Metalation and Grafting by Anionic Techniques

8 Metalation and Grafting by Anionic Techniques

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ADEL F. HALASA The Firestone Tire & Rubber Co., Akron Ohio 44317

Elastomers made by anionic initiators were metalated by organolithium reagents activated with chelating diamines. Polybutadiene and polyisoprene were metalated with nBuLi · TMEDA. The lithiated polymers were used as sites for grafting of various monomers that can be polymerized anionically. Grafting and catalyst efficiencies were determined. Useful block copolymers using this system of grafting were made. The number of active sites were determined from the molecular weight of the block styrene bound to the rubber. The grafting efficiencies were determined from the amount of unbound polystyrene formed during polymerization.

' T p h i s w o r k deals m a i n l y w i t h a n i o n i c graft c o p o l y m e r s , t h e i r m o d e of A

p r e p a r a t i o n , a n d t h e i r c h a r a c t e r i z a t i o n . T h e p r o c e d u r e u s e d is one i n

w h i c h anions are generated o n the b a c k b o n e of a p r e f o r m e d p o l y m e r , a n d are u s e d as sites for g r a f t i n g of v a r i o u s m o n o m e r s t h a t c a n b e p o l y m e r i z e d a n i o n i c a l l y . T h e reagent u s e d for g e n e r a t i n g sites o n the p o l y m e r b a c k b o n e is n - B u L i - ^ N j N ^ I V ' - t e t r a m e t h y l e t h y l e n e d i a m i n e C a t a l y s t efficiency

(TMEDA).

d e t e r m i n e d b y the site g e n e r a t i o n , as w e l l as t h e

efficiency of e a c h site to i n i t i a t e p o l y m e r i z a t i o n of grafts, is r e p o r t e d . Discussion and Results T h e r e are s e v e r a l types of reactions b y w h i c h graft c o p o l y m e r s c a n be produced:

(1)

free-radical, (2)

cationic, (3)

condensation, a n d

(4)

a n i o n i c . F r e e - r a d i c a l g r a f t i n g is a n o l d art. I t suffers f r o m t h e f a c t t h a t c o n t r o l of the g r a f t i n g p o s i t i o n is difficult. T r a n s f e r of the r a d i c a l to m o n o m e r gives large amounts of h o m o p o l y m e r .

W i t h unsaturated poly-

mers, g e l a t i o n a n d c r o s s - l i n k i n g c a u s e d b y c o u p l i n g reactions or p r o p a g a 177

In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

178

POLYAMINE-CHELATED

t i o n are often e n c o u n t e r e d .

ALKALI

METAL

COMPOUNDS

C a t i o n i c m e t h o d s are also difficult to c o n t r o l

a n d often l e a d to c r o s s - l i n k i n g . O n l y i n those cases i n w h i c h c a t i o n f o r m a t i o n is c o n t r o l l e d c a n e v e n l i m i t e d success b e a c h i e v e d . S i n c e the reagents u s e d to f o r m the sites for g r a f t i n g are u s u a l l y the same as those u s e d to cross

link

or

cyclize

polymers,

this m e t h o d

of

g r a f t i n g is u s u a l l y

undesirable. H o w e v e r the m o r e r e c e n t w o r k of K e n n e d y ( 1 ) seems to h a v e c i r c u m v e n t e d these difficulties. H e w a s a b l e to p r o d u c e w e l l - c h a r a c t e r i z e d


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

H o w e v e r , his a p p r o a c h w a s l i m i t e d to elastomers w i t h

a l o w p e r cent of u n s a t u r a t i o n a l o n g t h e p o l y m e r b a c k b o n e ;

otherwise,

g e l a t i o n ensues. C o n d e n s a t i o n p o l y m e r i z a t i o n c a n b e u s e d to p r o d u c e graft c o p o l y mers. H o w e v e r , l i k e the other t e c h n i q u e s , i t suffers f r o m self-condensa t i o n of t h e b a c k b o n e , r i n g f o r m a t i o n , a n d c y c l i z a t i o n , w h i c h u l t i m a t e l y leads to g e l a t i o n . Before

d i s c u s s i n g the m e t h o d s

a n d the procedures

of

obtaining

a n i o n i c graft c o p o l y m e r s , the n e w t e r m i n o l o g y u s e d i n this t e c h n i q u e needs to b e defined. F i r s t , g r a f t i n g efficiency is a m e a s u r e of t h e a m o u n t of g r a f t e d m o n o m e r c o m p a r e d w i t h the t o t a l a m o u n t of m o n o m e r p o l y erized.

