Anionic Polymerization - ACS Publications - American Chemical Society

26 Industrial Applications of Anionic Polymerization: Past, Present, and Future ADEL

F.

HALASA

1

Downloaded by COLUMBIA UNIV on September 26, 2014 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch026

Central Research Laboratories, The Firestone Tire and Rubber Co., Akron, OH 44717

The first report on anionic polymerization appeared in the patent literature in 1910-1911. Matthews and Strange (1) in 1910 and later Harries (2)in1911, described the preparation of polyisoprene using sodium and potassium as i n i t i a t o r s . They mentioned the use of lithium as a possible i n i t i a t o r for this polymerization, but there seems to be no description ofthepolymer made from it. Similarly, Schlenk et al (3) described the polymerization of 1,3 butadiene using sodium dust. The modern day concept of anionic polymerization was not appreciated by earlier researchers anditwas not u n t i l 1920 that Staudinger (4) recognized the chain character of the addition of polymerization. The new "non-termination" concept that l a i d the foundation for l i v i n g polymerization was actually put forth by Ziegler and co-workers (5,6,7). They have conducted an extensive investigation ontheaddition of a l k a l i metal and its organic derivatives, particularly lithium and alkyl-lithium compounds with butadiene, i s o prene, piperlyene and 2,3 dimethyl-butadiene in polar media. The products described by Ziegler and his coworkers were resinous and rubber-like substances resembling polybutadiene made by sodium. The polymeric materials prepared by Ziegler and previous workers were low in molecular weight and contained a large percentage of 2,3 addition products,in the case of polyisoprene, and 1,2 addition products, in the case of polybutadiene. These rubbery materials have a high glass-transition temperature, which gave them the resinous-like behaviour described by Ziegler. It was not u n t i l 1955 that a process was developed for the synthesis- of an elastomer closely resembling natural rubber and the technological methods fortheuse of this elastomer in the compound were disclosed. This 1

Current address: Kuwait Institute for Scientific Research, P.O. Box 24885, Safat, Kuwait. 0097-6156/81/0166-0409$05.00/0 © 1981 A m e r i c a n Chemical Society

In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

410

ANIONIC POLYMERIZATION


p r o c e s s was d e v e l o p e d in the F i r e s t o n e r e s e a r c h l a b o r a t o r i e s •under c o n t r a c t t o the U n i t e d S t a t e s D e p a r t m e n t o f D e f e n s e and the O f f i c e o f S y n t h e t i c R u b b e r , F e d e r a l F a c i l i t i e s C o r p o r a t i o n (9). T h i s work a p p e a r e d in the l i t e r a t u r e in d e t a i l a t the A n n u a l M e e t i n g o f the A m e r i c a n C h e m i c a l S o c i e t y (.10). The d e t a i l e d d e s c r i p t i o n s p u b l i s h e d l a t e r l a i d the f o u n d a t i o n s f o r f u t u r e work on a n i o n i c p o l y m e r i z a t i o n (.11). T h i s o p e n e d many a r e a s o f i n v e s t i g a t i o n on t h i s s u b j e c t in s e v e r a l l a b o r a t o r i e s a r o u n d the U n i t e d S t a t e s and the w o r l d . I n h i s e a r l y work S z w a r c ( 1 2 , 1 3 ) r e d i s c o v e r e d the l i v i n g n a t u r e o f a n i o n i c p o l y m e r i z a t i o n and de m o n s t r a t e d its p o t e n t i a l s . He c l e a r l y showed t h a t a l i v i n g c h a i n o f p o l y s t y r e n e w o u l d a c c e p t a n o t h e r monomer s u c h a s i s o p r e n e and f o r m a b l o c k c o - p o l y m e r o f p o l y s t y r e n e - p o l y isoprene. The n a t u r e o f the l i v i n g p o l y m e r was r e v e a l e d by the s t e p a d d i t i o n o f monomers in t h e s e e x p e r i m e n t s . S z w a r c d e m o n s t r a t e d t h a t the c h a i n e n d s resume t h e i r g r o w t h w h e n e v e r a monomer is a d d e d . I f the monomer was d i f f e r e n t f r o m the one p r e v i o u s l y u s e d , a b l o c k c o p o l y m e r resulted (ΐΛ,1,16). T h i s , i n d e e d , was the most v e r s a t i l e t e c h n i q u e f o r the p r e p a r a t i o n o f b l o c k c o p o l y m e r s and w i l l be d i s c u s s e d in more d e t a i l l a t e r . Much o f the e a r l y work on a n i o n i c p o l y m e r i z a t i o n was s p e n t on the d e v e l o p m e n t o f s y n t h e t i c r u b b e r h a v i n g the same m i c r o s t r u c t u r e as n a t u r a l r u b b e r , w h i c h l i m i t e d the i n v e s t i g a t i o n t o the p o l y m e r i z a t i o n o f i s o p r e n e t h u s n e g l e c t i n g the e a r l y work o f S z w a r c on b l o c k c o p o l y m e r s . A f t e r many y e a r s o f r e s e a r c h on the u s e o f s y n t h e t i c p o l y i s o p r e n e made b y a n i o n i c i n i t i a t o r s in the compounds, it was c o n c l u d e d t h a t p h y s i c a l p r o p e r t i e s s u c h as s t r e s s in duced c r y s t a l l i z a t i o n , g r e e n - s t r e n g t h and wind-up t a c k were much i n f e r i o r t o n a t u r a l r u b b e r . So, in the e a r l y I 9 6 0 s , the p r o g r a m on s y n t h e t i c p o l y i s o p r e n e and v a r i o u s m o d i f i c a t i o n s t o i m p r o v e the a b o v e - m e n t i o n e d p r o p e r t i e s came t o a s t a n d s t i l l . P u b l i c a t i o n s b y B r o c k and H a c k a t h o r n (ij) h a v e s h e d some l i g h t on the l a c k o f t h e s e f u n d a m e n t a l p r o p e r t i e s f o u n d in p o l y i s o p r e n e made b y l i t h i u m . I n t h e i r work, t h e y c o n c l u d e d t h a t e v e n t h o u g h p o l y i s o p r e n e made by l i t h i u m has 9\% C i c 1,U m i c r o s t r u c t u r e , the s e q u e n c e d i s t r i b u t i o n o f h e a d - t a i l a r r a n g e m e n t o f the i s o p r e n y l u n i t s a r e l o w and l a c k u n i f o r m i t y in p a c k i n g o f the u n i t c e l l . Meanwhile, development o f c o o r d i n a t i o n c a t a l y s t was p r o c e e d i n g f u l l s c a l e . The p o l y i s o p r e n e p r e p a r e d u s i n g this coordination catalyst (TiCl : AIR) p r o v e d t o be more s u i t a b l e in p h y s i c a l p r o p e r t i e s t h a n the one made by l i t h i u m m e t a l o r o r g a n o l i t h i u m compounds in h y d r o c a r b o n m e d i a . The Z i e g l e r p o l y i s o p r e n e , a s it was c a l l e d , has g r e a t e r s t e r e o r e g u l a r i t y and s t r e s s - i n d u c e d c r y s t a l l i z a t i o n p r o p e r t i e s t h a n p o l y i s o p r e n e made by the a l k y l l i t h i u m c a t a l y s t . How1


26.

