Styrenic- and Acrylic-Siloxane Block and Graft Copolymers - American

Chapter 7

Styrenic- and Acrylic-Siloxane Block and Graft Copolymers 1

Downloaded by UNIV OF MISSOURI COLUMBIA on June 6, 2013 | http://pubs.acs.org Publication Date: December 22, 1988 | doi: 10.1021/bk-1988-0364.ch007

S. D. Smith, G. York, D. W. Dwight , and J . E . McGrath Department of Chemistry and Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, V A 24061-8699

The synthesis and characterization of graft copolymers, where the backbones were either acrylic or styrenic with siloxane grafts, were prepared and characterized in order to elucidate the molecular and solid state structures, as well as general physical behavior. Although two microphases could be achieved, the results showed that miscibility (as measured by several techniques) increased with lower graft molecular weights and as the solubility parameters of the backbone were designed to be closer to that of the poly(dimethylsiloxane) (PSX) grafts. An i m p o r t a n t polymer m o d i f i c a t i o n r e a c t i o n i s t h e g r a f t i n g t o o r from a polymer backbone by some c h e m i c a l method t o produce a branched s t r u c t u r e ( 1.). The c h a r a c t e r i z a t i o n of t h e p r o d u c t s of t h e s e r e a c t i o n s i s o f t e n somewhat l e s s w e l l d e f i n e d t h a n b l o c k copolymers (2) due t o t h e c o m p l e x i t y o f t h e m i x t u r e o f p r o d u c t s formed. It is t h e r e f o r e u s e f u l t o p r e p a r e and c h a r a c t e r i z e more w e l l d e f i n e d branched systems as models f o r t h e l e s s w e l l d e f i n e d c o p o l y m e r s . The macromonomer method [3) a l l o w s f o r t h e p r e p a r a t i o n o f more w e l l d e f i n e d copolymers than p r e v i o u s l y a v a i l a b l e . A n i o n i c p o l y m e r i z a t i o n i n s u i t a b l e systems a l l o w s t h e p r e p a r a t i o n of polymers w i t h c o n t r o l l e d m o l e c u l a r weight, narrow m o l e c u l a r weight d i s t r i b u t i o n s and f u n c t i o n a l t e r m i n a t i o n . The f u n c t i o n a l t e r m i n a t i o n of a l i v i n g a n i o n i c p o l y m e r i z a t i o n w i t h a p o l y m e r i z a b l e group has been used f r e q u e n t l y i n t h e p r e p a r a t i o n o f macromonomers ( 4 ) . Our r e s e a r c h has encompassed t h e a n i o n i c homo and b l o c k c o p o l y m e r i z a t i o n s o f D o r hexamethyl c y c l o t r i s i l o x a n e w i t h o r g a n o l i t h i u m s t o p r e p a r e w e l l d e f i n e d p o l y m e r s . As e a r l y a s 1962 PSX macromonomers were r e p o r t e d i n t h e l i t e r a t u r e by Greber (5) b u t the c o p o l y m e r ! z a t i o n o f t h e s e macromonomers d i d n o t become a c c e p t e d t e c h n i q u e u n t i l t h e i r v a l u e was demonstrated by M i l k o v i c h and C u r r e n t address: P.O. Box 160, Sumneytown, P A 18084

0097-6156/88/0364-0085$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

86

CHEMICAL REACTIONS ON POLYMERS


coworkers ( 6 ) . S i n c e t h e n , c o n s i d e r a b l e work has been d e d i c a t e d t o t h e macromonomer t e c h n i q u e i n many l a b o r a t o r i e s around t h e w o r l d . In o u r own r e s e a r c h , t h e f u n c t i o n a l t e r m i n a t i o n of t h e l i v i n g s i l o x a n o l a t e with a c h l o r o s i l a n e f u n c t i o n a l methacrylate leading to s i l o x a n e macromonomers w i t h number average m o l e c u l a r w e i g h t s from 1000 t o 20,000 g/mole has been emphasized. M e t h a c r y l i c and s t y r e n i c monomers were then c o p o l y m e r i z e d w i t h t h e s e macromonomers t o produce g r a f t copolymers where t h e s t y r e n i c o r a c r y l i c monomers comprise t h e backbone, and t h e s i l o x a n e c h a i n s a r e pendant as g r a f t s as d e p i c t e d i n Scheme 1. Copolymers were p r e p a r e d w i t h s i l o x a n e c o n t e n t s from 5 to 50 w e i g h t p e r c e n t .

