Highly effective free-radical-catalyzed curing of hyperbranched polycarbosilane for near stoichiometric SiC ceramics

Liquid hyperbranched polycarbosilane (LHBPCS) is an excellent preceramic polymer of SiC. Before thermolysis, curing of LHBPCS is favorable for higher ceramic yield and molding. In order to avoid some unfavorable factors arising from traditional thermal curing, we introduced a free-radical initiator tert-butyl peroxybenzoate (TBPB) to trigger the crosslinking of allyl group on LHBPCS in this study. FT-IR, NMR and DSC measurements indicated only allyl group was consumed during the cross-linking process. The cross-linking reaction rate was monitored by a rotational rheometer, and results confirmed LHBPCS could be cured in 4minutes with the help of 1wt% TBPB at 80 degrees C. TGA and SEM demonstrated the catalytic-cured LHBPCS had a high ceramic yield of 79.0wt% and dense structure. The effect of TBPB on crystallization behavior of the obtained SiC was also explored by XRD, and little impact was detected. After 1600 degrees C thermolysis, a near stoichiometric and crystalline SiC with ceramic yield of 77.5wt% was obtained.