HALASA

Industrial Applications

of

Polymerization


e v e r , the Z i e g l e r c a t a l y s t f a i l e d t o c o p o l y m e r i z e v i n y l a r o m a t i c and c o n j u g a t e d d i e n e t o y i e l d b l o c k c o p o l y m e r s . T h i s d e f i c i e n c y in the Z i e g l e r c a t a l y s t t o p r o d u c e b l o c k c o p o l y m e r s a n d the a b i l i t i e s o f a n i o n i c i n i t i a t o r s t o p r o d u c e it k e p t the i n t e r e s t in a n i o n i c i n i t i a t o r s a c t i v e in many i n d u s t r i a l l a b o r a t o r i e s . T h i s i n t e r e s t in a n i o n i c r e s e a r c h in t h e s e l a b o r a t o r i e s p a i d o f f h a n d s o m e l y in the a r e a s o f b l o c k a n d random c o p o l y m e r s . In t h i s review m a j o r e m p h a s i s w i l l be f o c u s e d on the m a j o r p r o d u c t s f r o m b o t h homo a n d b l o c k c o p o l y m e r s c u r r e n t l y b e i n g m a n u f a c t u r e d b y a n i o n i c t e c h n i q u e a n d f u t u r e t r e n d s in t h i s a r e a . HOMOPOLYMERIZATION As o f t h i s d a t e , t h e r e is no l i t h i u m o r a l k y l l i t h i u m c a t a l y z e d p o l y i s o p r e n e m a n u f a c t u r e d b y the l e a d i n g s y n t h e t i c r u b b e r p r o d u c e r s in the i n d u s t r i a l n a t i o n s . Howe v e r , t h e r e a r e s e v e r a l r u b b e r p r o d u c e r s who m a n u f a c t u r e a l k y l - l i t h i u m c a t a l y z e d s y n t h e t i c p o l y b u t a d i e n e a n d comm e r c i a l i z e it u n d e r t r a d e names l i k e " D i e n e R u b b e r " ( F i r e s t o n e ) " S o l e p r e n e " ( P h i l l i p s P e t r o l e u m ) , " T u f d e n e " ( A s h a i KASA Japan). I n the e a r l y s t a g e o f d e v e l o p m e n t o f a l k y l l i t h i u m c a t a l y z e d p o l y - b u t a d i e n e it was f e l t t h a t a n a r r o w m o l e c u l a r d i s t r i b u t i o n was n e e d e d t o g i v e it the e x c e l l e n t wear p r o p e r t i e s o f p o l y b u t a d i e n e . However, it was found l a t e r t h a t its n a r r o w m o l e c u l a r d i s t r i b u t i o n , c o u p l e d w i t h the p u r i t y o f the r u b b e r , made it the c h o i c e r u b b e r t o be u s e d in the r e i n f o r c e m e n t o f p l a s t i c s , s u c h a s h i g h i m p a c t polystyrene. T i l l the p r e s e n t t i m e , p o l y b u t a d i e n e made b y alkyl-lithium catalyst is,for many c h e m i c a l a n d t e c h n o l o g i c a l reasons, still the u n d i s p u t e d r u b b e r in the r e i n forced plastics applications industries. The u n i q u e f e a t u r e a b o u t a n i o n i c p o l y m e r i z a t i o n o f d i e n e t o p r o d u c e homopolymer was t h a t the m i c r o s t r u c t u r e o f the homopolymer c o u l d be a l t e r e d a n d c h a n g e d a t w i l l t o p r o d u c e u n i q u e p h y s i c a l and c h e m i c a l p r o p e r t i e s . . These m i c r o s t r u c t u r a l c h a n g e s c a n be i n t r o d u c e d b e f o r e , a f t e r o r d u r i n g the p o l y m e r i z a t i o n . F o r e x a m p l e , c h e l a t i n g d i a m i n e s , s u c h a s t e t r a m e t h y l e t h y l e n e and d i amine (TMEDA) (18), w i t h the a l k y l - l i t h i u m c a t a l y s t h a v e b e e n u s e d t o p r o d u c e p o l y m e r w i t h Q0% 1,2 a d d i t i o n p r o d u c t s , w h i l e the u s e o f d i p i p e r i d i n e e t h a n e ( D P E ) , w i t h same c a t a l y s t has p r o d u c e d p o l y b u t a d i e n e w i t h 100$ 1,2 a d d i t i o n p r o duct. T h i s new d e v e l o p m e n t in the m i c r o s t r u c t u r a l a r c h i t e c t u r e o f p o l y b u t a d i e n e h a s o p e n e d the d o o r f o r the p r e p a r a t i o n o f v a r i o u s b l o c k c o p o l y m e r s made f r o m the same monomer. F o r e x a m p l e , one c a n u s e t h i s c o n c e p t t o p r e p a r e v a r i o u s p o l y b u t a d i e n e r u b b e r s in w h i c h the c h a i n segment contains various g l a s s t r a n s i t i o n temperatures, depending on its m i c r o s t r u c t u r a l a r r a n g e m e n t s . Similarly, manipulating the p o l y m e r i z a t i o n t e m p e r a t u r e u s i n g the same m o d i f i e r a n d


411

412


c a t a l y s t , one c a n a l t e r the m i c r o s t r u c t u r e o f the same p o l y b u t a d i e n e c h a i n . F o r e x a m p l e , r a i s i n g the p o l y m e r i z a t i o n t e m p e r a t u r e o f n - B u L i TMEDA c a t a l y z e d 1,3 - b u t a d i e n e f r o m 50C...t o 100C...c a u s e s a d e c r e a s e in the 1,2 c o n t e n t o f the p o l y b u t a d i e n e f r o m 80% t o Uo$, w h i c h , when t r a n s l a t e d i n t o p h y s i c a l p r o p e r t i e s , m e a n s t h a t the g l a s s t r a n s i t i o n temp e r a t u r e was c h a n g e d f r o m -20°C... t o -55°C. A more d r a m a t i c change in the 1,2 c o n t e n t is i l l u s t r a t e d when n - B u L i DPE is u s e d a s c a t a l y s t f o r 1,3-butadiene p o l y m e r i z a t i o n . A d j u s t i n g the p o l y m e r i z a t i o n t e m p e r a t u r e f r o m 5' t o 50 c a u s e s a d r o p in 1,2 c o n t e n t f r o m 100$ t o 70$. T h i s means t h a t the g l a s s t r a n s i t i o n t e m p e r a t u r e changes f r o m +5C...t o -30 C a r a t h e r d r a m a t i c change in the c o l d t e m p e r a t u r e p r o p e r t i e s o f t h i s r u b b e r (19). T h i s v e r s a t i l i t y g i v e s the s y n t h e t i c p o l y m e r c h e m i s t a t o o l t o t a i l o r the c h a i n o f the p o l y b u t a d i e n e t o f i t the d e s i r e d a p p l i c a t i o n . I t c a n be u s e d t o m a n i p u l a t e the l o w t e m p e r a t u r e p r o p e r t i e s i m p o r t a n t in r u b b e r goods a n d t i r e a p p l i c a t i o n s . M o r e o v e r , the c h e m i c a l r e a c t i o n t h a t c h e m i s t s want t o p e r f o r m o n t h e s e r u b b e r s c a n b e a l t e r e d , d e p e n d i n g o n the r e a c t i v i t y o f the 1,2 p o l y b u t a d i e n e d o u b l e bonds f r a c t i o n v e r s u s t h a t o f 1,U p o l y b u t a d i e n e . The work o f H a l a s a a n d c o - w o r k e r s (21 ) i l l u s t r a t e s this point. These w o r k e r s h y d r o g e n a t e d medium v i n y l p o l y b u t a d i e n e (1,2 c o n t e n t v a r i e d b e t w e e n 6θ-6θ$ 1,2 a d d u c t ) t o p r o d u c e t h e r m o p l a s t i c e l a s t o m e r s b a s e d on p o l y b u t a d i e n e , b u t t a k i n g a d v a n t a g e o f the v e r s a t i l i t y o f a n i o n i c p o l y m e r i z a t i o n b y c h a n g i n g the m i c r o s t r u c t u r e a t the end o f the p o l y m e r i z a t i o n . The d a t a in T a b l e I i l l ustrate these findings.


5

TABLE I B l o c k Copolymer o f P o l y ( B d ) o f 1,1+ P o l y ( B d ) - 1,2 Mn B - l . U

Mn B-1,2

Tg°C...

