Brominated Poly(Phenylene Oxide)s. I. Polymerization of Mono-, Di

11 Brominated Poly(Phenylene Oxide)s. I. Polymerization of Mono-, Di- and Tribromo-2,6-Dimethylphenol D W A I N M . W H I T E and H O W A R D J. K L O P F E R

Downloaded by PURDUE UNIV on November 7, 2017 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0006.ch011

General Electric Research and Development Center, Schenectady, Ν. Y. 12301

The i n t r o d u c t i o n o f halogen atoms onto the aromatic r i n g s of the backbone o f poly(phenylene oxide)s i s o f i n t e r e s t because of the e f f e c t s the halogen can have on the flammability and on the s o l u t i o n and thermal p r o p e r t i e s o f the polymer. T h i s paper d e s c r i b e s poly(2,6-dimethyl-1,4-phenylene oxide)s which c o n t a i n monobromo and dibromo repeating u n i t s and have bromine contents ranging from approximately 5 t o over 50 wt. %. The general approach f o r the i n t r o d u c t i o n o f t h e bromine was via synthesis o f polymers utilizing di- and tribromophenols as monomers and comonomers. A second method, the d i r e c t bromination o f p o l y ( phenylene oxide)s i n s o l u t i o n , and the p r o p e r t i e s o f the brominated polymers are described i n the f o l l o w i n g paper. Polymerization o f 3,4-dibromo-2,5-dimethylphenol (I) pro vided a route t o polymer in which the bromine was only on the aromatic r i n g s and not on the methyl groups ( r e a c t i o n 1 ) . The r e a c t i o n was found t o proceed under c o n d i t i o n s similar t o the r e a c t i o n described by S t a f f i n and Price f o r the p o l y m e r i z a t i o n of 4-bromo-2,6-dimethylphenol, I I I ( r e a c t i o n 2). Poly(3-bromo1

169

Vandenberg; Polyethers ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

POLYETHERS

170 2,6-dimethyl-1,4-phenylene oxide), II, was formed in quantitative yield and with high molecular weight (intrinsic viscosities in chloroform

were

as

high

as

0.91

dl/g

and

correspond

to

molecular

weights up to M ca. 1.5 x 10 ). H nmr and elemental analyses 5

n

1

confirmed the presence of one bromine atom per repeating unit. The nmr analyses (both H nmr and C nmr) also showed that the 1

13

displacement of bromine had only occurred at C-4, i.e., the repeating unit was indeed the moiety shown in structure II. The infrared spectrum of the polymer was consistent with structure II except in one respect. In addition to a weak hydroxyl absorption at the normal end group frequency for unbrominated polymer (3610 cm in CS ), there was a slightly weaker absorption at -1

2

3525 cm . Both absorptions were more intense in lower molecular


-1

weight polymers and absent in acetylated samples. One characteristic of 2,6-disubstituted polyphenylene oxides is the tendency to redistribute with phenols when heated in the presence of an initiator. The polymers are converted to low 2-4

molecular weight oligomers terminated at the non-phenolic end of the molecule with the aryl ether derived from the phenol. The application of this redistribution reaction to II (reaction 3) is

II summarized of

the

and a

the

Table

initiator

either

cited as

in

x

in

Table

yields

with

unbrominated

,

or

I)

low

With

polymer,

VII

at

normally yields II

were

8 0 °

(the

causes

of

milder

sate

for

caused

by

molecular The

chlorobenzene the

extensive

rates

high

II

phenolic

end

group

Possibly

the

3525

of

end

group

at

at

8 0 ° , more

1 3 0 ° ) may

atom.

polymer

indicate in

is

Even at

TPDQ,

in

less

When p o l y m e r i z a t i o n

a

for

reaction

(1)

which

corresponded to

molecular

basis

of

elemental

intractable

unbrominated

polymer

under

arise

forcing

weight and from

of

group

reaction.

proceed The to

represent

at

terminal proceed.

a

second

type

redistribution. applied

intractable

analysis

products

was

compenend

lower

amount

polymer.

