Synthesis of novel colorless polyimides from benzimidazole diamines with various linearity

To synthesize colorless superheat‐resistant polyimide films, one of the valid approaches is the incorporation of the asymmetric and warped structures in the main chain. Applying this approach on 5(6)‐amino‐2‐(4‐aminobenzene)benzimidazole (PABZ) and changing its linearity, 6, 5′‐diamine‐2′‐methyl‐1‐methyl‐2‐phenylbenzimidazole (5a) and 6, 3′‐diamine‐2′‐methyl‐1‐methyl‐2‐phenylbenzimidazole (5b) were devised and synthesized successfully, then polymerized with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride (HPMDA). The prepared poly(benzimidazole imide)s (PBIIs) with the rigid main chain and loose packing had the excellent heat‐resistant level (Tg> 400°C) and optical properties (T400> 80%). Besides, the alterations resulting from various linearities were discussed comprehensively. This research is beneficial to the application of optical field, providing a promising candidate of heat‐resistant colorless materials.