Tm°C... T e n s i l e ( p s i )

9,000 162,000 58,000

29,000 306,000 396,000

-52 -55 -U0

None. None. None.

120 1**0 250

Elong % 100 120 130

The p h y s i c a l p r o p e r t i e s o f t h i s b l o c k c o p o l y m e r a r e i m p r o v e d b y hydrogénation u s i n g c o b a l t - c o p r a l a c t a m r e d u c e d b y t r i - i s o b u t y l alumimium. T h i s homogeneous c a t a l y s t r e d u c e s the 1,2 d o u b l e bond a t a rate f o u r t i m e s f a s t e r t h a n it r e d u c e s the 1,U d o u b l e bond. The s a t u r a t e d 1,U d o u b l e b o n d , y i e l d s p o l y e t h y l e n e b l o c k a n d w h i l e s a t u r a t i n g the 1,2 d o u b l e b o n d , y i e l d s a n e l a s t o m e r w i t h


26.


HALASA

of

413

Polymerization

a l o w g l a s s t r a n s i t i o n t e m p e r a t u r e o f -25°C... The r e s u l t s o f s a t u r a t i n g b l o c k c o p o l y m e r o f l k a n d 1 , 2 u n i t s ment i o n e d in T a b l e I a r e shown in T a b l e I I . I t c a n be sea~i in T a b l e I I t h a t a s u b s t a n t i a l i m p r o v e m e n t in t e n s i l e o t r e n g t h h a s o c c u r r e d . This i m p r o v e m e n t h a s b e e n a t t r i b u t e d t o some u n i q u e f e a t u r e s in the p o l y m e r c h a i n i n t r o d u c e d v i a hydrogénation. One o u t s t a n d i n g f e a t u r e o f t h i s b l o c k c o p o l y m e r is t h a t the h a r d segment is made o f c r y s t a l l i n e p o l y e t h y l e n e . The m o l e c u l a r w e i g h t o f t h i s h a r d segment is much g r e a t e r t h a n t h a t o f the s t y r e n e 1 , 3 - b u t a d i e n e - s t y r e n e in w h i c h the h a r d segment m o l e c u l a r w e i g h t is o n l y 1 5 , 0 0 0 - 2 0 , 0 0 0 . The p h y s i c a l p r o p e r t i e s shown in T a b l e I I i l l u s t r a t e t h a t t h e s e p o l y m e r s a r e d i b l o c k , n o t t r i b l o c k , a n d t h a t the p h y s i c a l p r o p e r t i e s a r e due t o the crystallζable p o l y e t h y l e n e c h a i n segments. I t is- i n t e r e s t i n g t o n o t e t h a t s o f t segments in the d i b l o c k c o p o l y m e r shown above is the h y d r o g e n a t e d 1 , 2 polybutadiene. The r e a s o n f o r the r u b b e r c h a r a c t e r i s t i c o f p o l y b u t a d i e n e 1 , 2 is the p r e s e n c e o f the c h i r a l c a r b o n c a r r y i n g the v i n y l u n i t s . T h i s a s s y m m e t r i c c a r b o n is n o t a l t e r e d b y hydrogénation s i n c e the v i n y l g r o u p is o n the s i d e c h a i n o f polymers-. T h e r e f o r e , the f i n a l p r o d u c t is h e t e r o t a c t i c rubbery poly-1-butène, which has a g l a s s t r a n s i t i o n temperature o f -25°C. One w o u l d e x p e c t t h a t a d d i t i o n f i l l e r o f s i m i l a r s t r u c t u r e w o u l d r e i n f o r c e the h a r d s e g m e n t s . I t was f o u n d t h a t the a d d i t i o n o f t h e r m o p l a s t i c p o l y o l e f i n s o f h i g h m e l t i n g p o i n t d i d i m p r o v e the p h y s i c a l p r o p e r t i e s . The d a t a in T a b l e I I I i l l u s t r a t e t h a t the a d d i t i o n o f p o l y p r o p y l e n e showed a n i m p r o v e m e n t in p h y s i c a l p r o p e r t i e s s i m i l a r t o the c o m m e r c i a l l y a v a i l a b l e SBS t r i b l o c k c o polymer. T h i s T P E , shown in T a b l e I I I , shows o u t s t a n d i n g p h y s i c a l p r o p e r t i e s . This- u n i q u e b l o c k c o p o l y m e r c a n o n l y be made u s i n g the a n i o n i c p o l y m e r i z a t i o n t e c h n i q u e .


9

TABLE I I H y d r o g e n a t e d B-1,U Mn

B-1,U

9,000 162,000 58,000

Mn

B-1,2

9,000 306,000 396,000

Tg°C... 100 100 100

-25 -29 -27

* Hydrogénation c a n be v a r i e d

- B-1,2

Tensile(psi) Tm°C... 89 101 100

625 1106

U03

Elong 950 770 573

(.60-100$)


%

414

ANIONIC

POLYMERIZATION

TABLE I I I B l e n d o f 30$ I P P * w i t h the h y d r o g e n a t e d d i b l o c k copolymers o f B-1,UH - B-1.2EU 2

Mn B-l.U

Mn

9,000 162,000 58,000

29,000 306,000 396,000

100 100 100

-

-


K r a t o n IL01

B-1,2

$

H

2

Tg°C... -25 -29 -27 -60

Tm°C... 89

101 100

-

Tensile P s i g . Elong. U250 5320 221*0

76Ο 1+50 1+60

3300

1200

$

* A b r o a d t r a n s i t i o n was n o t e d . I t was a s s i g n e d t o the g l a s s t r a n s i t i o n o f the i s o t a c t i c p o l y p r o p y l e n e . A b l o c k c o p o l y m e r o f h y d r o g e n a t e d Β-Ι,Ι+ΗB-1,2H g a v e the b e s t p h y s i c a l p r o p e r t i e s i r r e s p e c t i v e o f the s o f t s e g m e n t s m o l e c u l a r w e i g h t . These phenomena a p p e a r t o be i n c o n s i s t e n t w i t h the u s u a l t h e r m o p l a s t i c e l a s t o m e r , e s p e c i a l l y the s t y r e n e - b u t a d i e n e t y p e . The c o m p a r i s o n b e t w e e n the SBS a n d t h e s e b l o c k c o p o l y m e r s may n o t be a c c u r a t e s i n c e the s t r e n g t h o f t h e s e d i b l o c k e l a s t o m e r s is due t o the c r y s t a l i i z a b l e p o l y e t h y l e n e c h a i n , w h i l e the SBS u s e is due t o the h a r d p o l y s t y r e n e chain. The f u n d a m e n t a l c o n c e p t one h a s t o a d d r e s s o n e s e l f t o is the e n h a n c e d p h y s i c a l p r o p e r t i e s p r e s e n t in t h i s d i b l o c k and the n a t u r e o f i n t e r a c t i o n t h a t t a k e s p l a c e in t h e s e p o l y m e r s . P e r h a p s e x a m i n a t i o n o f the m i c r o s t r u c t u r e o f the p a r e n t b l o c k p o l y m e r B-1,1*-B1,2 b e f o r e hydrogénation and the r e s u l t i n g b l o c k p o l y m e r a f t e r hydrogénation may be o f i n t e r e s t f o r the u n d e r s t a n d i n g o f t h e s e f o r c e s . The B-1,U b l o c k c o n t a i n s 13-15$ 1,2: 32-30$ C i s 1 , U ; 5 5 - 5 0 $ t r a n s l h. Hydrogénation o f the B-1,U b l o c k g i v e s p o l y e t h y l e n e , and hydrogénation o f the B-1,2 b l o c k g i v e amorphous p o l y b u t a n e - 1 . The d i b l o c k c o p o l y m e r h a s Tm o f p o l y e t h y l e n e (+103 t o 115°C.; p u r e p o l y e t h y l e n e is ll8-125°C...). The hydrogénation o f the B-1,2 u n i t s u s u a l l y g i v e s a r u b b e r segment o f p o l y b u t a n e - 1 . However, the random d i s t r i b u t i o n o f the amorphous p o l y b u t a n e - 1 in first b l o c k , the p o l y e t h y l e n e f o r m e d f r o m the B - l , i * b l o c k c h a i n s , a r e p o s t u l a t e d t o f o r m a m i c r o p h a s e t h a t a l l o w s the r u b b e r y s e c o n d b l o c k p o l y b u t a n e - 1 , r e s u l t i n g f r o m B - 1 , 2 H , t o be t r a p p e d in the c h a i n f o l d i n g o f the c r y s t a l l i z a b l e p o l y e t h y l e n e . This t y p e o f c h a i n f o l d i n g appears- t o f o r m h a r d - s o f t r e p e a t i n g u n i t s s i m i l a r t o t r i b l o c k copolymer. I f t h i s e x p l a n a t i o n is p l a u s i b l e , t h e n the a d d i t i o n o f p u r e p o l y e t h y l e n e w o u l d r e i n f o r c e these types o f block copolymers. This indeed was f o u n d t o be the c a s e . The a d d i t i o n o f 30$ p o l y e t h y l e n e 1

