The synthesis and characterization of a novel heat-resistant boron-silicon hybrid polymer containing acetylene (PBSA) and its conversion to a highly crosslinked thermoset were discussed. The polymer was synthesized from phenylboron dichloride using Grignard reagent method. The structure of PBSA was characterized by using Fourier transform infrared spectra, 1H-NMR, 13C-NMR, and gel permeation chromatography. PBSA was thermosetting, highly heat-resistant, high-viscous, orange liquid at room temperature and good solubility in common organic solvents. Differential scanning calorimetry and thermogravimetric analysis analyses showed that the PBSA had excellent thermal and oxidative stability and the temperature of 5% weight loss (Td5) were 650 and 638 degrees C under nitrogen and air, respectively, and the residue at 1000 degrees C were 93.3 and 91.3%, respectively, which indicated that the incorporation of boron and silicon into polymeric backbone was found to improve thermal and oxidative properties. X-ray diffraction and scanning electron microscope were also used to analyze the formation of pyrolytic products. The results showed that the pyrolysis of PBSA resin was made up of beta-SiC and graphite. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012