S/O and vinyl isomerization enables ultrafast cationic ring-opening polymerization toward CO2-derived polythioester with migrated in-chain C=C substituents

Developing high-performance CO₂-based polymers is promising to address the challenges of CO₂ sequestration and the environmental impact of petroleum-based plastics. The δ-lactone 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one and its derivatives, synthesized from CO₂ with 1,3-butadiene, have emerged as very promising CO₂-derived monomers. However, their general ring-opening polymerizations face challenges with thermodynamics and kinetics, generally resulting in long reaction times, low conversions, and low-molecular-weight polyesters with poor mechanical properties. Herein, we report a dual isomerization-driven cationic ring-opening polymerization (DI-CROP) of a CO₂-derived thionolactone, 3-ethyl-6-vinyltetrahydro-2H-pyran-2-thione, in which the relayed S/O and vinyl isomerizations significantly enhance polymerization activity, enabling the rapid synthesis of high-molecular-weight CO₂-based polythioesters, achieving near-quantitative conversion within just a few minutes. Also, the relayed S/O and vinyl isomerizations in DI-CROP can easily migrate C=C substituents on the ring of thionolactone into its backbone. These features further enable the production of sustainable CO₂-based materials through efficient copolymerization and post-polymerization functionalization. This study enriches the realm of isomerization-driven polymerizations, and provides a new synthetic approach to CO₂-derived polymeric materials.