Metathesis‐Sourced Epoxides in Ring‐Opening Copolymerization: Selective Access to Degradable Polythioesters

Ester-substituted cyclopentene epoxides were synthesized via ring-closing metathesis and epoxidation, providing selective access to monomers suited for highly controlled ring-opening copolymerization (ROCOP). The new epoxide enables fully alternating phthalic thioanhydride (PTA)/epoxide ROCOP without scrambling side reactions, yielding well-defined poly(ester-alt-thioester)s with molecular weights up to ∼38 kg/mol after optimization of purity and catalyst preparation. Its performance extends to phthalic anhydride (PA) ROCOP and selective terpolymerizations. Substituent variation confirms the robustness of the cyclopentene scaffold. Comparative degradation studies reveal clear chemical differences between oxygen- and sulfur-containing analogues. These results establish metathesis-derived cyclopentene epoxides as versatile, accessible monomers for degradable polyesters and polythioesters.