Chemical Reactions on Polymers - American Chemical Societyhttps://pubs.acs.org/doi/pdf/10.1021/bk-1988-0364.ch007a polym...
1 downloads
121 Views
1MB Size
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
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
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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
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
H
S 0
t
h
e
n
d
i
s
t
i
l
l
d
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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
88
CHEMICAL REACTIONS ON POLYMERS
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
SMITH ET AL.
Styrenic- and Acrylic-Siloxane
Copolymers
MAX. = 0.605 AT 214 nm.
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
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
90
CHEMICAL REACTIONS ON POLYMERS
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
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
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)
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
7.
SMITH ET AL.
Styrenic- and Acrylic-Siloxane
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 .
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
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.
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
7.
Styrenic- and Acrylic-Siloxane
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°
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
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
94
CHEMICAL REACTIONS ON POLYMERS
μ 1.6
Y 1.2
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
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.
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
H W ξ H
7.
Styrenic- and Acrylic-Siloxane
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)
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
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
96
CHEMICAL REACTIONS ON POLYMERS
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
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
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
In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