Scheme 1, ΡΜΠΑ

ΑΛΛΛ/ννννννννννΛΛΛ

PSX

PSX

PSX

The i n i t i a t i o n o f t h e c y c l i c s i l o x a n e monomers w i t h a l i v i n g p o l y m e r i c l i t h i u m s p e c i e s such as p o l y s t y r y l l i t h i u m l e a d s t o b l o c k c o p o l y m e r s , as o u t l i n e d i n Scheme 2, were a l s o of i n t e r e s t . These s t y r e n i c - s i l o x a n e b l o c k copolymers were p r e p a r e d w i t h s i l o x a n e c o n t e n t s from 10 t o 50 w e i g h t p e r c e n t .

Scheme 2.

3

(CH 0

2

CH)T

ι

A

3

,' Ϊ lAAAAAÎSi-OÎ^^Si-CHj.

II

D

CH.

I

CH,

R= H, C H , t-C^Hg 3

R e c e n t l y , the importance of i n c o r p o r a t i n g s i l i c o n c o n t a i n i n g segments i n t o copolymers has become i n c r e a s i n g l y w e l l a p p r e c i a t e d . The d e s i r a b l e p r o p e r t i e s o f s i l i c o n i n c l u d e i o n e t c h r e s i s t a n c e f o r m i c r o l i t h o g r a p h y ( 2 * 8 ) , and h i g h e r oxygen p e r m e a b i l i t y i n membrane m a t e r i a l s ( 9 ) , as w e l l as b i o c o m p a t a b i l i t y . u n f o r t u n a t e l y , homo- o r random copolymers of p o l y s i l o x a n e s o f t e n have Tg's t o o low t o be u s e f u l as f i l m f o r m i n g m a t e r i a l s . In c o n t r a s t , t h e phase s e p a r a t i o n of t h e s e g r a f t and b l o c k m a t e r i a l s d i s c u s s e d i n t h i s paper a l l o w t h e i n c o r p o r a t i o n of s i l i c o n moieties at r e l a t i v e l y high l e v e l s while


7.

Styrenic- and Acrylic-Siloxane

SMITH ET AL.

Copolymers

87

m a i n t a i n i n g the s o l u b i l i t y and i n t e g r i t y of t h e g l a s s y polymer phase. A l l o y s o f t h e s e m u l t i p h a s e copolymers a r e a l s o b e i n g i n v e s t i g a t e d . Experimental Cyclohexane ( P h i l l i p s 99+ mole %) was p u r i f i e d by s t i r r i n g o v e r 2 4 e from a sodium d i s p e r s i o n . Tetrahydrofuran ( F i s h e r ) was d i s t i l l e d from a sodium/benzophenone complex. T o l u e n e ( F i s h e r ) was degassed t h o r o u g h l y and used d i r e c t l y i n radical polymerizations. ( P e t r a r c h ) was p u r i f i e d by m e l t i n g and s t i r r i n g i n the p r e s e n c e o f f i n e l y d i v i d e d c a l c i u m h y d r i d e t h e n sublimed under vacuum. The was then d i s s o l v e d i n p u r i f i e d c y c l o h e x a n e and s t o r e d under N_. S t y r e n e ( F i s h e r ) , p - m e t h y l s t y r e n e ( M o b i l ) , and t - b u t y l s t y r e n e (DOW) were p u r i f i e d by p a s s i n g through a column of a c t i v a t e d alumina and then c a r e f u l l y degassed t o remove a l l t r a c e s o f 0^. F u r t h e r p u r i f i c a t i o n by vacuum d i s t i l l a t i o n from d i b u t y l magnesium r e s u l t e d i n a n i o n i c a l l y pure monomers. M e t h a c r y l a t e monomers were d i s t i l l e d from c a l c i u m h y d r i d e and s t o r e d i n a f r e e z e r u n t i l use. Macromonomers were p r e p a r e d by i n i t i a t i o n of the D i n c y c l o h e x a n e w i t h s - B u L i a f t e r which p u r i f i e d t e t r a h y d r o t u r a n was added t o promote p r o p a g a t i o n of the s i l o x a n o l a t e s p e c i e s . Termination with 3-methacryloxypropyl d i m e t h y l c h l o r o s i l a n e ( P e t r a r c h , Inc.) a f f o r d e d the macromonomer i n h i g h y i e l d s which was t h e n p r e c i p i t a t e d i n methanol and d r i e d under vacuum. Macromonomers were a n a l y z e d by s e v e r a l t e c h n i q u e s t o c o n f i r m not o n l y t h e i r m o l e c u l a r weight and m o l e c u l a r weight d i s t r i b u t i o n but a l s o t h e i r m e t h a c r y l a t e end group functionality. Vapor phase osmometry (VPO), run i n t o l u e n e u s i n g s u c r o s e o c t a c e t a t e as a s t a n d a r d , was used as a method f o r d e t e r m i n a t i o n of number average m o l e c u l a r w e i g h t . NMR a n a l y s i s (IBM 270 MHz SL i n s t r u m e n t ) a l l o w e d a r a t i o i n g of a l p h a methyl p r o t o n s on t h e m e t h a c r y l a t e group t o the s i l i c o n m e t h y l s as a d e t e r m i n a t i o n of f u n c t i o n a l i t y . NMR was not s u f f i c i e n t l y p r e c i s e f o r m o l e c u l a r weights above a p p r o x i m a t e l y 2000 and a n o t h e r t e c h n i q u e based on the UV a n a l y s i s of the m e t h a c r y l a t e f u n c t i o n a l i t y was d e v e l o p e d . UV s p e c t r a run on a P e r k i n Elmer 552 i n s t r u m e n t (scanned from 350 nm t o 190 nm a t 20 nm/minute) e s t a b l i s h e d a wavelength maximum a t 214 nm f o r t h e c a r b o n y l group of our m e t h a c r y l a t e f u n c t i o n a l endgroup ( F i g u r e 1 ) . Then, absorbance measurements were determined a t 214 nm and a c a l i b r a t i o n p l o t u s i n g B e e r s law w i t h methyl m e t h a c r y l a t e as a s t a n d a r d i n THF was p r e p a r e d . The end group a n a l y s i s of known macromonomer c o n c e n t r a t i o n s t h u s was used t o e s t a b l i s h the f u n c t i o n a l i t y . F r e e r a d i c a l c o p o l y m e r i z a t i o n s o f the a l k y l m e t h a c r y l a t e s were c a r r i e d out i n t o l u e n e a t 60°C w i t h 0.1 weight p e r c e n t (based on monomer) AIBN i n i t i a t o r , w h i l e t h e s t y r e n i c systems were p o l y m e r i z e d i n c y c l o h e x a n e . The s o l v e n t c h o i c e s were p r i m a r i l y based on systems which would be homogeneous but a l s o show low c h a i n t r a n s f e r c o n s t a n t s . M e t h a c r y l a t e p o l y m e r i z a t i o n s were c a r r i e d out a t 20 w e i g h t p e r c e n t s o l i d s


