Mesomorphic Order in Polymers - ACS Publications - American

6 Influence of Mesomorphic Order on the Physical Properties of Poly(p-Biphenyl Aerylate) and Related Polymers B. A. NEWMAN

Mesomorphic Order in Polymers Downloaded from pubs.acs.org by UNIV LAVAL on 07/11/16. For personal use only.

Department of Mechanics and Materials Science, Rutgers, The State University, New Brunswick, NJ 08903

V. FROSINI and P. L. MAGAGNINI Università di Pisa, Istituto di Chimica Industriale ed Applicata, 56100 Pisa, Italy

In previous investigations (1,2) the influence of the chemi cal structure on the physical properties of aromatic polyacrylates and polymethacrylates, obtained by r a d i c a l polymerization, has been extensively studied. The most interesting and stimulating result (3-6) was the discovery that some of these polymers, namely, poly(p-biphenyl acrylate) (PPBA), poly(p-cyclohexyl phenyl acrylate (PPCPA) and poly(p-acryloyloxyazobenzene) (PPAAB), display thermo dynamic properties t y p i c a l of c r y s t a l l i n e polymers. Recently the c r y s t a l l i n e character of atactic PPBA and PPCPA has been pointed out by the study of their dynamic mechanical behavior (7). How ever x-ray studies (8,9) have shown that the structure of these polymers is not c r y s t a l l i n e in the conventional sense. A onedimensional ordering showing in some cases as many as four sharp reflections and a p e r i o d i c i t y of 23.2 Å was observed i n a direc tion perpendicular to the main chain, together with a diffuse halo i n the wide angle region. In order to account for these results a smectic structure was proposed (8), the long rigid side groups being randomly directed at right angles on both sides of the main chain to form a layered structure. On the basis of this model it was anticipated (8) that a syndiotactic configuration of the macromolecules would have favor ed the attainment of a higher degree of order and perhaps also the formation of conventional c r y s t a l l i n e structures. Studies have therefore been undertaken i n order to synthesize samples of PPBA having different types of stereoregularity and to determine their morphology and physical properties. Experimental Materials. Atactic PPBA was prepared by radical polymer ization i n bulk or i n benzene solution at 60-75°C, using B z 0 as i n i t i a t o r . I t contained ^55% syndiotactic diads. Isotactic PPBA was prepared by polymerizing the monomer i n toluene at -78°C with Bu L i as i n i t i a t o r . The procedure was very similar to that reported i n the l i t e r a t u r e for the preparation of other i s o t a c t i c 2

0-8412-0419-5/78/47-074-071$05.00/0 © 1978 American Chemical Society

2

MESOMORPHIC


72

ORDER I N P O L Y M E R S

polyacrylates. The d e g r e e o f i s o t a c t i c i t y was ^90%. Fractiona t i o n w i t h a p p r o p r i a t e s o l v e n t s l e d t o a sample w i t h a d e g r e e o f i s o t a c t i c i t y h i g h e r than 97%. Monomers w i t h b u l k y s i d e g r o u p s do n o t f o r m s y n d i o t a c t i c r i c h polymers r e a d i l y . Several attempts t o prepare s y n d i o t a c t i c PPBA were made. The b e s t r e s u l t s were a c h i e v e d b y p o l y m e r i z i n g t h e monomer i n t o l u e n e s o l u t i o n a t -78° u n d e r U.V. i r r a d i a t i o n , when a sample was o b t a i n e d w i t h ^ 6 5 % s y n d i o t a c t i c d i a d s . A t a c t i c p o l y ( p - b i p h e n y l m e t h a c r y l a t e ) PPBMA was p r e p a r e d b y r a d i c a l p o l y m e r i z a t i o n i n b u l k a t 75°C. I s o t a c t i c a n d s y n d i o t a c t i c PPBMA were o b t a i n e d b y p o l y m e r i z a t i o n w i t h B u L i a s i n i t i a t o r a t -78°C i n t o l u e n e a n d THF r e s p e c t i v e l y . T e c h n i q u e s . N.M.R. s p e c t r a o f a t a c t i c , i s o t a c t i c a n d s y n d i o t a c t i c s a m p l e s were r e c o r d e d u s i n g a J e o l PS-100 i n s t r u m e n t a n d a V a r i a n 220 s p e c t r o m e t e r , e q u i p p e d w i t h v a r i a b l e t e m p e r a t u r e c o n t r o l l e r a n d f r e q u e n c y m e t e r ( 1 0 ) . S p e c t r a were o b t a i n e d u s i n g 5-10% (W/V) s o l u t i o n s i n C C l ^ o r 0 - c h l o r o b r o m o - b e n z e n e w i t h HMDS as i n t e r n a l s t a n d a r d . S p e c i f i c h e a t measurements were made u s i n g a P e r k i n - E l m e r DSC-IB 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 . The sample s i z e was g e n e r a l l y ^ 1 5 mg. a n d t h e d a t a was o b t a i n e d f o r a sample s u r r o u n d e d b y a d r y n i t r o g e n a t m o s p h e r e . S y n t h e t i c s a p p h i r e was used as a r e f e r e n c e . I n each run, c a r r i e d out a t a r a t e o f 8°/min, a t e m p e r a t u r e r a n g e o f 20°Κ was e x p l o r e d . D.S.C. s c a n s were o b t a i n e d a t s c a n n i n g r a t e s o f 32°C/min. The t h e r m a l o p t i c a l d a t a were o b t a i n e d u s i n g a p h o t o c e l l i n c o n j u n c t i o n w i t h a Bausch-Lomb 500yV V0M7 r e c o r d e r , programmed b y a M e t t l e r hot stage. X - r a y d i f f r a c t i o n d a t a were o b t a i n e d u s i n g a N o r e l c o w i d e a n g l e d i f f r a c t o m e t e r w i t h Cu Κα r a d i a t i o n . X-ray d i f f r a c t i o n p a t t e r n s were a l s o r e c o r d e d o n f i l m u s i n g a f l a t p l a t e , w i t h a s p e c i m e n t o f i l m d i s t a n c e o f 7.0 cm. Cu Κα r a d i a t i o n was u s e d s o

