Structure and properties of aromatic poly(benzimidazole‐imide) copolymer fibers

A series of co‐polyimide fibers were prepared by thermal imidization of copolyamic acids derived from 3,3′,4,4′‐biphenyltertracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) in various molar ratios with 2‐(4‐aminophenyl)?5‐aminobenzimidazole (BIA). The dynamic mechanical behaviors of these polyimide (PI) fibers revealed that the glass transition temperature (T_g) was significantly improved upon increasing PMDA content. Heat‐drawing process led to dramatic change on the glass transition behavior of BPDA/BIA system, but had a small impact on BPDA/PMDA/BIA co‐polyimide fibers. This difference for PI fibers is attributed to the different degree of ordered structure of the fibers affected by heat‐drawing. The incorporation of PMDA obviously improved the dimensional stability against high temperature, due to the restricted movement of polymer chains. In addition, the obtained fibers show excellent mechanical and thermal properties because of the strong hydrogen bonding due to the incorporation of benzimidazole moieties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41474.