F o r e x a m p l e , take styrene as the m o n o m e r to b e g r a f t e d o n a

metalated polybutadiene.

I n this case, g r a f t i n g efficiency is the a m o u n t

of g r a f t e d styrene d i v i d e d b y the t o t a l a m o u n t of p o l y m e r i z e d styrene f o u n d i n the s y s t e m :

% G r a f t i n g efficiency

"gTf f

=

afted

. X homopoiystyrene

styrene grafted +

f

100

I n c o m p l e t e m e t a l a t i o n w o u l d leave u n r e a c t e d b u t y l l i t h i u m a v a i l a b l e to i n i t i a t e styrene a n d f o r m h o m o p o i y s t y r e n e . g r a f t i n g efficiency.

T h i s w o u l d result i n p o o r

S i m i l a r l y , a c h a i n - t r a n s f e r process t o m o n o m e r w o u l d

also g i v e p o o r g r a f t i n g efficiency. T h e second aspect to consider is catalyst efficiency of the m e t a l a t i n g reagent.

T h i s is a m e a s u r e of h o w m a n y of the anions a d d e d t o t h e

system a c t u a l l y i n i t i a t e c h a i n s .

I t is t h e e x p e c t e d

molecular

weight

( M ) of the graft ( d e t e r m i n e d f r o m the m o l e s of m o n o m e r a n d moles of n

the m e t a l a t i n g agent a d d e d ) d i v i d e d b y the e x p e r i m e n t a l l y d e t e r m i n e d n u m b e r average m o l e c u l a r w e i g h t ( M ) . T h e f o u n d ( M ) c a n b e deter n

n

m i n e d b y i s o l a t i n g t h e styrene b l o c k after o x i d a t i v e d e g r a d a t i o n of t h e p o l y b u t a d i e n e b a c k b o n e a n d d e t e r m i n i n g its m o l e c u l a r w e i g h t .

% C a t a l y s t efficiency

=

^ ^ Mn c

u

l

a

t

e

found

d

χ

100


8.

HALASA

Metalation

and

179

Grafting

A n y process t h a t destroys the a n i o n i c sites or o t h e r w i s e p r e v e n t s i n i t i a t i o n or p r o p a g a t i o n results i n grafts of

higher than calculated

m o l e c u l a r w e i g h t s . I m p u r i t i e s h a v i n g a c t i v e h y d r o g e n are the u s u a l cause o f r e d u c e d catalyst efficiency. T h e o v e r a l l effectiveness of t h e m e t h o d , therefore, is defined as t h e p r o d u c t of g r a f t i n g efficiency a n d catalyst efficiency ( o v e r a l l effectiveness of the g r a f t i n g process =

catalyst efficiency

X

grafting

efficiency).

C a t a l y s t efficiency a n d g r a f t i n g efficiency p l a y i m p o r t a n t roles i n d e t e r Downloaded by UNIV OF CALIFORNIA DAVIS on October 22, 2014 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0130.ch008

m i n i n g the o v e r a l l effectiveness copolymers.

of m e t a l a t i o n reagents i n a n i o n i c graft

T h e structure of the c o p o l y m e r

formed

depends

on

the

n u m b e r of sites t h a t i n i t i a t e p o l y m e r i z a t i o n . T h i s is i m p o r t a n t i n o b t a i n i n g the d e s i r e d p h y s i c a l p r o p e r t i e s . Organometallic compounds

a n d a l k o x i d e s a d d to a c t i v a t e d d o u b l e

b o n d s a n d to f u n c t i o n a l g r o u p s s u c h as ketones, esters, nitriles, a n d a l d e hydes.

M a n y w o r k e r s h a v e t a k e n a d v a n t a g e o f this t e n d e n c y a n d h a v e

a t t e m p t e d to p r e p a r e graft p o l y m e r s b y this m e t h o d

(2).

A detailed

d e s c r i p t i o n of these t e c h n i q u e s a n d others l i k e i t is g i v e n i n a recent review by Heller

(3).

T h i s r e p o r t is l i m i t e d to the most recent w o r k o n c h e l a t i n g d i a m i n e s w i t h organolithium compounds

a n d t h e i r a p p l i c a t i o n to m e t a l a t i o n a n d

grafting. Anion

Generation

on the Polymer

Backbone

T h e a p p r o a c h to synthesis of a n i o n i c graft c o p o l y m e r s

described

h e r e is to create anions o n t h e p o l y m e r b a c k b o n e a n d use these anions as sites for g r a f t i n g onto the b a c k b o n e .