ο t h a t t h e 23.2 A s p a c i n g a p p e a r e d o n t h e same f i l m w i t h t h e w i d e angle d i f f r a c t i o n . A t h e r m o g r a v i m e t r i c a n a l y s i s was c a r r i e d o u t f o r a l l p o l y m e r s using a M e t t l e r thermogravimetric a n a l y s i s device. Both t h e a b s o l u t e w e i g h t a n d t h e r a t e o f w e i g h t l o s s were r e c o r d e d a s a f u n c t i o n o f temperature. R e s u l t s and D i s c u s s i o n a. N u c l e a r M a g n e t i c R e s o n a n c e . The t a c t i c i t i e s o f a l l t h e p o l y m e r s s t u d i e d were d e t e r m i n e d f r o m N.M.R. measurements u s i n g t h e method d e s c r i b e d i n a p r e v i o u s (10) p u b l i c a t i o n . The method i s b a s e d o n t h e c o n s i d e r a t i o n t h a t t h e two b a c k b o n e m e t h y l e n e protons o f i s o t a c t i c sequencies, because o f t h e i r d i f f e r e n t s h i e l d i n g , are magnetic non-equivalent, w h i l e those o f syndio t a c t i c s e q u e n c e s , e x p e r i e n c i n g t h e same m a g n e t i c e n v i r o n m e n t , a r e e q u i v a l e n t . F o r i s o t a c t i c PPBA t h r e e bands w i t h 1:1:1 relative

6.

NEWMAN ETAL.

Influence of Mesomorphic Order

73

i n t e n s i t i e s a r e e x p e c t e d , w h e r e a s s y n d i o t a c t i c PPBA s h o u l d g i v e two g r o u p s o f l i n e s w i t h 1:2 r e l a t i v e i n t e n s i t i e s . The p e r c e n t t a c t i c i t y c a n be d e r i v e d f r o m t h e s p e c t r a u s i n g t h e r e l a t i v e a r e a s u n d e r c o r r e s p o n d i n g p e a k s . These r e s u l t s f o r a l l p o l y m e r s i n v e s t i g a t e d i n t h i s s t u d y a r e shown i n T a b l e I . TABLE I


Polymer A t a c t i c PPBA S y n d i o t a c t i c PPBA I s o t a c t i c PPBA (a) (b) (c) A t a c t i c PPBMA S y n d i o t a c t i c PPBMA I s o t a c t i c PPBMA

