Design of High-Performance, Robust, and Recyclable Epoxy Resins

The inherent non-recyclability of epoxy resins (ERs), a major sustainability barrier, can be addressed by incorporating dynamic covalent linkages. However, conventional approaches to design reprocessable ERs typically require the preinstallation of dynamic motifs within monomers, making synthesis a multistep process. Besides, their thermal and mechanical robustness often remains inferior to that of the conventional ERs. Here, we present a strategy for designing robust yet fully reprocessable ERs via thiol-epoxy "click" reactions that rely on thioether exchange for the dynamic exchange. Unlike conventional thiol-epoxy "click" reactions that generate permanent thioether linkages upon polymerization, the current study demonstrates the in-situ generation of dynamic thioether linkages during the thiol-epoxy "click" reaction, thus obviating the need for pre-installed dynamic motifs within monomers. The resulting ERs exhibited thermal stability and storage modulus at 30 °C (G'30°C) comparable to those of various commercial ERs. Notably, control over Tg, modulus, and relaxation dynamics can be achieved by regulating the cross-link density in the ERs. The networks demonstrated superior creep resistance, with negligible permanent deformation even up to 120 °C. Additionally, the robust and dynamic thioether linkages in the ERs were leveraged to demonstrate a reversible dual shape-memory effect and a promising adhesion ability to aluminum and steel substrates. Finally, the degradation of ERs in the presence of excess thiol was demonstrated. To the best of our knowledge, this is the first report to introduce dynamic thioether linkages for designing robust, fully reprocessable, and creep-resistant ERs, demonstrating their adhesive behavior and a suitable end-of-life degradability.