T h e advantages of this m e t h o d

are t h a t it c a n g i v e a c o n t r o l l e d n u m b e r of g r a f t e d side c h a i n s ; i t m i n i mizes

homopolymer

formation; it provides

narrow

molecular-weight

d i s t r i b u t i o n of the graft; a n d i t p e r m i t s p r e p a r a t i o n of different types of graft c o p o l y m e r s .

D i s a d v a n t a g e of t h e m e t h o d is that i t is a p p l i c a b l e

o n l y to h y d r o c a r b o n p o l y m e r s c o n t a i n i n g a c t i v e h y d r o g e n s s u c h as a l l y l i c o r b e n z y l i c h y d r o g e n , or e x c h a n g e a b l e f u n c t i o n a l groups s u c h as h a l i d e s , or b o t h . T h e d i s c o v e r y of the p o w e r f u l m e t a l a t i n g agent,

n-BuLi-N,N,N',N'-

tetramethylethylenediamine, opened a new chapter i n anionic grafting. T h i s c o m p l e x has b e e n r e p o r t e d to m e t a l a t e t o l u e n e a n d b e n z e n e w i t h i n a f e w m i n u t e s to g i v e q u a n t i t a t i v e y i e l d s of b e n z y l l i t h i u m a n d p h e n y l l i t h i u m , r e s p e c t i v e l y (4).

I t also has b e e n r e p o r t e d to p o l y l i t h i a t e a r o -

m a t i c c o m p o u n d s (24, 2 5 ) . S e v e r a l w o r k e r s h a v e u s e d this c o m p l e x to m e t a l a t e h y d r o c a r b o n polymers. Plate a n d co-workers ( 5 ) , for example, metalated polystyrene w i t h n - B u L i · T M E D A a n d m o n i t o r e d b u t a n e e v o l u t i o n b y gas c h r o m a -


180

POLYAMINE-CHELATED

tography.

ALKALI

T h e y r e p o r t e d 4 0 % catalyst efficiency.

the g r a f t i n g efficiency

METAL

COMPOUNDS

T h e y d i d not report

o r t h e o v e r a l l effectiveness

of this m e t a l a t i n g

reagent. C h a l k , H a y , a n d H o o g e n b o o m (6, 7) u s i n g the same c o m p l e x , r e p o r t e d l i t h i a t i n g p o l y ( 2 , 6 - d i m e t h y l - l , 4 - p h e n y l e n e ) ether a n d p o l y ( 2 , 6 - d i p h e n y l 1,4-phenylene ) ether. T h e l i t h i a t i o n w a s d o n e b o t h at r o o m t e m p e r a t u r e o v e r a l o n g t i m e a n d at reflux f o r a shorter t i m e . T h e y r e p o r t e d c a t a l y s t efficiency of 1 7 % as d e t e r m i n e d b y t h e l i t h i u m content i n t h e p o l y m e r .


T h e y a t t r i b u t e d t h e l o w l e v e l of l i t h i a t i o n to t h e attack o n T H F b y t h e metalating complex. Table I. Change in Intrinsic Viscosity and M with Increasing Metalation Levels

n

Polymer

n-BuLi, m moles 100 grams Polymer

T, °C

5.0 10.0 20.0 30.0

50 50 50 50

4 4 4 4

4.0 8.0 16.0

70 70 70

2 2 2

8 16 24

80 80 80

4.8 4.8 4.8

Polybutadiene

Polyisoprene

a b c

M n Values* Time, hr

Wl/

gram

a

2.40 2.0 1.60 1.20 2.0 1.5 1.05 0.77

Before Met

After Met

83,000 90,000 72,000 87,000

80,000 60,000 38,000 30,000

c

e

A t 25°C in toluene. G P C values. Initial [η].