9

2


26.

HALASA

Industrial

Applications

of Polymerization

415

to the hydrogenated polymers (Table II) increased the tensile strength to maintain an acceptable ultimate elongation, as shown in Table IV. TABLE IV Block copolymers of Hydrogenated B-1,UH-B-1, 2H,., f i l l e d with high density polyethylene


B-1,U

%PE Ult.Tensile(psi)

B-1,U-B-1,2

9U,000 162,000 58,000

29,000 306,000 396,000

30 30

Elong. %

1120 2130 1880

30

U07 5 0 36Ο

A thermoplastic elastomer similar to the above structures was made by u t i l i z i n g conjugated 1,3 d i olefins that can be polymerized anionically. The work of Halasa and co-workers(25) i l l u s t r a t e the point. These workers polymerized 1,3-butadiene and isoprene to pro duce a diblock copolymer of poly(butadiene)-poly(isoprene) (see Table V). These copolymers were made by anionically poly merizing 1,3-butadiene with n-Buli followed by the add i t i o n of isoprene to the l i v e cement. The molecular weight was varied in the l h poly(bd) block to produce the maxi mum physical properties. The content of the Bd/isoprene in the copolymer was varied 30/70. Similarly, (Table VI) the molecular weight of the diblock was kept constant at 6 0 / U 0 Bd isoprene ratio, while the molecular weight of the individual block was varied. In Tables V and VI the physical properties of the diblock of the conjugated diene rubber showed elastomeric properties typical of that of the uncrossed elastomer. 9

TABLE V Block Copolymer of Polybutadiene-Isoprene Bd/Isoprene 30/70

No. Blocks. Total Mn. 2 3 3 3

100,000 50,000 100,000 150,000

Poly(Bd) of Poly (isoprene) (lBlock) of (lBlock) 30,000 7,500 15,000 22,000

70,000 25,000 70,000 105,000


416


TABLE V I D i b l o c k Copolymer o f B d / I s o p r e n e No.


60/1+0

Poly(butadiene)-Poly(isoprene).

Blocks. 2 3 5 Τ 11

T o t a l Mn. 100,000 100,000 100,000 100,000 100,000

Poly(Bd)of (1 B l o c k )

Poloprene) o f (1 B l o c k )

60,000 30,000 20,000 15,000 10,000

1+0,000 1+0,000 20,000 13,300 8,000

The b l o c k c o p o l y m e r s shown in b o t h T a b l e V and V I were h y d r o g e n a t e d . The B-ll+ b l o c k p r o d u c e d p o l y e t h y l e n e and the p o l y i s o p r e n e b l o c k p r o d u c e d e t h y l e n e p r o p y l e n e a l t e r n a t i n g copolymer. The p h y s i c a l p r o p e r t i e s o f t h i s c o p o l y m e r , composed o f c r y s t a l l i n e p o l y e t h y l e n e b l o c k and a s o f t e l a s t o m e r i c segment made o f an EPR b l o c k , is t a b u l a t e d in T a b l e V I I . The d a t a in t h i s t a b l e i l l u s t r a t e the f a c t t h a t a d i b l o c k of hydrogenated polybutadiene-polyisoprene g a v e e x c e l l e n t p h y s i c a l p r o p e r t i e s . This- is a f u r t h e r i l l u s t r a t i o n o f the new c o n c e p t o f s o f t c h a i n i n t e r p e n e t r a t i n g the c r y s t a l l i z a b l e p o l y e t h y l e n e c h a i n v i a chain folding.

TABLE V I I

to

PE/PER 30/70

6oAo

Hydrogenated D i b l o c k o f Poly(Butadiene)-Poly(isoprene) give Polyethylene-propylene rubber. MODULUS 1 0 0 $ 300$

Tensile

Elongation

at

210

270

283 250 266

1+89

280 600

1+70

350 373

1+15 1+95

375 520

550 550 650

725 750

I65O 2000

825

2025

680 760 750

390

The h y d r o g e n a t e d c o p o l y m e r s o f polyCbutadienep o l y ( i s o p r e n e ) have been m i l l e d w i t h 30$ i s o t a c t i c p o l y p r o p y l e n e and h i g h d e n s i t y p o l y e t h y l e n e . These t h e r m o p l a s t i c e l a s t o m e r s (TPR's) showed e x c e l l e n t p h y s i c a l p r o p e r t i e s u H u s t r a t e d in T a b l e V I I I ) .


26.

HALASA


of

417

Polymerization

TABLE V I I I Hydrogenated d i b l o c k 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 ) f i l l e d -with i s o t a c t i c p o l y p r o p y l e n e and h i g h d e n s i t y p o l y e t h y l e n e .


Mn p o l y ( B d )

60,000 30,000 20,000 10,000

Mn p o l y ( l ) T o t a l Mn Diblock.

U0,000 70,000 80,000 90,000

$Polyolefin Tensile % ( p s i ) Elong.

100,000 100,000 100,000 100,000

30 30 30 30

2250 2560 2210 2lU0

PE PE PP PP

620

hOO 1*50 600

The d a t a f r o m t h i s t a b l e i l l u s t r a t e the s e m i c o m p a t i b i l i t y o f the p h a s e b e t w e e n i s o t a c t i c p o l y p r o p y l e n e and the h i g h d e n s i t y p o l y e t h y l e n e w i t h b l o c k c o p o l y m e r w i t h o u t g r o s s i n t e r f e r e n c e in the domain s t r u c t u r e o r the c r y s t a l l i n e p h a s e s t h a t e x i s t in t h e s e T P R s . f

I f one c a n t a k e a d v a n t a g e o f the m i c r o s t r u c t u r e changes caused by a n i o n i c p o l y m e r i z a t i o n produced by v a r i a t i o n in the q u a n t i t i e s o f p o l a r m o d i f i e r s a n d the t e m p e r a t u r e a t d i f f e r e n t s t a g e s o f the r e a c t i o n , one c a n p r o d u c e the p r o p e r p o l y m e r s w i t h the d e s i r e d m i c r o s t r u c t u r e . A f t e r t h i s t a i l o r i n g t a k e s p l a c e in m i c r o s t r u c t u r a l c h a n g e s , the p o l y m e r is s u b j e c t e d t o hydrogénation r e a c t i o n ; the r e s u l t i n g t h e r m o p l a s t i c p o l y m e r c a n be compounded t o g i v e the p r o p e r p h y s i c a l p r o p e r t i e s . T h i s is u s u a l l y done b y adding a p l a s t i c o f h i g h m e l t i n g p o i n t , such as i s o t a c t i c p o l y p r o p y l e n e , t o f o r m p h a s e s e g r e g a t e d domain o f h a r d c r y s t a l l i n e segments a n d r u b b e r y s o f t s e g m e n t s , w h i c h l e a d s t o r e i n f o r c e d t h e r m o p l a s t i c elastomers (TPD s) as i l l u s t r a t e d below (Table I X ) . f

TABLE I X Hydrogenated P o l y ( b d ) - P o l y ( B d Mn B-1,1*

Mn B-1,2

9l*,000 162,000 58,000

200,000 lUU,000 338,000

Mn B-1,U - B-1,2

29U,000 306,000 396,000

1,2) %E

2

100 100 100

Tg

-25 -30 -27

T e n s i l e % Elong.

