Synthesis and properties of novel colorless polyimide containing indene and amide groups

Abstract Two novel diamines 1‐(4‐aminophenyl)‐1,3,3‐trimethyl‐2,3‐dihydro‐1H‐indene‐5‐amine and 4‐amino‐ N ‐(4‐(5‐(4‐aminobenzamide)‐1,3,3‐trimethyl‐2,3‐dihydro‐1H‐inden‐1‐yl) phenyl) benzamide containing indene and amide groups were successfully designed and synthesized, and a series of colorless polyimides (CPIs) derived from the two diamines with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride in various ratios were copolymerized. The introduction of aliphatic ring structures was conducive to the improvement of optical properties, while the incorporation of amide groups improved thermal and mechanical properties. These CPI films exhibited excellent optical properties ( T 400 > 80%), high heat resistance ( T g > 300 °C) and mechanical properties with the synergistic action of the two groups. Furthermore, the effect of the content of amide groups on the intermolecular interaction of CPIs was systematically analyzed. This study provides a fancy method for the development of heat‐resistant colorless materials for optical applications.