toward

IV,

low

an

the

redistribution

reactive

4-chloroto

phenolic

only

and,

contrast,

conditions and

reactions

may

in

needed

the

moderate

group

bromo-2,6-dimethylphenol,

Similar

1 3 0 ° ,

unbrominated

required

been

of

redistribution

cm~^ h y d r o x y l is

(TMDQ)

conditions

Since,

forcing

have

potential

underwent

that

than

which

y i e l d ,

combination

redistribution

recovered polymer.

oxidation

bromine

weight

results

slower

higher

the

the

reaction

,

in

—

,

(3,3*,5,5 -tetraphenyl-4,4'-diphenoquinone, phenol

1/2,3

3 , 3 » , 5 , 5 - t e t r a m e t h y l - 4 , 4 - d i p h e n o q u i n o n e

phenol

result,

I.

=

to

product

3,4,5-triwas

homopolymer

infrared

the

spectrum.

exhaustive

conditions

produced

V on

(see

bromination the

of

following


11.

WHITE

Motio-, Di-, and

AND KLOPFER

Tribromo-2,6-Dimethylphenol

TABLE Redistribution [η]

of

of

171

I Phenols with

II Yield

I n i t i a l

(dl/g)

Initiator

0.35

TMDQ

0.35

TPDQ

Temperature

Phenol

p-chloro-

Polymer

80

75

130

55

80

86

130

83

VII

of

Recovered

Reaction

Polymer

(%)


phenol 0.91

TMDQ

phenol

0.91

TPDQ

p-chlorophenol

paper). zation 2:1.

Soluble products of

IV

The

dibromo-

I

products and

repeating

the

with

random

even were

structure a

copolymers because

than

did

or

Phenols was

possible

bear (a

I

however, a

I

and by

VI.

ratio

The

random copolymer

unsuccessful either

obtained, the

however, of

copolymers which

were

VII,

were when

IV

to

by I

from III

1

contained

similarity

nmr

either

I

or

polymerized

as

the

IV

VI

Attempts with

a

as

oxide

spectrum o f

at

high

3,4was to

monomer

much

faster

III rate

IV.

IV

were

the to

C

structure.^

copolymerized with

employing oxidative

since

3

copolymeri-

was

3-bromo-2,6-dimethyl-l,4-phenylene

units,

consistent prepare

with

conditions

the

oxidative

cuprous halide/amine

catalyst;

2,6-dimethylphenpl

coupling

for

conditions.

polymerization

of

coupling conditions reaction

4).6-8

I for

This and

IV

VII

Polymerization

catalyst n

H O - O ^

+

n/2

0

t

2

H

^

-

VII of

of

^

H

+

H 0 2

(4)

VIII

4-bromo-2,6-dimethylphenol

quantity

^

a

base

and

a

requires

catalytic

at

amount

least

a

of

oxidizing

an

stoichiometric


agent.*

172

POLYETHERS

We found that when using the c a t a l y s t system f o r r e a c t i o n (4), the amine ( i n s u f f i c i e n t excess) functioned as base and the copper/amine complex functioned as i n i t i a t o r f o r r e a c t i o n (1) as w e l l as c a t a l y z i n g o x i d a t i v e c o u p l i n g . T h i s r e s u l t d i f f e r s from the r e p o r t by Blanchard and coworkers^ i n which r e a c t i o n (2) could not be i n i t i a t e d by a copper/amine ( p y r i d i n e ) c a t a l y s t . The suggested route f o r r e a c t i o n i s s i m i l a r to the proposed route f o r r e a c t i o n ( 2 ) and i n v o l v e s coupling between a phenoxy r a d i c a l and a monomer anion:


1


11.

WHITE

Additional

steps

redistribution leading

1

they


y

were

are 0,

reactions

).

onto

rings

XII.

been

Copolymer with

lead

for dl/g;

II

serving

(a s a m p l e with

o f the product

structure

f o r the product.

did II

range

not redistribute I

shows II

VIII from

not arise

notoccur

χa n d

to the product

o f polymer

does

H nmr

and that

was XI where

T h ep r o d u c t

l i t t l e

prepared with

under

from

VII

the direct

o f a second until

that

mild

IV and

bromine

almost

a l l o f the

can be viewed

a mixture

f o r VII

o f I

and

andi n i t i a t o r

2,6-dimethylphenol.

