Mesomorphic Order in Polymers - American Chemical Society

1 X-Ray Diffraction from Polymers with Mesomorphic Order S. B. CLOUGH and A. BLUMSTEIN Polymer Program, Department of Chemistry, University of Lowell, Lowell, MA 01854

Downloaded by 117.253.107.184 on February 12, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0074.ch001

A. deVRIES Liquid Crystal Institute, Kent State University, Kent, OH 44242

Polymers with side chain s t r u c t u r e s i m i l a r to that of low molecular weight liquid crystalline com pounds can achieve various l e v e l s of o r g a n i z a t i o n i n the b u l k . These polymers are sometimes formed by p o l y merization of v i n y l monomers that themselves e x h i b i t mesomorphic behavior. I n other cases, they can be obtained from monomers that do not form liquid crys talline s t a t e s . At one extreme the s t r u c t u r e of the polymer i s h i g h l y organized, approaching that of crys talline polymers and g i v i n g r i s e to a number of x-ray diffraction peaks. At the other extreme the polymer chains are

diso r g a n i z e d ,

with

x-ray

diffraction

pat

terns that resemble those from amorphous polymers. The relation between the molecular s t r u c t u r e and the mesomorphic order has been p r e v i o u s l y discussed (1). In t h i s paper, the x-ray diffraction results for a number of polymers with stiff and/or bulky side groups are discussed. X-ray diffraction photographs from unoriented liquid crystalline states of low molecular weight compounds are c h a r a c t e r i z e d by an i n n e r r i n g (at 2θ = 2-5 degrees) r e l a t e d to the length of the mole c u l e , and an outer r i n g ( 2 0 - 2 0 deg). The former i s sharp f o r smectic s t a t e s where the molecules are mutually parallel and arranged in planes. The spacing c a l c u l a t e d (Bragg equation) i s the distance between these planes. The i n n e r r i n g is diffuse in the case of nematic s t a t e s , where the molecules in a volume element lie approximately parallel to each other but are not organized into a l a m e l l a r s t r u c t u r e . The sharpness of the outer r i n g ( s ) depends principally on the extent of lateral packing between molecules. In many cases a diffuse halo near 2θ = 20 deg shows the absence of long range lateral order between the molecules. 0-8412-0419-5/78/47-074-001$05.00/0 © 1978 American Chemical Society

In Mesomorphic Order in Polymers; Blumstein, Alexandre; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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


2

POLYMERS

A n u m b e r o f d i f f e r e n t s m e c t i c s t a t e s e x i s t among t h e low m o l e c u l a r w e i g h t m e s o m o r p h i c compounds. The m o l e c u l e s , f o r e x a m p l e , m i g h t be n o r m a l t o t h e p l a n e s or t i l t e d r e l a t i v e t o the normal. The different s t a t e s have been g i v e n v a r i o u s l e t t e r d e s i g n a t i o n s ( S m e c t i c A, B, C e t c . ) a n d d e V r i e s ( 2 ) h a s classified the x-ray p a t t e r n s obtained from the v a r i o u s types of s m e c t i c (and a l s o n e m a t i c ) s t a t e s . The p a t t e r n s o b t a i n e d f r o m t h e p o l y m e r s d i s c u s s e d h e r e show f e a t u r e s s i m i l a r t o t h o s e o f l o w m o l e c u l a r w e i g h t compounds. The i n n e r r i n g i s now r e l a t e d t o the o r g a n i z a t i o n and l e n g t h o f the p o l y m e r s i d e g r o u p s , w h i l e t h e o u t e r r i n g s d e p e n d on t h e l a t e r a l p a c k i n g between the s i d e groups. X-ray patterns and p o l y m e r o r g a n i z a t i o n are d i s c u s s e d h e r e i n t e r m s of the c l a s s i f i c a t i o n of deVries. T h i s does n o t nec e s s a r i l y i m p l y m i s c i b i l i t y w i t h a low molecular w e i g h t l i q u i d c r y s t a l o f t h e same l e t t e r d e s i g n a t i o n . Indeed, the polymers d i s cussed here are not f l u i d m a t e r i a l s b u t a r e h a r d a n d b r i t t l e , and a r e n o t l i q u i d c r y s t a l s i n the u s u a l sense of t h i s term. I n most c a s e s h e a t i n g does n o t change t h e l e v e l o f o r g a n i z a t i o n up t o t e m p e r a t u r e s w h e r e t h e p o l y m e r s t a r t s t o decompose. O t h e r c o m p a r i s o n s a n d d i s t i n c t i o n s w i l l be drawn b e t w e e n t h e s e p o l y m e r s and low m o l e c u l a r w e i g h t mesomorphic s t a t e s below. Some comments w i l l a l s o be made on t h e o r g a n i z a t i o n o f t h e p o l y m e r s as c o m p a r e d t o s e m i - c r y s t a l l i n e polymers with s m a l l extent of crystallinity. Experimental The m e t h o d s o f p r e p a r a t i o n o f t h e monomers a r e i n the references i n Tables I-III. X - r a y d i f f r a c t i o n d a t a w e r e o b t a i n e d w i t h a Warh u s v a c u u m c a m e r a , and R i g a k u w i d e a n g l e ( m o d e l SG-7B) and s m a l l a n g l e d i f f r a c t o m e t e r s , a l l w i t h Cu radiation. A L e i t z Ortholux p o l a r i z i n g microscope with a M e t t i e r FP5 2 h o t s t a g e was u s e d f o r e x a m i n a t i o n of biréfringent f i l m s o f t h e p o l y m e r s and f o r d e t e r m i n i n g monomer t r a n s i t i o n t e m p e r a t u r e s . A P e r k i n Elmer DSC1B 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 was a l s o u s e d t o o b t a i n t h e t r a n s i t i o n t e m p e r a t u r e o f monomers. given

