Multiphase Polymers: Blends and Ionomers - American Chemical

Chapter 4

Blends of Polystyrene with Phenylene Oxide Copolymers P. Padunchewit, D. R. Paul, and J. W. Barlow

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Department of Chemical Engineering and Center for Polymer Research, The University of Texas at Austin, Austin, TX 78712 Blends of both a t a c t i c polystyrene, PS, and 90 mole% i s o t a c t i c polystyrene, i-PS, with 2,6-dimethyl-1,4-phenylene oxide-co2,3,6-trimethyl-1,4-phenylene oxide copolymers, PEC, containing up to 20 mole% trimethyl comonomer, were prepared by solution casting methods and found to be miscible by the presence of a single glass t r a n s i t i o n temperature, Tg. The equilibrium melting behavior of i-PS c r y s t a l s in the blends with PEC was c a r e f u l l y determined by the Hoffman-Weeks method. Analysis of the observed depression i n equilibrium melting temperatures suggests that the interaction between i-PS and PEC i s exothermic and becomes increasingly exothermic with increasing PEC trimethyl comonomer content. These results are d i s cussed i n the context of recently developed theories for copolymer blends with homopolymers. Owing t o i t s c o n s i d e r a b l e c o m m e r c i a l s i g n i f i c a n c e , t h e m i s c i b l e blend of poly(2,6-dimethyl-l,4-phenylene oxide), PPO, and a t a c t i c p o l y s t y r e n e , PS, h a s been e x t e n s i v e l y s t u d i e d , a s summarized i n r e c e n t a r t i c l e s and r e v i e w s (1-9). An e x o t h e r m i c h e a t o f m i x i n g , A H « i x , between component r e p e a t u n i t s i s g e n e r a l l y h e l d t o be n e c e s s a r y f o r f o r m a t i o n o f a m i s c i b l e p o l y m e r b l e n d ( 3 ) , and t h i s i s t h o u g h t t o a r i s e i n PPO/PS b l e n d s f r o m p h e n y l g r o u p c o u p l i n g ( 8 , 9 ) between t h e a r o m a t i c r i n g o f PPO and t h a t o f PS. B l e n d s b a s e d on t h e m i s c i b l e m i x t u r e o f PS w i t h poly(2,6-dimethyl-l,4-phenylene oxide-co-2,3,6t r i m e t h y l - 1 , 4 - p h e n y l e n e o x i d e ) , PEC, a l s o have c o n s i d e r a b l e commercial s i g n i f i c a n c e , although very little has b e e n p u b l i s h e d c o n c e r n i n g t h e i r t h e r m o d y n a m i c b e havior (10). One o f t h e g o a l s o f t h i s work i s t o c h a r a c 0097-6156/89/0395-0084$06.00/0 © 1989 American Chemical Society

Utracki and Weiss; Multiphase Polymers: Blends and Ionomers ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

4.

Polystyrene with Phenyiene Oxide Copolymers

PADUNCHEWIT ET AL.

t e r i z e t h e b e h a v i o r o f PEC b l e n d s and t o compare, where p o s s i b l e , t h e thermodynamic p r o p e r t i e s o f t h e s e m a t e r i a l s w i t h t h o s e o f PPO c o n t a i n i n g b l e n d s . S i n c e PEC i s a c o p o l y m e r , d e s c r i p t i o n o f i t s i n t e r a c t i o n w i t h PS i s more complex t h a n i f i t were s i m p l y a homopolymer. B i n a r y i n t e r a c t i o n m o d e l s have b e e n presented which suggest t h a t copolymer m i s c i b i l i t y with a homopolymer c a n be e n h a n c e d by e n d o t h e r m i c interactions between t h e u n l i k e r e p e a t u n i t s o f t h e c o p o l y m e r (11-13) . I n i t s s i m p l e s t f o r m ( 1 1 ) , t h e b i n a r y i n t e r a c t i o n model f o r t h e h e a t o f m i x i n g , A H n i x , o f a c o p o l y m e r , A, c o n t a i n i n g r e p e a t u n i t s 1 and 2, w i t h a homopolymer, B, c o n t a i n i n g r e p e a t u n i t s 3, i s g i v e n by AH«ix/V

= B A 4>B

(1)

where 4>A i s t h e volume f r a c t i o n o f c o p o l y m e r , 4>B t h a t o f t h e homopolymer, V i s t h e volume o f t h e s y s t e m , and B t h e i n t e r a c t i o n p a r a m e t e r f o r m i x i n g A w i t h B, g i v e n by, B = Bl3$l

A

+ B2 3 $ 2

A

-

A

Bl2$l $2

A

(2)

A

where $ i i s t h e volume f r a c t i o n o f r e p e a t u n i t i i n c o p o l y m e r A. Equation 2 suggests that a v a r i e t y of p a r a m e t e r c o m b i n a t i o n s , l e a d i n g t o n e g a t i v e B and a m i s c i b l e b l e n d , a r e p o s s i b l e , d e p e n d i n g on t h e n a t u r e s o f the polymers. Some o f t h e s e a r e i l l u s t r a t e d i n F i g u r e 1. Of most i n t e r e s t i s t h e s u g g e s t i o n t h a t e x o t h e r m i c o r n e g a t i v e heats o f mixing a r e p o s s i b l e , i n d i c a t i n g misc i b i l i t y o f t h e c o p o l y m e r w i t h t h e homopolymer, e v e n though a l l B i j parameters a r e p o s i t i v e . Provided (Bi2) > (B13) ' + ( B 2 3 ) ' , t h e r e w i l l be a r e g i o n i n c o p o l y m e r c o m p o s i t i o n , $ i , where B and A H . i x a r e n e g a t i v e when t h e c o p o l y m e r and homopolymer a r e m i x e d , s i g n i f y i n g the formation of a m i s c i b l e blend. T h i s simple r e s u l t w o u l d a p p e a r t o e x p l a i n t h e " m i s c i b i l i t y window" s e e n w i t h v a r i a t i o n o f comonomer c o n t e n t i n many d i f f e r e n t s y s t e m s (14-17) where t h e homopolymer i s n o t m i s c i b l e w i t h t h e homopolymers made f r o m e i t h e r comonomer, yet i s m i s c i b l e with the copolymer. 1 / 2

