Effect of molecular rigidity and hydrogen bond interaction on mechanical properties of polyimide fibers

Six kinds of polyimide (PI) fibers with different molecular rigidity and hydrogen bond interactions were designed and prepared in order to investigate the relationship between structure and mechanical properties. The rigidity, aggregation structure, fracture morphology, hydrogen bond, and charge transfer (CT) interactions were investigated in detail. Conformational rigidity of six PI fibers were simulated and measured by D-values of energy barrier and bottom in potential energy curves of PI units. Rigid rod-like PI macromolecules tend to pack in order and show better mechanical properties. However, with the increase of D-values, fracture mechanisms change from ductile fracture to brittle fracture. Brittle fracture resulting from high conformational rigidity is adverse to improvement of mechanical properties of PI fibers. Besides, strength of hydrogen bond and CT interactions are characterized by infrared spectroscopy and ultraviolet absorption spectra, respectively. The results indicate that higher interactions lead to higher tensile strength and initial modulus. Finally, PI fibers, which possess moderate conformational rigidity and strong hydrogen bond interactions, exhibit highest tensile strength (1.82 GPa) and initial modulus (85.7 GPa) in six kinds of PI fibers. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43677.