Polypeptides bearing a reactive alkene moiety, including poly-DL-allylglycine (PGly(allyl)) and poly-DL-pentenylglycine (PGly(pent)) have been prepared through the polycondensation of activated urethane derivatives, N-phenoxycarbonyl derivative of alpha-amino acids. These urethane derivatives of DL-allylglycine (NPC-Gly(allyl)) and DL-pentenylglycine (NPC-Gly(pent)), are prepared by the N-carbamylation of the onium salt of the corresponding a-amino acid with diphenyl carbonate. The polycondensation of urethane derivatives proceeds when heated at 60 degrees C in N, N-dimethylacetamide, using amines as initiators, along with the elimination of phenol and CO2, to give the corresponding polypeptides without any degradation of alkene moieties. Varying the feed ratio of the urethane derivative to the initiator gives a predictable molecular weight with a narrow polydispersity index. Post-polymerization modifications of the alkene moiety of polypeptide are achieved with a high efficiency through a typical radical thiol-ene addition using a range of thiol-containing compounds, indicating the broad scope of this method as a conjugation tool for functional molecules. (C) 2016 Elsevier Ltd. All rights reserved.