Compatibility driven self-strengthening during the radical-responsive remolding process of poly-isoprene vitrimers†
Vitrimers usually show decreased mechanical properties after welding, recycling or remolding processes due to the hysteresis of topology network rearrangement. Herein, we propose a strategy for developing self-strengthening vitrimers whose mechanical properties increase upon network rearrangement. Such vitrimers are constructed based on the exchangeable β-hydroxyl ester network formed by two immiscible polymers, epoxidized poly-isoprene (EPIP) and poly-(thioctic acid) (PTA). A radical capture agent, 1,3-diisopropenylbenzene (DIB), is introduced into vitrimers. DIB is miscible with EPIP while immiscible with PTA, yet it can react with PTA by capturing the free radicals released by the dynamic disulfide bonds of PTA at high temperature, thereby improving the compatibility between EPIP and PTA during network rearrangement. As a result, more β-hydroxyl ester linkages are formed between EPIP and PTA, and the density of the crosslinking network in the vitrimers increases after repeated remolding process, which result in improved mechanical properties after network rearrangement. This strategy of compatibility driven self-strengthening can be easily extended to other vitrimers composed of immiscible components.