An Introduction to Inorganic and Organometallic Polymers

Chapter 1

Downloaded by 95.181.176.77 on June 24, 2016 | http://pubs.acs.org Publication Date: January 7, 1988 | doi: 10.1021/bk-1988-0360.ch001

An Introduction to Inorganic and Organometallic Polymers Kenneth J. Wynne Chemistry Division, Office of Naval Research, Arlington, V A 22217-5000

"Inorganic and organometallic" in the context of t h i s Symposium is meant to describe macromolecules which usually contain inorganic elements in the chain and organic moieties as pendant groups. The s u b t i t l e delineates elements of primary focus: "Macromolecules Containing S i l i c o n , Phosphorus and Other Inorganic Elements." The term "macromolecules" implies that the subject matter includes chain molecules that may be b u i l t up of repeat u n i t s , as well as more complex r i n g , branched, or crosslinked species (for example, see Organo-Oxo-Element Macromolecules Related to Sol-Gel Processes, and contributions by Murray (p. 408) or Seyferth (p. 143)). P r i o r reviews concerning inorganic and organometallic macromolecules are contained in texts by Stone and Graham (1), Andrianov (2), Borisov (3), Allcock (4,5), and Voronkov (6), and volumes based on previous ACS symposia edited by Rheingold (7), and Carraher, Sheats and Pittman (8, 9). The present e f f o r t is t o p i c a l in nature, and the order of presentation approximates that of the Symposium presentations. The impetus for t h i s symposium volume is the considerable progress which has been made in the l a s t few years in inorganic and organometallic macromolecules. T o t a l l y new macromolecules have been brought into existence by the development of new synthetic methods or improvement of known synthetic routes. Thus, Neilson (p. 283) describes a new polymerization reaction that gives high molecular weight poly(diorganophosphazenes), -(R PN)n -, in which organic pendant groups are bonded through P-C bonds. These polyphosphazene analogs of polysiloxanes were not previously accessible, and the development of structure-property relationships in this new subclass of macromolecules w i l l no doubt y i e l d important information and perhaps s i g n i f i c a n t applications. 2

This chapter is not subject to U.S. copyright. Published 1988 American Chemical Society Zeldin et al.; Inorganic and Organometallic Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

