Tri[diphenylphenylethynylsilyl-oxide]-borane(TSOB) was prepared based on dichlorodiphenylsilane,boric acid,phenylacetylene and n-butyllithium,catalyzed by chloroplatinic acid.The resulting product was characterized by FT-IR.Differential scanning calorimetry and FT-IR were used to study the curing mechanisms.The phenylethynyl groups underwent Diels-Alder reaction to form polycyclic aromatic hydrocarbon structures,which took benefit of high thermal stability for the thermoset.Thermogravimetric analysis was performed to characterize the heat-resistance of TSOB thermoset in nitrogen and air.The results show that Td10(the temperature of 10% mass loss) in nitrogen and in air is 502 ℃ and 554 ℃ respectively,the residue at 900 ℃ in nitrogen and air reaches 71% and 31% respectively.