Rubber-Modified Polymers. Location of Block Copolymers in Two

22 Rubber-Modified Polymers. Location of Block Copolymers in Two-Phase Materials Downloaded by STONY BROOK UNIV SUNY on December 19, 2016 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0142.ch022

G. RIESS and Y. JOLIVET Ecole Supérieure de Chimie, 3 rue A. Werner, 68093 Mulhouse Cédex, France

In heterophase polymeric materials, outstanding mechanical properties are obtainable only by regulating dispersed phase particle size and adhesion between phases, usually by adding block or graft copolymers. The emulsifying effect of block and graft copolymers was demonstrated for the PS-PI system. Since characteristics of the blend polymers (e.g., molecular weight and composition) determine whether the copolymer is situated in the continuous phase, in the dispersed phase, or at the interface, we tried to establish the conditions for the last. Different techniques for locating a PS-PI block copolymer were studied: use of a copolymer containing a fluorescent group, x-ray scanning microanalysis, and quantitative analysis of the gel formed after crosslinking the elastomeric phase by γ-irradiation. For these PS-PI blends, the amount of copolymer at the interface correlated with impact resistance.

I

n h e t e r o p h a s e p o l y m e r i c m a t e r i a l s s u c h as r u b b e r m o d i f i e d p o l y s t y r e n e o r a c r y l o n i t r i l e - b u t a d i e n e - s t y r e n e ( A B S ) resins, o u t s t a n d i n g m e c h a n i c a l p r o p erties c a n b e o b t a i n e d o n l y b y r e g u l a t i n g t h e d i s p e r s e d r u b b e r p a r t i c l e size a n d b y achieving adhesion between the rubber a n d the resin phase. T h i s c a n usually b e a c h i e v e d b y a d d i n g b l o c k o r g r a f t c o p o l y m e r s , o r b y t h e i r f o r m a t i o n in situ, as i n i n d u s t r y . I n this p a p e r w e report o n interfacial adhesion a n d e m u l s i f y i n g properties in relation to locating block copolymers i n two-phase materials. T h e polystyrene ( P S ) - p o l y i s o p r e n e ( P I ) system w a s studied i n order to locate P S - P I block c o p o l y m e r s a n d to define the c o n d i t i o n s u n d e r w h i c h these c o p o l y m e r s are s i t u a t e d at t h e r e s i n - r u b b e r i n t e r f a c e . Emuhifying

Effect

Oil-in-Oil E m u l s i o n s . W e demonstrated previously that block a n d graft c o p o l y m e r s a c t as o i l - i n - o i l e m u l s i f i e r s f o r t h e c o r r e s p o n d i n g i n c o m p a t i b l e h o m o p o l y m e r s , e.g., P S a n d P I (1, 2, 3). T o p r o v e t h a t t h i s e m u l s i f y i n g effect o f A B b l o c k a n d g r a f t c o p o l y m e r s is g e n e r a l , w e s t u d i e d t h e s i m p l e r c a s e o f two nonmiscible liquids a a n d b w h i c h d o not have the inconvenient high v i s c o s i t y t y p i c a l o f p o l y m e r i c s y s t e m s . F u r t h e r m o r e , a is a g o o d s o l v e n t f o r 243

Platzer; Copolymers, Polyblends, and Composites Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

244

COPOLYMERS,

POLYBLENDS,

AND

COMPOSITES

Downloaded by STONY BROOK UNIV SUNY on December 19, 2016 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0142.ch022

