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

Poly(methylsilanes) produced by sodium coupling of methyldichlorosilan e (2:1 molar ratio) contain residual chlorine which can be removed by reduction with LiAlH4 at low temperature. Following this reduction, th e polymers contain catalytically active centers (presumed to be silyl anions) which, in THF solution, further polymerize and crosslink the p olymer at room temperature, while in toluene solution they are inactiv e. 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 dim ethylzirconocene (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 format ion, relative to Si-Si bond formation, during the pyrolysis.