H

S 0

t

h

e

n

d

i

s

t

i

l

l

d



88


and t h e s t y r e n i c systems were s t a r t e d a t 50 weight p e r c e n t s o l i d s then d i l u t e d w i t h time t o p r e v e n t s o l i d i f i c a t i o n o f t h e mixture. Copolymers a f t e r workup were e x t r a c t e d e x t e n s i v e l y w i t h hexanes o r i s o p r o p a n o l , depending on polymer s o l u b i l i t y , t o remove any p o l y s i l o x a n e homopolymer. Under a p p r o p r i a t e c o n d i t i o n s , t h e s e amounts were q u i t e low. The a n i o n i c p o l y m e r i z a t i o n o f t h e s t y r e n e monomers was c o n d u c t e d a t -78°C i n THF w i t h s-BuLi as t h e i n i t i a t o r . The second b l o c k was p r e p a r e d by a d d i n g t o t h i s l i v i n g polymer a c a l c u l a t e d amount o f D^/cyclohexane m i x t u r e . S i l o x a n o l a t e i n i t i a t i o n was e v i d e n c e d by l o s s o f t h e c h a r a c t e r i s t i c orange c o l o r o f t h e l i v i n g s t y r e n e a n i o n . The r e a c t i o n was a l l o w e d t o warm t o room temperature and g i v e n adequate time (5-20 hours) f o r p r o p a g a t i o n t o near q u a n t i t a t i v e c o n v e r s i o n . Termination was a c h i e v e d by r e a c t i o n w i t h t r i m e t h y l c h l o r o s i l a n e i n s l i g h t molar e x c e s s a t room t e m p e r a t u r e . The copolymers were then p r e c i p i t a t e d , d r i e d and e x t r a c t e d t o remove any s i l o x a n e homopolymer. GPC i n d i c a t e s ( F i g u r e 2) a t y p i c a l l y narrow d i s t r i b u t i o n f o r these copolymers which were a l s o noted t o be f r e e of s t y r e n i c homopolymer. T y p i c a l number average m o l e c u l a r weights p r e p a r e d were 100-150,000 f o r t h e f i r s t b l o c k . The p o l y s i l o x a n e c o n s t i t u t e d 10 t o 60 weight p e r c e n t o f t h e o v e r a l l copolymers. Thus, t h e t o t a l m o l e c u l a r w e i g h t was as h i g h as 300,000 gm/mole. V i s c o s i t i e s become v e r y h i g h and must be c o n t r o l l e d t o keep t h e m o l e c u l a r weight d i s t r i b u t i o n s from broadening. Polymers were a n a l y z e d by G e l Permeation Chromatography (GPC) w i t h a Waters 150-Ç GPC f i t t e d w i t h m i c r o s t y r a g e l columns o f 500Â, 10 , 10 , 10 , and 10 Â p o r o s i t i e s i n THF. P o l y ( m e t h y l m e t h a c r y l a t e ) (PMMA) and p o l y s t y r e n e s t a n d a r d s ( P o l y s c i e n c e s ) were g e n e r a l l y used t o e s t i m a t e number average molecular weights. Number average m o l e c u l a r w e i g h t s o f g r e a t e r than 150,000 were d e s i r e d f o r o p t i m a l polymer p r o p e r t i e s . NMR s p e c t r a on an IBM 270 MHz SL i n s t r u m e n t were used t o determine t h e s i l o x a n e i n c o r p o r a t i o n i n t o t h e copolymer. FTIR s p e c t r a were r u n on a N i c o l e t MX-1 s p e c t r o p h o t o m e t e r . 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 (DSC) thermograms were o b t a i n e d on a P e r k i n Elmer DSC-2 r u n a t 10°C p e r minutes. Dynamic M e c h a n i c a l Thermal A n a l y s i s (DMTA) s p e c t r a were o b t a i n e d on a Polymer Labs DMTA a t a f r e q u e n c y o f 1Hz w i t h a temperature range from -150°C t o +150°C a t a scan r a t e o f 5°C per m i n u t e . C o n t a c t a n g l e measurements were o b t a i n e d u s i n g a goniometer, measuring t h e a d v a n c i n g a n g l e from 2 t o 20 m i c r o l i t e r drop s i z e s , o f p u r i f i e d water upon polymer f i l m s a t room temperature. F i l m s were c a s t on m e t a l p l a t e s and a l l o w e d t o d r y s l o w l y from c h l o r o f o r m s o l u t i o n s . S e v e r a l s p o t s were measured on each f i l m and t h e r e s u l t s a v e r a g e d . ESCA s p e c t r a were o b t a i n e d w i t h a K r a t o s XSAM -800 i n s t r u m e n t w i t h Mg anode 200 watts under a vacuum o f 10-9 t o r r . TEM a n a l y s i s was done on a P h i l l i p s I L 420 Τ STEM a t 100 KV i n t h e TEM mode. M o r p h o l o g i c a l s t u d i e s were conducted on model copolymers c o n t a i n i n g a methyl m e t h a c r y l a t e backbone and a p p r o x i m a t e l y