c o m p o n e n t A of the c o p o l y m e r a n d a nonsolvent for c o m p o n e n t B ; conversely, b is a s o l v e n t f o r c o m p o n e n t Β a n d a n o n s o l v e n t f o r c o m p o n e n t A . F o r P S - P I b l o c k c o p o l y m e r s , these r e q u i r e m e n t s are m e t b y t h e s y s t e m d i m e t h y l f o r m a m i d e ( D M F ) - h è x a n e as n o n m i s c i b l e s o l v e n t s ( 4 , 5 ) . T h e e m u l s i f y i n g effect of a c o p o l y m e r c a n b e c h a r a c t e r i z e d b y d e t e r m i n i n g t h e t y p e of e m u l s i o n ( D M F i n h e x a n e o r h e x a n e i n D M F ) , its s t a b i l i t y , its viscosity, a n d the particle size of the dispersed phase. T h e s e characteristics of o i l - i n - o i l e m u l s i o n s o b t a i n e d w i t h P S - P I b l o c k c o p o l y m e r s w e r e s t u d i e d as f u n c t i o n s of s o l v e n t v o l u m e r a t i o , m o l e c u l a r w e i g h t , c o m p o s i t i o n , a n d s t r u c t u r e of t h e c o p o l y m e r ( 5 ) . A l t h o u g h B a n c r o f t ' s r u l e w a s e s t a b l i s h e d f o r c o n v e n t i o n a l o i l - w a t e r e m u l s i o n s , i t a p p e a r s t o a p p l y also t o o i l - i n - o i l e m u l s i o n s — t h e c o n t i n u o u s p h a s e of t h e e m u l s i o n is p r e f e r e n t i a l l y f o r m e d b y t h e s o l v e n t h a v i n g t h e b e s t s o l u b i l i t y f o r t h e e m u l s i f i e r (6, 7). T h u s , b l o c k or g r a f t c o p o l y m e r s c a n b e p r e p a r e d g i v i n g h e x a n e / D M F , D M F / h e x a n e , or b o t h t y p e s o f e m u l s i o n s . F o r h i g h molecular w e i g h t block copolymers, the e m u l s i f y i n g efficiency seems to b e g r e a t e r f o r t w o b l o c k c o p o l y m e r s t h a n f o r t h r e e , a n d e f f i c i e n c y is m a x i m u m w h e n t h e t w o b l o c k s , P S a n d P I , are of s i m i l a r m o l e c u l a r w e i g h t . U n d e r these c o n d i t i o n s , c o p o l y m e r s o l u b i l i t y is r e d u c e d , a n d m o s t of it is l o c a t e d at t h e i n t e r f a c e . F o r o t h e r c o m p o s i t i o n s , a n d e s p e c i a l l y f o r l o w m o l e c u l a r w e i g h t s , t h e c o p o l y m e r c a n f o r m m i c e l l e s i n e i t h e r s o l v e n t p h a s e , a n d its e m u l s i f y i n g e f f i c i e n c y is t h e r e b y g r e a t l y d e c r e a s e d . A b l o c k o r g r a f t c o p o l y m e r is e f f i c i e n t as e m u l s i f i e r i f it is s i t u a t e d m a i n l y at t h e i n t e r f a c e , i.e., t h e r e is n o preferential s o l u b i l i t y i n either phase. R e g u l a t i n g the m o l e c u l a r characteristics o f t h e c o p o l y m e r ( c o m p o s i t i o n , m o l e c u l a r w e i g h t , a n d s t r u c t u r e ) c a n alter its s o l u b i l i t y a n d t h e r e f o r e its e f f i c i e n c y . P S - P I b l o c k c o p o l y m e r s w i t h t h e l o w e s t a s s o c i a t i o n d e g r e e ( m i c e l l i z a t i o n ) , i n h e x a n e as w e l l as i n D M F , are m o s t e f f i c i e n t as o i l - i n - o i l e m u l s i f i e r s f o r t h e D M F - h e x a n e s y s t e m (8). E m u l s i f y i n g E f f e c t of C o p o l y m e r s i n t h e S o l i d S t a t e . T h e n e x t s t e p w a s to a s c e r t a i n i f t h e findings f o r t w o n o n m i s c i b l e l i q u i d s are a p p l i c a b l e t o t w o i n c o m p a t i b l e p o l y m e r s s u c h as P S a n d P I , a n d i f a b l o c k c o p o l y m e r also f u n c t i o n s as a n e m u l s i f i e r . A r e l a t i v e l y s i m p l e m e t h o d of s t u d y i n g t h e d i s p e r s i o n d e g r e e f o r p o l y m e r s i n t h e s o l i d state is t o d e f i n e t h e l i m i t s w h e r e films m a d e b y s o l v e n t e v a p o r a t i o n of p o l y m e r m i x t u r e s pass f r o m h a z y to c l e a r . F i l m s o f a t w o - p h a s e s y s t e m m a y a p p e a r h a z y i f t h e a v e r a g e p a r t i c l e size of t h e d i s p e r s e d p h a s e is g r e a t e r t h a n 8 0 0 - 1 0 0 0 A , or r o u g h l y 1/5 t h e w a v e l e n g t h of v i s i b l e l i g h t ( λ / 5 ) , a n d also if t h e r e f r a c t i v e i n d e x e s of t h e t w o p o l y m e r s are d i f f e r e n t . T h e r e f o r e , i f t h e p o l y b l e n d film is c l e a r , t h e d i m e n s i o n s o f t h e d i s p e r s e d p h a s e are less t h a n 8 0 0 - 1 0 0 0 A , a n d o n l y b y electron microscopy can a two-phase system be distinguished from a compatible blend (9). So the e m u l s i f y i n g effect of a c o p o l y m e r f o r p o l y m e r s i n t h e s o l i d state is a p p a r e n t i f t h e c o p o l y m e r c a n transform a h a z y b l e n d into a clear one. T h e film p r e p a r a t i o n t e c h n i q u e has b e e n d e s c r i b e d e l s e w h e r e ( 3 ) . It s h o u l d b e n o t e d t h a t films are o b s e r v e d d i r e c t l y a n d b y p h a s e c o n t r a s t m i c r o s c o p y . T h u s , w e c a n c o m p a r e t h e e m u l s i f y i n g effect of d i f f e r e n t s t y r e n e - i s o p r e n e c o p o l y m e r s ( r a n d o m , b l o c k , a n d graft c o p o l y m e r s ) of the same o v e r a l l c o m position (40 w t % P S , 60 w t % P I ) a n d practically the same molecular weight (M - 5 0 , 0 0 0 ) i n a g i v e n P S - P I b l e n d , w h e r e M of P S is 4 5 , 0 0 0 a n d M of P I is 2 5 , 0 0 0 . T h e a p p e a r a n c e o f t h e films o b t a i n e d w i t h d i f f e r e n t b l e n d c o m p o s i t i o n s is d e p i c t e d i n F i g u r e 1. H a z y o r o p a q u e areas are s t r i p e d . F r o m F i g u r e 1, it a p p e a r s t h a t r a n d o m c o p o l y m e r s a l w a y s c a u s e h a z y films w h i c h m e a n s n

n


n


/

\

PS

PI

Figure 1.

[

I hazy

films

I

I clear

films

Emulsifying effect of PS-PI copolymers

that this t y p e c o p o l y m e r has n o e m u l s i f y i n g effect. ings f o r o i l - o i l emulsions.

T h i s agrees w i t h t h e

find

O n the other h a n d , t h e fact that b l o c k a n d graft

c o p o l y m e r s at some p o l y b l e n d compositions d o give transparent

films

proves

t h a t t h e s e c o p o l y m e r s a c t as o i l - i n - o i l e m u l s i f i e r s i n t h e s o l i d state, a n d t h a t b l o c k c o p o l y m e r s are generally m o r e efficient t h a n graft c o p o l y m e r s . On

t h e basis

copolymers PMM)

of a systematic

in PS-PI

s t u d y of t h e e m u l s i f y i n g effect of b l o c k

a n d in polystyrene-poly(methyl

methacrylate)

(PS~

p o l y b l e n d s ( 3 ) , it w a s possible to represent

schematically the appear

a n c e o f t h e films f o r d i f f e r e n t b l e n d c o m p o s i t i o n s

as f u n c t i o n s o f m o l e c u l a r

w e i g h t a n d c o m p o s i t i o n o f t h e b l o c k c o p o l y m e r ( C o p ) , as w e l l as o f m o l e c u l a r weight of the h o m o p o l y m e r s

(see F i g u r e 2 ) . T h u s i n a p o l y b l e n d c o n t a i n i n g

PS a n d P I of practically the same molecular w e i g h t

(M

1

^

M ) , t h e best 2

e m u l s i f y i n g properties are obtained w i t h a t w o block c o p o l y m e r whose

com

p o s i t i o n is a b o u t 5 0 : 5 0 a n d w h o s e m o l e c u l a r w e i g h t is h i g h e r t h a n t h o s e o f t h e homopolymers

(Μ

Ά

> M

1

— M >). L

I n fact the area w h e r e transparent

Cop(M3)

PS(Mj)

M

3

Cop ( M 3 )

PI(M ) 2

> Mj - M

2

Figure 2.

