Homopolyimides containing both benzimidazole and benzoxazole with high Tg and low coefficient of thermal expansion

A pair of isomer diamines containing both benzimidazole and benzoxazole and derived homopolyimides were synthesized for the first time. Due to rich rigid and linear benzoazole units, as well as the strong intermolecular interactions from the hydrogen bonding and the charge transfer complexation (CTC), the obtained polyimides (PIs) exhibited outstanding thermal properties, including high thermal weight loss temperature (T-d5% = 540-561 degrees C), high glass transition temperature (T-g = 392-421 degrees C), and low coefficient of thermal expansion (CTE = 1.3-20.9 ppm/degrees C). In addition, the obtained PIs also showed ideal mechanical properties (T-S = 189-240 MPa, T-M = 4.1-5.0 GPa and E-B = 2.9%-4.7%). These potential novel PI films with high T-g and low CTE were expected to be applied to next generation of flexible display substrate material.