SMITH ET AL.


Copolymers

MAX. = 0.605 AT 214 nm.


CONC. = 0.210 g / l i t e r

'

210

1

250

290

1

330

WAVELENGTH (nm) F i g u r e 1. UV spectrum o f m e t h a c r y l a t e f u n c t i o n a l PSX macromonomer w i t h M 1600.

η

(A)

(Β)

A

1 t • ι *—Γ 25

30

ι

ι ι I I I

25

30

E l u t i o n Volume (ml) F i g u r e 2. S i z e e x c l u s i o n chromatograms of p o l y s t y r e n e (A) and p ( t - b u t y l s t y r e n e ) - b - P S X ( B ) .

standard


90


5,000, 10,000 and 20,000 m o l e c u l a r weight (Mn) p o l y d i m e t h y l s i l o x a n e s i d e c h a i n s . The weight f r a c t i o n of s i l o x a n e was h e l d a p p r o x i m a t e l y c o n s t a n t a t 20% and 50%. T h i n ( a p p r o x i m a t e l y 100 nm) f i l m s were c a s t on water and t h i c k ( a p p r o x i m a t e l y 1 mm) f i l m s were c a s t on s t a i n l e s s s t e e l . Specimens from t h e l a t t e r f i l m s were microtomed a t c r y o s c o p i c t e m p e r a t u r e s . R e s u l t s and D i s c u s s i o n


The p r e p a r a t i o n of m e t h a c r y l a t e f u n c t i o n a l p o l y d i m e t h y l s i l o x a n e (10,11,12) o f h i g h f u n c t i o n a l i t y v i a E q u a t i o n 1 was an

CH. THF R L i + D^

CH.

