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

ABSTRACT 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.