1

1

2

2

A

PEC, PPO, and PS a r e amorphous m a t e r i a l s a s n o r m a l l y melt p r o c e s s e d , a f a c t which p r e v e n t s t h e use o f m e l t i n g point depression analyses f o r experimentally determining AHmix o r B f o r t h e b l e n d s w i t h PS. Isotactic polystyrene, i-PS, i s able to c r y s t a l l i z e , i s m i s c i b l e with PPO, and has b e e n s u c c e s s f u l l y u s e d t o d e t e r m i n e t h e p a r a m e t e r s r e l a t e d t o AHmix ( 7 . 1 2 , 1 8 ) . T h i s s t u d y shows t h a t i - P S i s a l s o m i s c i b l e w i t h PEC c o p o l y m e r s w h i c h c o n t a i n up t o 20 m o l e % t r i m e t h y l comonomer. This fact permits t h e use o f i-PS m e l t i n g p o i n t d e p r e s s i o n a n a l y s i s t o d e t e r m i n e t h e e f f e c t o f comonomer c o n t e n t on AHmix w i t h i-PS.


85

86

MULTIPHASE POLYMERS: BLENDS AND IONOMERS

Experimental

Procedures

A l l o f t h e m a t e r i a l s u s e d i n t h i s s t u d y have w e i g h t a v e r a g e m o l e c u l a r w e i g h t s between 28000 and 35000. The PEC c o p o l y m e r s and t h e PPO were p r o v i d e d and c h a r a c t e r i z e d by Dr. B i l l P a v e l i c h , Borg-Warner C h e m i c a l s , P a r k e r s b u r g , West V i r g i n i a . The p r o p e r t i e s o f t h e s e m a t e r i a l s a r e summarized i n T a b l e I . The i - P S , w h i c h c o n t a i n e d 90 m o l e % i s o t a c t i c u n i t s , was p u r c h a s e d f r o m S c i e n t i f i c Polymer P r o d u c t s , Inc. Table Polymer

I.

Physical

Abbreviation

Properties Mw

Tg

T«

(°C)

(°C)

PS

28, 000

96.3

Isotactic Polystyrene (90 m o l e % i s o t a c t i c u n i t s )

i-PS

35, 000

92.0

232*

Poly(2,6-dimethyl oxide)

PPO

30,000

212

256**

Poly(2,6-dimethyl phenylene co-2,3,6-trimethyl-l,4phenylene o x i d e ) , 1 mole% t r i m e t h y l comonomer 1%PEC

30, 000

214

256

P h e n y l e n e c o p o l y m e r , as above, 9 m o l e % t r i m e t h y l comonomer

9%PEC

30, 000

220

264


15%PEC

30, 000

221

264


20%PEC

30, 000

222

266

Atactic

Polystyrene

phenylene

A f t e r Hoffman-Weeks p r o c e d u r e . C r y s t a l l i z e d f r o m s o l u t i o n , no a n n e a l i n g , phenylene oxide m a t e r i a l s .

for a l l

B l e n d s were p r e p a r e d by d i s s o l v i n g t h e components i n t e t r a h y d r o f u r a n , THF, a t 75 °C t o f o r m a s o l u t i o n c o n t a i n i n g a b o u t 10 wt.% s o l i d s . F i l m s were p r e p a r e d by e v a p o r a t i n g t h e THF f r o m s o l u t i o n a t room t e m p e r a t u r e f o r 1-2 d a y s , f o l l o w e d by vacuum d r y i n g a t 90 °C f o r 24 h o u r s t o remove f i n a l t r a c e s o f t h e s o l v e n t . Films, prepared i n t h i s way, were opaque due t o c r y s t a l l i z a t i o n o f t h e


4.

PADUNCHEWIT ET AL.

Polystyrene with Phenylene Oxide Copolymers

PEC, i n agreement w i t h p r e v i o u s o b s e r v a t i o n s ( 1 9 , 2 0 ) , and to the presence of c r y s t a l l i n e i-PS. Amorphous, o p t i c a l l y t r a n s p a r e n t , f i l m s c o u l d be p r e p a r e d by h e a t i n g t h e s o l u t i o n c a s t f i l m s f o r a few m i n u t e s a t 270 °C, f o l l o w e d by r a p i d c o o l i n g t o t e m p e r a t u r e s below t h e b l e n d 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 , Tg , t~> p r e v e n t c r y s t a l l i z a t i o n o f the i-PS. Once t h e p h e n y l e n e e t h e r c r y s t a l s a r e m e l t e d out o f the b l e n d , c r y s t a l l i z a t i o n o f t h i s m a t e r i a l does not r e c u r . The i - P S m a t e r i a l w i l l c r y s t a l l i z e r e a d i l y from t h e m e l t when t h e b l e n d t e m p e r a t u r e i s above Tg and b e l ow a b o u t 200 °C f o r s e v e r a l m i n u t e s . B l e n d T g ' s were measured w i t h a P e r k i n - E l m e r DSC-7 d i f f e r e n t i a l s c a n n i n g c a l o r i m e t e r by f i r s t h e a t i n g 10 mg samples o f t h e b l e n d s a t 20 ° C / m i n t o 270 ° C , a n n e a l i n g f o r 10 min t o m e l t any c r y s t a l l i n i t y , t h e n r a p i d l y c o o l i n g t o a b o u t 60 ° C . The b l e n d Tg was t h e n o b t a i n e d by r e h e a t i n g a t 20 ° C / m i n . M e l t i n g temperatures, T « , o f i-PS i n the pure s t a t e and i n b l e n d s were measured a f t e r c r y s t a l l i z i n g t h e blends at s e v e r a l c r y s t a l l i z a t i o n temperatures, T , to p e r m i t e s t i m a t i o n o f the e q u i l i b r i u m m e l t i n g temperat u r e s , v i a t h e Hoffman-Weeks method (21 ). Typically, a 10 mg sample was h e a t e d i n t h e DSC-7 a t 20 ° C / m i n t o 270 ° C , h e l d a t t h a t t e m p e r a t u r e f o r 10 min, t h e n r a p i d l y c o o l e d t o Tc where i t was h e l d f o r a t l e a s t 100 min. The m e l t i n g t e m p e r a t u r e , T« , was t h e n d e t e r m i n e d on r e h e a t i n g t h e sample i n t h e DSC-7 a t 10 ° C / m i n . The 100 min a n n e a l i n g t i m e a t Tc was f o u n d t o be t h e minimum t i m e r e q u i r e d t o a c h i e v e t h e maximum d e g r e e o f c r y s t a l l i n i t y f o r i-PS i n e i t h e r the pure s t a t e or i n b l e n d s w i t h phenylene ethers. A t a n n e a l i n g t e m p e r a t u r e s below 210 ° C , t h e i - P S d e g r e e o f c r y s t a l l i n i t y was f o u n d t o be t h e same a f t e r 1 h r as a f t e r 15 h r s , a r e s u l t w h i c h i s s i m i l a r t o t h a t d e t e r m i n e d by O v e r b e r g h , e t a l . ( 2 2 ) . c

