Synthesis of colorless polyimides derived from benzimidazole diamines with bis‐amide structures

Abstract To make the colorless polyimides (CPIs) suitable for the application of flexible display technology, the polyimide (PI) films need to have both good optical properties and thermal properties. To get the wanted properties, 2‐(2‐methyl‐4‐(2‐methyl‐4‐aminobenzamido)phenyl)‐5‐(2‐methyl‐4‐aminobenzamido)‐ N ‐phenylbenzimidazol (5a) and 2‐(2‐methyl‐4‐(2‐trifluoromethyl‐4‐aminobenzamido)phenyl)‐5‐(2‐trifluoromethyl‐4‐aminobenzamido)‐ N ‐phenylbenzimidazol (5b) were synthesized, which both contained benzimidazole and bis‐amide structures. Two kinds of PI films were polymerized with cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CBDA). With the contribution of side groups (CH 3 or CF 3 ), the resulting PI films presented relatively superior optical properties (transmittance at 400 nm was 59% and 68% respectively) and low coefficient of thermal expansion (CTE = 22 and 25 ppm K −1 ). These good properties suggest that these PI films have the potential for flexible display usage.