Effects of Molecular Weight and Crosslinking Density on the Tribological Properties of Shape Memory Polyimides

In recent years, owing to the self-responsive ability of shape memory polymers (SMPs) towards thermal, optical, magnetic, electrical and other external stimulus, this smart material has attracted more and more attention in the self-lubricating materials field. In this study, 3, 3′, 4, 4′-biphenyl tetracarboxylic acid dianhydride (BPDA), 4, 4′-diamino diphenyl ether (ODA) and melamine were used as precursor to prepare a series of thermoplastic polyimides (TPIs) with different molecular weights (M_n) and thermoset polyimide (CPIs) with different crosslinking densities (d). Moreover, dry sliding tests were performed on a ball-on-disc reciprocating wear tester to characterize the tribological performance of materials. The results show different friction and wear mechanisms for the two kinds of polymers. And with the increase of molecular weight M_n and the introduction of crosslinking agent, a significantly decrease were exhibited in the friction coefficient and volume wear rate of materials. In addition, local friction heat in the process of friction induced the local shape memory effect of linear polyimides, which reduced the coefficient of friction and wear rate to a certain extent. However, the shape memory effect on thermoset polyimides was insignificant.