Polymeric routes to silicon carbide

Several classes of organosilicon polymers are effective precursors for silicon carbide ceramic compositions. These include polydimethylsilane (via a two-step process), ‘polysilastyrene’, polycarbosilazanes or polysilazanes, and certain siloxanes, plus the branched polycarbosilanes, branched polysilahydrocarbons, and vinylic polysilanes developed at Union Carbide. The latter three classes are prepared by active metal dechlorinations of appropriate chlorosilane blends, leading to recognition of branching at backbone silicon atoms (either as prepared or during processing) as a prerequisite for obtaining useful ceramic yields. Fundamental reactivity differences between the active metals (potassium and sodium) allow the preparation of sodium-derived vinylic polysilanes. The latter offer certain economic and performance advantages as ceramic precursors.