Polyimides with low coefficient of thermal expansion derived from diamines containing benzimidazole and amide: Synthesis, properties, and the N-substitution effect

Three novel diamines, incorporating benzimidazole and amide moieties, namely 4-amino-N-(5-amino-benzimidazol-2-yl)-benzamide (6a), 4-amino-N-(5-amino-1- methyl-benzimidazol-2-yl)-benzamide (6b), and 4-amino-N-(5-amino-1-phenyl -benzimidazol-2-yl)-benzamide (6c), were designed and synthesized. A series of poly(benzimidazole-amide-imide) (PBIAI) films were prepared from the resulting diamines and 4,4-biphthalic dianhydride (BPDA). These flexible polyimides (PIs) showed high glass transition temperatures ( T g = 353–379°C), low coefficients of thermal expansion (CTE = 3.7–12.3 ppm K −1 ) and good mechanical properties ( σ = 152–207 MPa and E = 4.5–7.7 GPa), promising candidates for applications in flexible-display substrates. Furthermore, the data guided a feasible method to enhance T g and reduce CTE by introducing benzimidazole and amide units into PI main chains, and the effect of different N-substituents on performance was revealed. Graphical