Improving the high temperature tribology of polyimide by molecular structure design and grafting POSS

Abstract In this paper, the method of enhancing glass transition temperature of polyimide (PI) composite for ultrasonic motor was employed from the three aspects by molecular dynamics simulation. First, polyimide with different molecular stiffness was designed and their mechanical and thermal properties were calculated after optimization. The simulated results showed that polyimide with stronger stiffness had higher glass transition temperature ( T g ), higher Young's modulus and shear modulus. Besides, PI composite was designed by filling different proportional polyhedral oligomeric silsesquioxane (POSS) to improve the thermostability continuously. Simulated results showed that the glass transition temperature of PI composites increased with an increase of POSS content. The third method was filling grafted POSS (POSS‐PI) with PI molecular into PI matrix to improve the compatibility. It was found that the thermal properties were slightly improved compared with PI filled with single POSS. PI composite with 9% POSS‐PI2 had the highest glass transition temperature. More importantly, the friction coefficient and the temperature rise on the friction interface were calculated and the result showed that the friction coefficient decreased with the increase of environment temperature. Finally, the improvement mechanism of grafted POSS was analyzed by extracting the energy of intermolecular interaction, mean square displacement, atomic relative concentration and velocity.