A Hybrid Cross-Linking Point Strategy To Reconcile Reprocessability and Creep Resistance in Mechanically Robust Rubbers

The recyclability of vulcanized rubbers remains a critical challenge due to the irreversibility of conventional covalent cross-linking networks. Here, we report a hybrid cross-linking point strategy that integrates conventional vulcanization bonds with reversible β-hydroxy ester bonds within a single cross-linking point, enabling the simultaneous achievement of mechanical robustness, reprocessability, and creep resistance, and overcoming the trade-offs typically observed in conventional hybrid networks. Copolymers of sulfur and vinylacetic acid (CSVA), synthesized via inverse vulcanization, are employed to cross-link epoxidized natural rubber (ENR). In this system, CSVA functions as a dual cross-linker: sulfur units form vulcanization networks, while carboxyl groups react with epoxidation groups of ENR to generate dynamic β-hydroxy ester bonds. These hybrid cross-linking points ensure dimensional stability at service temperatures through permanent bonds, while facilitating network flow at elevated temperatures via dynamic ester bonds. Notably, increasing the CSVA content leads to simultaneous improvements in the mechanical performance, reprocessability, and creep resistance. Rheological results show thermally activated rearrangements of the networks. This study demonstrates that hybrid cross-linking points offer a generalizable design principle for creating vulcanized rubbers that are both mechanically robust and malleable, providing a viable pathway toward sustainable elastomer development.