R e s u l t s and

Discussion

The m e l t i n g b e h a v i o r o f t h e i - P S m a t e r i a l seems t o i n d i c a t e t h e p r e s e n c e o f two c r y s t a l l i n e f o r m s , w i t h two m e l t i n g t e m p e r a t u r e s marked H and L i n F i g u r e 2. The beh a v i o r of the m u l t i p l e m e l t i n g peaks i n i-PS i s a c t u a l l y q u i t e complex, and as t h e c r y s t a l l i z a t i o n t e m p e r a t u r e , T c , i s i n c r e a s e d t h e t e m p e r a t u r e o f peak L i s f o u n d t o i n c r e a s e i n d i r e c t p r o p o r t i o n w h i l e t h a t o f peak H i n creases only s l i g h t l y . As Tc i s f u r t h e r i n c r e a s e d , t h e L endotherm i n c r e a s e s i n s i z e w h i l e the H endotherm d i m i n i s h e s and e v e n t u a l l y d i s a p p e a r s . T h e s e t r e n d s g e n e r a l l y c o n f i r m t h o s e r e p o r t e d p r e v i o u s l y ( 2 ) , and s u g g e s t t h a t t h e m u l t i p l e p e a k s a r e most l i k e l y t h e r e s u l t of l a m e l l a r t h i c k e n i n g p r o c e s s e s , perhaps r e q u i r i n g melti n g and r e c r y s t a l l i z a t i o n ( 2 3 ) .


87


F i g u r e 1. I l l u s t r a t i o n o f ways the i n t e r a c t i o n parameter may v a r y w i t h copolymer c o m p o s i t i o n f o r m i x t u r e s o f a copolymer w i t h a homopolymer. (Reproduced w i t h p e r m i s s i o n from r e f . 11. C o p y r i g h t 1984 B u t t e r w o r t h . )

-J 200J)

I

L_

210.0

220.0

TEMPERATURE, C F i g u r e 2. V a r i a t i o n i n i - P S m e l t i n g t a l l i z a t i o n temperature.

behavior

with


crys-

4.

PADUNCHEWIT ET AL.

Polystyrene with Phenylene Oxide Copolymers 89

A good s t r a i g h t l i n e r e s u l t s when T» o f t h e L peak i s p l o t t e d a g a i n s t Tc f o r i - P S m a t e r i a l s c r y s t a l l i z e d between 150 - 180 ° C , s e e F i g u r e 3. E x t r a p o l a t i o n of t h i s l i n e t o t h e T« = Tc l i n e , s u g g e s t e d by Hoffman-Weeks ( 21) , y i e l d s an e q u i l i b r i u m m e l t i n g t e m p e r a t u r e , T « ° , f o r i - P S e q u a l t o 232 ° C . T h i s v a l u e i s a p p r o x i m a t e l y 8 ° C l o w e r t h a n v a l u e s r e p o r t e d by o t h e r i n v e s t i g a t o r s (4,23,24). T h i s d i s c r e p a n c y i s p r o b a b l y a consequence o f o u r u s e o f 90 m o l e % i s o t a c t i c m a t e r i a l i n s t e a d o f 100 mole% i-PS f o r t h i s study. B l e n d Tg B e h a v i o r . Blends of both a t a c t i c p o l y s t y r e n e w i t h PEC and i - P S w i t h PEC show t h e p r e s e n c e o f a s i n g l e Tg w h i c h v a r i e s m o n o t o n i c a l l y w i t h b l e n d c o m p o s i t i o n and w i t h t h e p e r c e n t t r i m e t h y l comonomer i n t h e PEC. Typical r e s u l t s a r e shown i n F i g u r e 4 f o r t h e i - P S / P E C b l e n d s . The PS/PEC b l e n d s a r e n o t shown. The p r e s e n c e o f a s i n g l e Tg f o r e a c h b l e n d c o m p o s i t i o n i s i n d i c a t i v e o f t h e p r e s e n c e o f a s i n g l e amorphous p h a s e ( 2 . 3 ) , and on t h i s b a s i s we c o n c l u d e t h a t i-PS/PEC and PS/PEC b l e n d s a r e m i s c i b l e f o r t r i m e t h y l c o m p o s i t i o n s i n t h e copolymer from 0 t o 20 m o l e % . The Tg o f p u r e PEC i s r a i s e d by o n l y 12 ° C w i t h r e s p e c t t o PPO by t h e a d d i t i o n o f 20 m o l e % comonomer, and t h i s d o e s l i t t l e t o r a i s e t h e b l e n d Tg a t i n t e r m e d i a t e PEC c o n c e n t r a t i o n s . The l i n e s t i o n 1251,

i n F i g . 4 are calculated

1/Tg,b

= £i

by t h e Fox e q u a -

(ui/Tg.i )

