Ultra-heat resistance and low CTE polyimides with spirobis(indene)bis(benzoxazole)-benzimidazole unite for flexible substrate applications

• A series of PIs containing spirobis(indene)bis(benzoxazole)-benzimidazole were synthesized. • These PI films exhibited ultra-high T g and low CTE . • These PI films also demonstrated excellent mechanical properties. • The effects of intermolecular H-bonding and final annealing temperature on the properties of the polymers were investigated. The advancement of new technologies has driven the demand for the development of higher-performance polyimides (PI), especially in terms of heat resistance, dimensional stability, and mechanical properties. In this study, four highly rigid, twisted diamine isomers featuring a spirobis(indene)bis(benzoxazole) structure were synthesized. By their co-polycondensation with 5-amino-2-(4-aminobenzene)-benzimidazole (PABZ) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) followed by thermal imidization, a series of PIs with benzoxazole and benzimidazole structures were prepared. Owing to the rigid and linear structure and the formation of intermolecular hydrogen bonding, the PI films showed ultrahigh heat resistance ( T g : 417–510 °C; T d 5% = 514–562 °C) and excellent dimensional stability (CTE: 2.1–23.5 ppm/K). Meanwhile, they also demonstrate excellent mechanical properties, with a tensile strength of up to 238.5 MPa and an initial modulus of up to 6.8 GPa. These polyimide films have great application potential in flexible display substrates.