Results

and

Discussion

The p o l y m e r s a r e p r e s e n t e d i n o r d e r o f d e c r e a s i n g l e v e l s of o r g a n i z a t i o n , s t a r t i n g with h i g h l y ordered s m e c t i c and p r o c e e d i n g t o p o o r l y o r g a n i z e d n e m a t i c states.



1.

CLOUGH E T A L .

X-Ray Diffraction from Polymers

3

Smectic. T a b l e I l i s t s t h e monomers o f some p o l y m e r s t h a t show a s h a r p i n n e r r i n g a n d t h u s h a v e smectic organization. P o l y ( a e r y l o y l o x y b e n z o i c a c i d ) , (ΡABA). When t h e c o r r e s p o n d i n g monomer i s p o l y m e r i z e d i n t h e m e l t t o h i g h degrees o f c o n v e r s i o n , * x-ray d i f f r a c t i o n from t h e p o l y m e r shows a s h a r p r i n g c o r r e s p o n d i n g t o 1 7 . 7 ^ , and t h r e e s h a r p o u t e r r i n g s i n a d d i t i o n t o t h e o u t e r h a l o (JO . The s p a c i n g o f t h e i n n e r r i n g i s l e s s t h a n twice the length o f t h e side groups, suggesting t h a t the l a t t e r a r e s t r o n g l y t i l t e d w i t h r e s p e c t t o t h e smectic planes. We w e r e u n a b l e t o o r i e n t t h e s a m p l e to confirm t h i s t i l t i n g . In the smectic state o f a low m o l e c u l a r w e i g h t a n a l o g , n o n y l o x y b e n z o i c acid, t h e m o l e c u l e s a r e t i l t e d a t a p p r o x i m a t e l y 45 d e g r e e s t o t h e p l a n e n o r m a l (J4). The x - r a y p a t t e r n m o s t c l o s e l y r e s e m b l e s t h a t o f t h e S m e c t i c E-f- ( 2 ) . The t h r e e o u t e r r i n g s show t h a t t h e r e e x i s t s some r e g u l a r p a c k i n g b e t w e e n t h e s i d e g r o u p s . I t m i g h t b e n o t e d t h a t f o r p o l y m e r s we w o u l d e x p e c t t o observe t h e h a l o , even i f t h e r e a r e sharp o u t e r r i n g s present. T h i s w o u l d b e due t o p o o r l y o r g a n i z e d r e gions . The o r d e r e d d o m a i n s a r e n o t e x p e c t e d t o e x t e n d u n i f o r m l y throughout t h e specimen. The p r e s e n c e o f the h a l o i s s i m i l a r t o t h e case o f s e m i - c r y s t a l l i n e polymers. P o l y ( m e t h a c r y l o y l o x y b e n z o i c a c i d ) , (PMBA). Films of t h i s polymer cast from dimethyIformamide give x-ray p a t t e r n s w i t h a sharp i n n e r and a sharp outer r i n g , (_5 ) i n a d d i t i o n t o t h e h a l o . This p a t t e r n resembles the p a t t e r n o f Smectic B (JO. I t i s i n t e r e s t i n g t o remark t h a t i n both abovem e n t i o n e d c a s e s , t h e monomers a r e n o t m e s o m o r p h i c . Poly(Ν-ρ-methacryloyloxybenzylidene-p-aminobenz o i c a c i d ) , (PMBABA). P o l y m e r i z a t i o n a t 213°C f r o m the nematic s t a t e g i v e s a polymer w i t h a s m e c t i c structure. The s p a c i n g c a l c u l a t e d f r o m t h e s h a r p inner r i n g i s approximately twice the length o f the s i d e c h a i n s (6_) . This suggests Smectic A o r g a n i z a t i o n w i t h t h e s i d e groups normal t o t h e planes and t h e p o l y mer m a i n c h a i n c o n t a i n e d w i t h i n t h e p l a n e s . Polyme r i z a t i o n o f t h e monomer f r o m t h e n e m a t i c s t a t e i n a l O k O e m a g n e t i c f i e l d g a v e an o r i e n t e d s p e c i m e n . X-ray t