PS(Mj)

M

3

Pl(M ) 2

< Mj - M

2

Emulsifying effect of block copolymers PS-PI


films

246

COPOLYMERS,


Cop

POLYBLENDS,

AND

COMPOSITES

(M ) 3

PS(M,)

P1(M ) 2

Figure 3.

Emubifying

effect of block copolymers PS-PI

are o b t a i n e d is s m a l l w h e n Μ < M — M . B o t h P I / P S a n d P S / P I e m u l s i o n s are o b t a i n e d , w h i c h means that the c o p o l y m e r has n o p r e f e r e n t i a l s o l u b i l i t y i n either phase. λ

2

1

A g i v e n C o p is t h e r e f o r e a b e t t e r e m u l s i f i e r i n a p o l y b l e n d i f s m a l l e r a m o u n t s are r e q u i r e d to o b t a i n t r a n s p a r e n t films, i.e., s m a l l p a r t i c l e size of t h e d i s p e r s e d phase. I n order to c o m p a r e the e m u l s i f y i n g efficiencies of different p o l y b l e n d s , it is c o n v e n i e n t t o d e f i n e t h e r a t i o of t h e m o l e c u l a r w e i g h t s of t h e h o m o p o l y m e r a n d t h e c o r r e s p o n d i n g c o m p o n e n t o f t h e b l o c k c o p o l y m e r as follows :

α =

M of P S homopolymer

(1)

zzz

M of P S component of copolymer _ M of P I homopolymer

(2)

M of P I component of copolymer w h e n ΑΪ· > M , ^ Λ

β >

1.

M.,a

1 and β

1 >

and 1.

It

s h o u l d b e n o t e d , h o w e v e r , t h a t t h i s d i s t i n c t i o n is o n l y s e m i q u a n t i t a t i v e b e c a u s e t h e l i m i t s b e t w e e n h a z y a n d c l e a r areas c o r r e s p o n d t o a g i v e n b u t p a r t i c l e size of the d i s p e r s e d phase.

arbitrary

N e v e r t h e l e s s , i t is i m p o r t a n t t o n o t e t h a t

t h e e m u l s i f y i n g e f f e c t of C o p d e p e n d s o n t h e m o l e c u l a r w e i g h t o f t h e

different

species i n the p o l y b l e n d . F u r t h e r m o r e , the s y m m e t r i c a l e v o l u t i o n of the e m u l s i f y i n g effect i f M

1

— M

w h o s e c o m p o s i t i o n is ^

2

i n the presence of a b a l a n c e d c o p o l y m e r

(copolymer

5 0 : 5 0 ) , w h i c h m e a n s t h a t a — β, i n d i c a t e s t h a t t h e r e

is n o p r e f e r e n t i a l s o l u b i l i t y i n e i t h e r

phase.

O n the other h a n d , o n l y a s m a l l a m o u n t of P I c a n be e m u l s i f i e d b y c h a n g i n g t h e m o l e c u l a r w e i g h t of o n e o f t h e h o m o p o l y m e r s , e.g., I n t h i s case, a

1.

M

1

1 ; e m u l s i f i c a t i o n o f P S is b e t t e r t h a n t h a t o f P I w h e n P S f o r m s t h e c o n t i n u o u s phase of the b l e n d . I n a s m u c h as t h e e m u l s i f y i n g e f f e c t w a s s t u d i e d s e m i q u a n t i t a t i v e l y b y a g i v e n film t e c h n i q u e , t h e b o u n d a r i e s b e t w e e n areas m a y n o t b e as s h a r p as i n F i g u r e 5 . A r e a size m a y d e p e n d o n p o l y b l e n d t y p e a n d o n t h e t e c h n i q u e u s e d f o r b l e n d i n g t h e d i f f e r e n t p o l y m e r s . A l t h o u g h s t u d y o f t h e e m u l s i f y i n g effect of b l o c k c o p o l y m e r s i n t h e P S - P I a n d P S - P M M s y s t e m s h a s l e d q u a l i t a t i v e l y to s i m i l a r c o n c l u s i o n s , t h e areas d e f i n e d i n F i g u r e 5 c a n n o t b e s u p e r i m p o s e d exactly f o r these t w o systems. W i t h t h e film t e c h n i q u e , w h i c h seems to b e t h e m o s t r e p r o d u c i b l e , a s h i f t o f t h e d i f f e r e n t b o u n d a r i e s c a n also b e o b s e r v e d w h e n v a r i o u s s o l v e n t s a r e u s e d f o r film p r e p a r a t i o n , e s p e c i a l l y p r e f e r e n t i a l s o l v e n t s f o r e i t h e r p o l y m e r (10). It c a n b e c o n c l u d e d t h a t t h e b e s t e m u l s i f y i n g p r o p e r t i e s a r e o b t a i n e d w i t h t w o - b l o c k c o p o l y m e r s , a n d that these are superior to three-block c o p o l y m e r s a n d t o g r a f t c o p o l y m e r s . F u r t h e r m o r e , a t w o - b l o c k c o p o l y m e r is m o s t efficient if i t s c o m p o s i t i o n is a b o u t 5 0 : 5 0 a n d i f its m o l e c u l a r w e i g h t is h i g h e r t h a n those of t h e c o r r e s p o n d i n g h o m o p o l y m e r s . T h e s e results agree w i t h those o b t a i n e d r e c e n t l y b y S k o u l i o s a n d c o - w o r k e r s (11). A n e x p l a n a t i o n of these p h e n o m e n a b y M e i e r is b a s e d o n t h e d i f f e r e n t p r e c i p i t a t i o n rates o f t h e v a r i o u s polymers d u r i n g solvent evaporation (12). Mechanical

Properties

of Two-Phase

Polymer

Blends

Study of impact-resistant p o l y m e r blends has elucidated the fundamental role of block a n d graft copolymers ( C o p ) i n a t y p i c a l system like P S - P I - C o p (I, 2) a n d also i n t h e case o f t w o - p h a s e m a t e r i a l s f o r m e d b y t w o resins Table I.

