Epitaxial Growth of Polydiacetylenes - ACS Symposium Series (ACS

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Epitaxial Growth of Polydiacetylenes S C O T T E. R I C K E R T , J E R O M E B. L A N D O , and S T E P H E N C H I N G Case Western Reserve University, Department of Macromolecular Science, Cleveland, OH 44106

The two-step process of epitaxial polymerization has been applied to symmetrically substituted diacetylenes. F i r s t , the monomers have been crystallized epitaxially on a l k a l i halides substrates from solution and the vapor phase. The oriented monomer crystals are then polymerized under the substrate's influence by gamma- i r r a d i a t i o n . The diacetylenes in this study are 2,4hexadiyn-1,6-diol (HD) and the bis-phenylurethane of 5,7-dodecadiyn-1,12-diol (TCDU). The polydiacetylene crystal structures and morphologies have been examined with the electron microscope. Reactivity and polymorphism are found to be controlled by the substrate. E p i t a x i a l p o l y m e r i z a t i o n i s a general process a p p l i c a b l e to monomers that may be polymerized i n the s o l i d s t a t e . The study of d i s u l f u r n i t r i d e vapor phase c r y s t a l l i z a t i o n on a l k a l i h a l i d e s with thermal p o l y m e r i z a t i o n to p o l y t h i a z l , (SN) , has shown that subs t r a t e c o n t r o l l e d r e a c t i o n l e d to three new c r y s t a l phases of (SN)^_(l-2). Diacetylenes are monomers that can be polymerized from the monomer c r y s t a l s to v a r y i n g degrees of conversion and c r y s t a l l i n i t y depending on the nature of the s u b s t i t u e n t s and t h e i r packing w i t h i n the monomer l a t t i c e ( 3 ) . Furthermore, the polymer backbone may adopt e i t h e r an a c e t y l e n i c ^RC-CEC-CR^ or a b u t a t r i e n e 4RC=C=C=CR)- bonding. The u r e t h a n e - s u b s t i t u t e d p o l y d i a c e t y l e n e s e x h i b i t thermochromic t r a n s i t i o n with low and high temperature c r y s t a l phases favoring a c e t y l e n i c and b u t a t r i e n e backbone, r e s p e c t i v e l y (4-6). Our i n t e r e s t i n the a p p l i c a t i o n of e p i t a x i a l p o l y m e r i z a t i o n to diacetylenes has been the p o s s i b i l i t y of substrate c o n t r o l over o r i e n t a t i o n , s t r u c t u r e , and the s i n g l e c r y s t a l nature of t h i n f i l m s .

0097-6156/83/0233-0229$06.00/0 © 1983 American Chemical Society

Williams; Nonlinear Optical Properties of Organic and Polymeric Materials ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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NONLINEAR OPTICAL PROPERTIES

Experimental


2,4-hexadiyne-l,6-diol (DMDA) from Farchan L a b o r a t o r i e s was r e c r y s t a l l i z e d from toluene. S o l u t i o n s up to 1 wt. % i n toluene were prepared f o r e p i t a x i a l c r y s t a l l i z a t i o n . Bis-phenylurethane of 5,7-dodecadiyne-l, 1 2 - d i o l (TCDU) was supplied by A l l i e d Chemical Co. The monomer was extracted from the p a r t i a l l y p o l y merized l a t t i c e with acetone. The monomer was d i s s o l v e d i n e t h y l acetate to make a 0.4 wt. % s o l u t i o n . Table

I.

TCDU Phase 2

Phase 1

Monomer

a = 0.708 nm b = 3.397 nm c = 0.523 nm 3 = 115.85°

a = 1.160 nm b = 1.897 nm c = 0.519 nm Ύ = 91.0°

Polymer

a = 0.623 nm b = 3.903 nm c = 0.491 nm 3 = 106.85°

a = 1.184 nm b = 1.987 nm c = 0.495 nm Ύ = 94.94°

E p i t a x i a l c r y s t a l l i z a t i o n was accomplished by the immersion of a preheated substrate (the substrates f o r e p i t a x i a l c r y s t a l l i z a t i o n were s i n g l e c r y s t a l s of a l k a l i h a l i d e s from Harshaw Chemical Co.) i n t o the monomer s o l u t i o n followed by i t s i n - s i t u cleavage to expose two f r e s h (100) surfaces. Table I I .