Tacticity 55% 65% 97% 90% 78% 80% 90% 90%

syndiotactic syndiotactic isotactic isotactic isotactic syndiotactic syndiotactic isotactic

b. D i f f e r e n t i a l Scanning Calorimetry. D.S.C. s c a n s f r o m i s o t a c t i c , a t a c t i c a n d s y n d i o t a c t i c PPBA were made a n d t h e s p e c i f i c heats a t various temperatures c a l c u l a t e d . This data i s shown i n F i g u r e 1 f o r b o t h a t a c t i c a n d i s o t a c t i c s a m p l e s . The t a c t i c i t y o f t h e i s o t a c t i c sample u s e d f o r t h i s f i g u r e was 9 7 % . I t c a n be s e e n t h a t a l t h o u g h t h e g l a s s t r a n s i t i o n o c c u r s a t t h e same t e m p e r a t u r e f o r b o t h s a m p l e s , t h e i s o t a c t i c s a m p l e m e l t s a t a t e m p e r a t u r e a p p r o x i m a t e l y 40°K l o w e r t h a n t h e a t a c t i c s a m p l e . I t was f o u n d t h a t t h e m e l t i n g p o i n t o f a t a c t i c , i s o t a c t i c and s y n d i o t a c t i c p o l y m e r v a r i e d w i t h t a c t i c i t y a n d t h e r m a l h i s tory. I n order t o i n v e s t i g a t e f u r t h e r these e f f e c t s , polymer samples were c r y s t a l l i z e d i s o t h e r m a l l y a t v a r i o u s t e m p e r a t u r e s and t h e m e l t i n g p o i n t o f e a c h sample e s t a b l i s h e d u s i n g t h e D.S.C. scans. The r e s u l t s a r e s u m m a r i z e d i n F i g u r e 2. The d a t a shown here f o r t h e i s o t a c t i c sample were o b t a i n e d from a sample w i t h a m e a s u r e d t a c t i c i t y o f 90%. I t was f o u n d t h a t t h e m e l t i n g t e m p e r ature increased l i n e a r l y w i t h c r y s t a l l i z a t i o n temperature b u t t h a t the r a t e o f i n c r e a s e depended on t h e polymer c o n f i g u r a t i o n as shown i n F i g u r e 2. The r a t e o f i n c r e a s e o f m e l t i n g t e m p e r a t u r e w i t h c r y s t a l l i z a t i o n t e m p e r a t u r e was c o n s i d e r a b l y s m a l l e r f o r t h e a t a c t i c polymer than f o r the i s o t a c t i c and s y n d i o t a c t i c polymers. An e q u i l i b r i u m m e l t i n g t e m p e r a t u r e c a n be d e t e r m i n e d b y e x t r a p o l a t i o n o f t h e m e a s u r e d m e l t i n g p o i n t s a s shown i n F i g u r e 2. The v a l u e s o b t a i n e d were 511°K f o r t h e i s o t a c t i c p o l y m e r (90% i s o t a c t i c ) , 550°K f o r t h e a t a c t i c p o l y m e r a n d 578°K f o r t h e s y n d i o t a c t i c sample. As we have a l r e a d y d i s c u s s e d , t h e e x t e n t o f s y n d i o t a c t i c i t y i n t h e p o l y m e r h e r e d e s c r i b e d a s s y n d i o t a c t i c was a c t u a l l y q u i t e low ((^65%) T a b l e I ) , a n d i n f a c t o n l y s l i g h t l y h i g h e r t h a n t h e polymer obtained by r a d i c a l p o l y m e r i z a t i o n and here d e s c r i b e d as a t a c t i c ( 5 5 % s y n d i o t a c t i c d i a d s ) . From F i g u r e 2 i t c a n be s e e n


M E S O M O R P H I C ORDER I N P O L Y M E R S


6.

NEWMAN ETAL.


