THERMAL AND PHOTOCHEMICAL CONVERSION OF POLY(METHYLSILANE) TO POLYCARBOSILANE

The use of some highly branched soluble copolymers, -[(CH3SiH)(x)(CH3Si)(y)](n)-, as pyrolytic precursors to silicon carbide (SiC) was examined. A progressive increase in the ceramic yield with increased branching was observed, parallel to a drastic decrease in the soluble polymer synthetic yield. Poly(methylsilane), PMS, was thermally and photochemically cross-linked before its conversion to SiC. The changes in the PMS structure were monitored by FTIR and Si-29, C-13, and H-1 NMR spectra. An increase in the ceramic yields for irradiated polymers was observed. This effect was stronger when the polymer irradiation was performed in the presence of AIBN. The PMS thermolysis was also studied using n-hexane or toluene as solvent, at 70 degrees C, in the presence of AIBN. Toluene showed an inhibiting effect on Kumada rearrangement, while n-hexane was a good solvent to obtain the conversion of PMS to polycarbosilane, at a relatively low temperature.