Synthesis of Polyborocarbosilane With Low Carbon Content and Investigation of Its Pyrolysis Process

This study presents the synthesis of low-carbon polyborocarbosilane (PBCS) through a high-temperature and high-pressure method using polysilacarbosilane (PSCS) and o-carborane, addressing the issue of excess carbon and difficulty in introducing boron (B) in conventional polycarbosilane (PCS) precursors. The incorporation of o-carborane significantly accelerates the reaction kinetics compared to conventional PCS synthesis, and structural characterization (FTIR, NMR) confirms the successful integration of boron into the polymer backbone. The PBCS precursor exhibits a reduced carbon content (C/Si molar ratio: 1.48) and enhanced branching degree. During pyrolysis, TG-MS and FTIR analyses reveal accelerated polymer-to-ceramic conversion below 800°C, due to the crosslinking reactions among B─H, Si─H, and Si─CH 3 groups, which promote hydrocarbon release and yield near-stoichiometric SiC ceramics (C/Si = 1.08 at 1800°C). Furthermore, ultrafine PBCS fibers are fabricated via electrospinning of PBCS, after direct thermal curing (without oxidative crosslinking) and pyrolysis, ultrafine near-stoichiometric crystalline SiC ultrafine fibers with low oxygen content and dense structure are obtained. During the sintering process, the formation of B─C/B─Si bonds promotes densification of the SiC ultrafine fibers and suppresses abnormal grain growth, potentially through the formation of boron solid solutions.