0 CH.

I I II I I I + I " • R-(-Si-O-)Li + C l - S i - ( C H ^ ) -Q-C-C=CH_ *2'3 " 2 CH

CH

3

3

0 CH.

I

(1)

|_o-c-C=CH,

important f i r s t step i n the p r e p a r a t i o n of the w e l l defined g r a f t copolymers. The macromonomers p r e p a r e d were c h a r a c t e r i z e d f o r number average m o l e c u l a r weights v i a VPO. The f u n c t i o n a l i t y o f t h e end groups were a l s o determined by NMR o r UV a n a l y s i s which s h o u l d p r o v i d e i d e n t i c a l m o l e c u l a r weights f o r p e r f e c t l y m o n o f u n c t i o n a l m a t e r i a l s . As can be seen i n T a b l e I , a good c o r r e s p o n d e n c e was o b t a i n e d . I n c o r p o r a t i o n of the macromonomers i n t o copolymers v i a f r e e r a d i c a l c o p o l y m e r i z a t i o n can a l s o be used as a check on f u n c t i o n a l i t y s i n c e n o n f u n c t i o n a l m a t e r i a l s o b v i o u s l y w i l l n o t be incorporated. P r o t o n NMR was used t o c o n f i r m t h e amount o f PSX

T a b l e I . Mn V a l u e s of M e t h a c r y l a t e F u n c t i o n a l Poly(Dimethyl Siloxane) v i a Spectroscopic and Osmotic Techniques u

SAMPLE 1 2 3

1H NMR* 1600 0900

VPO 6500 1500 1030

uv

6000 1700 0900

Comparison o f s i l i c o n m e t h y l / a c r y l a t e methyl Solvent: Toluene From e s t e r c a r b o n y l a t absorbance 214 nm (UV)


7.

SMITH ET AL.


Copolymers

i n c o r p o r a t i o n ( T a b l e s I I and I I I ) i n t o the c o p o l y m e r s . In g e n e r a l , the i n c o r p o r a t e d amounts a r e r e l a t i v e l y c l o s e t o the charged amounts, i n d i c a t i n g b o t h h i g h macromonomer f u n c t i o n a l i t y and a p p r o p r i a t e c o p o l y m e r i z a t i o n c o n d i t i o n s .


T a b l e I I . NMR A n a l y s i s of P o l y ( D i m e t h y l S i l o x a n e ) Content i n S t y r e n i c G r a f t and B l o c k Copolymers Sample D e s c r i p t i o n Grafts; Ρ(Styrene)-g-PSX P(p-Methyl Styrene)-g-PSX P ( t - B u t y l Styrene)-g-PSX

Charged

Blocks: Ρ(Styrene)-b-PSX P(p-Methyl S t y r e n e ) - b - P S X P ( t - B u t y l Styrene)-b-PSX P ( t - B u t y l Styrene)-b-PSX

Found

30 10 20

27 9 20

20 20 10 40

20 19 10 42

T a b l e I I I . I n f l u e n c e of S i l o x a n e Content and M o l e c u l a r Weight on the Water C o n t a c t A n g l e s of P o l y ( M e t h y l M e t h a c r y l a t e ) - P o l y ( D i m e t h y l S i l o x a n e ) G r a f t Copolymers Macro Monomer M

Weight % Charged

PMMA Homopolymer C o n t r o l 5 1,000 10 15 20 5,000

10,000

20,000

Weight % via NMR

4.0 7.6 9.0 15.0

Contact Angle 74° 97°

105° 99°

5 10 15 20

4.3 6.8 12.4 16.8

5 10 15 20

5.8 9.6 14.0 15.9

108°

5 10 20

4.0 7.0 12.0

109°

107°

109°

109°

Copolymer work-up i n c l u d e d e x t r a c t i o n w i t h hexane t o remove any p o l y s i l o x a n e homopolymer.



92

CHEMICAL REACTIONS ON

POLYMERS

Very w e l l d e f i n e d b l o c k copolymers of s t y r e n e , p-methyl s t y r e n e , p - t e r t - b u t y l s t y r e n e and PSX were p r e p a r e d , as judged by GPC, w i t h m o l e c u l a r weights o f over 100,000 g/mole. I m p u r i t y l e v e l s a t t h i s m o l e c u l a r weight become e x t r e m e l y c r i t i c a l and c a r e f u l vacuum t e c h n i q u e s must be used where appropriate t o exclude a l l contaminations. As mentioned e a r l i e r , t h e g r a f t m o l e c u l a r weight and copolymer c o m p o s i t i o n s d i c t a t e the p r o p e r t i e s o f t h e system. DSC measurements i n d i c a t e p a r t i a l phase m i x i n g f o r low m o l e c u l a r weight g r a f t s , a s e v i d e n c e d by a s h i f t i n g o f the Tg of PMMA t o lower temperatures ( T a b l e I V ) . A l t h o u g h the Tg o f the p o l y m e t h y l m e t h a c r y l a t e systems w i t h g r a f t m o l e c u l a r weights of 5K, 10K and 20K a r e r o u g h l y e q u i v a l e n t , changes i n t h e b r e a d t h o f the t r a n s i t i o n i n d i c a t e d i f f e r e n c e s i n the phase m i x i n g , which i s t o be e x p e c t e d . S i m i l a r r e s u l t s are observed by Dynamic M e c h a n i c a l Thermal A n a l y s i s ( F i g u r e 3, T a b l e I V ) .