(3)

where (Ji i s t h e mass f r a c t i o n o f s p e c i e s i , T g , i i t s 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 , ° K , and Tg,b i s t h e g l a s s t r a n s i t i o n temperature o f the blend. While d e r i v e d t o e x p l a i n t h e v a r i a t i o n o f Tg w i t h c o p o l y m e r c o m p o s i t i o n , t h e Fox e q u a t i o n h a s s u c c e s s f u l l y p r e d i c t e d t h e c o m p o s i t i o n d e p e n d e n c e o f Tg i n m i s c i b l e b l e n d s y s t e m s ( 2 , 2 6 ) . As f o u n d p r e v i o u s l y f o r t h e PPO/PS s y s t e m ( 2 ) , t h e a g r e e ment between t h i s p r e d i c t i o n and e x p e r i m e n t i s f a i r l y good when t h e t r i m e t h y l comonomer l e v e l i n t h e c o p o l y m e r i s low. As t h e t r i m e t h y l comonomer l e v e l i n c r e a s e s , however, t h e o b s e r v e d Tg v a r i a t i o n w i t h PEC i n t h e b l e n d f a l l s i n c r e a s i n g l y b e l o w t h e l i n e p r e d i c t e d by t h e Fox equation. The r e a s o n f o r t h i s b e h a v i o r i s u n c l e a r . The c o n c a v e upward Tg b e h a v i o r shown f o r t h e s e b l e n d s i s r e l a t i v e l y n o r m a l f o r m i s c i b l e s y s t e m s , and t h e r e i s no e v i d e n c e o f s t r o n g i n t e r a c t i o n s , s u c h a s h y d r o g e n bondi n g , between t h e components w h i c h c a n l e a d t o c o n v e x upward Tg v s . c o m p o s i t i o n c u r v e s (26) . Blend Melting Behavior. The m e l t i n g p o i n t d e p r e s s i o n shown by a m i s c i b l e , h i g h m o l e c u l a r w e i g h t , crystall i z a b l e b l e n d component i n a h i g h m o l e c u l a r w e i g h t d i l u e n t c a n be a n a l y z e d by t h e F l o r y - H u g g i n s e q u a t i o n (27),


90



4.

PADUNCHEWIT ET AL.

ATm

= Tm

-T»°

Polystyrene with Phenylene Oxide Copolymers = - -CV2u - B - T » ° / A H 2 u > - ^ l

2

(4)

t o o b t a i n t h e i n t e r a c t i o n d e n s i t y , B, c h a r a c t e r i s t i c o f the polymer-polymer i n t e r a c t i o n . Accurate determination o f B r e q u i r e s a c c u r a t e v a l u e s f o r t h e volume f r a c t i o n PEC amorphous d i l u e n t i n t h e b l e n d , $1 , f o r t h e m e l t i n g temp e r a t u r e s i n b o t h t h e b l e n d , Tm, and i n t h e p u r e s t a t e , T m ° , and f o r t h e h e a t o f f u s i o n p e r u n i t volume o f i - P S c r y s t a l , AH211/V211. T h i s l a t t e r v a l u e i s t a k e n t o be 20.56 c a l / c c ( 4 ) . As d i s c u s s e d a b o v e , t h e m e l t i n g temp e r a t u r e f o r i - P S i s a s e n s i t i v e f u n c t i o n o f T c , and t h e Hoffman-Weeks c o n s t r u c t i o n i s n e c e s s a r y t o a c c u r a t e l y e s t a b l i s h Tm and Tm° f o r t h i s m a t e r i a l , b o t h i n t h e p u r e s t a t e and i n b l e n d s w i t h PEC. The m o r p h o l o g y o f c r y s t a l l i n e i s o t a c t i c p o l y s t y r e n e , i - P S , has been i n v e s t i g a t e d by o t h e r s , and t h e y have c o n c l u d e d t h a t i - P S n o r m a l l y c r y s t a l l i z e s as s t a c k s o f f o l d e d c h a i n l a m e l l a e w h i c h a r e a r r a n g e d i n volume f i l l ing s p h e r u l i t e s (2). The m e l t i n g p o i n t o f l a m e l l a r p o l y m e r c r y s t a l s d e p e n d s on t h e l a m e l l a t h i c k n e s s , L , as follows (28) Tm

=

Tm°{

1

-

B

2a /(AHf L) e

}

(5)

where a i s t h e s p e c i f i c s u r f a c e f r e e e n e r g y o f t h e end f a c e o f t h e c r y s t a l and AHf i s t h e h e a t o f f u s i o n p e r u n i t volume. H o f f m a n and Weeks (21) d e v e l o p e d a t h e o r y r e l a t i n g the o b s e r v e d m e l t i n g p o i n t t o the c r y s t a l l i z a t i o n temperature, e

T„

=

T.°{

1 - 1/P

} + Tc/P

(6)

Provided P i s independent of temperature, a p l o t of Tm v s . Tc i s l i n e a r and s h o u l d i n t e r s e c t t h e l i n e Tm = Tc a t T m ° , the e q u i l i b r i u m m e l t i n g temperature of the i n f i n i t e l y large crystal. F i g u r e s 5 and 6 show H o f f m a n Weeks c o n s t r u c t i o n s f o r i - P S i n PEC c o p o l y m e r s c o n t a i n i n g 1 m o l e % and 20 m o l e % t r i m e t h y l comonomer, r e s p e c t i v e l y , t h e l i m i t s o f PEC c o m p o s i t i o n s investigated. Similar p l o t s , n o t shown, were a l s o o b t a i n e d u s i n g t h e p r o t o c o l o u t l i n e d above, f o r i - P S b l e n d s w i t h t h e r e m a i n i n g PEC m a t e r i a l s , d e s c r i b e d i n Table I. D e v i a t i o n s from s t r a i g h t l i n e Tm v s . Tc b e h a v i o r a r e e v i d e n t i n a l l PEC b l e n d s y s t e m s when t h e a n n e a l i n g t e m p e r a t u r e i s r a i s e d above 180 ° C , i n d i c a t i n g t h a t t h e d e v i a t i o n s a r e r e l a t e d more t o t h e i - P S and l e s s t o t h e PEC comonomer c o n t e n t . D e v i a t i o n s o f t h e s o r t s e e n i n F i g u r e s 5 and 6 a r e n o t r a r e and c a n r e s u l t f o r a v a r i e t y o f r e a s o n s ( 2 8 ) . F o r example, c r y s t a l l i z a t i o n - i n d u c e d c h e m i c a l r e o r g a n i z a t i o n has been r e p o r t e d (29-34) t o c a u s e s u c h b e h a v i o r f o r a v a r i e t y o f m a t e r i a l s , i n c l u d i n g p o l y e s t e r s and v a r i o u s random and b l o c k c o p o l y m e r s . I t would n o t be un-


