Thermoresponsive Oligo(ethylene glycol) Functionalized Poly-l-cysteine

Abstract

A series of new functional amino acids were prepared in high yield via thiol–ene Michael addition between l-cysteine and monomethoxy oligo(ethylene glycol) (OEG) functionalized methacrylates (OEGxMA) and acrylate (OEGxA). These OEGylated cysteine derivatives were converted into polymerizable N-carboxyanhydride (NCA) monomers using triphosgene. Subsequent ring-opening polymerization (ROP) of these NCA monomers gave a series of OEGylated poly-l-cysteine (poly-EGxMA-C or poly-EGxA-C) homopolypeptides. Depending on the length of OEG side chains, poly-EGxMA-C and poly-EGxA-C polypeptides displayed different solubility and secondary structure in water. More importantly, the obtained polypeptides can display reversible thermoresponsive properties in water when the x value is between 3 and 5. The synthetic strategy represents a highly efficient method to prepare nonionic functional polypeptides with tunable thermoresponsive properties.