T a b l e IV. I n f l u e n c e o f G r a f t M o l e c u l a r Weight on G l a s s T r a n s i t i o n Temperature f o r PMMA-g-PSX Copolymers (~16 wt.% PSX) Macronomer Mn 1000 5000 10000 20000 C o n t r o l PMMA determined

Tq by DSC (°C) 111 123 125 127 127

by M e c h a n i c a l Loss P l o t

Λ

β

Tq by ϋ Μ Τ Α ( Ο 110 123 126

(1 Hz)

S i n c e p o l y ( d i m e t h y l s i l o x a n e ) i s w e l l known t o d i s p l a y a low s u r f a c e energy, i t was e x p e c t e d t o dominate t h e s u r f a c e o f the microphase s e p a r a t e d copolymers. Contact angle a n a l y s i s i n d e e d i n d i c a t e d a change i n s u r f a c e c o m p o s i t i o n w i t h m o l e c u l a r weight and c o m p o s i t i o n o f t h e g r a f t s . Copolymers c o n t a i n i n g h i g h e r m o l e c u l a r weight g r a f t s , which a r e b e l i e v e d t o phase s e p a r a t e t o a h i g h e r e x t e n t , have h i g h e r c o n t a c t a n g l e s due t o the p r e s e n c e o f the h i g h e r c o n c e n t r a t i o n o f the p o l y s i l o x a n e a t the s u r f a c e ( T a b l e I I I ) . T h i s agrees w i t h s e v e r a l r e s u l t s from our l a b o r a t o r y and elsewhere (1^3). A g a i n t h e 5000 mw g r a f t system does n o t dominate t h e s u r f a c e a t low p e r c e n t s i l o x a n e t o t h e same e x t e n t , i n d i c a t i n g a p a r t i a l phase m i x i n g . ESCA was used as a t o o l t o q u a n t i f y the s u r f a c e c o m p o s i t i o n . Through t h e use o f a n g u l a r dependent depth p r o f i l i n g the d o m i n a t i o n o f the s u r f a c e was o b s e r v e d t o be g r e a t e r f o r h i g h e r m o l e c u l a r weight g r a f t s . I t i s noteworthy t o p o i n t o u t t h a t h i g h e r a n g l e s p e n e t r a t e deeper i n t o t h e s u r f a c e and as an a p p r o x i m a t i o n , an a n g l e o f 10 degrees measures about the t o p 510Â o f t h e s u r f a c e , w h i l e the 90 degree measurement i n d i c a t e s t h e c o m p o s i t i o n over t h e t o p 60 Â . Another f a c t o r i s t h a t the number o f e l e c t r o n s e s c a p i n g f o l l o w s an i n v e r s e e x p o n e n t i a l r e l a t i o n s h i p w i t h d e p t h , so t h a t s u r f a c e c o m p o s i t i o n has a


7.


SMITH ET AL.

Copolymers

l a r g e e f f e c t on even t h e l a r g e a n g l e s . I n T a b l e V we can see t h e t r e n d s i n c o m p o s i t i o n w i t h g r a f t m o l e c u l a r weight and

T a b l e V. I n f l u e n c e o f S i l o x a n e G r a f t M o l e c u l a r Weight and Composition on S u r f a c e C o m p o s i t i o n o f PMMA-g-PSX Copolymers by V a r i a b l e A n g l e XPS (ESCA) (Copolymers ~5 wt.% PSX) % Poly(Dimethyl Siloxane) Detected 30° 90° 10°


E x i t Angle Macromonomer Mn

1000 5000 10000 20000

52 86 97 100

79 86 100 100

41 69 72 90

depth. I n o u r s t y r e n i c b l o c k copolymers, t y p i c a l PSX b l o c k m o l e c u l a r weights were g r e a t e r than 10K and h i g h s u r f a c e c o n c e n t r a t i o n s o f PSX were a g a i n o b s e r v e d . R e s u l t s from t h e s t y r e n i c b l o c k and g r a f t copolymers a r e somewhat s i m i l a r and are presented i n Table V I .