91

92


Figure 5. Hoffman-Weeks c o n s t r u c t i o n f o r i - P S c r y s t a l l i z e d f r o m b l e n d s w i t h 1%PEC.


4.

PADUNCHEWIT ET Al*


Figure 6. Hoffman-Weeks c o n s t r u c t i o n s f o r i - P S l i z e d f r o m b l e n d s w i t h 20%PEC.

crystal-


93

94


reasonable to speculate that c r y s t a l l i z a t i o n - i n d u c e d c h e m i c a l r e o r g a n i z a t i o n of the i-PS i s r e s p o n s i b l e f o r t h e i n c r e a s e i n m e l t i n g t e m p e r a t u r e s above t h e H o f f m a n Weeks l i n e . The p h y s i c a l p i c t u r e c o u l d s i m p l y be t h a t t h e a t a c t i c PS u n i t s i n t h e i n i t i a l l y random c o p o l y m e r are e l i m i n a t e d , through chemical rearrangements at high c r y s t a l l i z a t i o n temperatures, to produce a block copolymer of i s o t a c t i c s t r i n g s which can c r y s t a l l i z e a t h i g h e r t e m p e r a t u r e due t o t h e i r i m p r o v e d p e r f e c t i o n . Such a mechanism, known t o be o p e r a t i v e i n o t h e r s y s t e m s , would i m p l y t h a t a n n e a l i n g a t h i g h t e m p e r a t u r e s p r o d u c e s an i - P S m a t e r i a l t h a t i s p h y s i c a l l y d i f f e r e n t from t h a t a n n e a l e d a t l o w e r t e m p e r a t u r e s where c h e m i c a l r e a r r a n g e ment i s l e s s p o s s i b l e . What i s i m p o r t a n t t o t h e p r e s e n t s t u d y i s t o examine t h e e f f e c t o f PEC comonomer, n o t i - P S c o p o l y m e r s t r u c t u r e , on t h e t h e r m o d y n a m i c s o f i n t e r a c t i o n w i t h i-PS. C o n s e q u e n t l y , we l i m i t e d c r y s t a l l i z a t i o n t e m p e r a t u r e s t o v a l u e s l e s s t h a n 180 °C t o i n h i b i t t h e T« enhancement p r o c e s s . As c a n be s e e n from F i g u r e s 5 and 6, good s t r a i g h t l i n e s , w h i c h a p p e a r t o f o l l o w E q u a t i o n 6, c a n be drawn t h r o u g h t h e s o l i d d a t a p o i n t s c o r r e s p o n d ing to these lower c r y s t a l l i z a t i o n temperatures, and r e a s o n a b l e e q u i l i b r i u m m e l t i n g temperatures r e s u l t from t h e i n t e r s e c t i o n o f t h e s e l i n e s w i t h t h e T» = Tc l i n e s f o r e a c h b l e n d f r a c t i o n o f PEC. The A T * v a l u e s , computed f o r e a c h PEC b l e n d s y s t e m from t h e e q u i l i b r i u m m e l t i n g t e m p e r a t u r e s o f i - P S i n t h e b l e n d s and i n t h e p u r e s t a t e a r e shown i n F i g u r e 7. As s u g g e s t e d by E q u a t i o n 4, good s t r a i g h t l i n e s r e s u l t f o r e a c h PEC b l e n d s y s t e m when ATn i s p l o t t e d a g a i n s t t h e s q u a r e o f t h e volume f r a c t i o n o f PEC. Straight lines s u g g e s t t h a t t h e t h e i n t e r a c t i o n d e n s i t y , B, i s i n d e p e n d e n t o f PEC c o n c e n t r a t i o n f o r b l e n d s c o n t a i n i n g l e s s t h a n 25% PEC, a r e s u l t w h i c h c o n t r a s t s somewhat w i t h t h e extreme c o n c e n t r a t i o n d e p e n d e n c e i n B r e p o r t e d by P l a n s , e_t a l ( 4 ) . T h e s e s t r a i g h t l i n e s a l s o show i n c r e a s i n g l y p o s i t i v e s l o p e s as t h e t r i m e t h y l comonomer c o n t e n t i n t h e PEC i s i n c r e a s e d , i n d i c a t i n g t h a t B, t h e i n t e r a c t i o n d e n s i t y , becomes more e x o t h e r m i c w i t h i n c r e a s i n g comonomer c o n t e n t i n t h e PEC. T h e s e r e s u l t s a r e summarized i n F i g u r e 8. E r r o r bars are i n c l u d e d f o r each B value to i n d i c a t e t h a t e a c h has l e s s t h a n 10% r e l a t i v e u n c e r t a i n t y , b a s e d on t h e m e l t i n g p o i n t d e p r e s s i o n d a t a . As shown i n F i g u r e 8, we e s t i m a t e t h e i n t e r a c t i o n e n e r g y d e n s i t y f o r i-PS/PPO b l e n d s t o be B = -2.9 c a l / c c a t 232 ° C . T h i s value i s comparable to the v a l u e , B = -1.4 c a l / c c , c a l c u l a t e d from x = -0.17, r e p o r t e d by Plans, et a l (4), v i a B = xRT/Vi


(7)

4.

