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 (OEG(x)MA) and acrylate (OEG(x)A). 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-EG(x)MA-C or poly-EG(x)A-C) homopolypeptides. Depending on the length of OEG side chains, poly-EG(x)MA-C and poly-EG(x)A-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.