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

Abstract 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.