PADUNCHEWIT ET AL.


Figure 8. I n t e r a c t i o n p a r a m e t e r v s . c o p o l y m e r f o r i - P S i n PEC c o p o l y m e r s .

composition


95

96


where x i s t h e F l o r y - H u g g i n s i n t e r a c t i o n p a r a m e t e r , V i t h e s e g m e n t a l m o l a r volume o f t h e PPO, t a k e n i n o u r c a l c u l a t i o n t o be 121 c c / g m o l e . We b e l i e v e t h a t t h e d i f f e r e n c e between t h e P l a n s B v a l u e and o u r s i s l a r g e l y t h e r e s u l t o f a c o n c e n t r a t i o n dependency i n t h e i r m e l t i n g p o i n t d e p r e s s i o n d a t a w h i c h were o b t a i n e d a t PPO c o n c e n t r a t i o n s up t o 35%. I f one r e s t r i c t s t h e i r d a t a t o PPO c o n c e n t r a t i o n s l e s s t h a n 25%, t h e r e b y e l i m i n a t i n g one of the t h r e e d a t a p o i n t s used i n t h e i r c o n s t r u c t i o n , t h e i r F i g . 6, one c a n e a s i l y b r i n g t h e i r B p a r a m e t e r i n t o agreement w i t h o u r s f o r m i x t u r e s w i t h t h e 1% comonomer c o n t a i n i n g PEC. The d i f f i c u l t y o f d i r e c t l y m e a s u r i n g t h e h e a t s o f m i x i n g f o r two p o l y m e r s i s w e l l known (35) , b u t i n d i r e c t r o u t e s w h i c h measure t h e h e a t o f d i l u t i o n (36.37) s u g g e s t t h a t B f o r t h e PPO/PS s y s t e m i s -4 t o -5 c a l / c c a t 35 ° C . Gas s o r p t i o n e x p e r i m e n t s (38) a r e a l s o c o n s i s t e n t w i t h B v a l u e s i n t h i s range. Our measured B v a l u e f o r i - P S / l % P E C i s g e n e r a l l y more e x o t h e r m i c t h a n t h e e s t i m a t e o b t a i n e d by Maconn a c h i e , e t a l . (39) f r o m n e u t r o n s c a t t e r i n g i n d i l u t e d a t a c t i c p o l y s t y r e n e / d e u t e r a t e d PPO s y s t e m s . They o b t a i n an e q u a t i o n , X = 0.121 - 77.9/T w h i c h c a n be u s e d w i t h E q u a t i o n 7 t o o b t a i n B = -0.3 c a l / c c a t 505 °K. The x i n E q u a t i o n 8 c o n t a i n s an e n t r o p i c c o n t r i b u t i o n w h i c h c a n be e v a l u a t e d from t h e temperature dependency ( 2 7 ) . D o i n g so, a l l o w s one t o e v a l u a t e t h e p u r e l y e n t h a l p i c p o r t i o n and t o o b t a i n B = -1.5 cal/cc.

(8)

G i v e n t h e v a r i o u s e x p e r i m e n t a l and t h e o r e t i c a l d i f f i c u l t i e s a s s o c i a t e d with measuring B or x f o r t h i s system, o u r v a l u e seems r e a s o n a b l e ; however, i t i s i m p o r t a n t t o n o t e t h a t we have measured B f o r b l e n d s c o n t a i n i n g i - P S n o t PS. I n v e s t i g a t o r s o f o t h e r b l e n d s y s t e m s (4042) have c o n s i s t e n t l y shown t h a t i s o t a c t i c and s y n d i o t a c t i c b l e n d components i n t e r a c t l e s s e x o t h e r m i c a l l y t h a n t h e i r a t a c t i c c o u n t e r p a r t s , a s i t u a t i o n which can l e a d t o the i m m i c i b i l i t y of polymers w i t h r e g u l a r t a c t i c i t y . On t h i s b a s i s , we c o u l d e x p e c t o u r B v a l u e s f o r i-PS/PPO b l e n d s t o be somewhat l e s s e x o t h e r m i c t h a n v a l u e s obt a i n e d f o r PS/PPO b l e n d s . S i n c e o n l y f o u r c o p o l y m e r c o m p o s i t i o n s were s t u d i e d and p a r t i c u l a r l y s i n c e t h e maximum t r i m e t h y l comonomer c o n t e n t a v a i l a b l e was o n l y 20%, i t i s d i f f i c u l t t o p r e c i s e l y determine the t h r e e b i n a r y i n t e r a c t i o n p a r a m e t e r s , s u g g e s t e d by t h e " c o p o l y m e r model", E q u a t i o n s 1 and 2, from t h e o b s e r v e d v a r i a t i o n o f B w i t h t r i m e t h y l comonomer c o n t e n t i n t h e PEC, F i g u r e 8. I t i s none t h e l e s s i n t e r e s t i n g , however, t o q u a l i t a t i v e l y a s s e s s t h e


4.

PADUNCHEWIT ET AL.


