Polysilanes are of interest because of several unusual properties associated with repeating silicon-silicon bonds which exhibit extensive electron delocalization. This unusual delocalization is associated directly or indirectly with high refractive index, high extinction coefficients of absorption at ultraviolet light frequencies, and olefin-like behavior.
Polymeric phenylsilanes were apparently obtained by Kipping early in this century, and permethylpolysilane, also known as poly(dimethylsilane), was prepared as early as 1949 by the sodium condensation of Me.sub.2 SiCl.sub.2, wherein Me signifies a methyl (CH.sub.3) group. However, no noteworthy applications exploiting optical or photosensitive properties of these materials have emerged. This is a consequence of the intractable nature of high molecular weight silane polymers which exhibit little or no solubility in the usual organic solvents such as benzene, toluene, xylene, and naphtha petroleum thinners.
Several approaches have been followed to modify the polymer structure so as to circumvent the problem of intractability. Perhaps the most well known is the polysilane derived by Wurtz-Fittig condensation of one to two mole ratios of phenylmethyldichlorosilane and dimethyldichlorosilane, which results in the introduction of a phenyl group in place of a methyl group on alternating silicon atoms. Crystallinity drops sharply with increasing numbers of phenyl groups. At phenyl/methyl ratios near 1:3 the polymer is amorphous, with a melting temperature near 200 degrees C., and is highly soluble in organic solvents at room temperature. This compound entitled "polysilastyrene" was reported by Robert West et al, Journal of the American Chemical Society, 103:7352 (1981).
Other attempts to circumvent the problem of intractability have included the replacement of methyl groups with other hydrocarbon moieties, such as ethyl or n-propyl groups. While all of these substitutions solve to various degrees the problems of solubility, they increase the ratio of hydrocarbon to silicon, and thereby significantly alter optical and thermal characteristics of the polysilanes.