Abstract
Thermoset polymers are indispensable but their environmental impact has been an ever-increasing concern given their typical intractability. Although concepts enabling their reprocessing have been demonstrated, their practical potential is limited by the deteriorated performance of the reprocessed materials. Here, we report a thiourea based thermoset elastomer that can be reprocessed with enhanced mechanical properties. We reveal that the thiourea bonds are dynamic which leads to the reprocessibility. More importantly, they can undergo selective oxidation during high temperature reprocessing, resulting in significant chemical strengthening within certain reprocessing cycles. This is opposite to most polymers for which reprocessing typically results in material deterioration. The possibility of having materials with inherent reprocessing induced performance enhancement points to a promising direction towards polymer recycling.
Highlights
Thermoset polymers are indispensable but their environmental impact has been an everincreasing concern given their typical intractability
We describe our successful attempt in this direction with a dynamic thiourea-based thermoset elastomer
We note here that linear polymers containing thiourea bonds have been reported in the literature[27,28], but their dynamic covalent nature is not known
Summary
Thermoset polymers are indispensable but their environmental impact has been an everincreasing concern given their typical intractability Concepts enabling their reprocessing have been demonstrated, their practical potential is limited by the deteriorated performance of the reprocessed materials. We reveal that the thiourea bonds are dynamic which leads to the reprocessibility They can undergo selective oxidation during high temperature reprocessing, resulting in significant chemical strengthening within certain reprocessing cycles. This is opposite to most polymers for which reprocessing typically results in material deterioration. We emphasize that non-cross-linked thiourea polymers are known to exhibit unusual room temperature selfhealing behavior via their unique zig-zag hydrogen bonds[27], but such a principle is different from the utilization of the dynamic covalent characteristics for designing reprocessable thermosets
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