T h e same w o r k e r s ( S ) also f o u n d , f r o m t h e a d d i t i o n of v i n y l m o n o mers

to the l i t h i a t e d

poly(2,6-dimethyl)-

and poly(2,6-diphenyl-l,4-

p h e n y l e n e ) ethers, that t h e g r a f t i n g efficiency w a s v e r y l o w . H o w e v e r , w h e n t h e styrene w a s a d d e d o v e r f o u r h o u r s to t h e l i t h i a t e d p o l y m e r , t h e g r a f t i n g efficiency w a s v e r y h i g h . T h i s w a s d e t e r m i n e d b y a q u e n c h i n g r e a c t i o n w i t h c h l o r o t r i m e t h y l s i l a n e , after w h i c h the S i M e

3

group was

f o u n d o n t h e e n d of t h e p o l y s t y r e n e graft. H o w e v e r , w h e n t h e styrene w a s a d d e d r a p i d l y to t h e l i t h i a t e d p o l y m e r a n d t h e r e a c t i o n q u e n c h e d w i t h chlorotrimethylsilane, the silyl group was found o n the polyether aromatic group.

T h i s suggests t h a t t h e i n i t i a t i o n rate of styrene b y t h e

l i t h i a t e d p o l y e t h e r is v e r y s l o w c o m p a r e d w i t h t h e p r o p a g a t i o n .

Thus,

r a p i d a d d i t i o n of styrene r e s u l t e d i n r e l a t i v e l y f e w l i t h i u m atoms h a v i n g the c h a n c e to start grafts. O n s l o w a d d i t i o n , h o w e v e r , most a n i o n i c sites p a r t i c i p a t e i n i n i t i a t i n g grafts.


8.

181

Metalation and Grafting

HALASA

T h i s m e t h o d of d e t e r m i n i n g g r a f t i n g efficiency p r o v e d

successful

since S i M e groups o n p o l y s t y r e n e a p p e a r at 10.1 to 10.3 τ b y N M R w h i l e 3

the S i M e

3

groups o n the p o l y p h e n y l e n e a r o m a t i c ethers a p p e a r at 10.4 τ.

C h a l k a n d his associates r e p o r t e d 60 to 9 0 % catalyst a n d g r a f t i n g efficiencies. polymers

U s i n g t h e a b o v e reagents, t h e y w e r e a b l e to p r e p a r e graft

of

styrene a n d m e t h y l a c r y l a t e to p o l y ( 2 , 6 - d i m e t h y l ) -

and

p o l y ( 2 , 6 - d i p h e n y l - l , 4 - p h e n y l e n e ) ether. I n o u r s t u d y , n - B u L i · T M E D A was u s e d as a l i t h i a t i n g agent for m e t a l a t i n g p o l y b u t a d i e n e , p o l y i s o p r e n e , Downloaded by UNIV OF CALIFORNIA DAVIS on October 22, 2014 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0130.ch008

a n d c o p o l y m e r s of o- a n d p - c h l o r o s t y r e n e w i t h 1,3-butadiene

elastomers.

W h i l e this w o r k was i n progress, M i n o u r a w a s d o i n g s i m i l a r m e t a l a t i o n w o r k ( 9 , 10). q u i t e different.

T h e q u a n t i t y of m e t a l a t i o n reagent u s e d , h o w e v e r ,

was

H e u s e d e x t r e m e l y large a m o u n t s of m e t a l a t i n g agents

a n d p r o b a b l y h a d l o w efficiency. We

h a v e a t t e m p t e d to d e t e r m i n e g r a f t i n g efficiency

a n d catalyst

efficiency. T h i s was d o n e b y d e t e r m i n i n g the p e r cent h o m o p o l y m e r , size of the g r a f t e d c h a i n , a n d the n u m b e r of the g r a f t e d chains. P o l y b u t a d i e n e a n d p o l y i s o p r e n e w e r e m e t a l a t e d w i t h the n - B u L i · T M E D A several m e t a l a t i o n levels (12); subject elsewhere

(12-16).

at

s i m i l a r w o r k has b e e n r e p o r t e d o n t h i s

A f t e r m e t a l a t i o n , the p o l y m e r w a s h y d r o

lyzed and compared w i t h the original polymer. T h e M

n

polybutadiene was lowered drastically (Table I ) .

of t h e r e s u l t i n g

The mechanism

of

this m o l e c u l a r - w e i g h t m o d i f i c a t i o n r e a c t i o n is n o t clear at this t i m e , b u t w e f e e l that i t i n v o l v e s scission at the v i n y l or i s o p r o p e n y l sites i n t h e polybutadiene

or

polyisoprene,

respectively.

Grafting

efficiency

was

d e t e r m i n e d b y i n j e c t i n g f r e s h l y d i s t i l l e d styrene i n t o t h e p r e m e t a l a t e d r u b b e r , a l l o w i n g the styrene to react for five h o u r s , a n d t h e n d e t e r m i n i n g the a m o u n t of h o m o p o i y s t y r e n e either b y acetone e x t r a c t i o n o r b y g e l permeation chromatography

(GPC).

