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(o-aminophenol)s with aromatic dicarboxylic acid chlorides yielding precursor poly(o-trimethylsiloxy-amide)s, followed by thermal cyclocondensation. Four aromatic PBOs had glass transition temperatures (Tg) in the range of 275–375°C, and the Tg values were slightly lower than those of the structurally related polyimides. The temperatures of 10% weight loss of these PBOs ranged from 545–615°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.