The in situ generation of thiols by nucleophilic ring-opening of a thiolactone with amines, followed by a UV-initiated radical thiol-ene reaction in a one-pot fashion, has been evaluated as an accelerated and versatile protocol for the synthesis of several types of polymeric architectures. After elaboration of a model amine-thiol-ene conjugation reaction, a number of routes based on readily available thiolactone-containing structures have been developed to successfully assemble functional, linear polymers and networks via a mild and facile radical photopolymerization process.
A straightforward, isocyanate-free methodology for the synthesis of functionalized 8 polyurethanes, based on amine-thiol-ene conjugation, was elaborated. Aminolysis of a readily 9 available AB'-urethane monomer, containing both an acrylate (A) and a thiolactone unit (B'),
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, thiolmaleimide 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
A thiolactone derivative of 10-undecenoic
acid was used as a renewable
AB′ monomer for the one-pot synthesis of diversely substituted
polyamide structures, containing amide moieties both in the polymer
backbones and in their side chains. Nucleophilic aminolysis of the
thiolactone entity liberates a thiol, which further reacts in a stepwise
thiol–ene photopolymerization reaction. Using different primary
amines, several structurally diverse polyamides, with physical properties
dependent on the length and chemical identity of the side chain, were
obtained. Postpolymerization oxidation of the sulfide linkages in
the polymer backbone to their corresponding sulfoxides and sulfones
altered the material, with the degree of oxidation having an impact
on the final mechanical properties. Furthermore, this mild and straightforward
polymerization procedure was applied for the synthesis of functional
polymer networks.
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