Lithium

atoms

a t t a c h e d to

the

c h a i n act as sites f o r i n i t i a t i n g the p o l y m e r i z a t i o n of styrene grafts. T y p i c a l results for g r a f t i n g efficiency are s h o w n i n T a b l e I I .

Table I I .

Polymer

Efficiency of Grafting

n-BuLi, TMEDA, m moles/ m moles/ Metalation Time, 100 grams 100 grams hrs Polymer Polymer

%

Styrene as % Styrene Grafting Added Efficiency

Polybutadiene

6 10 20

7.2 12.0 25

16 16 23

22.8 28.6 29.8

65.4 66.7 95.0

Polyisoprene

2.5 5.3 24.0

3.3 6.7 30.0

4 4 20

19.7 16.3 29.5

69.5 75.0 96.8


182

POLYAMINE-CHELATED

ALKALI

METAL

COMPOUNDS

S o m e 5 to 2 5 % h o m o p o i y s t y r e n e is g e n e r a l l y o b s e r v e d e v e n after a long metalation time. proposed.

S e v e r a l explanations for this o b s e r v a t i o n c a n

be

T h e r e m a y b e c h a i n transfer b e c a u s e of t r a n s m e t a l a t i o n of

u n r e a c t e d styrene b y t h e m e t a l a t e d p o l y b u t a d i e n e , i n c o m p l e t e m e t a l a t i o n of the p o l y b u t a d i e n e b e c a u s e of a n e q u i l i b r i u m b e t w e e n m e t a l a t e d p o l y b u t a d i e n e a n d m e t a l a t e d T M E D A , or t h e presence of l o w - m o l e c u l a r w e i g h t i m p u r i t i e s c a p a b l e of i n i t i a t i n g p o l y m e r i z a t i o n .

Since

TMEDA

is itself m e t a l a t e d b y n - B u L i u n d e r the r e a c t i o n c o n d i t i o n s u s e d , i t is


c o n c e i v a b l e t h a t m e t a l a t e d T M E D A a n d m e t a l a t e d p o l y b u t a d i e n e are i n e q u i l i b r i u m a n d are b o t h i n i t i a t i n g p o l y m e r i z a t i o n . I f that is the case t h e n the h o m o p o i y s t y r e n e s h o u l d c o n t a i n n i t r o g e n . T h e rate of the m e t a l a t i o n r e a c t i o n w a s f o l l o w e d b y the d i s a p p e a r a n c e of n - B u L i .

A l l the n - B u L i w a s c o n s u m e d i n t w o hours. T h i s w a s

d e t e r m i n e d b y q u e n c h i n g the m e t a l a t i o n r e a c t i o n w i t h c h l o r o t r i m e t h y l silane a n d f o l l o w i n g the d i s a p p e a r a n c e chromatography.

of t r i m e t h y l b u t y l s i l a n e b y

T h e analysis for t r i m e t h y l b u t y l s i l a n e a n d the

m i n a t i o n of h o m o p o i y s t y r e n e

b y acetone e x t r a c t i o n are g o o d

gas

deter-

methods

f o r d e t e r m i n i n g w h e t h e r the p o l y m e r w a s c o m p l e t e l y m e t a l a t e d . silylation reaction followed

by

gas-chromatographic

The

analysis i n d i c a t e s

whether T M E D A metalation occurred. T h e m e t a l a t e d p o l y m e r c a n be u s e d to i n i t i a t e f o r m a t i o n of p o l y m e r s w i t h v e r y h i g h g r a f t i n g efficiency.

graft

T h e n u m b e r of g r a f t i n g sites

is c o n t r o l l e d b y the a m o u n t of m e t a l a t i n g agent u s e d w h i l e the l e n g t h of t h e g r a f t e d c h a i n is c o n t r o l l e d b y the r a t i o of m o n o m e r to a c t i v e sites. C a t a l y s t efficiency is a m e a s u r e of the n u m b e r of a c t i v e sites t h a t i n i t i a t e p o l y m e r i z a t i o n of the a d d e d m o n o m e r . T h e l e n g t h of the g r a f t e d c h a i n is d e t e r m i n e d b y f r a g m e n t a t i o n of the p o l y b u t a d i e n e

p o r t i o n of

the g r a f t e d c o p o l y m e r

with

OsO^/tert-

b u t y l p e r o x i d e o x i d a t i o n a n d e x a m i n a t i o n of the p o l y s t y r e n e r e s i d u e b y G P C . T h e results are g i v e n i n T a b l e I I I . T h e results i n t h a t t a b l e are consistent w i t h the p i c t u r e of c h a i n m e t a l a t i o n since the d a t a demonstrate the f o r m a t i o n of m u l t i p l e p o l y styrene b l o c k s .

