A Photochemical Approach to Realizing an On-Demand Switchable Polymer between a Thermoset and a Vitrimer

The inability of thermosets to be melt-processed significantly limits their recycling potential because the simplest and most economical way to recycle polymers is to repair or remelt them into new items. A new class of polymer, known as a vitrimer, which features exchangeable covalent bonds, has garnered significant attention as a recyclable and repairable alternative to thermosets. However, the bond exchange chemistries in conventional vitrimers are thermally activated, suggesting that a limited temperature range exists for vitrimers to function as strong thermosets. In this presentation, we propose a sequential photochemical approach to convert a thermoset into a vitrimer and then back into a thermoset on demand. This can be achieved by incorporating a set of latent, heat-stable photo-active catalysts into a model epoxy thermoset. Two photo exposures with different irradiating wavelengths were applied. The first photo exposure releases a catalyst, activating the bond exchange, while the subsequent photo exposure deactivates the catalyst. This approach allows for an on-demand switchable polymer that can alternate between a thermoset and a vitrimer.