Superheat-resistant polyimides with ultra-low coefficients of thermal expansion

To achieve the superheat-resistant polymers for flexible display substrates, two new diamines, namely 6-amine-2-(4-aminobenzene)-1-methyl-benzimidazole (m-MePABZ), 5-amine 2-(4-amino-benzene)-1-methyl-benzimidazole (p-MePABZ) containing N-methyl benzimidazole (BI) were synthesized and a serials of poly(benzimidazole imide) (PBII) films were prepared through thermal imidization. Among them, the flexible polyimide (PI) film derived from m-MePABZ and pyromellitic dianhydride (PMDA) has an ultra-low coefficient of thermal expansion (CTE) down to 2.5 ppm K-1 and an outstanding high glass-transition temperature (T-g) up to 431 degrees C. Furthermore, the employment of N-methyl overcame an issue of the high H2O-absorption of traditional PBIIs, and the effect of para- and meta-connecting methyl on molecular packing and properties of these PIs was investigated. These data provided a useful guide to develop high performance PBIIs by incorporating N-methyl.