SOME FURTHER OBSERVATIONS ON POLYMETHYLSILANE AS A PRECURSOR FOR SILICON-CARBIDE

Poly(methylsilanes) produced by sodium coupling of methyldichlorosilane (2:1 molar ratio) contain residual chlorine which can be removed by reduction with LiAlH4 at low temperature. Following this reduction, the polymers contain catalytically active centers (presumed to be silyl anions) which, in THF solution, further polymerize and crosslink the polymer at room temperature, while in toluene solution they are inactive. The reduced polymethylsilane gives high yields (ca 75%) of ceramic product on pyrolysis, but the composition is rich in silicon, compared with pure silicon carbide (SiC). Addition of catalytic amounts of dimethylzirconocene (DMZ) to this polymer gives a product which pyrolyzes to a product with stoichiometry close to that of SiC. It is concluded that the DMZ has an important influence in promoting Si-C bond formation, relative to Si-Si bond formation, during the pyrolysis.