Blends of Polystyrene with Phenylene Oxide Copolymers - American

Chapter 4

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

Downloaded via TUFTS UNIV on July 1, 2018 at 00:02:53 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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


Blends of Polystyrene with Phenylene Oxide Copolymers - American

Recommend Documents