75

t h a t t h e m e l t i n g p o i n t o f t h e a t a c t i c p o l y m e r may be g r e a t e r t h a n the m e l t i n g p o i n t o f t h e s y n d i o t a c t i c polymer a t l o w c r y s t a l l i z a t i o n t e m p e r a t u r e s . However t h e e x t r a p o l a t e d m e l t i n g t e m p e r a t u r e f o r t h e s y n d i o t a c t i c p o l y m e r i s 28°K h i g h e r t h a n f o r t h e a t a c t i c p o l y m e r . These r e s u l t s i n d i c a t e t h a t t h e e q u i l i b r i u m m e l t i n g p o i n t o f PPBA i n c r e a s e s w i t h i n c r e a s i n g s y n d i o t a c t i c i t y . This supports the conclusion that a s y n d i o t a c t i c c o n f i g u r a t i o n o f the m a c r o m o l e c u l e s o f PPBA f a v o r s t h e r e g u l a r p a c k i n g o f t h e a r o m a t i c s i d e groups, a c c o r d i n g t o t h e suggested model. The t h e r m a l p r o p e r t i e s o f i s o t a c t i c , a t a c t i c a n d s y n d i o t a c t i c PPBMA a r e i l l u s t r a t e d by t h e D.S.C. t r a c e s i n F i g u r e 3. None o f t h e s e s a m p l e s showed a m e l t i n g e n d o t h e r m . Thus e v e n a s y n d i o t a c t i c c o n f i g u r a t i o n ( e x t e n t o f t a c t i c i t y 90%) i s n o t a b l e t o promote e f f i c i e n t p a c k i n g o f t h e s i d e groups f o r these p o l y m e r s . I n t e r e s t i n g p e c u l i a r i t i e s were n o t e d i n t h e m e l t i n g b e h a v i o r o f i s o t a c t i c PPBA w i t h a l o w e r d e g r e e o f i s o t a c t i c i t y . Figure 4 shows t h e D.S.C. t r a c e s f o r a sample 78% i s o t a c t i c . The most i n t e r e s t i n g o b s e r v a t i o n i s t h a t f o r t h i s p o l y m e r two w i d e l y s e p a r a t e d e n d o t h e r m i c p e a k s c a n be o b s e r v e d , a t 490°K a n d 540°K. On t h e c o r r e s p o n d i n g c o o l i n g c u r v e two e x o t h e r m i c p e a k s a t 500°K a n d 460°Κ were o b s e r v e d . Upon r e h e a t i n g t h e e n d o t h e r m i c p e a k s were a g a i n o b s e r v e d a t somewhat l o w e r t e m p e r a t u r e s b u t t h e i n t e n s i t y o f t h e h i g h t e m p e r a t u r e peak was f o u n d t o be g r e a t l y r e d u c e d . The h i g h e r e n d o t h e r m i c p e a k , f o r t h e i s o t a c t i c s a m p l e , occurs a t a temperature c l o s e t o the m e l t i n g p o i n t o f the a t a c t i c p o l y m e r , a n d w o u l d a p p e a r , a t f i r s t s i g h t , t o be a s s o c i a t e d w i t h the f u s i o n o f a t a c t i c polymer p r e s e n t i n t h e i s o t a c t i c sample. T h i s e x p l a n a t i o n was t e s t e d b y t h e s t u d y o f b l e n d s o f i s o t a c t i c p o l y m e r ( 9 7 % i s o t a c t i c ) a n d a t a c t i c p o l y m e r . The D.S.C. t r a c e s d i d show two e n d o t h e r m i c p e a k s a t ^490°K a n d ^540°K. However, upon c o o l i n g a n d r e h e a t i n g , b o t h h i g h a n d l o w t e m p e r a t u r e p e a k s a p p e a r e d a g a i n w i t h o u t a n y a p p r e c i a b l e change. The e x p l a n a t i o n t h a t t h e i s o t a c t i c sample w i t h a s m a l l e r e x t e n t o f t a c t i c i t y c a n be s i m p l y r e g a r d e d a s a b l e n d o f i s o t a c t i c a n d a t a c t i c p o l y m e r i s t h e r e f o r e n o t s u f f i c i e n t f o r a complete e x p l a n a t i o n . c. Thermal O p t i c a l A n a l y s i s . A t h i n f i l m o f t h e polymer, cast from s o l u t i o n and o b s e r v e d between c r o s s e d p o l a r s i n t h e p o l a r i z i n g m i c r o s c o p e , showed u n i f o r m e x t i n c t i o n a n d i n d i c a t e d t h a t p o l y m e r p r e c i p i t a t e d f r o m s o l u t i o n was e s s e n t i a l l y amor phous . However f o r t h e c a s e o f a t a c t i c PPBA, upon h e a t i n g , some b i r e f r i n g e n c e d e v e l o p e d a n d a t 200°C e x t e n s i v e r e g i o n s o f s t r u c t u r e were o b s e r v e d . F u r t h e r h e a t i n g o f t h e f i l m l e d t o a m e l t i n g w i t h a consequent decrease i n b i r e f r i n g e n c e t o uniform e x t i n c t i o n . Upon c o o l i n g f r o m t h e m e l t , s t r u c t u r e w i t h b i r e f r i n g e n c e a g a i n appeared. A q u a n t i t a t i v e measure o f t h i s b e h a v i o r was p r o v i d e d b y r e p l a c i n g one t h e e y e p i e c e s w i t h a p h o t o c e l l a n d a t t a c h i n g t h e p h o t o c e l l t o a r e c o r d e r t o p r o v i d e a measure o f t h e l i g h t r e a c h ing the eyepiece. The h e a t i n g a n d c o o l i n g was programmed u s i n g

