Recyclable Soft Elastomers Derived from Biobased δ -Valerolactones

Soft elastomers are widely used in applications requiring low modulus and resilience, yet their chemical recyclability, particularly the recovery of original monomers to counteract property degradation from repeated thermal processing, remains a significant challenge. To create recyclable soft elastomers, we integrated the chemical recyclability of polyesters with dynamic boronic ester crosslinking chemistry. Through sequential ring-opening polymerization (ROP) of α-methyl-δ-valerolactone (αMeVL) and α,α-spirocyclohexenyl-δ-valerolactone (αSpiroCyEVL), followed by post-modification and crosslinking, a series of soft elastomers with an outstanding service temperature range from –50 to 116 °C were obtained. Introducing δ-valerolactone (δVL) into the soft segment further enabled tunable mechanical properties (modulus of 0.22–6.42 MPa, tensile strength of 0.06–6.40 MPa, elongation at break of 536–1587%, tensile toughness of 0.44–22.0 MJ m–3). The soft elastomers derived from δVL are comparable to a commercial soft polyolefin elastomer. Moreover, these soft elastomers not only exhibit physical recyclability but also enable chemical closed-loop recycling via an ‘alcoholysis–depolymerization–repolymerization’ pathway after multiple physical recycling cycles, demonstrating potential for biomedical devices, flexible electronics, and soft robotics.