Table VI. ESCA Study o f S t y r e n i c - S i l o x a n e B l o c k and G r a f t Copolymers (Copolymer C o m p o s i t i o n ~10 wt.% PSX) % PSX

10°

30°

90°

Copolymer Ρ(Styrene)-b-PSX Ρ(Styrene)-g-PSX IK

91 79

80 52

52 32

P(p-Methyl

48

20

12

82 39

56 24

40 29

Angle

S t y r e n e ) - g - P S X IK

P ( t - B u t y l Styrene)-b-PSX P ( t - B u t y l S t y r e n e ) - q - P S X IK

From T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y (TEM), t h e morphology o f t h e p o l y ( m e t h y l m e t h a c r y l a t e ) g r a f t system changed s i g n i f i c a n t l y as a f u n c t i o n o f a r c h i t e c t u r e and c o m p o s i t i o n ( F i g u r e 4). The average domain s i z e s v a r y from 12 nm f o r t h e 5K g r a f t s t o 21 nm f o r t h e 20K g r a f t s , w h i l e t h e IK g r a f t systems showed no a p p a r e n t phase s e p a r a t i o n . F u r t h e r d e t a i l s o f t h i s i n t e r e s t i n g morphology w i l l be r e p o r t e d l a t e r . However, i t i s a l r e a d y c l e a r t h a t remarkably w e l l d e f i n e d s o l i d s t a t e g r a f t s t r u c t u r e s c a n be d e v e l o p e d . As a comparison t o t h e TEM measurements o f domain s i z e , S m a l l A n g l e X-ray s c a t t e r i n g (SAXS) ( c o u r t e s y o f P r o f . G. L. W i l k e s ) was a l s o r u n on t h e PMMA-g-PSX copolymers ( T a b l e V I I ) . Two t r e n d s a r e


94


μ 1.6

Y 1.2


0.8

0.4

-130

-70 TEMPERATURE °C

Figure 3. Dynamic mechanical behavior of PMMA-g-PSX copolymer: 20 wt.% siloxane of M 10 000. η f

5K

10K

2 OK

Figure 4. Comparison of the morphologies of PMMA-g-PSX (16 wt.% PSX) of 5000, 10000 and 20000 g/mole siloxane grafts by TEM.


H W ξ H

7.


SMITH ET AL.

Copolymers

T a b l e V I I . Comparison of S m a l l A n g l e X-Ray A n a l y s i s o f PMMA-g-PSX Copolymers w i t h TEM Domain S i z e Data (Copolymers ~16 wt.% PSX)


Macromonomer Mn 1000 5000 10000 20000

Domain S i z e (TEM) 8 nm. 15 nm. 20 nm.

Interdomain Spacing 12.4 nm. 18.8 nm. 28.6 nm. 37.6 nm.

Max. S c a t t e r i n g Intensity 30 110 260 540

a p p a r e n t , one b e i n g t h a t t h e r e i s a c o r r e s p o n d i n g i n c r e a s e i n interdomain spacing with g r a f t molecular weight. The o t h e r t r e n d i s t h a t the n o r m a l i z e d s c a t t e r i n g i n t e n s i t y a l s o v a r i e s w i t h g r a f t m o l e c u l a r weight, i n d i c a t i n g t h a t ^ b e t t e r phase s e p a r a t i o n i s o c c u r r i n g a t l e a s t up u n t i l 10 g/mole. Also SAXS c o n f i r m s t h a t even a t g r a f t l e n g t h s o f as low as 1000 t h e r e i s a phase s e p a r a t i o n a l t h o u g h domain s i z e i s s m a l l and phase d e f i n i t i o n i s p r o b a b l y t o o weak t o be d e f i n e d i n t h e TEM technique. F u r t h e r a n a l y s i s of t h e s e phenomena w i l l be reported i n forthcoming papers. S i m i l a r s t u d i e s were u n d e r t a k e n as a comparison i n t h e s t y r e n i c systems, a l t h o u g h i n t h e s e systems we a l s o were a b l e t o compare t h e g r a f t systems t o d i b l o c k systems of s i m i l a r composition. DSC a l s o shows a d e p r e s s i o n o f the h i g h temperature Tg f o r a l l of t h e s t y r e n e s f o r the IK g r a f t systems. The 5K systems showed a s m a l l e r d e p r e s s i o n b u t s t i l l a s l i g h t l o w e r i n g o f t h e Tg ( T a b l e V I I I ) . C l e a r l y , the t b u t y l s t y r e n e system i s most i n f l u e n c e d , as a n t i c i p a t e d .

Table V I I I . Dependence of A r c h i t e c t u r e and M o l e c u l a r Weight o f S t y r e n i c - S i l o x a n e B l o c k and G r a f t Copolymers on Tg (Copolymers ~20 wt.% PSX) Copolymer Type Ρ(Styrene)-b-PSX Ρ(Styrene)-g-PSX Ρ(Styrene)-g-PSX Ρ(Styrene)-g-PSX P(p-Methyl P(p-Methyl P(p-Methyl P(p-Methyl

Tg IK 5K 10K

Styrene)-b-PSX Styrene)-g-PSX IK S t y r e n e ) - g - P S X 5K Styrene)-g-PSX 10K

P ( t - B u t y l Styrene)-b-PSX P ( t - B u t y l Styrene)-g-PSX IK P ( t - B u t y l Styrene)-g-PSX 5K P ( t - B u t y l S t y r e n e ) - g - P S X 10K B l o c k Copolymers a r e of ~100K-20K weights and a r e d i b l o c k s .

