In Situ Reductive Polymerization of Bio-Based α-Lipoamides toward Functional Poly(β-Hydroxy Thioether)s

Abstract

Thanks to the high reactivity of thiol groups, thiol-based polymerizations enable the efficient construction of structurally diverse macromolecules. However, free thiols readily undergo oxidation, which disrupts the equimolar stoichiometry of reactive groups, while conventional disulfide monomers offer limited versatility for functional group installation.To address these challenges, we report an in situ reduction strategy that converts cyclic disulfides into dithiols for step-growth polymerization. This approach not only eliminates thiol oxidation and ensures equimolar stoichiometry, but also facilitates the introduction of various functional groups via the disulfide backbone. Specifically, bio-sourced α-lipoic acid was derivatized into N-substituted α-lipoamides as cyclic disulfide-containing monomers, which were in situ reduced using sodium borohydride and polymerized with diepoxides to afford poly(β-hydroxy thioether)s. After optimizing polymerization conditions, a siries of structurally diverse polymers were synthesized with a maximum weight-average molecular weight of 25.2 kDa. Their structural diversity allows tunable glass transition temperatures and thermal stabilities. Furthermore, the polymers can be oxidized to sulfone-containing analogs with enhanced intermolecular forces, and post-polymerization modification enables the introduction of acetoacetate and β-enamino ester groups, enriching their structural and functional diversity.