Impact Resistance i n B i n a r y P S - P I B l e n d s

PS M

w

91,000 420,000

PI In Blend, %

87.5 87.5

M

w

50,000 50,000

In Blend, %

R

12.5 12.5

0.6 2.0

a

Impact resistance, R, was determined by Charpy method on compression-molded, unnotched, 60 X10 X I . 7 m m samples of the polyblend. Blending was achieved by precipitating with methanol dilute solutions of the polymers i n benzene or toluene. Values of R are only relative. a


22.

RIESS A N D JOLI V E T

Table II.

Rubber-Modified

I m p a c t R e s i s t a n c e , R, i n T e r n a r y P S - P I - C o p B l e n d s

PS

PI*

a

In Blend, %

Mw

91,000 123,000 420,000

249

Polymers

67.5 67.5 67.5

In Blend, %

Mw

50,000 270,000 50,000

16.25 16.25 16.25

Cop , %

R

16.25 16.25 16.25

1.2 2.0 2.6

b

Homopolymers were prepared by anionic polymerization; M„./M„ ^ 1.1. _ Two-block copolymer P S - P I was prepared by anionic polymerization; M„ 41 wt % P I . a


b

=

146,000;

[e.g., p o l y s t y r e n e - p o l y ( m e t h y l m e t h a c r y l a t e ) - C o p o r p o l y s t y r e n e - p o l y ( v i n y l c h l o r i d e ) - C o p ] i n w h i c h o n e o f t h e p h a s e s c a n b e p l a s t i c i z e d s e l e c t i v e l y (13, 14). T h e d e g r e e o f d i s p e r s i o n o f o n e p h a s e i n t h e o t h e r , e v e n i n t h e s o l i d state, c a n b e r e g u l a t e d b y C o p . S o C o p acts f o r t h e c o r r e s p o n d i n g h o m o p o l y m e r s as a n oil-in-oil emulsifier, a n d t h e dispersion degree depends o n C o p concentration, s t r u c t u r e , c o m p o s i t i o n , a n d m o l e c u l a r w e i g h t (1, 2 ) . C o n c e r n i n g t h e m e c h a n i c a l properties a n d especially t h e i m p a c t resistance of s u c h b l e n d s , w e h a v e t o c o n s i d e r t h e n a t u r e o f t h e c o n t i n u o u s p h a s e , t h e nature a n d amount of t h e dispersed rubber phase, a n d t h e nature o f t h e interface. N a t u r e o f t h e C o n t i n u o u s P h a s e . I m p a c t resistance is a f u n c t i o n of t h e intrinsic properties of the p o l y m e r f o r m i n g the continuous phase, especially its m o l e c u l a r w e i g h t (1, 2 ) . T h i s is s u m m a r i z e d i n T a b l e I f o r b i n a r y P S - P I b l e n d s a n d i n T a b l e I I f o r t e r n a r y P S - P I - C o p b l e n d s . T a b l e I s h o w s that, f o r a g i v e n b l e n d , increase i n m o l e c u l a r w e i g h t of P S f o r m i n g t h e continuous phase of t h e m a t e r i a l i n c r e a s e s i m p a c t r e s i s t a n c e . T h e s a m e o b s e r v a t i o n c a n b e m a d e from Table II for a ternary P S - P I - C o p blend. N a t u r e a n d A m o u n t of t h e D i s p e r s e d R u b b e r P h a s e . T h e effect of t h e nature of t h e dispersed rubber phase became apparent d u r i n g o u r w o r k o n s e l e c t i v e p l a s t i c i z a t i o n o f s y s t e m s c o n t a i n i n g t w o resins A a n d B , a c o r r e s p o n d i n g A B C o p , a n d a s e l e c t i v e p l a s t i c i z e r o f p o l y m e r A o r Β (13, 14) w h e r e A w a s polystyrene ( P S ) a n d Β was poly (methyl methacrylate) ( P M M ) or poly (vinyl c h l o r i d e ) ( P V C ) . S e l e c t i v e p l a s t i c i z a t i o n is a n e w m e t h o d o f o b t a i n i n g r e s i n e l a s t o m e r i c s y s t e m s w h i c h h a v e t h e a d v a n t a g e t h a t t h e p h y s i c a l p r o p e r t i e s (e.g., mechanical properties a n d refractive index) of the rubbery phase c a n b e v a r i e d b y the nature a n d a m o u n t o f the plasticizer. F o r s u c h systems, i m p a c t resistance is m a x i m u m w h e n t h e e n e r g y a b s o r p t i o n c a p a c i t y o f t h e r u b b e r y p h a s e is m a x i m u m (e.g., f o r a g i v e n a m o u n t o f p l a s t i c i z e r w i t h r e s p e c t t o t h e d i s p e r s e d phase). I m p a c t resistance f o r a system c o n t a i n i n g 5 0 % P M M , 2 5 % P S , a n d 2 5 % b l o c k c o p o l y m e r P S - P M M ( 4 2 % P S , M = 1 2 0 , 0 0 0 ) is p l o t t e d i n F i g u r e 6. P S , t h e dispersed phase of the system, w a s plasticized selectively w i t h increas i n g a m o u n t s o f d i i s o b u t y l a z e l a t e . I m p a c t r e s i s t a n c e is m a x i m u m w h e n t h e a m o u n t o f p l a s t i c i z e r is 5 0 % w i t h r e s p e c t t o t h e d i s p e r s e d P S p h a s e . n