T h e g r a f t e d p o l y s t y r e n e r e c o v e r e d has a r a t h e r b r o a d

m o l e c u l a r - w e i g h t d i s t r i b u t i o n s k e w e d t o w a r d the range.

low-molecular-weight

T h e h i g h v a l u e of catalyst efficiency as d e t e r m i n e d i n p o l y m e r s

1 a n d 3 c o u l d r e s u l t f r o m either l i m i t a t i o n s i n the analysis of m o l e c u l a r w e i g h t d i s t r i b u t i o n or f r o m some f o r m of c h a i n - t r a n s f e r m e c h a n i s m . O v e r a l l effectiveness r e a c t i o n is v e r y h i g h .

of t h e m e t a l a t i n g reagent i n this m e t a l a t i o n

T h i s suggests t h a t n - B u L i · T M E D A

effective m e t a l a t i n g agent.

is a v e r y

I t suggests too that t h e a n i o n i c sites i n t r o -

d u c e d are also efficient i n g r a f t i n g - a d d e d m o n o m e r because the i n i t i a t i o n a n d t h e p r o p a g a t i o n rates of these sites are a b o u t the same. T h e d a t a i n


8.

HALASA

183


Table III.

Polybutadiene-Grafted Styrene Structures


Polymer 1 n - B u L i (catalyst), mmoles 1.20 per 100 g r a m s p o l y m e r 6.0 Metalation: n-BuLi 12.0 T M E D A mmoles/100 grams polymer M o l e c u l a r weight graft c o p o l y m e r , 103,000 o s m o t i c pressure 0.0 % Homopoiystyrene 30.9 G r a f t styrene, % 100 C a t a l y s t efficiency, % M o l e c u l a r weight 31,800 S t y r e n e c a l c u l a t e d for 1 b l o c k M o l e c u l a r weight calculated 4,420 for t o t a l L i M o l e c u l a r weight f o u n d 3,453 Styrene b y G P C O v e r a l l effectiveness, % 128

Polymer 2

Polymer i 0.7 6.0 6.0

0.7 6.0 6.0 94,000 0.0 24.8 100

103,000 0.0 32.2 100

23,300

33,500

3,480

5,000

3,647 95

4,070 122

T a b l e III i n d i c a t e t h a t steric h i n d r a n c e or p e n u l t i m a t e effects are at a minimum.

( W h i l e this v o l u m e was i n p r e p a r a t i o n a p r e s e n t a t i o n w a s

m a d e o n the same subject b y C h a ( 1 7 ) .

A l t h o u g h his m e t h o d s of analyses

w e r e different f r o m ours, his results a n d conclusions are the same. ) A h i g h - i m p a c t p o l y s t y r e n e t h a t has m u c h better o p t i c a l c l a r i t y t h a n that o b t a i n e d b y u s u a l b l e n d i n g or g r a f t i n g t e c h n i q u e s c a n b e p r e p a r e d b y o u r t e c h n i q u e . P o l y m e r s c o n t a i n i n g 9 0 - 9 5 % styrene g r a f t e d to p o l y b u t a d i e n e r u b b e r b y use of 12 m m o l e R L i - T M E D A / 1 0 0 g r a m p o l y m e r showed quite good optical clarity. T h e r a w graft c o p o l y m e r s of b u t a d i e n e a n d styrene, as w e l l as isop r e n e a n d styrene, are t o u g h a n d elastomeric. T h i s is a t t r i b u t e d to t h e i r h a v i n g the s t r u c t u r a l elements c h a r a c t e r i s t i c of S B S b l o c k c o p o l y m e r s . P o l y b u t a d i e n e h a v i n g a c o m b - t y p e structure w a s p r e p a r e d b y a d d i n g a d d i t i o n a l b u t a d i e n e to m e t a l a t e d p o l y b u t a d i e n e . T h e g r a f t e d p o r t i o n of the p o l y m e r , h o w e v e r , has a p r e d o m i n a n t l y v i n y l structure because of the presence of T M E D A . A n o t h e r m e t h o d of g e n e r a t i n g anions o n the b a c k b o n e c h a i n is to h a v e r e p l a c e a b l e f u n c t i o n a l groups that exchange

with organolithium

c o m p o u n d s at m o d e r a t e temperatures w i t h o u t m o d i f y i n g or c r o s s - l i n k i n g the r e s u l t i n g elastomer. M e t a l - h a l o g e n exchange is w e l l k n o w n i n s i m p l e organic compounds

(18, 1 9 ) .

