Phase Separation-Driven Concurrent High Elasticity and Reextrudability for Biobased Elastomers

The recycling challenges of thermosetting polymers and the environmental burden from petroleum-based polymers drive the rapid development of recyclable biobased elastomers. However, cross-linked biobased elastomers face an inherent trade-off between high elasticity and high-throughput recycling: robust elastic recovery requires sufficiently cross-linked topologies, whereas efficient reprocessing favors low cross-linking densities. Herein, we address this dilemma by integrating phase separation modulation with dynamic covalent cross-linking to synthesize biobased thermoplastic elastomers via one-step in situ cross-linking. Using maleic anhydride-grafted ethylene-vinyl acetate copolymer (M-g-EVA) as the compatibilizer, biobased monomers, epoxidized soybean oil (ESO), and dimer acid (DFA) were in situ polymerized within the ethylene-propylene-diene rubber (EPDM) matrix to form a vitrimer dispersed phase. During thermal mechanical mixing, M-g-EVA was first selectively predispersed in the EPDM matrix. Subsequent in situ polymerization drives the cross-linked ESO/DFA aggregates to localize within the M-g-EVA phase, creating a distinct third phase. Meanwhile, M-g-EVA forms interfacial cross-linking with ESO and physically entangles with EPDM chains, thus constructing a stable multiphase network composed of a "continuous - interfacial - dispersed phase". The resulting material demonstrates enhanced elastic performance, featuring excellent room-temperature creep resistance (0.00184%/min), improved low-temperature compression set resistance (14% reduction at -25 °C relative to a traditional commercial TPV with similar hardness), and outstanding cyclic fatigue stability (stress retention rate >97% following 300 loading-unloading cycles). Owing to β-hydroxyester bond exchange and lubricating effect of EPDM, the multiphase polymer can be continuously extruded and reprocessed with high flux, retaining >85% of its mechanical property after 5 reprocessing cycles. In short, this study provides a scalable route to high-performance and recyclable biobased elastomers and offers design insights for sustainable elastomers.