Synthesis and properties of novel polyimides containing 2, 6-benzobisoxazole units

A series of aromatic polyimides based on 2, 6-bis(p-aminophenyl)-benzo[1, 2-d; 5, 4-d'] bisoxazole were synthesized in order to improve the thermal stability via a conventional two-stage procedure with a variety of dianhydrides. The reacting conditions of the intermediate poly(amic-acid)s were studied in detail. The poly(amic-acid)s had inherent viscosities over 1.0 dL/g and could be thermally converted into lightly yellow films. The IR spectra were used to identify the imidization of poly(amic acid)s to polyimides. The glass transition temperatures(T_g) of polyimides were over 280°C, and the 5% mass-loss temperatures were over 520°C in air, which showed excellent thermal stability.