Modification of a hyperbranched polycarbosilane with boron and its polymer-to-ceramic conversion

A boron-modified AHPCS was prepared by chemical reactions between allylhydridopolycarbosilane( AHPCS)with dimethylamine borane( DMAB),and then cross-linking at 170 ℃,followed by pyrolyzing at high temperatures to afford SiC-based ceramics. The cross-linking and polymer-to-ceramic conversion of the boron-modified AHPCS were characterized by FT-IR,TGA,XRD and SEM. The results indicate that the cross-linking of AHPCS was improved,involving hydroboration reaction between vinyl groups of AHPCS and B—H groups of DMAB,and dehydrocoupling reaction between Si—H groups of AHPCS and B—H groups of DMAB. As a result,the ceramic yield of the B-modified AHPCS was significantly enhanced. Moreover,the introduction of boron inhibits the crystallization of β-SiC at high temperatures obviously.