Synthesis of well-defined polypeptide-based materials via the ring-opening polymerization of α-amino acid N-carboxyanhydrides

The synthesis of well-defined polypeptide-based materials through the ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCA) was reviewed. Normal Amine Mechanism (NAM) is generally applied for the polymerization of NCAs initiated by nonionic initiators having at least one mobile hydrogen atom (base-H), such as primary and secondary amines, alcohols, and water. Water is a common impurity, which can influence the ROP of NCAs. The temperature of the system is also critical for the hydrolysis of NCAs, since at low temperatures it proceeds slower. Activated monomer mechanism (AMM) was proposed to explain the ROP of DL-phenylalanine NCA, initiated by a tertiary amine. Bamford's group found that Sar-NCA was almost unreactive when diisopropylamine was used as initiator, while the polymerization of γethyl-L-glutamate NCA is even faster under these conditions. The new developments in the ROP of NCAs hold tremendous promise that well-defined polypeptides with controllable molecular weight, sequence, composition, and molecular weight distribution can be synthesized.