N a t u r e of t h e Interface. T h e most i m p o r t a n t aspect is t h e nature of t h e m a t r i x - d i s p e r s e d phase interface w h i c h determines t h e a d h e s i o n b e t w e e n these t w o phases. T h e a n c h o r i n g effect b e t w e e n t w o phases w i t h a b l o c k c o p o l y m e r l o c a t e d at t h e interface d e p e n d s essentially o n t h e a m o u n t o f C o p i n t h e b l e n d , the a m o u n t o f elastomer, a n d t h e particle size o f t h e dispersed phase. P a r t i c l e size, i n t u r n , d e p e n d s o n t h e m o l e c u l a r c h a r a c t e r i s t i c s o f h o m o p o l y m e r a n d C o p , as w e l l as o n t h e c o m p o s i t i o n o f t h e b l e n d . I n o r d e r t o t a k e i n t o a c c o u n t t h e s e


250

COPOLYMERS,

POLYBLENDS,

A N D COMPOSITES


1 +

0,5.

0,2(

25

50

75

% plasticizer Figure 6.

Impact resistance as a function of the amount of plasticizer in a ternary blend PS-PMM-Cop(PS-PMM) with PS selectively plasticized

50% PMM, M n = 40,000; 25% PS, M n = 38,000; and 25% Cop (42 wt % PS, M

n

= 120,000)

d i f f e r e n t f a c t o r s , t h e o c c u p a t i o n d e n s i t y , D , is g i v e n b y :

^

_ number of AB links of the Cop in 1 cm polyblend total surface of rubber particles in 1 cm polyblend 3

^

3

D c a n b e c a l c u l a t e d w h e n t h e p o l y b l e n d c o m p o s i t i o n is k n o w n a n d t h e n u m b e r a n d the radius of the rubber particles are determined f r o m m i c r o t o m e d sections. A study of various P S - P M M polyblends i n w h i c h the dispersed P S phase was selectively p l a s t i c i z e d demonstrated that t h e i m p a c t resistance, R , varies i n t h e s a m e w a y as t h e o c c u p a t i o n d e n s i t y , D (see T a b l e I I I ) . S i n c e t h e d i s p e r s e d rubber particles are practically spherical, a simple relationship f o r R a n d D i s : R ~ Ζ) = Κ

+

(4)

ax y w h e r e χ is t h e a m o u n t o f C o p i n t h e b l e n d , y is t h e a m o u n t o f e l a s t o m e r i n t h e b l e n d ( p l a s t i c i z e d P S ) , a is t h e p r o p o r t i o n o f r u b b e r s e q u e n c e i n t h e C o p , Κ is a c o n s t a n t , a n d r is t h e m e a n r a d i u s o f t h e p a r t i c l e s . I n t h e s p e c i a l case w h e n t h e a m o u n t s o f C o p a n d P S a r e t h e s a m e (x = y), this relationship b e c o m e s : R ~ D = K'r


(5)

22.

RiESS

A N D

JOLIVET

Table III.

Rubber-Modified

251

Polymers

Effect of B l e n d C o m p o s i t i o n o n Impact Resistance a n d O c c u p a t i o n D e n s i t y of P S - P M M P o l y b l e n d s "


Blend Variable

1

2

Blend composition, % PS PMM Cop Radius of dispersed par μ Occupation density, D X 10" 14 Impact resistance

0 100 0 0 0 1

86 7 1.1 0.29 0.8

7

3

4

5

β

14 72 14 1.7 0.43 1

20 60 20 3.3 0.84 2.6

25 50 25 2.4 0.60 1.5

34 32 34 1.7 0.45 0.7

° PS M . = 172,000; P M M M„. = 590,000; Cop M„ = 445,000, 48 w t % P S ; amount of plas ticizer (butoxyethyl s t é a r a t e ) with respect to the PS phase, 50%. u

I n d e e d as is s e e n i n T a b l e I I I , f o r t h i s s p e c i a l case t h e i m p a c t r e s i s t a n c e v a r i e s i n t h e s a m e w a y as t h e p a r t i c l e s i z e o f t h e d i s p e r s e d p h a s e . F u r t h e r m o r e , s i n c e r is a f u n c t i o n o f x, E q u a t i o n 4 c a n b e w r i t t e n a s : R ~ 1) = Κ

(6)

- — f(x) ax + y t

w h e r e Κ is m a x i m u m i f a l l t h e C o p is s i t u a t e d at t h e i n t e r f a c e . Location

of the Copolymer

in

Polyblends

I n h e t e r o p h a s e p o l y m e r i c m a t e r i a l s , a d h e s i o n b e t w e e n t h e t w o p h a s e s is a c h i e v e d o n l y i f C o p is s i t u a t e d at t h e i n t e r f a c e . T h e r e a r e d i f f e r e n t t e c h niques b y w h i c h the location of C o p i n a two-phase material can be determined. O n e m e t h o d is b a s e d o n d e t e r m i n i n g t h e r e f r a c t i v e i n d e x e s o f t h e t w o phases b y interference m i c r o s c o p y . H o w e v e r this t e c h n i q u e , w h i c h gives semiquantative information, c a n b e a p p l i e d only if the particles of t h e dispersed phase are n o t too small ( I , 2 ) . W e therefore p r e p a r e d b y anionic p o l y m e r i z a tion different copolymers of P S - P I c o n t a i n i n g a fluorescent g r o u p like styrene9-phenyl-10-anthracene (see S t r u c t u r e 7 f o r s t r u c t u r e o f f l u o r e s c e n t c o p o l y m e r s ) . I n s u c h a P S - P I b l e n d , t h e P I p h a s e c a n b e d e t e c t e d first b y p h a s e

CH PS

2

- CH PI


252

COPOLYMERS,

Table I V .

