Synthesis of Superheat-Resistant Polyimides with High Tg and Low Coefficient of Thermal Expansion by Introduction of Strong Intermolecular Interaction

The development of polyimides (PIs) with a superheat resistance and a high thermal dimensional stability is required urgently for application in the rapidly growing area of flexible-display substrates. Based on an enhanced intermolecular interaction, 2,2'-p-phenylenebis(5-aminobenzimidazole) (DP) that contains bis-benzimidazole was synthesized, and two series of its copolyimides (PI-a and PI-b) were prepared by copolycondensation with 5-amino-2-(4-aminobenzene)-benzimidazole (PABZ) and 5-amino-2-(3-aminobenzene)-benzimidazole (i-PABZ), respectively. The high density and packing coefficient of the resulting PIs caused by the strong intermolecular interaction from the hydrogen bonds and the charge transfer complex provided the PI films with a very high glass-transition temperature (T-g > 450 degrees C) and an extremely low coefficient of thermal expansion (CTE) below 10 ppm/K for PI-a. Such good thermal properties expand their application as high thermostable materials. Furthermore, the PI-b had a higher T-g than PI-a, whereas the latter had lower CTE values because of the configuration difference of their polymer chains. These data indicate that the resultant thermostable copolyimides have potential application as a flexible-display substrate and provide a feasible method to improve the thermal properties-by incorporating bis-benzimidazole moieties.