Semicrystalline Polymacrolactone Networks via Disulfide Chemistry: Synthesis, Cross-Linking, and Chemical Degradation...

The development of sustainable polymers is a central challenge in advancing circular economy strategies for materials science. In this framework, the synthesis of disulfide-cross-linked polymer networks derived from epoxidized poly-(ω-6-hexadecenlactone-co-ω-pentadecalactone) (P6HDL/PDL), a family of biobased, semicrystalline polyesters, is herein described. Cross-linking was achieved via reaction with 4,4'-dithiodibutyric acid (DTDB), introducing disulfide bonds into the polymer matrix. The network formation process was monitored through rheological time-sweep experiments and differential scanning calorimetry (DSC), while FTIR spectroscopy confirmed the completion of the epoxy-acid reaction. Rheological analysis revealed a composition-dependent increase in complex viscosity upon cross-linking at 180 °C, with the 50/50 copolymer achieving the highest network stiffness. Notably, copolymers with different compositions (P6HDL/PDL = 50/50 and 25/75) retained significant crystallinity after cross-linking. This coexistence of disulfide bonds and crystalline domains resulted in a composition-dependent viscoelastic response while maintaining a significant degree of structural order within the polymer network. The copolymers' structure allowed tuning of cross-link density and crystallinity, offering a versatile platform for the design of renewable thermoset-like materials. The cleavage of disulfide bonds was achieved by treatment with 2-mercaptoethanol or 2-hydroxyethyl disulfide by UV light irradiation. These results demonstrated the feasibility of creating high-performance polymer networks from macrolactone-based polyesters using dynamic disulfide chemistry and laid the groundwork for the next generation of sustainable and possibly reprocessable plastics.