(DSC), °C 106 74 100 103 115 80 107 110 149 100 139 143

block molecular


96


ESCA a n a l y s i s showed a s i m i l a r t r e n d o f i n c o m p l e t e s u r f a c e c o v e r a g e f o r t h e IK systems. A l s o , no domains were v i s i b l e i n any o f t h e IK s t y r e n i c g r a f t systems by TEM. T h e r e i s an e x p e c t e d t r e n d w i t h r e s p e c t t o s o l u b i l i t y parameter, p ( t - b u t y l s t y r e n e ) (δ 8.1) has a s o l u b i l i t y parameter much c l o s e r t o t h a t o f p o l y d i m e t h y l s i l o x a n e (δ 7.3) t h a n does p(p-methyl s t y r e n e ) which i s c l o s e r than ρ(styrene) (δ 9.1). P r e l i m i n a r y d a t a does i n d i c a t e t h a t f o r a copolymer of s i m i l a r c o m p o s i t i o n t h e ρ(t-butylstyrene) polymer has s m a l l e r domains and, i n g e n e r a l , a p a r t i a l l y phase mixed s u r f a c e and s o l i d state structure. s

s


s

Conclusions The macromonomer t e c h n i q u e p r o v i d e s t h e p o s s i b i l i t y o f p r e p a r i n g g r a f t copolymers o f copolymers n o t s y n t h e t i c a l l y p o s s i b l e p r e v i o u s l y . The u s e f u l n e s s of t h e macromonomer t e c h n i q u e was d e m o n s t r a t e d and some i n t e r e s t i n g p r o p e r t i e s o f the a c r y l i c - s i l o x a n e and s t y r e n i c s i l o x a n e g r a f t polymers p r e p a r e d by t h i s t e c h n i q u e were r e p o r t e d . Complimentary v e r y w e l l d e f i n e d b l o c k copolymers o f s t y r e n e , p-methyl s t y r e n e and p - t e r t - b u t y l s t y r e n e w i t h p o l y d i m e t h y l s i l o x a n e were a l s o prepared. P r e l i m i n a r y c h a r a c t e r i z a t i o n shows t h a t b l o c k l e n g t h s and c o m p o s i t i o n s were c l o s e t o t h e d e s i r e d v a l u e s and t h a t narrow m o l e c u l a r w e i g h t d i s t r i b u t i o n s were a c h i e v e d . We have i l l u s t r a t e d t h e u t i l i t y o f t h e t e c h n i q u e and shown t h e need f o r f u r t h e r i n v e s t i g a t i o n s which a r e c o n t i n u i n g i n o u r laboratories.

Literature Cited 1. Battaerd, H.; Tregear, G. W. Graft Copolymers; Wiley: New York, 1967. 2. Noshay, Α.; McGrath, J. E. Block Copolymers: Overview and Critical Survey; Academic Press: New York, 1977. 3. Milkovich, R. In Anionic Polymerization: Kinetics, Mechanisms and Synthesis; ACS Symposium Series No. 166; American Chemical Society: Washington, DC, 1981. 4. Rempp, P.; Lutz, P.; Masson, P.; Franta, E. Makromol. Chem. 1984, Suppl. 8, 3. 5. Greber, G.; Reese, E. Makromol. Chem. 1962, 55, 96. 6. Milkovich, R.; Chiang, M. U.S. Patent 3 786 116, 1974. 7. Reichmanis, E.; Smolinsky, G. J. Electrochem. Soc.: Solid State Science and Tech., 1985, 132, 1178. 8. Bowden, M.; et al. PMSE Preprints, ACS Anaheim, September 1986. 9. Kawakami, Y.; Aoki, T.; Hisada, H.; Yamamura, Y.; Yamashita, Y. Polymer Comm., 1985, 26(5), 133. 10. Rempp, P.; Franta, E. Advances in Polymer Science, 1984 58. 11. Kawakami, Y.; Yamashita, Y. In Ring Opening Polymerization, Kinetics, Mechanisms and Synthesis; McGrath, J. E., Ed.; ACS 286, 1985, Chapter 19. 12. Cameron, G. G.; Chisholm, M. S. Polymer, 1985, 26, 437. 13. Gaines Jr., G. L. Macromolecules, 1981, 14, 208. RECEIVED

August 27,

1987


Styrenic- and Acrylic-Siloxane Block and Graft Copolymers - American

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