The structure and reactivity of active centres of ionic polymerization of heterocyclic compounds. Review

Abstract

Problems of the structure and reactivity of active centres of cationic, anionic and coordination-anionic polymerization of heterocyclic compounds are discussed. Reliable information on the structure of these active centres can be obtained from the kinetics of the isotopic effect with respect to 13C and 14C. By this method experimental proof was obtained for the first time, that the active centre in cationic polymerization of dioxolan is a cyclic oxonium ion. The polymer chain has a substantial effect on the structure, stability and activity of the centres of ionic polymerization of α-oxides, α-thio-oxides and N-carboxy-α-amino acid anhydrides. Around the metal (Zn, Mg, Cd, Al, Fe) or cation (Na +, K +, Rb +, Cs + the last units of the polymer chain form an asymmetric coordination sphere, like the right and left hand α-helices of polypeptides. This gives rise to enantiomorphic active centres, the stability and activity of which is dependent on the nature of the metal or cation and the structure of the last six to ten polymer chain units attached to it, especially their microstructure the donating power of the heteroatoms and the nature of the side groups. The occurrence of such active centres explains the occurrence of stereoelective as well as stereoselective polymerization of these heterocyclic compounds in coordination-anionic and anionic polymerization.