625 1106 1+03

950 370 1+73

The i n t e r e s t i n g phenomenon t h a t seemsto b e e v i d e n t in the above t a b l e is t h a t the m o l e c u l a r w e i g h t o f the h a r d c r y s t a l l i n e segments a p p e a r s t o be the c o n t r o l l i n g f a c t o r in the p h y s i c a l p r o p e r t i e s . F o r e x a m p l e , the p o l y e t h y l e n e s e g ment, r e s u l t i n g f r o m the hydrogénation o f B-l,U/Mn 58,000,had a l o w e r t e n s i l e s t r e n g t h t h a n the sample w i t h the h i g h e s t p o l y -



418


e t h y l e n e , r e s u l t i n g f r o m the h y d r o g é n a t i o n o f the same p o l y m e r with a higher molecular weight. S i m i l a r l y , many v a r i a t i o n s c a n be p r o d u c e d on t h e s e c o p o l y m e r s t o i m p r o v e t h e i r p h y s i c a l properties. Commercial methods f o r p r e p a r i n g b l o c k copolymers of styrene-butadiene-styrene u t i l i z e cyclohexane or toluene a s a s o l v e n t s i n c e the p o l y s t y r y l l i t h i u m is i n s o l u b l e in s t r a i g h t c h a i n a l p h a t i c s o l v e n t s . U s u a l l y the 1 , 3 - b u t a d i e n e is a d d e d t o the p o l y s t y r y l l i t h i u m t o p r o d u c e the d i b l o c k s t y r e n e - b u t a d i e n y l l i t h i u m . A t t h i s p o i n t in the r e a c t i o n two p r o c e s s e s a r e e m p l o y e d . One p r o c e s s - u t i l i z e s a d i f u n c t i o n a l j o i n i n g a g e n t s u c h a s m e t h y l e n e d i c h l o r i d e w h i c h g i v e s an SBBS a n d h e n c e the t o t a l Mn o f the b l o c k c o p o l y m e r and the Mn o f the m i d d l e b l o c k a r e c o n s t a n t , s i n c e h a l f o f the r e q u i r e d 1,3 butadiene and all the s t y r e n e were a d d e d t o make the d i b l o c k . The s e c o n d p r o c e s s u t i l i z e s the two s t a g e method in w h i c h h a l f o f the s t y r e n e a d d e d a t the b e g i n n i n g o f the r e a c t i o n f o l l o w e d b y all the 1 , 3 - b u t a d i e n e and t h e n the r e m a i n i n g h a l f o f s t y r e n e is a d d e d . A l l these polymeriza t i o n p r o c e s s e s a r e done in c y c l o h e x a n e s i n c e h o m o p o l y s t y r e n e w i t h o r w i t h o u t l i t h i u m t e r m i n a t e d is i n s o l u b l e in all s t r a i g h t c h a i n o r b r a n c h e d h y d r o c a r b o n s o l v e n t s s u c h as h e p t a n e , hexane p e t r o l e u m e t h e r s o r the b r a n c h e d d e r i v a t i v e s . The r e c e n t d e v e l o p m e n t o f u s i n g h e x a n e a s a s o l v e n t f o r the p r e p a r a t i o n o f SBS c o p o l y m e r s h a s b e e n a t t e m p t e d e v e n t h o u g h the p o l y s t y r y l . l i t h i u m is i n s o l u b l e in t h i s m e d i a ( 2 U ) . Polystyryl l i t h i u m was d i s p e r s e d in h e x a n e u s i n g 1% o f SBS r u b b e r as a d i s p e r s i n g agent. The b l o c k c o p o l y m e r t r i e d a s a d i s p e r s i n g a g e n t r e t a i n e d the c o l l o i d a l p r o p e r t i e s o f p o l y styrenyl lithium t i l l the a d d i t i o n o f the b u t a d i e n e monomer. I n t h i s p r o c e s s the s t y r e n e - b u t a d i e n y l l i t h i u m becomes s o l u b l e in h e x a n e . S u r p r i s i n g l y , the t r i b l o c k SBS made b y t h i s p r o c e s s had a r a t h e r narrow m o l e c u l a r d i s t r i b u t i o n . The p h y s i c a l p r o p e r t i e s o f SBS made b y the d i s p e r s i o n m e t h o d d e s c r i b e d a b o v e h a d p r o p e r t i e s s i m i l a r t o SBS made in c y c l o h e x a n e on all homogenous p r o c e s s e s . The h y d r o g é n a t i o n o f the c e n t r e b l o c k o f SBS c o p o l y m e r produced o x i d a t i o n s t a b l e t h e r m o p l a s t i c elastomer. This prod u c t was c o m m e r c i a l i z e d b y the S h e l l D e v e l o p m e n t Company u n d e r the t r a d e name o f K r a t o n G. The f i e l d o f t h e r m o p l a s t i c e l a s t o mers b a s e d on s t y r e n e , 1 - 3 - b u t a d i e n e o r i s o p r e n e h a s e x p a n d e d so much in the l a s t 10 y e a r s t h a t the s y n t h e t i c r u b b e r c h e m i s t p r o d u c e d more o f t h e s e p o l y m e r s t h a n the m a r k e t c o u l d h a n d l e . However, the a n i o n i c a l l y p r e p a r e d t h e r m o p l a s t i c s y s t e m is still the l e a d e r in t h i s f i e l d , s i n c e it p r o d u c e d the b e s t TPR s w i t h the b e s t p h y s i c a l p r o p e r t i e s . T h e s e TPR's c a n accommodate more f i l l e r , w h i c h r e d u c e s the c o s t . F o r e x a m p l e , the SBS K r a t o n t y p e c o p o l y m e r v a r i e s the monomer o f the m i d d l e b l o c k t o produce p o l y i s o p r e n e at v a r i o u s combinations, t h e n , f o l l o w e d $

f



26.