Blend 2

PI Dispersed Phase

+ +

PI Continuous Phase

+ +

PS Dispersed Phase

+

+ +

+ , blue fluorescence of the C o p in this phase;


A N D COMPOSITES

L o c a t i o n of B l o c k C o p o l y m e r ( C o p ) i n P S - P I Polyblends b y Fluorescence "

Blend 1 PS Continuous Phase

POLYBLENDS,

Location of Cop

PS phase not determined PI phase interface

+

no fluorescence.

c o n t r a s t m i c r o s c o p y . O n t h e s a m e s a m p l e , U V fluorescence m i c r o s c o p y w i l l t h e n r e v e a l t h e c o p o l y m e r i n t h e continuous phase, i n t h e d i s p e r s e d phase, or at t h e i n t e r f a c e . T h e l o c a t i o n o f t h e c o p o l y m e r w a s s t u d i e d as a f u n c t i o n o f t h e c h a r a c t e r i s t i c s o f t h e p o l y m e r s i n t h e b l e n d (e.g., h o m o p o l y m e r m o l e c u l a r w e i g h t s a n d c o p o l y m e r m o l e c u l a r w e i g h t a n d c o m p o s i t i o n ) w h i c h are related to the a a n d β of E q u a t i o n s 1 a n d 2. F o r a g i v e n P S - P I - C o p system, it w a s f o u n d t h a t t h e l o c a t i o n o f C o p is p r a c t i c a l l y i n d e p e n d e n t o f t h e a m o u n t s o f P S , P I , a n d C o p i n the p o l y b l e n d . Therefore for such a system, t w o types of blends were generally prepared: one rich i n P S w i t h P S f o r m i n g the continuous phase ( B l e n d 1), a n d one rich i n P I w i t h a continuous P I phase ( B l e n d 2 ) . T h e different fluorescence p o s s i b i l i t i e s are l i s t e d i n T a b l e I V . I f b l u e fluorescence is o b s e r v e d i n t h e c o n t i n u o u s P S p h a s e o f B l e n d 1, i t c a n b e i n f e r r e d t h a t C o p is s o l u b l e i n P S ; a n d i n f a c t t h e d i s p e r s e d P S p h a s e o f B l e n d 2 ( P I c o n t i n u o u s p h a s e ) is also fluorescent. H o w e v e r , w i t h a p o l y b l e n d film o b t a i n e d b y s o l v e n t e v a p o r a t i o n o r a s l i c e o f m o l d e d s a m p l e , t h e d i a m e t e r o f t h e d i s p e r s e d p a r t i c l e s is u s u a l l y s m a l l e r t h a n t h e t h i c k n e s s o f film o r s a m p l e . C o n s e q u e n t l y , i t is d i f f i c u l t t o s a y i f C o p is s o l u b l e i n t h e P I p a r t i c l e s o r i f i t is s i t u a t e d at t h e i n t e r f a c e w h e n t h e d i s Table V . Sample

film fluor.

molded

L o c a t i o n of B l o c k C o p o l y m e r i n P o l y b l e n d s

Technique

0

α

β

Location*

7.8 7.8 7.8 3.2 3.2 3.2 0.6 0.6 0.6 0.5 0.1 3.2

5.2 3 1.6 5.2 3 1.6 5.2 3 1.6 5 5 0.7

I I I I I I PS PS PS PS PS PI

5.4 3.2 0.9 23 0.6

5.2 3 3 23 8

I or PI I or PI PS I or PI PS

Fluorescence observed by U V microscopy, or x-ray scanning. ' 1, at interface; PS, in PS phase; and PI, in PI phase. • Compression-molded. 1


22.

Rubber-Modified

RiESS A N D J O L I V E T

Polymers

253


persed P I particles have a blue fluorescence. O n l y b y observing a second b l e n d , w h e r e P I is t h e c o n t i n u o u s p h a s e , is i t p o s s i b l e t o d i s t i n g u i s h b e t w e e n t h e t w o . I f t h e c o n t i n u o u s P I p h a s e is fluorescent, C o p is s o l u b l e i n P I ; b u t i f t h e d i s p e r s e d P S p h a s e is fluorescent, i t c a n b e c o n c l u d e d t h a t C o p is at t h e interface. T h e d a t a o b t a i n e d b y t h i s t e c h n i q u e f o r films a n d m o l d e d s a m p l e s a r e p r e s e n t e d i n T a b l e V a n d i n F i g u r e 7 w h e r e a vs. β is p l o t t e d o n a l o g a r i t h m i c scale. I n F i g u r e 7 a r e a C (a > 1 a n d β > 1 ) , C o p is m o s t l y at t h e i n t e r f a c e . I n a r e a Β (a > 1 a n d β < 1 ) , C o p h a s a c e r t a i n d e g r e e o f s o l u b i l i t y i n P I , w h e r e a s i n a r e a D (a < 1, β > 1) C o p is s o l u b l e i n P S . I t is m o r e d i f f i c u l t t o d r a w a c o n c l u s i o n a b o u t a r e a Α ( α < 1, β < 1 ) w h e r e s o m e s o l u b i l i t y i n P S a n d i n P I is i n d i c a t e d b y b l u e fluorescence o f b o t h p h a s e s ; h o w e v e r , b e c a u s e I

log*

X

X

©

®

/

/

/ /

/ X

/ /

-0.5

/

/

log [3

Ο ο

/

®

-0.5

4

®

ο Figure 7.

Location of block copolymers in polyblends by fluorescent Cop and x-ray scanning techniques

X—film, interface, fluorescence; Ο—film, PS phase, fluorescence; Λ—film, PI phase, fluorescence; Ο—compression-molded, PS phase, x-ray scanning; Θ—compression-molded, PS phase, fluorescence; and (8—compression-molded, PI phase or interface, fluorescence


254

COPOLYMERS,

Table V I .

