HYDROBORATION OF POLYMETHYLVINYLSILANE - A NOVEL ROUTE TO SILICON BORON-CARBIDE CERAMICS

Polymethylvinylsilanes (PMVS) of the general composition [R2Si]m [RR'Si]n with R = CH3 and R' = CH = CH2 (vinyl) have been synthesized by the dechlorination of dichlordimethylsilane (CH3)2SiCl2 and dichlormethylvinylsilane CH3(CH2 = CH) SiCl2 with sodium in toluene. Subsequently, the vinyl groups have been hydroborated by the reaction of the as-synthesized polysilane with various borane adduct compounds such as dimethylsulphide borane (CH3)2S.BH3. The hydroborated polymer was characterized by infrared and C-13-, H-1-, and B-11-NMR spectroscopy as well as by the measurement of the molecular weight distribution. The pyrolysis of the boron-containing polysilane at 1100-degrees-C in argon results in the formation of X-ray amorphous silicon boron carbide, Si(x)C(x+y)B(z) in 63% yield. The crystallization behaviour of the polymer-derived covalent ceramic product at temperatures up to 2200-degrees-C is discussed. The microstructure was characterized by transmission electron microscopy. Analytical results were obtained with the novel electron spectroscopic imaging (ESI) technique.