Synthesis of aromatic polybenzoxazoles by silylation method and their thermal and mechanical properties

Various aromatic polybenzoxazole (PBO) films were prepared through the two-step silylation method by low-temperature solution polycondensation of trimethylsilyl-substituted bis(α-aminophenol)s with aromatic dicarboxylic acid chlorides yielding precursor poly(α-trimethylsiloxy-amide)s, followed by thermal cyclocondensation. Four aromatic PBOs had glass transition temperatures (T g ) in the range of 275-375°C, and the T g values were slightly lower than those of the structurally related polyimides. The temperatures of 10% weight loss of these PBOs ranged from 545-616°C in nitrogen, and the values were somewhat higher than those of the structurally similar polyimides. The films of the PBOs had tensile strengths of 105-135 MPa, elongations at break of 11-25%, and tensile moduli of 2.1-2.8 GPa.