HALASA


of

419

Polymerization

b y h y d r o g é n a t i o n t o p r o d u c e EPR m a t e r i a l , h a v e l e a d t o s t y r e n e ethylene propylene-styrene type thermoplastic elastomers with u n i q u e p h y s i c a l p r o p e r t i e s a n d it is l e s s s u s c e p t i b l e t o o x i dation. T h e s e t y p e s o f t h e r m o p l a s t i c e l a s t o m e r s c a n be f i l l e d w i t h p o l y o l e f i n s , w h i c h r e d u c e s the c o s t a n d e n h a n c e s the physical properties. S i m i l a r l y , u s i n g t h e i r own v a r i a t i o n , H a l a s a a n d c o w o r k e r s made p o l y b u t a d i e n e 1 0 0 $ 1 , 2 m i c r o s t r u c t u r e . The e l a s t o m e r was f u r t h e r c o n v e r t e d t o amorphous p o l y ( b u t e n e - l ) r u b b e r by h y d r o g e n a t o r s . T h i s t y p e o f e l a s t o m e r is d i f f i c u l t t o produce by s i m p l e p o l y m e r i z a t i o n o f b u t e n e - 1 o r b u t e n e - 2 b y the Z i e g l e r t y p e o f c a t a l y s t . However, u t i l i z i n g a n i o n i c p o l y m e r i z a t i o n o f v a r i o u s c o n j u g a t e d 1 , 3 - o l e f i n s and t h e n s a t u r a t i n g the d o u b l e b o n d by h y d r o g é n a t i o n p r o d u c e s a n o t h e r u s e f u l and n o v e l e l a s t o m e r . As a f u r t h e r i l l u s t r a t i o n o f t h i s p o i n t , the p o l y m e r i z a t i o n s o f p i p e r y l e n e u s i n g o r g a n o - l i t h i u m compounds a n d p o l a r m o d i f i e r D P E ( d i p i p e r i d i n e e t h a n e ) g a v e p o l y p i p e r y l e n e in w h i c h the 1 - m e t h y l is on the t e r m i n a l v i n y l double bond. H y d r o g é n a t i o n o f t h i s e l a s t o m e r g a v e the p o l y ( l - p e n t a n e ) w i t h low g l a s s t r a n s i t i o n t e m p e r a t u r e . This type o f t r a n s f o r m a t i o n h a s o p e n e d the f i e l d f o r the s y n t h e t i c p o l y m e r c h e m i s t t o u s e h i s m i c r o s t r u c t u r a l a r c h i t e c t u r e in the l a b o r a t o r y and t o p r e p a r e a l a r g e v a r i e t y o f p o l y - d i e n e w i t h l k or 1,2 m i c r o s t r u c t u r e w i t h p h e n y l o r a l k y l s u b s t i t u e n t and t o p r o d u c e , w i t h h y d r o g é n a t i o n , a new c l a s s o f e l a s t o m e r s , i . e . p l a s t i c o r thermoplastic elastomers. 9

A n i o n i c p o l y m e r i z a t i o n o f c o n j u g a t e d d i e n e s and o l e f i n s r e t a i n s its l i t h i u m on the c h a i n e n d s as b e i n g a c t i v e m o i t i é s and c a p a b l e o f p r o p a g a t i n g a d d i t i o n a l monomer. This dist i n g u i s h i n g f e a t u r e has an a d v a n t a g e o v e r o t h e r methods o f p o l y m e r i z a t i o n such as r a d i c a l , c a t i o n i c and Z i e g l e r p o l y m e r ization. Many a t t e m p t s h a v e b e e n made t o p r e p a r e b l o c k c o p o l y m e r s b y the a b o v e m e t h o d s , b u t t h e y were n o t s u c c e s s f u l in p r e p a r i n g the c l e a r c h a r a c t e r i z e d b l o c k c o p o l y m e r p r o d u c e d by anionic technique.

BLOCK COPOLYMERS OF

HIGH VINYL SOFT SEGMENTS

The m i c r o s t r u c t u r e o f the s o f t b l o c k c a n be v a r i e d t o p r o d u c e SBS in w h i c h the m i d d l e b l o c k is f r o m 1 0 0 $ 1 , 2 t o U 5 $ or a mixture of v a r i e d composition. The work o f H a l a s a and c o w o r k e r s ( 2 £ ) is p r e s e n t e d in T a b l e X t o i l l u s t r a t e t h i s p o i n t . F u r t h e r m o r e , the m i c r o s t r u c t u r e o f the m i d d l e segment c a n be a l t e r e d b y s e q u e n t i a l a d d i t i o n t o p r o d u c e medium s i n g l e p o l y b u t a d i e n e (see T a b l e X I ) .


420

ANIONIC

POLYMERIZATION

TABLE X High V i n y l Poly(Bd)(SBS) Block Copolymer Composition I R

Copolymer Composition

Phys. Prop. Tensile % SB (Mn) % SBS (Mn) ( P s i ) Elong

Styrene % (Mn) 1,2 % Homo Sty. 31.k

(9,000)

(6U,ooo)

3.0

99.6

96.5

3157

397

3100

530

2900

U50


(86,000) 26.7(20,000)

98.7

6.7

28.5(15,000)

98.5

9.0

(17,000)

88.9 (227,000) (183,000) 91.0 (222,500)

TABLE XI Medium V i n y l Poly(Bd) Composition IR

Styrene % (Mn)

(SBS)

Block Copolyme r


1,2

% Homo.Sty.

Phys. Prop. Tensile %

SB (Mn) %SBS(Mn) ( P s i ) Elong

32.9

(15,000)

52.7

2.7

81,000

35.6

(15,000)

54.5

2.9

101,000

27.7

(23,000)

56.8

2.7

155,000

97.3 2111 (97,000) 97.2 4000 (122,000) 97.4 3267 (183,000)

900 735 890

When the above polymers were compounded, without adding r e i n f o r c i n g f i l l e r but u s i n g extendar aromatic o i l , the p h y s i c a l p r o p e r t i e s d i d drop, i l l u s t r a t i n g the c l o s e c o m p a t i b i l i t y o f aromatic o i l and the h i g h and medium v i n y l s o l u b i l i t y paratometer (Table X I I ) . TABLE X I I High V i n y l Poly(Bd) SBS Block Copolymer Compound w i t h 30% Aromatic O i l . Composition

(IR)


O i l Extended P o l y Tensile %

Styrene % (Mn)

1,2

% Homo Sty. % SBS (Mrî)% SBS (Mrî)

31.4

(15,000)

99.6

3.0

26.7

(20,000)

98.7

6.7

28.5

(15,000)

98.5

9.0

(64,000)

96.5 (86,000) (179,000) 88.9 (227,000) (183,000) 91.0 (222,000)

(Psi)Elong 589 580 923 500 850 683


26.

HALASA


of

Polymerization

421

F u r t h e r i l l u s t r a t i o n s can be seen when the d i b l o c k copolymers,of high and medium v i n y l a r e made in hexane s o l v e n t . This is i l l u s t r a t e d by the f a c t that 1,2-polybutadiene is made first. Then the styrene monomer is added to form B j S d i b l o c k . The S B d i b l o c k in which the styrene b l o c k is made first in c y c l o hexane, followed by the d i p i p e r i d i s e ethane m o d i f i e r to the s t y r e y l l i t h i u m then the butadiene to form t h i s b l o c k coplymer. The reader may see the d i f f e r e n c e as i l l u s t r a t e d in the f o l l o w i n g t a b l e s (XIII - XIV) as the p h y s i c a l p r o p e r t i e s vary from B S t o S B 1 2

1 2


TABLE XIII Block Copolymer Styrene-Poly(Bd) High V i n y l Composition (lR) Polymer Composition %S (Mn)

% 1,2

2k.

99.7

6

27.5

100

30.7

93.8

% Homo.Sty. (Mn)

11.0 (7,500) 5.0 (9,700) 1.2 (13,700)

% SB (Mn) 89.0 (72,500) 95.0 (**0,300) 98.8 (**2,900)

P h y s i c a l Prop. Tensile % ( P s i ) Elong ÎUOO

583

583

600

725

**00

T h i s d i b l o c k o f high v i n y l styrene copolymer was made in hexane but the v i n y l poly(Bd) was made i n i t i a l l y , followed by the styrene. The t a b l e below shows t h a t these polymers were s u p e r i o r in the p h y s i c a l p r o p e r t i e s t o the above diblock SB 12

TABLE XIV High V i n y l Poly(Bd) Styrene B--S Composition

P h y s i c a l Prop. Tensile % Tm °C... (Psi) Elong

% 1,2

% B-S (Mn)

Tg°C...

36.5(29,000)

98.5

(112,000)

-3.5

115

70**

160

28.1 (7,000)

98.5

(86,000)

-k

115

73**

207

3.1(15,000)

99.2

(18U,000)

-2.5

113

1220

1*37

26.6(19,000)

98.9

(181*, 000)

-2

11U

1232

633

%S (Mn)

The B12S b l o c k copolymers were subjected t o the hydrogénation r e a c t i o n in which o n l y the 1,2 poly(Bd) were hydrogenated t o improve its p h y s i c a l p r o p e r t i e s . These are i l l u s t r a t e d in Table XV.