INORGANIC AND ORGANOMETALLIC POLYMERS


2

A n o t h e r example o f i n t e r e s t i n g new i n o r g a n i c polymers is f o u n d in the work o f L a s o c k i (p. 166), who r e p o r t s the s y n t h e s i s of p o l y s i l a z o x a n e s , - [ ( R SiOj^CR^SiNR) ] -, and f i n d s s u r p r i s i n g l y b e t t e r t h e r m a l s t a b i l i t y compared wïtfi t h e i r p o l y s i l o x a n e a n a l o g s . The d e s i g n o f f u n c t i o n a l i z e d polymers w i t h a s p e c i f i c u t i l i z a t i o n is seen in new p o l y s i l o x a n e s used by Z e l d i n (p. 199) as phase t r a n s f e r c a t a l y s t s . N o v e l f u n c t i o n a l p o l y p h o s p h a z e n e s have been r e p o r t e d as w e l l by A l l c o c k (p. 250). The i n t r o d u c t i o n o f t r a n s i t i o n m e t a l c y c l o p e n t a d i e n y l , m e t a l c a r b o n y l and c a r b o r a n e m o i e t i e s i n t o p o l y p h o s p h a z e n e macromolecules is r e p r e s e n t a t i v e o f t r u l y n o v e l c h e m i s t r y a c h i e v e d a f t e r c a r e f u l model s t u d i e s w i t h corresponding molecular systems. West (p. 6 ) , M i l l e r (p. 4 3 ) , Z e i g l e r ( 1 0 ) , and Sawan (p. 112) o u t l i n e the s y n t h e s i s of a wide v a r i e t y o f s o l u b l e , p r o c e s s a b l e p o l y d i o r g a n o s i l a n e s , a c l a s s o f polymers which not l o n g ago was t h o u g h t t o be i n t r a c t a b l e . M a t y j a s z e w s k i (p. 78) has found s i g n i f i c a n t improvements in the s y n t h e t i c method f o r p o l y d i o r g a n o s i l a n e s y n t h e s i s as w e l l as new s y n t h e t i c r o u t e s t o unusual s u b s t i t u t e d polydiorganosilanes. S e y f e r t h (p. 21, 143) r e p o r t s s y n t h e t i c r o u t e s t o a number o f new p o l y c a r b o s i l a n e s and p o l y s i l a z a n e s w h i c h may be used as p r e c u r s o r s t o c e r a m i c m a t e r i a l s . New c a t a l y t i c p o l y m e r i z a t i o n r o u t e s t o p o l y s i l a n e s ( H a r r o d , (p. 89)) and p o l y s i l a z a n e s ( L a i n e , (p. 124)) have been d i s c o v e r e d . S i n g l e r ( p . 268) d e s c r i b e s t h e use o f B C l ^ in t h e more e f f i c i e n t s y n t h e s i s of - ( P N C 1 ) -, the s t a r t i n g h i g h polymer f o r most polyphosphazene p o l y m e r s c u r r e n t l y under i n v e s t i g a t i o n . These r e s u l t s in the a r e a o f p o l y m e r i z a t i o n c a t a l y s t s a r e i m p o r t a n t , as the s y s t e m a t i c development o f e f f i c i e n t c a t a l y t i c r o u t e s f o r i n o r g a n i c and o r g a n o m e t a l l i c macromolecules w i l l make such m a t e r i a l s more g e n e r a l l y a c c e s s i b l e and u t i l i z a b l e . T h i s r e s e a r c h is a l s o c l o s e l y r e l a t e d t o u n d e r s t a n d i n g o f mechanisms o f c h a i n growth. E f f o r t s aimed a t the e l u c i d a t i o n o f p o l y m e r i z a t i o n mechanisms i n c l u d e t h o s e o f S i n g l e r (p. 268) in p o l y p h o s p h a z e n e s , L i p o w i t z (p. 156) in p o l y s i l a z a n e s , and Z e i g l e r and W o r s f o l d in p o l y s i l a n e s . In c o n t r a s t w i t h c a r b o n c h e m i s t r y , the mechanisms o f p o l y m e r i z a t i o n r e a c t i o n s l e a d i n g t o i n o r g a n i c and o r g a n o m e t a l l i c m a c r o m o l e c u l e s a r e o f t e n not w e l l u n d e r s t o o d . Such s t u d i e s are c r i t i c a l in e l u c i d a t i n g pathways o f c h a i n growth, t e r m i n a t i o n , and b r a n c h i n g so t h a t t h e s e f e a t u r e s may be c o n t r o l l e d . O f t e n t i m e s m e c h a n i s t i c s t u d i e s l e a d t o more e f f i c i e n t s y n t h e t i c methods, f o r example b y i m p r o v i n g y i e l d s o r s h o r t e n i n g r e a c t i o n times. In the s e c t i o n on b o r o n - c o n t a i n i n g p o l y m e r s , P a i n e (p. 378), N e i l s o n ( p . 385), and P a c i o r e k (p. 392) p r e s e n t p i o n e e r i n g work aimed a t the p r e p a r a t i o n o f l i n e a r c h a i n m a c r o m o l e c u l e s w i t h B-N backbones. T h i s work is s i g n i f i c a n t because c o n d e n s a t i o n r e a c t i o n s o f B-N compounds tend to p r o d u c e compounds w i t h r i n g s t r u c t u r e s r a t h e r t h a n c h a i n s . One o b v i o u s p o t e n t i a l u t i l i z a t i o n o f such n o v e l macromolecules is as p r e c e r a m i c m a t e r i a l s , much in the same way as p o l y a c r y l o n i t r i l e is used as a p r e c u r s o r f o r c a r b o n . O r i e n t a t i o n o f t h e B-N polymer may be t r a n s f e r r e d in p a r t t o the c e r a m i c s o l i d s t a t e a g a i n in manner s i m i l a r to c a r b o n c h e m i s t r y . However, the p r o p e r t i e s o f BN p o l y m e r s and c e r a m i c m a t e r i a l s d i f f e r g r e a t l y from t h e i r c a r b o n a n a l o g s due t o l o c a l i z e d e l e c t r o n i c s t a t e s in t h e BN bond. The consequences o f t h i s c o n t r a s t i n g e l e c t r o n i c s t r u c t u r e on m a t e r i a l s p r o p e r t i e s w i l l be i n t e r e s t i n g t o see as t h i s new r e s e a r c h a r e a develops. 9

Zeldin et al.; Inorganic and Organometallic Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.


