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 C = C 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 degrees 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 degrees C ceramics derived from B-AHPCS were found to be significantly denser than that from AHPCS (C) 2010 Published by Elsevier Ltd