PYROLYTIC CONVERSION OF METHYLSILANE AND VINYLSILANE POLYMERS TO SI-CCERAMICS

Poly(methylsilane) and poly(vinylsilane) were synthesized using a tita nocene catalyst, and their pyrolytic conversion to ceramics was follow ed using a combination of thermal analysis and infrared spectroscopy. The two polymers have distinctly different backbone structures, as det ermined by Si-29 NMR; methylsilane polymerizes to a polysilane, while vinylsilane polymers have a predominately polycarbosilane backbone, wi th some polysilane structure as well. The pyrolysis path and char yiel d were dependent primarily on backbone structure, with little influenc e of polymer molecular weight. The majority of the weight loss on conv ersion occurs below 650 degrees C, although bond rearrangement continu es to 1400 degrees C. Poly (vinylsilane) produced a carbon-rich Si-C c eramic in which the carbon was dispersed on a sufficiently fine level to show resistance to oxidation on heating in air to 1400 degrees C. C opolymerization of methyl- and vinylsilane produced stoichiometric SiC ; however, polymers of methylsilane were sensitive to oxygen incorpora tion and sometimes pyrophoric. Polymerization of vinylsilane with disi lylethane permitted control of theology and imparted thermoset behavio ur.