Synthesis of poly(2-ethyl-2-oxazoline)-block-polypeptide copolymers by combination of ring-opening polymerization of oxazoline and polycondensation of activated urethane derivatives of α-amino acids

In this study, we examined the utilization of a primary-amine-terminated poly(2-ethyl-2-oxazoline) as macroinitiators for the chain-growth polycondensation of activated urethane derivatives of α-amino acids to obtain poly(2-ethyl-2-oxazoline)-block-polypeptide diblock copolymers. To incorporate polypeptide segments into the poly(2-ethyl-2-oxazoline), we prepared four N-phenoxycarbonyl derivatives of α-amino acids, namely, Z-l-lysine, l-alanine, l-phenylalanine, and benzyl-l-serine, which were readily synthesized by N-carbamylation of the tetrabutylammonium salts of the α-amino acids with diphenyl carbonate. We demonstrated that poly(2-ethyl-2-oxazoline)s possessing an amino terminal successfully served as initiators for the chain-growth polycondensation of these urethane derivatives; heating at 60 °C in N,N-dimethylacetamide eliminated phenol and CO2 to give the corresponding diblock copolymers. The structural and thermal properties of the obtained diblock copolymers were determined by FT-IR, 1H NMR, SEC, and TGA.