1. WYNNE

Introduction

3

A p l u r a l i t y o f p a p e r s in t h i s volume c o n c e r n l i n e a r c h a i n m a c r o m o l e c u l e s . Fundamental t o u n d e r s t a n d i n g t h e p h y s i c a l and m e c h a n i c a l b e h a v i o r and c h e m i c a l and p h y s i c a l s t a b i l i t y o f t h e s e m a c r o m o l e c u l e s is a f a m i l i a r i t y w i t h phase t r a n s i t i o n b e h a v i o r , an a r e a w e l l known in o r g a n i c polymer c h e m i s t r y ( 1 1 ) . As with organic p o l y m e r s , amorphous and s e m i c r y s t a l l i n e i n o r g a n i c and o r g a n o m e t a l l i c macromolecules a r e known. C r y s t a l l i n i t y a r i s e s f r o m m a i n c h a i n o r d e r o r s i d e c h a i n c r y s t a l l i z a t i o n as d i s c u s s e d by S i n g l e r (p. 268) f o r polyphosphazenes and West (p. 6) and M i l l e r ( p . 43) f o r p o l y s i l a n e s . The l a t t e r work d e m o n s t r a t e s that c r y s t a l l i z a t i o n b e h a v i o r p l a y s a c r i t i c a l r o l e in c o n t r o l l i n g main c h a i n c o n f o r m a t i o n and o p t i c a l t r a n s i t i o n s in p o l y ( d i o r g a n o s i l a n e s ) . Thus, i m p o r t a n t s t r u c t u r e / p r o p e r t y r e l a t i o n s h i p s a r e emerging t h a t a r e r e l e v a n t t o e l e c t r o n i c and o p t i c a l m a t e r i a l s a p p l i c a t i o n s f o r these m a t e r i a l s . In a d i f f e r e n t v e i n , s i d e chain c r y s t a l l i z a t i o n has r e s u l t e d in t h e f i r s t l i q u i d c r y s t a l l i n e i n o r g a n i c and o r g a n o m e t a l l i c macromolecules, v i z . , unusual p o l y ( d i a l k o x y phosphazenes) d e s c r i b e d by A l l c o c k (p. 250) and S i n g l e r (p. 2 6 8 ) . In t h i s c a s e , t h e f l e x i b l e n a t u r e o f t h e P-N c h a i n p l a c e s s t r i n g e n t s t r u c t u r a l r e q u i r e m e n t s on t h e n a t u r e o f t h e pendant group. Unique c o m b i n a t i o n s o f p r o p e r t i e s c o n t i n u e t o be d i s c o v e r e d in i n o r g a n i c and o r g a n o m e t a l l i c macromolecules and s e r v e t o c o n t i n u e a h i g h l e v e l o f i n t e r e s t w i t h r e g a r d t o p o t e n t i a l a p p l i c a t i o n s . Thus, A l l c o c k d e s c r i b e s h i s c o l l a b o r a t i v e work w i t h S h r i v e r (p. 250) t h a t l e d t o i o n i c a l l y c o n d u c t i n g p o l y p h o s p h a z e n e / s a l t complexes w i t h t h e h i g h e s t ambient temperature i o n i c c o n d u c t i v i t i e s known f o r p o l y m e r / s a l t e l e c t r o l y t e s . E l e c t r o n i c c o n d u c t i v i t y is found v i a t h e p a r t i a l o x i d a t i o n o f u n u s u a l p h t h a l o c y a n i n e s i l o x a n e s (Marks, p. 224) which c o n t a i n s i x - c o o r d i n a t e r a t h e r t h a n t h e u s u a l four-coordinate Si. P a r t o f t h i s symposium was d i r e c t e d t o t h e s y n t h e s i s , p r o p e r t i e s and a p p l i c a t i o n s o f i n o r g a n i c and o r g a n o m e t a l l i c m a c r o m o l e c u l e s w i t h network s t r u c t u r e s . The s e c t i o n on organo-oxo macromolecules r e l e v a n t t o s o l - g e l p r o c e s s i n g a d d r e s s e s t h e i n t e r e s t i n g s y n t h e s i s and c h a l l e n g i n g c h a r a c t e r i z a t i o n e f f o r t s in t h i s a r e a . B r i n k e r (p. 314) o u t l i n e s t h e complex c h e m i c a l and p h y s i c a l f a c t o r s w h i c h a f f e c t network f o r m a t i o n and s t r u c t u r e r e s u l t i n g from t h e h y d r o l y s i s o f a t e t r a a l k o x y s i l a n e . The i n t e r e s t i n g p r o p e r t i e s o f h y b r i d o r g a n i c / i n o r g a n i c network s t r u c t u r e s a r e d e s c r i b e d in the work o f Schmidt ( p . 333) and W i l k e s ( p . 354). In c o n c l u s i o n , some t r e n d s c a n be g l e a n e d from an e x a m i n a t i o n o f t h e c o n t e n t o f t h e symposium as a whole. The growth in r e s e a r c h e f f o r t s a d d r e s s i n g t h e s y n t h e s i s and p r o p e r t i e s o f p o l y ( d i o r g a n o s i l a n e s ) w i l l l i k e l y c o n t i n u e . The u n i q u e p h o t o p h y s i c a l p r o p e r t i e s o f t h i s newly d e v e l o p e d c l a s s o f i n o r g a n i c m a c r o m o l e c u l e s (12) t o g e t h e r w i t h ready s y n t h e t i c r o u t e s w i l l be c o n t r i b u t i n g f o r c e s h e r e , and no doubt new v e c t o r s w i l l a r i s e . A n o t h e r a r e a o f i n c r e a s e d a t t e n t i o n w i l l be organo-oxo macromolecules d e r i v e d from s o l - g e l p r o c e s s i n g methods, e i t h e r a s c o p o l y m e r s o r b l e n d s . Complex d e p e n d e n c i e s o f organo-oxo m a c r o m o l e c u l a r c o m p o s i t i o n and s t r u c t u r e on s t a r t i n g m a t e r i a l s a n d p r o c e s s i n g c o n d i t i o n s ( i n c l u d i n g k i n e t i c e f f e c t s ) w i l l l e a d to c h a l l e n g i n g and i n t e r e s t i n g s c i e n c e . Important m e c h a n i c a l , o p t i c a l and s t r u c t u r a l a p p l i c a t i o n s c o u p l e d a g a i n w i t h emerging s y n t h e t i c approaches w i l l be among t h e d r i v e r s f o r c o n t i n u e d h i g h a c t i v i t y in t h i s area.


