γ-Functionalized thioether, sulfoxide, and sulfone AB monomers for tunable aliphatic polyesters

Abstract

The development of sulfur-functionalized polyester building blocks remains limited despite their strong potential for tuning polymer properties. In this work, we report a sustainable route to a new family of γ-functionalized AB-type monomers bearing thioether, sulfoxide, or sulfone groups. Alternating ring-opening copolymerization of γ-thiobutyrolactone and ethylene carbonate yields aliphatic poly[(thioether-alt-ester)-stat-ethylene carbonate]s, which are fully depolymerized under mild alkaline methanolysis into a single α-methyl ester–ω-hydroxy building block. Controlled oxidation of the thioether moiety using various oxidants enables selective access to sulfoxide- and sulfone-containing monomers, providing precise control over sulfur oxidation state. These new building blocks are subsequently used in step-growth polycondensation to produce functional polyesters. The oxidation level of sulfur strongly influences polymer thermal properties, with increasing glass transition temperatures from thioether to sulfone. This work establishes versatile sulfur-containing building blocks for the design of recyclable and tunable functional polyesters.