m a g n i t u d e s and s i g n s o f t h e i n t e r a c t i o n p a r a m e t e r s . Bec a u s e B f o r i - P S / P E C i s n e g a t i v e and becomes i n c r e a s i n g l y n e g a t i v e as t h e t r i m e t h y l comonomer c o n t e n t i n t h e c o p o l y m e r i n c r e a s e s from z e r o , we c a n c o n c l u d e t h a t B i 3 f o r t h e i n t e r a c t i o n between t h e t r i m e t h y l comonomer and t h e i - P S r e p e a t u n i t i s more e x o t h e r m i c t h a n t h a t between t h e d i m e t h y l comonomer and i - P S , B 2 3 . W h i l e somewhat l e s s c e r t a i n , t h e downward c o n c a v i t y o f t h e c u r v e i n Figure 8 a l s o suggests that the s e l f - i n t e r a c t i o n , B i 2 , between t h e t r i m e t h y l and t h e d i m e t h y l comonomers i n PEC, i s a l s o negative or exothermic. The o b s e r v a t i o n t h a t B i 3 i s more e x o t h e r m i c t h a n B23 i s n o t s u r p r i s i n g when one c o n s i d e r s t h e f a c t t h a t b l e n d s of t e t r a m e t h y l b i s p h e n o l - A p o l y c a r b o n a t e w i t h p o l y s t y r e n e are m i s c i b l e while blends o f bisphenol-A polycarbonate w i t h p o l y s t y r e n e a r e i m m i s c i b l e (43 ) . A p p a r e n t l y , subs t i t u t i o n o f m e t h y l g r o u p s on t h e a r o m a t i c r i n g s i n t h e backbones of these m a t e r i a l s enhances m i s c i b i l i t y w i t h the s t y r e n e r e p e a t u n i t . The o b s e r v a t i o n t h a t B i 2 i s a l s o exothermic i s q u i t e s u r p r i s i n g , c o n s i d e r i n g the s i m i l a r i t y o f t h e t r i m e t h y l and d i m e t h y l e t h e r u n i t s . U s i n g r e g u l a r s o l u t i o n a p p r o x i m a t i o n s , one c o u l d r e a s o n a b l y e x p e c t t h e s e s i m i l a r m a t e r i a l s t o mix e n d o t h e r m i c a l l y , b u t t h e n e g a t i v e B i 2 s u g g e s t s t h e y do n o t . S t u d i e s o f o t h e r b l e n d s y s t e m s have o b s e r v e d t h a t c l o u d t e m p e r a t u r e s , a s s o c i a t e d w i t h t h e o n s e t o f immisc i b i l i t y on h e a t i n g , g e n e r a l l y i n c r e a s e as t h e i n t e r a c t i o n between b l e n d components becomes i n c r e a s i n g l y e x o t h e r m i c (44-46) . The r e s u l t s o f F i g u r e 8 m i g h t l o g i c a l l y l e a d one t o e x p e c t i - P S / P E C b l e n d s t o show h i g h e r c l o u d t e m p e r a t u r e s t h a n i-PS/PPO b l e n d s . T h i s poss i b i l i t y , w h i c h was a p a r t i a l r e a s o n f o r t h e r e s e a r c h r e p o r t e d h e r e , was examined by h e a t i n g b l e n d s a t a p p r o x i m a t e l y 10 ° C / m i n . i n a s i m p l e c l o u d p o i n t a p p a r a t u s , d e s c r i b e d p r e v i o u s l y (47) . No c l o u d p o i n t s i n any o f t h e b l e n d s were o b s e r v e d a t t e m p e r a t u r e s up t o 380 ° C , a t w h i c h p o i n t d e c o m p o s i t i o n became s e v e r e . These r e s u l t s c o n t r a s t w i t h r e p o r t s from t h e f i e l d which suggested t h a t PEC c o n t a i n i n g b l e n d s c o u l d be molded, w i t h o u t delaminat i o n (possibly a s s o c i a t e d with multiphase formation), at h i g h e r t e m p e r a t u r e s t h a n PPO c o n t a i n i n g b l e n d s (48) . One p o s s i b l e r e a s o n f o r t h e d i s c r e p a n c y between l a b o r a t o r y and f i e l d t e s t s f o r c l o u d p o i n t s i s t h e r a t h e r low m o l e c u l a r w e i g h t s o f t h e components i n t h e l a b o r a t o r y blends. By a n a l o g y w i t h o t h e r s y s t e m s (49) . c l o u d temp e r a t u r e s g e n e r a l l y r i s e as the m o l e c u l a r weights o f t h e components a r e r e d u c e d . Acknowledgments The a u t h o r s g r a t e f u l l y a c k n o w l e d g e an u n r e s t r i c t e d g r a n t by B o r g - W a r n e r C h e m i c a l s , I n c . f o r p a r t i a l s u p p o r t of t h i s r e s e a r c h .


97

98


Legend

of

Symbol

Symbols Typical

Units

B

J/m ,

Bi j

J/m ,

AHmix

J, c a l J/gmole, cal/gmole J/m , cal/cm

AH2u

T T«°

cal/cc

3

cal/cc

3

AHf

L R

3

3

m, cm J/gmole°K, cal/gmole° K °K °K

TB

°K °K

Tg

°K

Tc

V

Description

3

V2u

Vi

m , cc m /gmole, m /gmole, 3

3

cc/gmole cc/gmole

P O

2

e

J/m ,

4>i 4>iA Wi

cal/cm

2

B i n a r y i n t e r a c t i o n energy d e n s i t y between p o l y m e r repeat u n i t s I n t e r a c t i o n energy d e n s i t y between u n i t s i and j Enthalpy of mixing E n t h a l p y o f f u s i o n p e r mole pure c r y s t a l Enthalpy of f u s i o n per u n i t volume o f c r y s t a l Lamella thickness Gas C o n s t a n t Absolute temperature melting temperature of perfect crystal C r y s t a l l i z a t i o n temperature Observed m e l t i n g temperature G l a s s t r a n s i t i o n temperature System volume M o l a r volume p u r e c r y s t a l 2 M o l a r volume o f component 1,either solvent molecule or polymer r e p e a t u n i t Hoffman-Weeks p a r a m e t e r Surface f r e e energy of c r y s t a l end f a c e Volume f r a c t i o n i i n b l e n d Volume f r a c t i o n i i n polymer A Mass f r a c t i o n i i n b l e n d

Literature Cited 1. 2. 3. 4. 5. 6. 7.

