Biobased Cyclic Enoate Monomers: Enabling Intrinsically Crystalline, Chemically Recyclable, Ultratough Polymers.

Chemically recyclable polymers that depolymerize back to their monomers offer a promising alternative to non‑recyclable petroleum‑based plastics. However, three seemingly intractable trade‑offs have long hindered the rational design of circular polymers that combine high chemical recyclability with high performance: polymerizability versus depolymerizability, depolymerizability versus material performance, and crystallinity versus ductility. Here, we introduce a monomer design strategy based on renewable cyclic enoates that enables highly regioselective (exclusive head‑to‑tail) and stereoselective (E‑selective) ring‑opening metathesis polymerization (ROMP), yielding polyolefins/polyesters with high crystallinity and full chemical recyclability. Through modulation of the ring-chain equilibrium, both the forward polymerization and the reverse depolymerization proceeded to near-quantitative conversion. These polymers defy the aforementioned trade‑offs by exhibiting an unusual combination of desirable properties, including intrinsic crystallinity, chemical recyclability, and excellent performance metrics such as high thermal stability, high mechanical strength, ductility, and toughness.