T h e r e a c t i o n of o r g a n o l i t h i u m c o m p o u n d s

w i t h h a l o g e n a t e d p o l y e t h y l e n e has b e e n d i s c l o s e d ( 2 0 ) .

H o w e v e r , the

products were not w e l l characterized. W e h a v e f o u n d that c o p o l y m e r s of o- or p - c h l o r o s t y r e n e w i t h b u t a d i e n e c a n u n d e r g o m e t a l - h a l o g e n exchange w i t h n - B u L i i n the presence


184

POLYAMINE-CHELATED

ALKALI

METAL

COMPOUNDS

of T M E D A at m o d e r a t e temperatures. T h i s w a y t h e a m o u n t of h a l o g e n a n d s u b s e q u e n t m e t a l a t i o n o n the p o l y m e r are c o n t r o l l e d . T h e h a l o g e n a t t a c h e d t o t h e a r o m a t i c r i n g a n d its reactions are n o t c o m p l i c a t e d to a n y great extent b y side reactions. S u c h reactions are c o m m o n w i t h p o l y m e r s i n w h i c h the h a l o g e n is a t t a c h e d to a l i p h a t i c groups. T h e i n t e r c h a n g e is effected w i t h a c o m p l e x of a n a l k y l d e r i v a t i v e o f the a l k a l i m e t a l a n d the aliphatic chelating diamine. T h e copolymers

of o- a n d p - c h l o r o s t y r e n e w i t h b u t a d i e n e c a n


p r e p a r e d b y a n i o n i c i n i t i a t o r s (21).

S i n c e the r e a c t i v i t y ratios of

be 1,3-

b u t a d i e n e or o- a n d p - c h l o r o s t y r e n e are close to u n i t y , t h e r e s u l t i n g c o p o l y m e r s h a v e a constant c o m p o s i t i o n . Table IV.

Metal-Halogen

Interchange

Polymer 1 Polymer 2 Polymer 3 Polymer. Polymerization : n - B u L i initiator; mmoles p h m Exchange system : n - B u L i ; mmoles p h m T M E D A : mmoles p h m time, hrs t e m p e r a t u r e , °C T o t a l n - B u L i , mmoles p h m Theoretical % styrene in copolymer Homopoiystyrene in grafted p o l y m e r : % b y acetone e x t r a c t i o n % g r a f t i n g efficiency c a l c u l a t e d Mn f o u n d Mn c a t a l y s t efficiency

2.1

2.1

2.1

2.1

1.6

1.6 1.6 12 25 3.7

3.2 3.2 12 25 5.3

4.8 4.8 12 25 6.9

— 12

25 3.7 (24)

92.0 12 6,486

(32)

(39)

(44)

None 100 8,648 8,000 108

None 100 7,358 9,500 77

None 100 6,376 10,000 64

A c o p o l y m e r of 1,3-butadiene a n d o-chlorostyrene w a s m a d e w i t h a n a n i o n i c i n i t i a t o r at 5 0 ° C i n a h y d r o c a r b o n solvent (21). c o n t a i n e d 3 to 5 %

o-chlorostyrene.

The copolymer

T h i s c o p o l y m e r w a s s u b j e c t e d to a

m e t a l - h a l o g e n exchange r e a c t i o n . T h e results o f t h e e x c h a n g e reactions are s h o w n i n T a b l e I V . N o h o m o p o i y s t y r e n e w a s f o u n d b y acetone ext r a c t i o n of t h e graft p o l y m e r , suggesting t h a t catalyst efficiency ( exchange efficiency) is v e r y h i g h . I n a d d i t i o n to b e i n g a s y n t h e t i c r o u t e to u n u s u a l graft c o p o l y m e r s , t h e m e t a l a t i o n t e c h n i q u e offers a w a y to a d d f u n c t i o n a l g r o u p s to the c h a i n b y reactions c h a r a c t e r i s t i c of o r g a n o l i t h i u m c o m p o u n d s .

