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

The diamine monomer, 2,6-bis(p-aminophenyl)-benzo-[1,2-d; 5,4-d'] bisoxazole was successfully synthesized. Three aromatic polyimides (PI) based on 2,6-bis(p-aminophenyl)-benzo-[1,2-d; 5,4-d'] bisoxazole were prepared via a conventional two-stage procedure with a variety of dianhydrides. Their structures and properties were characterized by FTIR, ¹H NMR, TG, DSC and XRD. The intermediate poly(amic-aeid)s (PAA) had inherent viscosities of 1.18-1.70 dL/g and could be thermally converted into lightly yellow polyimide films. The resulted polyimides showed excellent thermal stability, and the glass transition temperatures (T_g) of all polymers were above 280 °C, and the 5% weight loss temperatures of polymers were about 550 °C in N ₂. The solubility of these polyimides in various solvents was evaluated. They were all insoluble in conventional polar aprotic solvents.