76



Ο

U

L J

ι

300

t 400

Γ

JLJ

500

Figure 3. D.S.C. traces for isotactic (1), atactic (2), and syndiotactic (3) PPBMA

450

500

T/°K

Figure 4. D.S.C. traces for isotactic PPBA sample (c); onfirstcooling (1 ) and second cooling (2)


6.

N E W M A N ET AL.


77

a M e t t l e r hot stage. Films were c a s t from chloroform s o l u t i o n d i r e c t l y on the microscope s l i d e . The thickness of the f i l m could be v a r i e d by changing the amount of polymer used. U s u a l l y a t h i c k ness of ^0.5 m i l was s u f f i c i e n t to give changes i n b i r e f r i n g e n c e of s u f f i c i e n t magnitude. The samples were heated and cooled a t 3°C/min. The r e s u l t s f o r a t a c t i c and i s o t a c t i c PPBA are shown i n Figure 5. The i s o t a c t i c sample shown here was 78% i s o t a c t i c . For both a t a c t i c and i s o t a c t i c sample the i n i t i a l c a s t f i l m shows e s s e n t i a l l y zero b i r e f r i n g e n c e . When the temperature exceeds ^388°K (the g l a s s t r a n s i t i o n temperature 385°K) the b i r e f r i n g e n c e s t a r t s to increase, and reaches a maximum a t ^532°K f o r the atact i c sample. Premelting and melting then reduce the b i r e f r i n g e n c e u n t i l a zero value i s reached at ^543°K. The i s o t a c t i c polymer however, with 78% t a c t i c i t y , showed an increase i n b i r e f r i n g e n c e up to 493°K. A f t e r a small d e c l i n e , a subsequent increase to a second maximum at 518°K was observed. Further increase i n temperature l e d to a melting which was complete by ^543°K. The highest b i r e f r i n g e n c e observed was i n f a c t only f i r s t order grey, so that the occurrence o f the second maximum was q u i t e unexpected. I s o t a c t i c and a t a c t i c polymers both d i s p l a y e d the same behavi o r during c o o l i n g and r e h e a t i n g . Upon c o o l i n g from the melt a biréfringent s t r u c t u r e was obtained which upon subsequent r e heating melted. For the a t a c t i c polymer zero b i r e f r i n g e n c e was obtained f o r temperature ^543°K. The i s o t a c t i c sample d i d not show a second maximum i n t h i s case; the melting appeared to occur a t the l o c a t i o n of the f i r s t maximum, zero b i r e f r i n g e n c e being observed at ^523°K. I t i s i n t e r e s t i n g to compare the T.O.A. data f o r a t a c t i c PPBA i n Figure 4 with the data obtained from i s o t a c t i c polystyrene f i l m s c a s t i n the same manner. T h i s data i s shown i n F i g u r e 6. Despite the d i f f e r e n t molecular conf i g u r a t i o n the o p t i c a l behavior d e s c r i b e d here i s e s s e n t i a l l y the same. We assume that b i r e f r i n g e n c e can a r i s e from two sources; a c r y s t a l l i z a t i o n (or o r d e r i n g phenomenon) from the amorphous phase to give biréfringent s t r u c t u r e s ; and an o r i e n t i n g of macromolecu l a r chains e i t h e r i n the c r y s t a l l i n e or the amorphous phases. The c l a r i f i c a t i o n of these e f f e c t s i s best achieved using x-ray d i f f r a c t i o n methods, and these r e s u l t s w i l l p r e s e n t l y be d e s c r i b e d . However a c o r r e l a t i o n of the T.O.A. data with the D.S.C. data can be made. I t appears t h a t the o r i g i n a l f i l m c a s t from s o l u t i o n i s amorphous and without extensive molecular o r i e n t a t i o n . At temperatures above Tg the molecular m o b i l i t y i s s u f f i c i e n t l y great to induce " c o l d " c r y s t a l l i z a t i o n . The T.O.A. data f o r i s o t a c t i c PPBA p a r a l l e l the D.S.C. data. I f changes of b i r e f r i n g e n c e were to be a s s o c i a t e d only with the melting process then a p l a t e a u i n the T.O.A. data should have been observed r a t h e r than a maximum. T h i s i n d i c a t e s that important t e x t u r a l changes must a l s o accompany the complex melting behavior d i s p l a y e d by t h i s i s o t a c t i c polymer.


