLE 16

PHYSICAL PROPERTIES


b.p.20 20 Infrared Absorption,a cm."1
Compound C./nm. nD d4 C0 C=C


Methyl Acrylate 80.5/760 1.4033 0.954 1732 1635,1622

Methyl Methacrylate 43.5/87 1.4150 0.944 1728 1642

Allyl Methacrylate 43.5/14 1.4372 0.9339 1728 1642

Vinyl Methacrylate 49/60 1.4029 --- 1739 1646

Methacrylic Anhydride 48/1 1.4541 1.0315 1787, 1730 1639

Methacrylic-Propionic
Anhydride 28-29/0.5 1.4300 1.023 1806, 1731 1638

Acrylic-Methacrylic
Anhydride 33/0.7 1.4517 1.056 1790, 1730 1633

Acrylic Anhydride 68/10 1.4484 1.0811 1797, 1734 1631

Propionic Anhydride 167.5/760 1.4040 1.011 1818, 1752


aThe infrared
Perkin-Elmer Model 21


spectra were obtained on the pure liquid using a
Double-beam Infrared Recording Spectrophotometer.




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