5 Liquid Crystalline Order in Polymers and Copolymers with Cholesteric Side Groups 1
Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on October 13, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0074.ch005
A. BLUMSTEIN, Y. OSADA, S. B. CLOUGH, E . C. HSU, and R. B. BLUMSTEIN Department of Chemistry, Polymer Program, University of Lowell, Lowell, MA 01854
We have recently shown (1, 2) that atactic polymers with side groups characterized by chemical constitution related to mesomorphic behavior tend to organize spontaneously and independently of the conditions of their preparation if given enough segmental mobility. The organization displayed can be lamellar (smectic) or directional (nematic). In the former case the macromolecular backbone is confined to a plane, while the side groups are either perpendicular or tilted with respect to the planes containing the backbone. The side groups are arranged either in single or in double arrays in which the individual side groups are mutually parallel (3). In the latter (nematic) type of organization, the backbones are not restricted to layers but the side groups keep a mutually parallel orientation throughout the domain which can reach submicroscopic dimensions. The development of liquid crystalline order in the polymer may or may not be accompanied by crystallinity. Polymers with benzoic acid side groups were studied and found to display ordering analogous to the smectic C structures of alkoxy benzoic acids (1, 2). Polymers with Schiff base side groups were found to display ordering of the smectic A (1) and nematic type (4). Literature X-ray data (5,6) can be interpreted as being generated by lamellar (smectic) structures and seem to point to the fact that in all cases the intrinsic tendency of side groups to organize is reinforced by the connectivity imposed by the polymeric backbone. Mesomorphic order in polymers with side groups containing the cholesterol moiety has scarcely been studied in spite of the importance of cholesterol derivatives in the field of liquid crystals and biological materials. The main focus of attention has been 'Present address: College of Liberal Arts and Science, Ibaraki University, Mito 310, Japan.
0-8412-0419-5/78/47-074-056$05.00/0 © 1978 American Chemical Society
Blumstein; Mesomorphic Order in Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on October 13, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0074.ch005
5.
BLUMSTEIN E T AL.
57
Liquid Crystalline Order
c e n t e r e d around t h e study o f phase t r a n s i t i o n s o f a c r y l i c ( 7 , 8, 9 ) a n d m e t h a c r y l i c ( 1 0 , 1 1 , 1 2 ) e s t e r s o f cholesterol. I n s p i t e o f c o n s i d e r a b l e c o n t r o v e r s y as to t h e l o c a t i o n o f t h e c h o l e s t e r i c phase t r a n s i t i o n i n t h e s e m o n o m e r s , t h e r e was a c o n s e n s u s t h a t p o l y m e r s o f c h o l e s t e r y l a c r y l a t e and c h o i e s t e r y l m e t h a c r y l a t e a r e amorphous. The amorphous s t r u c t u r e i s r e p o r t e d t o occur i n d e p e n d e n t l y o f t h e phase i n which t h e p o l y m e r i z a t i o n has been c a r r i e d o u t , though Hardy (7) has shown t h a t polymer-monomer m i x t u r e s ( p o l y m e r i z a t i o n a t 0 C) h a v e a s m e c t i c o r g a n i z a t i o n . From o u r p o i n t o f v i e w , t h e s e s t a t e m e n t s w e r e s u r p r i s i n g as we e x p e c t e d the c h o l e s t e r i c m o i e t i e s t o i n t e r a c t s t r o n g l y and o r ganize t h e polymer i n a fashion s i m i l a r t o other p o l y mers w i t h m e s o g e n i c s i d e g r o u p s . They w a r r a n t e d an i n q u i r y i n t o t h e s t r u c t u r e o f polymers with c h o l e s t e r i c side groups. A r e c e n t p u b l i c a t i o n (13) w h i c h a p p e a r e d w h i l e t h i s w o r k was i n p r o g r e s s d e s c r i b e d t h e s p o n t a n e o u s development o f l a y e r e d o r d e r i n polymers w i t h t h e cho l e s t e r i c moiety a t t a c h e d t o t h e backbone v i a a l o n g , f l e x i b l e m o l e c u l a r s p a c e r c o n s t i t u t e d by anCo-aminocarboxylie acid chain. L a y e r e d s t r u c t u r e s a r e deve loped w i t h t h e long s i d e groups roughly p e r p e n d i c u l a r to t h e main c h a i n . The a u t h o r s a t t r i b u t e d t h e d e v e l o p ment o f t h e s e s t r u c t u r e s t o t h e f l e x i b i l i t y o f t h e bridge connecting t h e c h o l e s t e r o l moiety. One o f t h e f a c t o r s l e a d i n g t o c o n f u s i o n i n i n t e r p r e t i n g d a t a on t h e development o f o r d e r i n p o l y m e r s w i t h mesogenic s i d e groups i s t h e f r e q u e n t phase sepa r a t i o n taking place during the polymerization process. The i n t e r m o l e c u l a r d i s o r d e r c h a r a c t e r i z i n g t h e p r e c i p i t a t e d polymer i s o f t e n "locked i n " i f the tempera t u r e o f p r e c i p i t a t i o n i s below t h e g l a s s t r a n s i t i o n temperature o f t h e polymer Tg. C a s t i n g o f f i l m s from good, s l o w l y e v a p o r a t i n g s o l v e n t s o r s k i l l f u l a n n e a l i n g i n v a r i a b l y leads t o t h e development o f mesomorphic order ( 1 , 3 ) . S i m i l a r r e s u l t s have been a c h i e v e d w i t h p l a s t i f i c a t i o n o f p o l y ( ^ f - L - b e n z y l g l u t a m a t e ) (_14). I n t h i s p a p e r we d e s c r i b e t h e s t u d y o f d i f f e r e n t polymers c o n t a i n i n g t h e c h o l e s t e r o l moiety i n t h e s i d e g r o u p a s w e l l a s c o p o l y m e r s o f ch οle s t e r y l m e t h a c r y 1 a t e (PChMA) w i t h n - a l k y l m e t h a c r y l a t e s o f v a r i o u s c h a i n lengths. The d e v e l o p m e n t o f o r d e r i n Ρ C h M A s o f d i f f e r e n t t a c t i c i t i e s i s a l s o d e s c r i b e d , p r o v i d i n g some i n s i g h t i n t o t h e f a c t o r s governing t h e development o f mesomorphic o r d e r i n polymers w i t h c h o l e s t e r i c s i d e groups. T
Blumstein; Mesomorphic Order in Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
58
M E S O M O R P H I C ORDER I N
POLYMERS
Experimental All
s o l v e n t s and
reagents
were d i s t i l l e d
prior
to
use.
Downloaded by UNIV ILLINOIS URBANA-CHAMPAIGN on October 13, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0074.ch005
Monomers. Choiesteryl p-acryloyloxybenzoate ( C h A B ) was p r e p a r e d i n t h r e e s t e p s by t h e f o l l o w i n g synthetic route : 0 Ho/0VcOOH+CH
2
0
=CH~C-Cl
Q H ^ C H = C H - C O Y Q V C 00H
Ρ
2
2) 0 S
Q
C
1
2
0
^ C H =CH-(:0-VQVCC1 9
H+
cholesterol
