Hydrogen Peroxide-Mediated Oxidation of Biobased Poly(thioether-ester) Nanoparticles in Aqueous Medium

Biobased poly(thioether-ester) (PTEe) nanoparticles were synthesized via thiol–ene miniemulsion polymerization using a sustainable monomer, offering a biodegradable alternative to fossil-derived polymers. To address intrinsic limitations such as hydrophobicity and low thermal stability, postpolymerization oxidation with hydrogen peroxide was employed to convert thioether groups into sulfoxide and sulfone functionalities. Two oxidation strategies were evaluated: direct latex oxidation and solution-phase oxidation. Both approaches effectively increased polymer polarity and thermal stability while preserving nanoparticle morphology. Structural analysis by IR spectroscopy confirmed the formation of sulfoxide and sulfone groups, while $^1$H NMR indicated complete thiol–ene conversion. Thermal analysis revealed a marked rise in melting temperature (from 71 °C to 138–148 °C), while contact angle measurements showed enhanced surface hydrophilicity (θ reduced from 104° to 77–80°). Notably, latex oxidation (L-OXI) significantly improved nanoparticle stability and resistance to enzymatic degradation by CalB. This enhanced resistance is attributed to the incorporation of sulfoxide/sulfone groups, which stiffen the polymer matrix and restrict enzyme access to ester bonds.