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
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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
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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 -
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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 .
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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.
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
8.
HALASA
183
Metalation and Grafting
Table III.
Polybutadiene-Grafted Styrene Structures
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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
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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)
In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
2
in
8.
HALASA
Metalation and Grafting
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 .
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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
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In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.