Polyester metamorphosis via carbonyl-to-thiocarbonyl editing for tuning polymer lifetime

Aliphatic polyesters such as poly(ε-caprolactone) (PCL) and polylactic acid (PLA) are biodegradable alternatives to conventional polymers, but their environmental degradation is often slow. This work introduces a polyester metamorphosis strategy for editing carbonyl-to-thiocarbonyl bonds in order to convert commercial polyesters into their sulfur-rich analogs, polythionoesters (–(C=S)– O– ). This underexplored class of materials is not easily accessible from sulfur-containing monomers due to monomer instability and purification challenges. This work circumnavigates these issues by achieving the first post-polymerization thionation of PCL derivatives. Controlled degrees of thionation with Lawesson's reagent allow systematic tuning of crystallinity, thermal transitions, and degradation. PLA resists thionation, a feature that enables selective modification of PCL domains in PCL-PLA copolymers. The resulting polythionoesters display accelerated degradation compared with polyester analogs, a characteristic that demonstrates how carbonyl-to-thiocarbonyl bond editing systematically tunes polymer lifetimes and properties. Beyond degradability, thiocarbonyl motifs provide opportunities in photochemistry, coordination chemistry, and catalysis, all of which highlights polyester metamorphosis as a versatile platform for polymer upcycling and functional diversification.