Gem-dimethylation promotes reversible polymerization/deploymerization of thionolactones

The development of chemically recyclable polymers represents a promising solution to address plastic pollution and the global energy crisis. In this study, a seven-membered thionolactone (5,5-dimethyloxepane-2-thione, tnCL-Me2) monomer was successfully synthesized using a gem-dimethyl strategy. This monomer exhibits excellent reactivity in both anionic and cationic ring-opening polymerization, yielding polymers with high thermal stability (thermal decomposition temperature (Td) up to 331 °C) and superior mechanical properties (tensile strength (σB)≈4.0 MPa, elongation at break (εB)≈570%). Notably, poly(5,5-dimethylthiepan-2-one (P(tCL-Me2)) enables highly efficient and selective chemical recycling via a “monomer-polymer-isomerized monomer” pathway, establishing a closed-loop life cycle for sustainable materials.