4

INORGANIC AND ORGANOMETALLIC POLYMERS

F i n a l l y , one a d d i t i o n a l comment c o n c e r n i n g t h e n a t u r e o f p r o g r e s s from i n t e r d i s c i p l i n a r y r e s e a r c h is e v i d e n t from t h e r e s u l t s r e p o r t e d in t h i s Symposium Volume. Once a g a i n i t is s e e n t h a t most r a p i d p r o g r e s s is made when s y n t h e t i c chemists c o l l a b o r a t e w i t h t h e i r c o l l e a g u e s in m a t e r i a l s s c i e n c e o r p h y s i c s t o d e t e r m i n e p r o p e r t i e s o f new i n o r g a n i c and o r g a n o m e t a l l i c po l y m e r s . Acknowledgment The a u t h o r thanks t h e O f f i c e o f N a v a l R e s e a r c h contribution.


Literature

f o r support of

this

Cited

1. Stone, F. G. Α., Graham, W. A. G. Inorganic Polymers, Academic Press, New York 1962 2. Andrianov, Κ. A. Metalorganic Polymers, Interscience Publishers, New York 1965. 3. Borisov, S. N., Voronkov, M. G., Lukevits, E. Ya. Organosilicon Heteropolymers and Heterocompounds, Plenum Press, New York 1970. 4. Allcock, H. R. Phosphorus-Nitrogen Compounds, Academic Press, New York 1972. 5. Allcock, H. R. Heteroatom Ring Systems and Polymers, Academic Press, New York 1967. 6. Voronkov, M. G., Mileshkevich, V. P., Yuzhelevskii, Yu. A. The Siloxane Bond, Consultants Bureau, New York 1978. 7. Rheingold, A. L. Homoatomic Rings, Chains and Macromolecules of Main-Group Elements, Elsevier Scientific Publishing Co., New York 1977. 8. Carraher, C. E., Sheats, J. E., Pittman, C. U. Organometallic Polymers, Academic Press, New York 1978. 9. Carraher, C. E., Sheats, J. E., Pittman, C. U. Advances in Organometallic and Inorganic Polymers, Marcel Dekker, Inc. New York 1982 10. Zeigler, J. M., Harrah, L. Α., Johnson, A. W., Polymer Preprints, 28 (1), 424 (1987). 11. Wunderlich, B. Macromolecular Physics/Crystal Melting, Academic Press, New York 1980. 12. Abkowitz, M., Knier, F. E., Stolka, M., Wigley, R. J., Yuh, H.-J., Solid State Commun., 62, 547 (1987). RECEIVED October 27,

1987


An Introduction to Inorganic and Organometallic Polymers

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