Modification of a liquid polycarbosilane with 9-BBN as a high-ceramic-yield precursor for SiC

Allyhydridopolycarbosilane (AHPCS) was partially modified with 9-borabicyclo-[3.3.1] nonane (9-BBN) via conventional hydroboration. The as-synthesized boron-modified AHPCS (B-AHPCS) was characterized by gel-permeation chromatography, Fourier transformed infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy. The results indicated that hydroboration did occur via the consumption of CC groups. In comparison with the parent AHPCS, the B-AHPCS retained the hyperbranched structure as expected. The thermal properties of B-AHPCS were investigated by thermal gravimetric analysis. The ceramic yield of B-AHPCS reached 75% at 1000 °C, 15% higher than that of the parent AHPCS. The structural evolution of the B-AHPCS during heat treatment was characterized by FTIR. At high temperatures, the introduction of <1 wt.% boron significantly inhibited SiC crystallization. The 1800 °C ceramics derived from B-AHPCS were found to be significantly denser than that from AHPCS.