POLYBLENDS,

Composition of Polyblends a n d Characterization of Polymers" Copolymer

Homopolymers PS

PI

Blend

II III IV V VI


a

A N D COMPOSITES

a, %

300,000 300,000 10,500 10,500 300,000

60.5 60 58.4 60 58.4

M

b, %

n

41,500 22,000 22,000 53,000 53,000

25 20 21.6 20 21.6

M

n

44,000 26,000 94,000 26,000 94,000

PS Fraction

c, %

0.72 0.51 0.61 0.51 0.61

14.5 20 20 20 20

a + b + c = 100%; PS + P I -1- C o p = 100%.

of t h e e m u l s i f y i n g e f f e c t d e m o n s t r a t e d p r e v i o u s l y , s o m e C o p is also a t t h e i n t e r f a c e , e s p e c i a l l y i f a — β ( a x i s Oz). T h e data o b t a i n e d b y this t e c h n i q u e w e r e c o n f i r m e d b y another tech nique using a P S - P I copolymer whose P I component was slightly chlorinated ( 1 - 2 % t o t a l c h l o r i n e ) . S u c h a c h l o r i n a t e d c o p o l y m e r is l o c a t e d i n a P S - P I b l e n d b y a n x-ray scanning microanalyzer (Castaing's M i c r o s o u n d ) . H o w e v e r t h i s t e c h n i q u e s e e m s t o h a v e t h e s a m e l i m i t a t i o n s as i n t e r f e r e n c e m i c r o s c o p y , especially f o r area A o f F i g u r e 7. A m o r e q u a n t i t a t i v e t e c h n i q u e is b a s e d o n t h e f a c t t h a t i n a b l e n d c o n taining polyisoprene ( o r polybutadiene) the rubber phase c a n b e selectively c r o s s l i n k e d b y γ-radiation ( 1 5 ) . T h e b l e n d w a s i r r a d i a t e d at 4 0 - 6 8 M r a d u n d e r n i t r o g e n so t h a t P I w a s q u a n t i t a t i v e l y c r o s s l i n k e d . T h e i n s o l u b l e f r a c tion w a s then isolated b y benzene extraction. Tests of binary blends of P S a n d P I h o m o p o l y m e r s demonstrated that P I a n d P S c a n b e w e l l separated after i r r a d i a t i o n , a n d t h a t t h e r e is p r a c t i c a l l y n o s o l u b i l i t y o f o n e h o m o p o l y m e r i n t h e o t h e r . T h i s t e c h n i q u e c a n b e a p p l i e d o n l y i f P S is t h e c o n t i n u o u s p h a s e . If C o p is s o l u b l e i n t h e P S p h a s e , i t is f o u n d i n t h e b e n z e n e - s o l u b l e f r a c t i o n , m o s t l y as a c o l l o i d a l d i s p e r s i o n . O n t h e o t h e r h a n d , i f C o p is s o l u b l e i n t h e P I p h a s e o r i f i t is a t t h e i n t e r f a c e , i t r e m a i n s i n t h e i n s o l u b l e f r a c t i o n . B y a n a l y z i n g t h e P S content of this f r a c t i o n a n d f r o m its w e i g h t increase w i t h respect to P I h o m o p o l y m e r , the amount of C o p c a n b e determined. H o w e v e r it is i m p o s s i b l e t o d i s t i n g u i s h b e t w e e n C o p i n t h e P I p h a s e a n d C o p at t h e interface b y this technique. T h u s , b y a n a l y z i n g a g i v e n P S - P I - C o p b l e n d f o r g e l c o n t e n t a n d a m o u n t o f P S i n t h e g e l , i t is p o s s i b l e t o l o c a t e t h e c o p o l y m e r i n e i t h e r t h e c o n t i n u o u s P S p h a s e o r at t h e i n t e r f a c e ( o r i n t h e r u b b e r p h a s e ) . F o r e x a m p l e , i f a l l c o p o l y m e r is i n t h e c o n t i n u o u s P S p h a s e , t h e a m o u n t o f g e l e q u a l s t h e P I c o n t e n t a n d i t s P S c o n t e n t is z e r o . W h e n C o p is at t h e i n t e r f a c e o r i n t h e r u b b e r p h a s e , t h e a m o u n t o f g e l e x c e e d s t h e P I c o n t e n t a n d its P S c o n t e n t is d i f f e r e n t f r o m z e r o . Table V I I .

Analysis of Polyblends b yIrradiation Technique

Blend

α

β

Blend Type

II III IV V VI

9.5 23 0.18 0.81 5.3

3.5 1.7 0.61 4.1 1.5

1 or 2 1 or 2 3 3 1 or 2

Cop at Interface or in Rubber Phase, %

93 91 26 29 88


± 4 ± 3 db 8 d= 3 =fc 3


22.

RiESS

A N D

J O L IV E T

Rubber-Modified

Polymers

255

T h e compositions of t h e different blends w h i c h h a v e b e e n a n a l y z e d a n d the characteristics of the polymers are g i v e n i n T a b l e V I . D a t a o n these blends o b t a i n e d b y the i r r a d i a t i o n t e c h n i q u e are g i v e n i n T a b l e V I I , a n d i t is a p p a r e n t t h a t t h e a m o u n t o f c o p o l y m e r at t h e i n t e r f a c e or i n t h e r u b b e r p h a s e v a r i e s . B l e n d s c a n also b e c l a s s i f i e d as f o l l o w s : type 1 or 2 — c o p o l y m e r at t h e i n t e r f a c e o r i n t h e r u b b e r p h a s e ( h o w e v e r t h e t w o c a n n o t b e d i s t i n g u i s h e d b y t h i s t e c h n i q u e ) , a n d type 3—copolymer i n the continuous P S phase. T h u s f o r a > 1 a n d β > 1, C o p is at t h e i n t e r f a c e o r i n t h e P I p h a s e , a n d , f r o m F i g u r e 7, w e m a y i n f e r t h a t i t is at t h e i n t e r f a c e . F o r b l e n d V , o n l y a s m a l l a m o u n t o f C o p is at t h e i n t e r f a c e , a n d t h e r e m a i n d e r is m o s t l y s o l u b l e i n t h e P S p h a s e ; t h i s agrees w i t h F i g u r e 7 ( a r e a D ) . F o r b l e n d I V ( c o r r e s p o n d i n g t o a r e a A w i t h a < 1 a n d β < 1 ) , s o m e C o p is p r o b a b l y s o l u b l e i n PS, and the remainder w h i c h wasinsolubilized b y irradiation may be distributed at t h e i n t e r f a c e a n d i n t h e P I p h a s e . It is i n t e r e s t i n g t o n o t e i n T a b l e s V I a n d V I I t h a t t h e s a m e c o p o l y m e r (M = 9 4 , 0 0 0 ) w i t h h o m o p o l y m e r s o f d i f f e r e n t m o l e c u l a r w e i g h t s ( b l e n d s I V a n d V I ) h a s d i f f e r e n t v a l u e s o f a a n d β, a n d t h e r e f o r e 8 8 % o r o n l y 2 6 % o f C o p is s i t u a t e d at t h e i n t e r f a c e ( o r i n t h e r u b b e r p h a s e ) . n