^ P o l y m e r i z a t i o n t o low degrees o f c o n v e r s i o n and c a s t i n g o f f i l m s from a dimethyIformamide s o l u t i o n g i v e s a s e m i - c r y s t a l l i n e p o l y m e r w i t h up t o e i g h t x-ray d i f f r a c t i o n l i n e s .



3

/—ν

3

6

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c: H = C H

/

2

•0CCH=CH 2

PdiABH •—ν C H = C H C O O ^ Q ) C H = N-N=CH

2

,—ν . -

C H =C r f O > N = C H / 0 ) c PPMAS MAS / — ν — CH 2 \ 0 ^ = C H / 0 \ : H =N

H

H

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Κ

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S

88. 3

Ν

120.6

97.5

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2

I

I

Κ 113 . 8 Ν 1 4 0 . 5 I

Monomer T r a n s i t i o n s , degrees C

Κ 140 N P o l y ' n

Κ 1 8 0 N Poly'n

29=3. 3

29=3.l

U

5.00

4.95

v e r y weak

4.2° ^ 2°

5

~

5,1

4.9

Polymer X-ray Data Inner Ring D,g

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Polymer X-ray Data Inner Ring D,g

Organization

Organization

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Polymers w i t h Nematic

1 3

J 4

2.

III.

C

C

PC3AS r LdAb / β — νν

Table

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=C H / Q V N = C H / O /

0

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CH

r^\

/

> =C H - ^ Q ^ - N ^ C i ^ O )

A b b r e v i a t i o n o f Polymer S t r u c t u r e o f Monomer

.

CH

PBBAS

Intermediate

Monomer T r a n s i t i o n s , degrees C

Polymers w i t h

A b b r e v i a t i o n o f Polymer S t r u c t u r e o f Monomer

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.

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10

MESOMORPHIC

ORDER I N

POLYMERS

c h a i n s c o n t a i n i n g t h e S c h i f f base s t r u c t u r e and p h e n y l r i n g s when r e g u l a r p a c k i n g i s a c h i e v e d ( 9 ) . Further, t h i s sharp peak i s absent from t h e x-ray p h o t o g r a p h s from samples p r e c i p i t a t e d from s o l u t i o n . This l a t t e r method o f sample p r e p a r a t i o n l e a d s t o a l e s s o r d e r e d structure than bulk polymerization. Thus, t h e sharp l i n e m u s t b e due t o p a r a l l e l p a c k i n g b e t w e e n s i d e groups, not other i n t r a m o l e c u l a r e f f e c t s . The l o w i n t e n s i t y o f t h e x - r a y i n n e r r i n g c o u l d be due t o t w o f a c t o r s . 1) The n e m a t i c o r g a n i z a t i o n m i g h t n o t be e x t e n s i v e . As m e n t i o n e d a b o v e , t h e o r d e r e d d o m a i n s may n o t e x t e n d c o n t i n u o u s l y t h r o u g h o u t t h e s ample i n p o l y m e r s , b u t w o u l d be i n t e r r u p t e d by disordered regions. 2) The d i f f u s e i n n e r r i n g f o r n e m a t i c s t a t e s i n s m a l l m o l e c u l e s i s caused by t h e low e l e c t r o n d e n s i t y a t t h e ends o f t h e m o l e c u l e s . In the case o f polymers w i t h nematic packing o f the s i d e c h a i n s , one e n d o f t h e n e m a t o g e n i c s t r u c t u r e i s b o n d e d t o t h e p o l y m e r main c h a i n w i t h no a b r u p t d e c r e a s e i n density. Thus, there a r e fewer e l e c t r o n d e n s i t y f l u c t u a t i o n s p e r u n i t volume. To o u r k n o w l e d g e , t h e r e a r e no r e p o r t e d c a s e s w h e r e p o l y m e r s w i t h n e m a t i c o r g a n i z a t i o n o f s i d e g r o u p s g i v e an I n n e r r i n g o f m o d e r a t e intensity. The t u r b i d i t y o f t h e n e m a t i c s t a t e s o f l o w m o l e c u l a r w e i g h t compounds i s due p r i m a r i l y t o f l u c t u a tions i n the o r i e n t a t i o n of the d i r e c t o r over distances on t h e o r d e r o f t h e w a v e l e n g t h o f v i s i b l e l i g h t ( 1 2 ) . The o p t i c a l c l a r i t y o f PCBAS i n d i c a t e s t h a t t h e r e g i o n s o f n e m a t i c o r g a n i z a t i o n a r e much s m a l l e r i n s i z e . Light i s not appreciably scattered, nor are the t y p i c a l nematic textures resolvable i n the p o l a r i z i n g mic r o s cope. Poly(p-phenylene-bis(N-methylene-p-aminostyrene)), (PPMAS), P o l y ( d i ( N - p - a c r y l o y l o x y b e n z y l i d e n e ) h y d r a z i n e ) , (PdiABH). T h e s e d i f u n c t i o n a l monomers y i e l d p o l y m e r n e t w o r k s upon b u l k p o l y m e r i z a t i o n . No i n n e r r i n g s have been d e t e c t e d from t h e nematic o r g a n i z a t i o n . This h a s b e e n e x p l a i n e d (9) b y t h e f a c t t h a t b o t h c h a i n e n d s o f t h e monomer a r e i n c o r p o r a t e d i n t o t h e p o l y m e r m a i n chains. I n t h e case o f complete c o n v e r s i o n t o polymer t h e r e a r e no s i d e group ends g i v i n g l a r g e e l e c t r o n density fluctuations. Comparison w i t h C r y s t a l l i n e Polymers. The s t r u c t u r e o f t h e p o l y m e r s d i s c u s s e d above d i f f e r s f r o m t h a t i n c r y s t a l l i z a b l e polymers w i t h low degrees o f c r y s t a l l i n i t y ( p o o r l y d e v e l o p e d s t r u c t u r e ) . Here t h e t e n d e n c y t o o r g a n i z e comes f r o m t h e p a r a l l e l p a c k i n g of the side groups. There i s no e v i d e n c e t h a t p o l y m e r