MESOMORPHIC

ORDER

IN

Figure 5. T.O.A. data for atactic and isotactic PPBA, on heating cast film (1), on solidification (2), and on reheating (3)

Figure 6.

T.O.A. data for isotactic polystyrene

POLYMERS

6.

NEWMAN

ET A L .

79


X-Ray D i f f r a c t i o n . X - r a y d i f f r a c t o m e t e r s c a n s o f v a r i o u s a t a c t i c PPBA s a m p l e s a r e shown i n F i g u r e 7. Sample A was o b t a i n ed b y p r e c i p i t a t i o n f r o m C H C 1 s o l u t i o n d i r e c t l y a f t e r p o l y m e r i zation. Samples Β a n d C w e r e o b t a i n e d b y c a s t i n g t h i n f i l m s f r o m CHC1 s o l u t i o n onto c l e a n f l a t s u b s t r a t e s ( l e a d and g l a s s ) . Sample D was o b t a i n e d b y s l o w c o o l i n g a n d s o l i d i f i c a t i o n o f m o l t e n p o l y m e r o n a g l a s s s u b s t r a t e t o g i v e a t h i n f i l m . The p r e p a r a t i o n o f s a m p l e C was e s s e n t i a l l y t h e same a s t h a t u s e d t o p r e p a r e f i l m s f o r t h e T.O.A. s t u d i e s . Sample D gave t h e d i f f r a c t i o n p a t t e r n d i s c u s s e d i n p r e s i o u s p u b l i c a t i o n s (9_) . I t i s c h a r a c t e r i z e d b y a s h a r p r e f l e c t i o n c o r r e s p o n d i n g t o a s p a c i n g o f 23.2 A and a b r o a d h a l o a t h i g h e r B r a g g a n g l e s w i t h a maximum i n t e n s i t y a t 19.5°. V e r y weak 2nd and 3 r d o r d e r s a r e p r e s e n t . Samples A a n d D show t h e same g e n eral characteristics. The l o w a n g l e p e a k s a r e n o t a s i n t e n s e a n d c a r e f u l measurement shows t h a t t h e s e c o r r e s p o n d t o a s p a c i n g o f 21.0 A. Sample C showed v e r y l i t t l e d i f f r a c t i o n a t a l l e x c e p t f o r a v e r y s m a l l peak a t t h e B r a g g a n g l e 19.5°. Some a n n e a l i n g t r e a t m e n t s were t h e n c a r r i e d o u t o n s a m p l e s A, Β a n d C a t v a r i o u s t e m p e r a t u r e s a n d t i m e s . T h e s e r e s u l t s a r e t a b u l a t e d i n Table I I and the d i f f r a c t i o n p a t t e r n s from samples Β a n d C a r e shown i n F i g u r e s 8 a n d 9. 3


3

TABLE I I Sample

Annealing T°C

A

Treatment

Ratio I / I s D

Time(hrs)

170 170 210 240

none 30 3 3 3

mins hrs hrs hrs

1:4 1:1 2:1 3:1 4:1

170 170 210 240

none 30 3 3 3

mins hrs hrs hrs

1:3 1:1 2:1 3:1 4:1

170 170 210 240

30 3 3 3

mins hrs hrs hrs

30:1 50:1 120:1 140:1

Β

A f t e r a n n e a l i n g , t h e l o w a n g l e p e a k s h i f t e d t o 3.8° ( c o r r e s p o n d i n g t o a n i n t e r p l a n a r s p a c i n g o f 23.2 A ) , became more s h a r p , a n d i n c r e a s e d i n i n t e n s i t y r e l a t i v e t o t h e w i d e - a n g l e h a l o . A mea s u r e o f t h i s i n c r e a s e i n i n t e n s i t y i s g i v e n i n T a b l e I I where t h e



Figure 7.

X-ray diffraction from atactic PPBA

6.

N E W M A N ET AL.

81



a-PPBA cast film on lead

26

25 24

23 22

21

20

18

If

« Figure 8.

17

16

15

14

13

— Bragg

12

11

10

9

έ

?

6

5

4—3

a ng ι

Mesomorphic Order in Polymers - ACS Publications - American

Recommend Documents