Synthesis and properties of polyimides containing <Emphasis Type="Italic">N</Emphasis>-substituted benzimidazole rings

A series of novel benzimidazole-containing aromatic polyimides with precise structures in high yields were synthesized by the catalyst-free nucleophilic substitution polycondensation of 4,4’-bis(4-fluorophthalimido) diphenyl ether with different molar ratios of 1,4-bis(2-benzimidazolyl) benzene to 4,4’-dihydroxydiphenyl sulfone via a C–N/C–O coupling reaction process. The reaction was carried out at 210°C in the presence of anhydrous potassium carbonate. The structures of the resulting polymers were characterized by means of FTIR, ¹H NMR spectroscopy, and elemental analysis, and the results were largely consistent with the proposed structure. DSC and TG measurements showed that the polymers had high glass transition temperatures (T_g > 215°C), good thermostability, and high decomposition temperatures (T_d5% > 456°C). These novel polymers also showed easy solubility. In addition, the obtained films have good optical transparency, and the mechanical properties exhibited tension strength of 48.2–74.8 MPa and tensile moduli of 1.3–1.9 GPa without any stretching.