Hydroxyl

or c a r b o x y l g r o u p s , for instance, c a n b e a d d e d b y t r e a t i n g the m e t a l a t e d p o l y i s o p r e n e or p o l y b u t a d i e n e (22)

s o l u t i o n w i t h ethylene o x i d e or C 0 ,

r e s p e c t i v e l y . T h e l i t h i u m a l k o x i d e a n d c a r b o x y l i c salt o b t a i n e d (23)


2

in

8.

HALASA


185

those reactions a r e h i g h l y associated a n d f o r m a s w o l l e n g e l a l m o s t i n stantly after exposure of t h e m e t a l a t e d p o l y m e r to e t h y l e n e o x i d e o r C 0 . 2

T h e r u b b e r y g e l f o r m s a surface s k i n that m a k e s i t v e r y difficult to m i x the reactants w e l l e n o u g h to get c o m p l e t e r e a c t i o n . T h e r e a c t i o n is best c a r r i e d o u t i n t h i n films o r sprays r a t h e r t h a n b y a d d i t i o n o f reagent t o the solutions.

T r e a t m e n t of this salt w i t h excess m e t h a n o l ,

however,

returns t h e p r o d u c t to a fluid state w h e r e w o r k - u p c a n b e a c c o m p l i s h e d .


Acknowledgment T h e a u t h o r a c k n o w l e d g e s t h e assistance of t h e R e s e a r c h A n a l y t i c a l a n d P o l y m e r S t r u c t u r e D i v i s i o n s of F i r e s t o n e C e n t r a l R e s e a r c h L a b o r a tories f o r p o l y m e r analyses a n d t h a n k s T h e F i r e s t o n e T i r e & R u b b e r C o . for p e r m i s s i o n to p u b l i s h this w o r k .

Literature Cited

1. Kennedy, J. P., Macromolecular Preprint1,Int. Congr. Pure Appl. Chem., Boston, Mass. (1971). 2. Webb, F. J., U.S. Patent 3,627,837 (1972). 3. Heller, J., Polym. Eng. Sci. (1971) 11, 6. 4. Rausch, M. D., Ciappenelli, D. J., J. Organometal. Chem. (1967) 10, 127. 5. Plate, Ν. Α., Jampolskaya, Μ. Α., Davydova, S. L., Kargin, V. Α.,J.Polym. Sci. C (1969) 547. 6. Hay, A. S., Chalk, A. J., French Patent 1,586,729 (1967); U.S. Patent 3,402,144 (1968). 7. Chalk, A. J., Hay, A. S., J. Polym. Sci., A-1 (1969) 7, 691. 8. Chalk, A. J., Hoogeboom, T. J., J. Polym. Sci., A-1 (1971) 9, 3679. 9. Minoura, Y., Shina, K., Harada, H., J. Polym. Sci., PartA-1(1968) 6, 559. 10. Minoura, Y., Harada, H., J. Polym. Sci., PartA-1(1969) 7, 3. 11. Tate, D. P., Halasa, A. F., Webb, F. J., Koch, R. W., Oberster, A. E., J. Polym. Sci., PartA-1(1971) 9, 139. 12. Dunlop Co. Ltd., French Patent 1,571,456 (1967). 13. Dunlop Co. Ltd., French Patent 1,566,853 (1967). 14. Borg-Warner Corp., Brit. Patent 1,172,477 (1967). 15. Sun Oil Co., Brit. Patent 1,121,195 (1968). 16. Sun Oil Co., French Patent 1,583,793 (1968). 17. Cha, C. Y., "Abstracts of Papers" 161st National Meeting, ACS, March, 1971, POLY 46. 18. Leavitt, F. C., U.S. Patent 3,234,193 (1966). 19. Husemann, E., German Patent 1,226,304 (1966). 20. Plate, Ν. Α., Daydova, S. L., Jampolskaya, Μ. Α., Mukhitdinova, Μ. Α., Kargin, V. Α., Vysokomol. Soedin. (1966) 8, 1562. 21. Halasa, A. F., Adams, Η. E., Hunter, C. J., J. Polym. Sci., PartA-1(1971) 9, 677. 22. Nylor, F. E., U.S. Patent 3,382,225 (1968). 23. Koch, R. W., U.S. Patent 3,598,793 (1971). 24. Halasa, A. F., Tate, D. P., J. Organometal. Chem. (1970) 24, 769. 25. Halasa, A. F., J. Organometal. Chem. (1971) 31, 369. RECEIVED February 12, 1973.


Metalation and Grafting by Anionic Techniques

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