Thermoset polymers with permanently cross-linked networks have outstanding mechanical properties and solvent resistance, but they cannot be reprocessed or recycled. On the other hand, vitrimers with covalent adaptable networks can be recycled. Here we provide a simple and practical method coined as "vitrimerization" to convert the permanent cross-linked thermosets into vitrimer polymers without depolymerization. The vitrimerized thermosets exhibit comparable mechanical properties and solvent resistance with the original ones. This method allows recycling and reusing the unrecyclable thermoset polymers with minimum loss in mechanical properties and enables closed-loop recycling of thermosets with the least environmental impact.

The low properties of recycled polymers associated with high cost of recycling hinder development of the thermoplastic recycling industry. Dynamic cross-linking of recycled thermoplastics with the formation of vitrimers enables superior mechanical properties, good reprocessability, and superior chemical and environmental resistance. Herein, a poly(ethylene-vinyl acetate) (EVA) vitrimer was formed by cross-linking with triethyl borate with the catalyst (bis-(acetylacetonato)dioxomolybdenum(VI)). The resultant EVA vitrimer shows enhanced thermal stability and mechanical properties with up to two times improvement in Young' modulus and storage modulus by comparison with the thermoplastic EVA. Moreover, 90% of Young's modulus was maintained in the EVA vitrimer after five times of recycling, whereas only 72% can be maintained for recycling the thermoplastic EVA. This dynamic cross-linked EVA also exhibits superior UV and solvent resistance, which helps extend the service time of the recycled material. This work introduces a facile and efficient method to recycle and reuse EVA with low property loss. It has the potential to enable the production of highperformance EVA from EVA waste for different applications.

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Flexible, light‐weight, and wearable electronics have significant potential for the development of Internet of Things. Flexible sensors with tunable piezoresistive properties are in high demand for various practical applications. Herein, different morphology thermoplastic polyurethane (TPU)/ carbon nanostructure (CNS) composites with segregated network are obtained by swelling the TPU powders using various solvents. The better solvent for TPU, dimethylformamide (DMF), renders the composites with 0.7 wt% CNS stronger polymer‐filler interactions, resulting in significantly improved piezoresistive sensitivity at strain larger than 150%. Also the gauge factors (GFs) for these composites are 9.7 in the range 0–60% strain and 19.3 for 60–100% strain. In contrast, the composites with ethanol (EtOH) and tetrahydrofuran (THF) which swell less the TPU show delayed increase in piezoresistivity and GFs of 2.2 and 3.5 for strain up to 100%, respectively, suggesting potential applications for stretchable conductors.

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