Double modular modification of thiolactone-containing polymers: towards polythiols and derived structures

Abstract

A conceptual proof for the double modification (aminolysis and subsequent thiol-click modification) of thiolactone units, incorporated in linear polymer scaffolds, was elaborated. These polymers were prepared by either reversible addition–fragmentation chain transfer (RAFT) or nitroxide mediated radical polymerization (NMP) starting from a stable, readily available styrenic thiolactone monomer (St-TLa). Successful copolymerization of the latter with styrene (St) or methyl methacrylate (MMA) yielded linear polymers with varying thiolactone content (4–25%). Upon amine treatment, the ring-opening of the pendent thiolactones resulted in the formation of linear polythiols. Reaction conditions were optimized to avoid cross-linking via disulfide formation, thus preserving the linear nature of the polymer. Different primary amines (propylamine, benzylamine, ethanolamine and Jeffamine M-1000) were attached to the polymer backbone, while the PDIs remained low. The resulting polythiols are versatile scaffolds for further modification by various thiol-click reactions. In this respect, thiol–maleimide conjugation was used as a model reaction. NMR- and SEC-analyses revealed a near-quantitative double modification of thiolactone containing polystyrene (PS) and poly(methylmethacrylate) (PMMA) by subsequent treatment with propylamine and N-benzylmaleimide.