I.

C L O U G H

E T

A L .

X-Rciij Diffraction from Polymers

11

main c h a i n s a r e p a r a l l e l t o each o t h e r o v e r l o n g d i s tances. I n t h e s m e c t i c A a n d C s t a t e s , we e n v i s i o n the p o l y m e r c h a i n as c o i l e d t h o u g h c o n f i n e d t o a p l a n e . In t h e u s u a l case o f polymer c r y s t a l s t h e main c h a i n s l i e p a r a l l e l i n the c r y s t a l l i n e regions. Acknowledgement T h a n k s a r e e x p r e s s e d t o t h e NSF f o r p a r t i a l p o r t u n d e r t h e G r a n t DMR-75-17397.

sup


Literature Cited 1. 2. "Liquid 3. 4. quid 5. 6. fillment 7. 8. 9. 10. 11.

12.

Blumstein, A., M a c r o m o l , ( 1 9 7 7 ) 1 0 , 872. deVries, Α., Ρramana, ( 1 9 7 5 ) 9, 93 Suppl. 1, a n d Crystals," C h a n d r a s e k a r , S. e d . , Indian Acad. Sci., Bangalore, 1975. Blumstein, A., Clough, S.B., Patel, L . , Blumstein, R.B., a n d H s u , E.C., M a c r o m o l . , ( 1 9 7 6 ) 9, 2 4 3 . Chystiakov, I., "Ordering a n d Structure of Li Crystals" in Adv. in Liquid Crystals, Vol. 1, B r o w n , G. ed., A c a d e m i c Press, (1975). Blumstein, A., Blumstein, R.B., Clough, S.B., a n d H s u , E.G., M a c r o m o l , ( 1 9 7 5 ) 8, 7 3 . L i m , L., Thesis in preparation for partial ful of requirements for Ph.D. d e g r e e . Poly mer Preprints, ( 1 9 7 5 ) 1 6 , No. 2, 2 4 1 . deVries, A., Mol. Cryst. Liq. Cryst., ( 1 9 7 0 ) 10, 219. H s u , E.C., Clough, S.B., a n d Blumstein, A., Polym. Lett., (1977) 15, 545. C l o u g h , S.B., Blumstein, A., a n d Hsu, E.C., M a c r o m o l . , ( 1 9 7 6 ) 9, 1 2 3 . H s u , E.C., a n d Blumstein, A., P o l y m . Lett., (1977) 15, 129. H s u , E.C., L i m , L . K . , Blumstein, R.B., a n d Blumstein, A., Mol. Cryst. Liq. Cryst. (1976) 33, 35. d e G e n n e s , P., The Physics of Liquid Crystals, Oxford University Press, London (1974).

Received December 8, 1977.


Mesomorphic Order in Polymers - American Chemical Society

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