Conclusion F r o m the data o n the e m u l s i f y i n g properties a n d the location of C o p i n p o l y b l e n d s , i t a p p e a r s t h a t t h e e m u l s i f y i n g e f f e c t is b e s t w h e n a — β < 1, w h e r e t h e p a r t i c l e s i z e o f t h e d i s p e r s e d p h a s e is s m a l l e s t , a l t h o u g h s o m e C o p m a y b e s o l u b l e as m i c e l l a r d i s p e r s i o n i n t h e P S o r P I p h a s e . W i t h i n c r e a s i n g v a l u e s o f a — β, t h i s s o l u b i l i t y d e c r e a s e s , as d o t h e C o p e m u l s i f y i n g p r o p e r t i e s for p o l y b l e n d s p r e p a r e d b y solvent evaporation or simultaneous precipitation. T h e o p t i m u m c o n d i t i o n s t h e r e f o r e m u s t b e a r o u n d a = β = 1. T h i s is d e p i c t e d i n F i g u r e 8 for a ternary b l e n d containing P S a n d P I of similar molecular w e i g h t i n t h e p r e s e n c e o f a t w o - b l o c k c o p o l y m e r w h o s e c o m p o s i t i o n is a b o u t 50:50. T o c o r r e l a t e t h e s e findings w i t h i m p a c t r e s i s t a n c e , w e s t u d i e d t h r e e p o l y blends of same c o m p o s i t i o n ( 6 7 . 5 % C o p , 1 6 . 5 % P I , a n d 1 6 . 5 % P S ) b u t w i t h d i f f e r e n t h o m o p o l y m e r s (1, 2 ) . S i n c e w e h a d p r e v i o u s l y d e m o n s t r a t e d t h e

Figure 8.

Location of block copolymers in ternary blends


256

COPOLYMERS,

Table VIII.

POLYBLENDS,

A N D COMPOSITES

Effect of H o m o p o l y m e r s a n d of Block C o p o l y m e r ( C o p ) on Impact Resistance of Polyblends

Homopolymer"

Cop

R 2.0 2.9 >5


a

Prepared by anionic polymerization; Λ/„./Λ/„

— 1.1.

effect o f P S m o l e c u l a r w e i g h t o n i m p a c t r e s i s t a n c e , w e s e l e c t e d b l e n d s c o n t a i n i n g P S w i t h a molecular w e i g h t average of 140,000 ( T a b l e V I I I ) . Since blends V I I a n d I X have the same P I a n d practically the same P S , the tremendous increase i n i m p a c t resistance c a n b e a t t r i b u t e d to t h e C o p . F u r t h e r m o r e , this i n c r e a s e i n R is n o t c a u s e d b y t h e s m a l l i n c r e a s e i n t o t a l P I c o n t e n t ( f r o m 1 6 . 5 % to 19.8%) r e s u l t i n g f r o m t h e c h a n g e i n C o p t y p e . I n c r e a s i n g P I m o l e c u l a r w e i g h t f r o m 1 6 0 , 0 0 0 t o 2 7 0 , 0 0 0 i n a g i v e n P S - C o p s y s t e m also i n c r e a s e s i m p a c t resistance ( b l e n d s V I I I a n d I X ) . It is i n t e r e s t i n g t o n o t e t h a t this m a x i m u m is f o r a = β = 0 . 9 w h i c h corresponds to t h e o p t i m u m area defined previously. T h i s confirms that i n impact-resistant m a t e r i a l , t h e particle size of t h e dispersed r u b b e r phase must b e c o n t r o l l e d , as w e l l as t h e o c c u p a t i o n d e n s i t y w h i c h c h a r a c t e r i z e s s o m e w h a t the a d h e s i o n b e t w e e n t h e t w o p h a s e s .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Kohler, J., Riess,G.,Banderet, Α., Eur. Polym. J. (1968) 4, 173. Kohler, J., Riess,G.,Banderet, Α., Eur. Polym. J. (1968) 4, 187. Riess, G., Kohler, J., Tournut,C.,Banderet, Α., Makromol. Chem. (1967) 101, 58. Periard, J., Banderet, Α., Riess, G., J. Polym. Sci. Part Β (1970) 8, 109. Periard, J., Riess, G., Kolloid Ζ. Z. Polym. (1973) 251, 97. Bancroft, W. D.,J.Phys. Chem. (1913) 17, 501. Bancroft, W. D.,J.Phys. Chem. (1915) 19, 275. Periard, J., Riess, C., Eur. Polym. J. (1973) 9, 687. Kohler, J., Job,C.,Banderet, Α., Riess, G., Rev. Gén. Caout. Plast. (1969) 46, 1317. Kohler, J., Thesis, Mulhouse, 1967. Skoulios, Α., Heifer, P., Gallot, Y., Selb, J., Makromol. Chem. (1971) 148, 305. Meier, D., private communication. Periard, J., Banderet, Α., Riess, G., Angew. Makromol. Chem. (1971) 15, 37. Periard, J., Banderet, Α., Riess, G., Angew. Makromol. Chem.(1971)15, 55. Jolivet, Y., Thesis, Mulhouse, 1971.

RECEIVED May 7, 1974. Work supported by the Compagnie Française de Raffinage.


Rubber-Modified Polymers. Location of Block Copolymers in Two

Recommend Documents