Clarifying the Effect of Drafting Conditions on Structure and Properties of Polyimide Fibers at Molecular Dynamic Level

Abstract A series of pyromellitic dianhydride/4,4′‐oxydianiline orientation models are constructed by molecular dynamic simulation, and the effects of drafting rate, drafting temperature, and imidization degree on structure and mechanical properties of polyimide fibers are studied. The high drafting rate is conducive to the orientation of molecular chains along the axis, but it is easy to form defects inside of the fibers, so the tensile modulus of the orientation model at a draft ratio of 6 is decreased from 21.6 to 9.8 GPa with increasing the drafting rate. The high drafting temperature reduced the intermolecular interaction, which is not conducive to the orientation of the molecular chain along the axis, the tensile modulus of orientation models at a draft ratio of 6 decreased from 21.6 to 11.7 GPa with the drafting temperature increasing from 298 to 598 K. Besides, the molecular chains of PI fibers drawn from the high imidization degree are arranged more regularly along the axis due to the PI units have greater rigidity than the polyamic acid units. This work provides guidance for the optimization of PI fibers heat‐drafting process from the perspective of molecular chain conformational evolution.