Impact of Polyimide Semi-Interpenetrating Polymer Networks on the Physicochemical Properties of Vulcanized Acrylonitrile–Butadiene Rubber

This work demonstrates the physicochemical property changes of composite thermoset elastomers prepared by incorporating mechanically and thermally stable polyimide (PI) into vulcanized acrylonitrile butadiene rubber (NBR) through a semi-interpenetrating polymer network (semi-IPN). Conventional NBR base materials and fillers were initially mixed with PI precursors in various forms—solid monomers, solid/liquid mixed monomers, and a liquid polyamic acid (PAA)—using a Banbury mixer, followed by processing on an open roll mill. Upon vulcanization at elevated temperature, linear PI was incorporated into the crosslinked NBR matrix to form a semi-IPN structure. The resulting thermoset elastomers retained essential elastomeric characteristics while exhibiting improved thermal and mechanical performance. Successful formation of the semi-IPN structure was confirmed through comprehensive characterization, and the corresponding physical and thermal properties were systematically evaluated before and after thermal aging, along with gel fraction measurements. Combined results suggested that incorporating the liquid PI precursor was more effective than introducing solid monomers and solid/liquid mixture. Although the present findings do not yet demonstrate fully sufficient improvement, optimization of the precursor content within the NBR matrix via semi-IPN is expected to achieve the desired thermal performance without significantly compromising elastomeric properties.