Hay, A. S.; Polym. Eng. S c i . , 1976, 16(1), 1. MacKnight, W. J . ; Karasz, F. E.; Fried, J. R. In "Polymer Blends, Vol. I," Paul, D. R.; Newman, S., Eds.; Academic Press, New York, 1978, Chapter 5. Paul, D. R.; Barlow, J. W.; J. Macromol. S c i . Rev. Macromol. Chem., 1980, C18, 109. Plans, J . ; MacKnight, W. J . ; Karasz, F. E.; Macromolecules. 1984, 7(4), 810. Prest, W. M.; Porter, R. S.; J. Polym. Sci., 1972, A2(10), 1639. Fried, J . R.;Karasz, F. E.; MacKnight, W. J . ; Polym. Eng. Sci., 1979, 19, 519. Runt, J. P.; Macromolecules, 1981, 14(2), 420.


4. PADUNCHEWITETAL. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.


A. F. Yee, A. F.; Engineering Science, 1977, 17, 213. Baer, E.; Wellinghoff, S.;Polymer Preparation, 1977, 18, 836. Warren, R. I.; Polym. Eng. Sci., 1985, 25, 477. Paul, D. R.; Barlow, J . W.; Polymer, 1984, 25, 487. Kambour, R. P.; Bendler, J . T.; Bopp, R. C.; Macromolecules, 1983, 16, 753. Ten Brinke, G.; Karasz, F. E.; MacKnight, W. J . ; Macromolecules, 1983, 16, 1827. Barnum, R. S.; Goh, S. H.; Paul, D. R.; Barlow, J. W.; J. A p p l . Polym. Sci., 1981, 26, 3917. Keitz, J . D.; Barlow, J. W.; Paul, D. R.; J. Appl. Polym. Sci., 1984, 29, 3131. Alexandrovich, P.; Karasz, F. E.; MacKnight, W. J.; Polymer, 1977, 18, 1022. Pfennig, J . L. G.; Keskkula, H.; Barlow, J. W.; Paul, D. R.; Macromolecules, 1985, 18, 1937. Plans, J . ; MacKnight, W. J . ; Karasz, F. E.; Macro molecules, 1984, 17(4), 810. H o r i k i r i , S.; J. Polym. Sci., 1972, A2(10), 1167. Butte, W. Α.; Price, C. C.; Hughes, R. E.; J . Polym. Sci., 1962, 61, 528. Hoffman, J . D.; Weeks, J. D.; J . Res. Nat. Bur. Stds., 1962, 66A(1), 13. Overbergh, N.; Berghmans, H.; Smets, G.; J . Polym. Sci., 1972, C(38), 237. Overbergh, N.; Berghmans, H.; Reynaers, H.; J . Polym. Sci.:Polym. Phys. Ed., 1976, 14, 1177. Lemstra, P. J . ; Kooistra, T.; Challa, G.; J. Polym. Sci., 1972, A2(10), 823. Fox, T. G.; B u l l . Am. Phys. Soc., 1956, 1, 123. O l a b i s i , O.; Robeson, L. M.; Shaw, M. T.; "PolymerPolymer M i s c i b i l i t y " , Academic Press, New York, N.Y., 1979. Flory, P. J . ; "Principles of Polymer Chemistry", Cornell University Press, Ithaca, New York, 1953, Chapt. 8. Wunderlich Β., "Macromolecular Physics, Vol. 3 Crys t a l Melting", Academic, New York, 1980. Barnum, R. S.; Barlow, J. W.; Paul, D. R.; J. A p p l . Polym. Sci., 1982, 27, 4065. Schulken, R. M.; Boy, R. E.; Cox, R. H.; J. Polym. Sci., Pt. C, 1964, 6, 17. Lenz, R. W.; Martin, E.; Schuler, A. N.; J. Polym. S c i . : Polym. Chem. Ed., 1973, 11, 2265. Lenz, R. W.; Schuler, A. N.; J . Polym. S c i . : Polym. Symp., 1978, 63, 343. Lenz, R. W.; Go, S.; J. Polym. S c i . : Polym. Chem. Ed., 1973, 11, 2927; 1974, 12, 1. Thiele, M. H.; Mandelkern, L.; J. Polym. Sci., 1970, A2(8), 957. Robeson, L. M. In "Polymer Compatibility and Incom p a t i b i l i t y : P r i n c i p l e s and Practice, V o l . 2"; Solc,


99

100

36. 37. 38.

39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49.


K., Ed.; M.M.I. Press Symposium Series; Harwood Academic Press: New York, 1982; p.177. Karasz, F. E.; MacKnight, W. J.; Pure Appl. Chem., 1980,

52, 409.

Weeks, N. E.; Karasz, F. E.; MacKnight, W. J.; J. Appl. Phys., 1977, 4 8 ( 1 0 ) , 4068. Maeda, Y; Paul, D. R.; Polymer, 1985, 26, 2055. Maconnachie, A.; Kambour, R. P.; White, D. M.; Rostami, S.; Walsh, D. J.; Macromolecules, 1984, 17, 2645.

Goh, S. H.; Paul, D. R.; Barlow, J. W.; Polym. Eng. Sci., 1982, 22, 34. Roerdink, E.; Challa, G; Polymer, 1980, 2 1 , 1161. Schurer, J. W.; de Boer, A.; Challa, G.; Polymer, 1975,

16, 201.

Fernandes, A. C.; Barlow, J. W.; Paul, D. R.; Polymer, 1986, 27, 1788. Bernstein, R. E.; D. C. Wahrmund, D. C.; Barlow, J. W.; Paul, D. R.; Polym. Eng. Sci., 1978, 1 8 ( 1 6 ) , 1225.

Barnum, R. S.; Goh, S. H.; Barlow, J. W.; Paul, D. R.; J. Polym. Sci. Polym. Lett. Ed., 1985, 23, 395. Pearce, E. M.; Kwei, T. K.; Min, B. Y.; J. Macromol. Sci. Chem., 1984, 2 1 , 1181. Bernstein, R. E.; Cruz, C. A.; Paul, D. R.; Barlow, J. W.; Macromolecules, 1977, 10, 681. Pavelich, W. A.; private communication. Kwei, T. K.; Wang, T. T.; Chapt. 4 in Ref. [2].

RECEIVED April 27, 1989


Multiphase Polymers: Blends and Ionomers - American Chemical

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