422 TABLE Hydrogenated Diblock Composition %S

Copolymer o f S t y r e n e - P o l y ( B d )

IR

(Mn)

36.5(29,000) 28.1 (7,000) 3h.1(15,000) 26.6(19,000)

%

1,2

%Ά

Tg°C...

91.0 95 96 95

-23

98.5 98.5 98.5 98.9

RANDOM COPOLYMERS OF


XV

2

-2k

-19 -20

:113 :IOU :102 :10k

(1,2)

Tensile B-l,2H-S(Mn) ( P s i )

(112,000) (86,000) (18U,000) (l8U,000)

706 hOO 1025 3686

$ Elong

30 h80 NB 650

STYRENE/BUTADIENE

The p r e p a r a t i o n o f random c o p o l y m e r styrene/butad i e n e h a s b e e n a c h i e v e d b y u s i n g o r g a n o - l i t h i u m compound as initiators. The a b i l i t y t o u s e l i v i n g a n i o n i c p o l y m e r i z a t i o n gave u s the v e r s a t i l i t y t o v a r y the s t y r e n e c o n t e n t a t w i l l . F o r e x a m p l e , p o l y m e r s c o n t a i n i n g as l o w a s 18$ s t y r e n e and a s h i g h a s 33$ s t y r e n e h a v e b e e n made. T h e s e c o p o l y m e r s a r e made in a random f a s h i o n b y a p r o c e s s p a t e n t e d b y F i r e s t o n e w i t h o u t i n c r e a s i n g the v i n y l s t r u c t u r e o f the p o l y b u t a d i e n e c o n t e n t u n d e r 15$. Such a p r o c e s s has been a b l e t o p r o d u c e what is known in the i n d u s t r y as s o l u t i o n SBR. The p h y s i c a l p r o p e r t i e s o f s o l u t i o n SBR were e q u i v a l e n t t o , and in some c a s e s e v e n b e t t e r t h a n , e m u l s i o n SBR. Living anionic poly m e r i z a t i o n c a n be u s e d t o p r e p a r e s u c h a p o l y m e r , b e c a u s e one. c a n p r o d u c e : ( a ) v a r i a t i o n in the m i c r o s t r u c t u r e ; (b) the sequence d i s t r i b u t i o n o f s t y r e n e ; (c) m o l e c u l a r weight d i s t r i b u t i o n , and (d) b r a n c h i n g . The l a s t p r o p e r t y is r e l a t e d t o the p r o c e s s i n g o f the r u b b e r in the t i r e m a k i n g e q u i p m e n t . By u s i n g o r g a n o l i t h i u m compound in t h i s c a s e , it was p o s s i b l e t o m a i n t a i n a v i n y l c o n t e n t n o t g r e a t e r t h a n 18$, but t o produce a p o l y b u t a d i e n e s t y r e n e c o p o l y m e r t h a t has random b l o c k s t y r e n e and w i t h o u t the u s e o f p o l a r m o d i f i e r s , w h i c h n o r m a l l y w i l l i n c r e a s e the 1,2 content. T h i s c o p o l y m e r , when compounded in the t r e a d r e c i p e , a s shown in the T a b l e X V I , g a v e p r o p e r t i e s t h a t a r e a c t u a l l y e q u i v a l e n t t o t h a t o f e m u l s i o n SBR and in some c a s e s e v e n b e t t e r . T h i s is p a r t i c u l a r l y t r u e in the p r o p e r t i e s o f the Y o u n g m o d u l u s i n d e x , w h i c h showed b e t w e e n -38 t o -5 C.; the S t a n l e y L o n d o n S k i d R e s i s t a n t , in w h i c h the c o n t r o l is 100, shows t h a t 110-115 was obtained. The b r e a k i n g i n d e x was a l s o i n t e r e s t i n g . S o l u t i o n SBRS c o n t a i n i n g 18 t o 33$ s t y r e n e showed a w e a r i n g i n d e x o f b e t w e e n 100 a n d 105$ i n c r e a s e in w e a r , as c o m p a r e d t o an e m u l s i o n SBR o f 100. T h i s s u g g e s t s t h a t the amount o f s t y r e n e i n c r e a s e d a c c o r d i n g l y , because l i v i n g p o l y m e r i z a t i o n was u s e d and b e c a u s e the s t y r e n e c a n be a d d e d a t d i f f e r e n t i n c r e m e n t s during polymerization. The f a c t t h a t one. c a n make t h i s t y p e o f p o l y m e r f r e e o f g e l a t h i g h p u r i t y g i v e s the s o l u t i o n SBR



5U

Shore A hardness

5

280

56

590

2800

1050

Styr.

-1*1*

29b

58

650

2750

1000

All

Styr.

59

-37

281*

good

620

2800

1100

Styr.

Styr.

-38

280

57

630

2875

1125

28%

18% 23$

32$

Evaluation

Copolymer

Laboratory

S o l u t i o n Butadiene/Styrene

Recipe,

-1*3

280

660

2500

850

Polar* modif.

Wet s k i d r e s i s t a n c e 110.2 102. k 100 112.2 105.1 107.7 ( C . F . 0.39) * B u t a d i e n e / s t y r e n e c o p o l y m e r c o n t a i n i n g 18% s t y r e n e p r e p a r e d in h e x a n e s o l u t i o n w i t h n - B u L i modified with diethylene g l y c o l dimethyl ether (diglyme).

1

-1*0

YOUNG's m o d u l u s i n d e x (°C...)

STANLEY-LONDON

290

R u n n i n g Temp. (°F)

rating

600

Ultimate elonga t i o n (%)

Processing

2750

1000

Emulsion SBR

Tensile strength (lbs./sq.in)

S t r e s s - s t r a i n prope r t i e s . C u r e 23 m i n . a t 300 F 300$ Modu l u s ( l b s . / s q . in.)

