How controlled and versatile is N-carboxy anhydride (NCA) polymerization at 0 °C? Effect of temperature on homo-, block- and graft (co)polymerization

We have investigated the polymerization of various amino acid N-carboxyanhydrides (NCAs) at 0 °C. Detailed MALDI-ToF analysis of homopolymerizations of three amino acid NCAs clearly confirms that frequently occurring end-group termination and other side-reactions are absent at 0 °C. The polymerization is thus controlled and homo and copolypeptides with low polydispersities, around 1.1, were obtained for soluble polypeptides. MALDI-ToF contour plot analysis confirmed the randomness of the copolymers. The controlled character of the low temperature NCApolymerization was further verified by the successful block copolymer synthesis from polypeptide macroinitiators, which confirms the availability of the amino end-groups for chain extension. Moreover, graft copolymers were obtained by grafting of benzyl-L-glutamate NCA from lysine-containing copolymers. The formation of gels from the graft and corresponding block copolymers was investigated. While for the block copolymers interconnected polymer particles were observed by optical microscopy, the graft copolymers form an open cell structure.