D i o l Unit C e l l Parameters 3

a

b

Monomer

.409

1 60

.477

106 .3

Polymer

.411

1 61

.482

106 .1

Polymer/KBr

.421+.04

1 02+. 10

c

u n i t s i n nm The i s o t h e r m a l l y c r y s t a l l i z e d monomers were polymerized with 2-4 Mrad γ-irradiation. The polymer f i l m was removed from the substrate a f t e r C , Pt coating by d i s s o l v i n g the s a l t . A JEOL JEM 100B e l e c t r o n microscope was used to examine the samples. Results and D i s c u s s i o n Large domains of o r i e n t e d s i n g l e c r y s t a l s of poly(TCDU) and poly(DMDA) were produced on the a l k a l i h a l i d e s u r f a c e . Figures 1 and 2 show the t y p i c a l elongated p l a t e l e t morphology. Selected



RICKERT ET AL.

Epitaxial Growth of Polydiacetylenes

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Figure 1. Poly(TCD U) polymerized on KCl and depositedfrom α0.4\νίψο ethyl acetate solution at 30 °C

Figure 2. DM DA polymerized on ΚBr and deposited from a w/% toluene solution at 78 °C


NONLINEAR OPTICAL PROPERTIES


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area e l e c t r o n d i f f r a c t i o n from such domains gave s i n g l e c r y s t a l l i n e p a t t e r n as i n Figures 3 and 4. The u n i t c e l l parameters are given i n Tables 1 and 2. Poly(TCDU) i n t h i n f i l m e x i s t s i n the a c e t y l e n i c phase 2, as opposed to the b u t a t r i e n e phase 1 found i n bulk c r y s t a l s p o l y merized from macroscopic monomer c r y s t a l s (7). Polymerization to completion i n t h i n f i l m , thereby removing the c o n s t r a i n t of the monomer l a t t i c e , could account f o r the a c e t y l e n i c phase. The orthogonal p r o j e c t i o n of the e p i t a x i a l poly(DMDA) could not be indexed using the u n i t c e l l data f o r the bulk polymerized c r y s t a l (8). However, poly(DMDA) cannot u s u a l l y be polymerized to completion or to high c r y s t a l l i n i t y i n the bulk due to c r o s s linking. The use of an e p i t a x i a l substrate may have c o n t r o l l e d the polymerization process that l e d to o r i e n t e d s i n g l e c r y s t a l s . Conclusion Two d i a c e t y l e n e s have been e p i t a x i a l l y polymerized as t h i n f i l m s i n contact with a l k a l i h a l i d e s u b s t r a t e s . These f i l m s i n contact with a l k a l i h a l i d e s u b s t r a t e s . These f i l m s c o n s i s t e d of h i g h l y o r i e n t e d s i n g l e c r y s t a l s a l i g n e d along both direct i o n s of the substrate. The s t r u c t u r e s of both poly(TCDU) and poly(DMDA) were modified by t h i s technique and, i n a l l cases, h i g h l y c r y s t a l l i n e near-perfect f i l m s were achieved.

Figure 3. Electron diffraction of poly (TC DU) formed under conditions specified in Figure I.



11.

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Figure 4. Electron diffraction ofpoly (DMDA ) from Figure 2.

Acknowledgments The authors would l i k e to acknowledge the support of Army Research O f f i c e Grant No. DAAG 29-80C-0099 f o r f i n a n c i a l a s s i s t ance of t h i s work.

Literature Cited 1. Rickert, S. E; Lando, J. B.; Hopfinger, A. J.; Baer, E. Macromolecules 1979, 12, 1053. 2. Rickert, S. E.; Ishida, H.; Lando, J. B.; Koenig, J. L.; Baer, E. J. Appl. Phys. 1980, 10, 5194. 3. Baughman, R. H. J. Polym. S c i . , Polym. Phys. Ed. 1974, 12, 1511. 4. Chance, R. R.; Baughman, R. H.; M i l l e r , H.; Eckhardt, C. J. J. Chem. Phys. 1977, 67, 3616. 5. M i l l e r , H.; Eckhardt, C.J. Mol. Cryst. L i q . Cryst. 1978, 45, 313. 6. Eckhardt, H.; Eckhardt, C. J. J. Chem. Phys. 1979, 70, 5498. 7. Enkelmann, V.; Lando, J. B. Acta Cryst. 1978, B34, 2352. 8. Baughman, R. H. J. Appl. Phys. 1972, 43, 4362. RECEIVED June 6, 1983


Epitaxial Growth of Polydiacetylenes - ACS Symposium Series (ACS

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