ABSTRACT

Systematic studies of polymerizations of N-carboxyanhydrides (NCAs) and the properties of the resulting polypeptides began with the work of Wessely's group in Vienna in the years around 1925. Since then, the interest of polymer chemists and biochemists in the polymerizations process itself and in the properties of polypeptides has steadily increased. However, primary (or secondary) amine-initiated polymerization of NCAs do not result in narrow molecular weight distributions. By means of kinetic measurements based on CO2 evolution, three independent groups detected in 1956 two types of chain effects. In this chapter both these chain effects are discussed. The key points of this mechanism are: the NCA possesses an N-H group which can act as an H-bond donor with respect to the polymeric initiator. The preferred binding sites of the polymeric initiators are the carbonyi oxygens. The polymerization follows the "amine mechanism", and thus involves a kind of macrocyclic transition state.