Polymer

Tread Stock

TABLE X V I


424

ANIONIC

POLYMERIZATION


an a d v a n t a g e o v e r the e m u l s i o n SBR. S i n c e e m u l s i o n SBR c o n t a i n s a s i g n i f i c a n t amount o f s o a p c a t a l y s t r e s i d u e , a n d in some c a s e s a h i g h c o n c e n t r a t i o n o f g e l , it was n o t a c c e p t e d in the p l a s t i c a p p l i c a t i o n , and i n d e e d , an a l k y l i t h i u m s y s t e m c a n be u s e d t o p r e p a r e a more n a r r o w m o l e c u l a r w e i g h t l i n e a r p o l y m e r o f good c o l o u r , f r e e o f g e l a n d h i g h p u r i t y . This type of p o l y m e r h a s been u s e d , n o t o n l y in the t i r e a p p l i c a t i o n f i e l d , b u t a l s o in the p l a s t i c i n d u s t r y . The u s e o f c o u p l i n g a g e n t s a n d the f a c t t h a t the p o l y m e r end has a l i t h i u m on it a r e r a t h e r i n t e r e s t i n g . This l i t h i u m c a n be r e a c t e d w i t h d i f f e r e n t a d d i t i v e s t o f u n c t i o n a l l y t e r m i n a t e the p o l y m e r c h a i n . F o r example, e t h y l e n e o x i d e and c a r b o n d i o x i d e , a s w e l l as v a r i o u s e l e c t r o n a c t i v a t e d g r o u p s , s u c h as g r o u p s w i t h v a r i o u s f u n c t i o n a l i t y , h a v e b e e n a d d e d t o the p o l y m e r c h a i n t o t e r m i n a t e it. T h u s , the r h e o l o g y o f the p o l y m e r c a n be a d j u s t e d t o f i t v a r y i n g p r o c e s s i n g r e q u i r e m e n t s . The 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 , f o r e x a m p l e , h a s b e e n q u i t e u s e f u l in p r o d u c i n g u n s a t u r a t e d r u b b e r s t h a t c a n be p r o c e s s e d on c o n v e n t i o n a l t i r e e q u i p m e n t . For example, a branched polymer o f polybutadiene l i t h i u m o r s t y r e n e b u t a d i e n e l i t h i u m h a s b e e n made b y c o u p l i n g w i t h s i l i c o n t e t r a c h l o r i d e , dichloromethane, carbon t e t r a c h l o r i d e and c h l o r o f o r m . The work o f H a l a s a and c o w o r k e r s (26 and 2J.) has shown t h a t even s e c o n d a r y b u t y l c h l o r i d e c a n be r e a c t e d w i t h the l i v e l i t h i u m c h a i n . T h i s has p r o d u c e d what is known as a p r e - r a d i c a l p o l y m e r i z a t i o n in n o n - a q u e o u s s o l v ents. T h i s work h a s shown t h a t the a l l y l i c r a d i c a l a t the end o f the c h a i n c a n o n l y be c o u p l e d t o p r o d u c e a v e r y b r o a d , molecular weight w i t h a bi-model d i s t r i b u t i o n o f molecular w e i g h t o f what was i n i t i a l l y a n a r r o w m o l e c u l a r w e i g h t p o l y m e r . T h i s a r e a n e e d s more i n v e s t i g a t i o n t o show the u t i l i t y o f u s i n g l i v e l i t h i u m w i t h m o n o h a l o g e n a t e d compounds, s u c h a s s e c o n d a r y b u t y l - c h l o r i d e , t o p r o d u c e p o l y m e r s t h a t c a n have a r a d i c a l a t the end o f the p o l y m e r c h a i n . I t g i v e s the u t i l i t y t o a d d the monomers t h a t w o u l d n o r m a l l y be a t t a c k e d b y the o r g a n o l i t h i u m compound s p e c i e s , b u t w i l l o n l y c o p o l y m e r i z e w i t h f r e e r a d i c a l i n i t i a t o r s . Such a v e r s a t i l i t y o f l i v i n g p o l y m e r i z a t i o n is u n i q u e and c a n n o t be f o u n d in o t h e r s y s t e m s . SUMMARY I n summary, one c a n s a y t h a t the v e r s a t i l i t y o f l i v i n g p o l y m e r i z a t i o n makes it a v e r y u s e f u l a n d u n i q u e t e c h n i q u e . S y n t h e t i c p o l y m e r c h e m i s t s c a n u t i l i z e the l i t h i u m a t the end o f the c h a i n t o add p o l y m e r - l i k e c o n j u g a t e d monomers in o r d e r t o t a i l o r make the p o l y m e r c h a i n , o r t h e y c a n u s e c h e l a t i n g d i a m i n e s t o change the m i c r o s t r u c t u r e o f the p o l y m e r c h a i n . They a l s o can r u n hydrogénation t o produce t h e r m o p l a s t i c e l a s t o m e r s . They c a n t r a n s f o r m a n i o n i c a l l y made p o l y m e r by a d d i n g h a l o g e n s t o p r o d u c e v i n y l c h l o r i d e c o p o l y m e r s o r b y r e a c t i n g it w i t h c a r b e n e r e a c t i o n t o s a t u r a t e the p o l y m e r c h a i n t o g i v e d i h a l o -



26.

HALASA


of

Polymerization

425

carbene. They can cyclise the vinyl portion with cationic catalyst to give a copolymer of linear chains with cyclic rings. They can use it to prepare ladder polymers. Obviously this review cannot adequately accommodate all the areas for which anionic polymerization can be used, either in preparation or leading to the preparation of unique polymers. It needs much more extensive studies are needed. This author believes i't is time for people who are working in anionic polymerization to sit down and write a comprehensive review. Previous reviews in this area have been very sketchy, concentrating on one small area that neglects to take into consideration all the work done on anionic polymerization by competent researchers. This tends to expand certain authors1 ideas without giving proper consideration to others who have published extensively. A review which looks at the whole area critically, comprehensively, and informatively would enable young synthetic polymer chemists to benefit from the experience of others. I believe it' is the duty of young scientists to do this, one who does not yet have rigid ideas and one who has not taken any school of thought as his guiding light. He should be one who can look at the work of Szwarc, Morton, Bywater, Shue, Halasa, Fetters and various others who have worked and published in this field of anionic polymerization and write a comprehensive review in an unbiased fashion. Acknowledgment The author acknowledges the help and suggestions of various colleagues at Firestone - J. Hall, D. Cadson, J. Spewiak, Don Schultz, Tai Cheng, Pete Bathea, J. Ozomiak, V. Mochel, S. Futamura, G. Hamad, L. Vescelius and G.G. Bohn. Many thanks to the Firestone management for permission to publish this work. Literature Cited 1-

F.E. Matthews and E.H. Strange. British Pat. 24790 (1910)

2- C. Harries, Ann., 383 184 (1911); U.S. Pat. 1,058,056 (To Bayer & Co. 1913). 3- W. Schlenk, J. Appenrodt, A. Michael and A.Thal, Chem.Ber., 47, 473 (1914). 4- H. Standinger, Chem.Ber., 53 1073 (1920) 5-

K. Zeigler and K. Bahr, Chem. Ber., 61, 253 (1928)

6-

K. Zeigler, H. Colonius and O. Schater, Ann. Chem. 473 36 (1929).

7-

K. Zeigler and O. Schater, Ann. Chem, 479 150 (1930).

8-

K. Zeigler, L. Jakob, H. Wolltham and A. Wenz, Ann. Chem. 511, 64(1934). In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


426

9-

Private Communication to the Office of Synthetic Rubber of the Federal Facilities Corporation; Chem. Eng.News 33 (Aug. 5, 1955).

10- F.W. Stavely, F.C. Forster, J.L. Binder and L.E. Forman Ind. Eng.Chem., 418 778 (1956), paper presented to the Div. Rubber Chem., Am. Chem. Soc. Philadelphia, Pa. Nov. 55. 11- F.C. Forster and J.L. Binder, Advances in Chem. Series No.19 Am. Chem. Soc. P-26 (1957).


12- M. Szwarc, Nature, 178

1168 (1956).

13- M. Szwarc,M. Levy and R. Milkovich, J. Am. Chem. Soc., 78, 2656 (1956). 14- M. Szwarc, Advance Chem. Phys., 2 147 (1959) 15- M. Szwarc, Makromol. Chem., 35 132 (1960). 16- M. Szwarc, Proc. Roy. Soc(London) Ser.A. 279

(1964).

17- M.J. Brock and J. Hackathron, Rubber Chem. Techn. 40,590(1967) 18- A.W. Langer, Jr. Trans. N.Y. Acad.Sci. 27 741 (1965). 19- T.A. Antkowiak, A.E. Oberster, A.F. Halasa, J. Polymer Sci., A-1 10 1319 (1972) 20- A.F. Halasa F.G. Lohr & J.E. Hall, J. Polymer Letters(In press) 21- A.F. Halasa, D.W. Carlson Private communication. 22- A.F. Halasa, R. Cohn,Polymer Reprint, Div. of Polymer Chem. ACS 22 No. 1 (1980). 23- A.F. Halasa private communication U.S. Patent Applications. 24- A.F. Halasa, J.E. Hall, D.W. Carlson, Firestone Library report 23. 25- A.F. Halasa, G. Hamed, J.E. Hall, L. Vescelius and S. Futamura Private Communication (1979). 26- D.N. Schulz and A.F. Halasa, J Polymer Sci. A-1 1S 2401 (1977). 27- A.F. Halasa and D.N. Schulz, U.S. Patent 3,862100. RECEIVED March 5, 1981.


Anionic Polymerization - ACS Publications - American Chemical Society

Recommend Documents