Thephysical

(intrinsic

under

during

Since

i t

the mild

equilibration

methylene

with

stopper

chloride

suggested a block i s likely conditions with

that o f

monomer

as a monofunctional

co-equilibrate as a chain

viscosities as high

the other

by structure

XIII.

I.

phenol

a s0 . 6 8 complex-

copolymer

polymer

II

polymerization

even

a t8 0 ° ) ,

component oligomers.

f o r reaction

VII f o r

wasused a s a

nmre f f e c t s )

can be represented

from

[ η ]0.35 dl/g)

was f u n c t i o n i n g

not readily

product

random c o p o l y m e r s .

structure

as oxidant

o f VIII

no long

(Table

extensive

monobrominated.

no f r a c t i o n a t i o n

polymer

does

eventually

and V I I ,

copolymers d i d form,

the introduction

unit

a t i o n ; H did

I

t h e normal

anion

XI was i d e n t i c a l

product

since

copolymerization

properties

produce

paper).

XI wasa l s o

dioxide

Polymer

monomers

bromination

This

o f VIII

involve

of halide

the general

Polymer

a repeating

have

would

the direct

structure

atom

With

( s e ef o l l o w i n g

bromination

sequence

andloss

0

suggested that

(i.e.,

2

from

conditions

1

polymers.

random 1,

resulted had

i n the reaction

C nmr s p e c t r a

3

173

3

reactions

to high

crosscoupling and

Μ οπό-, Di-, and Tribromo-2 6-Dimethylphenol

A N D KLOPFER

which Polymer

(4) a n d t h e

Colorless,

XIII


hazy

POLYETHERS

174 films

resulted

composed With

of

after

equal

an i n i t i a l

product

were

The Table were

solution

molar

2:1

ratio

of

Both

found

VII

to

short

on both

Chemical

type

C H OBr 8

w h i c h was

of

repeating

units,

7

the bromopolymers

^

ο

range

the aryl

and methyl

protons.

Shifts

films

of

unit. the

summarized

effects

of

in

bromine

II

f o r Protons

i n

Υ

the Polymer

Ζ

Segment

Ζ

_ 0 . ο - ^ . ο - ^ - ο - ^ - | Α

Α

Β

Β

Chemical Polymer Br

are

and longer

Υ

Structure

a polymer

each

range

TABLE


of

of

homogeneous. nmr s p e c t r a o f

II.

casting

quantities

Aryl

VIII

None

II

Y,Z

XI

Y

Η with

m-H

Location

Shift

a

( δ )

Methyl

Η with

an

o-Br

o-H

m-Br

2.08

6.50 6.07 6.40

6.12

2.00

2.32

2.08

2.35

(3

& 4)

2.02 (1 XII

A,Y

2)

6.42(4)

2.07(4)

2.30(1)

6.30(3)

1.93(3)

2.23(2)

1.98

2.20

6.02(4)

Α , Υ , Ζ

VI

&

5.83(3) (a)

Number

i n parenthesis

methyl

i s

When the

same

an aromatic ring,

additional ring

the

proton

ring

was o r i e n t e d

t h e r e s o n a n c e was s h i f t e d

upfield

shift

shielded an aryl

bromine.

specifies

on which

the Η or

located.

The e f f e c t

was n o t e d

proton

when

meta

a bromine

on the adjacent

was p r o n o u n c e d

to

upfield

(ranging

a bromine 0.4

ppm.

atom

1

2

i n An

i n one

ring

ortho

from

0.1

to

to


the

0 . 3 ppm)

11.

in

WHITE

polymers

bromine

on

adjacent

ring

long

short

and at

ppm

relative

The

methyl

bromines in

the

ppm) in

of

and

adjacent

accounted

The in

3

were

para

for

the

two

an

when

relative

samples

was

the

VI

the

two

above both

peak

shifted

the

the

for

the

upfield

0.7

VIII. in

several

(0.1

ppm)

rings.

ortho

pronounced u p f i e l d

allowed

occurred

in

of

polymer

II)

upfield

methyl

one

directly

p o s s i b l e and

(Table

dibrominated an

lie

For

affected

shifted

since

to

175

In

methyl

upfield

methyl

ways by

addition,

downfield

(

Brominated Poly(Phenylene Oxide)s. I. Polymerization of Mono-, Di

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