Design of Epoxy-Functionalized Styrene-Butadiene Rubber with Bio-Based Dicarboxylic Acid as a Cross-Linker toward the Green-Curing Process and Recyclability

The covalently curing process for rubbers is indispensable in the rubber industry; however, there have been several inherent issues caused by traditional curing methods, such as the utilization of toxic curing additives, release of volatile organic compounds (VOCs), and difficulties in the recycling of end-of-life rubbers. In this work, a simple and effective curing strategy for epoxy-functionalized rubbers was provided to obtain a green-curing process, excellent mechanical properties, and good recyclability. The epoxy-functionalized styrene-butadiene rubbers (SBR-GMA) with different epoxy group contents were synthesized by introducing glycidyl methacrylate (GMA) during emulsion polymerization. This work highlights a green-curing strategy in which bio-based dicarboxylic acid serves as a cross-linker to cross-link epoxy-functionalized rubbers without additional additives. By the reaction between the epoxy groups in SBR-GMA rubber chains and carboxyl groups of dicarboxylic acid, the covalently cross-linking network-containing ester linkages are formed. Because the epoxy groups in SBR-GMA chains have high reactivity, the SBR-GMA with a small amount of dicarboxylic acid as a cross-linker can achieve an excellent cross-linking efficiency and rate. Additionally, the cross-linked rubber exhibits excellent mechanical properties, which could be widely regulated by changing the type and content of dicarboxylic acids. Moreover, due to the incorporation of ester linkages into the cross-linking network structure, we provide a facile and cost-effective chemical methodology for the recovery of end-of-life rubbers by the selective cleavage of the ester linkages. We envision that the epoxy-functionalized rubber may be a promising base material for the green-curing strategy, which could be interesting candidates for technical applications.