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Rigid-rod polyimides (PI) containing benzimidazole moieties were synthesized and spun into fibers by a wet-spinning method. The resultant fibers exhibited an optimum tensile strength of 2.15 GPa and an initial modulus of 105 GPa with a low elongation of 2.2%. The PI fibers consisting of various ratios of 2,2 0 -bis(trifluoromethyl)-4,4 0 -diaminobiphenyl (TFMB) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) were investigated by Fourier transform infrared spectroscopy and two-dimensional wide angle X-ray diffraction (2D WAXD). Direct evidence of hydrogen-bonding involving the N-H groups of BIA and the imide carbonyls is presented. Qualitative and quantitative information of this molecular interaction was obtained and discussed. This has been considered as a main factor responsible for the significantly improved mechanical properties of the PI fibers. 2D WAXD and molecular mechanics modeling were used to simulate the structure of the aromatic PI fibers. As a result, the addition of BIA in the main chains is to increase the regularity of the molecule packing, which plays an important role in the enhanced strength of the PI fibers with more BIA loadings.

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Cover: Co‐polyimide fibers are prepared successfully. The introduction of benzimidazole units in the polymer chains enhances the hydrogen‐bonding intermolecular interaction and increases the regularity of the molecule packing. Therefore, the fibers exhibit excellent mechanical properties and outstanding thermal stabilities. Further details can be found in the article by J. Dong, C. Yin, Z. Zhang, X. Wang, H. Li, Q. Zhang* http://doi.wiley.com/10.1002/mame.201400081.