Preparation of silicon carbide ceramics from the modification of an Si-H containing polysilane

A method of forming modified preceramic polymers comprising mixing organopolysilanes having a plurality of Si-H functional groups with an effective amount of a metallocene compound, and allowing the mixture to undergo a dehydrogenative reaction is disclosed. Pyrolysis of the modified polymer provides in high yields ceramic residues that approach stoichiometric SiC in composition. Preferably the organopolysilane starting material contains a plurality of tertiary Si-H bonds and has the general formula of [(RSiH)x(RSi)y]n where the sum of the coefficients x and y equal 1, n is an integer greater than 1, R is a lower alkyl group having from 1 to about 8 carbon atoms, a substituted or unsubstituted lower alkenyl group having from 2 to about 8 carbon atoms, a cycloalkyl group having from 3 to about 10 carbon atoms, substituted or unsubstituted aryl group having from 6 to about 10 carbon atoms. More preferably R is a lower alkyl group having from 1 to about 8 carbon atoms, and still more preferably R is methyl so that the molar ratio of carbon to silicon of the polymer is about 1. The organopolysilanes can be prepared from silyl halides by alkali metal condensation reactions.