ASYMMETRIC RING-OPENING POLYMERIZATION

Different types of asymmetric polymerizations involving ring-opening of racemic, scalemic or prochiral heterocyclic monomers (oxiranes, thiiranes, beta-lactones) in the presence of chiral or achiral initiators are described. The rules of chiral recognition in enantioasymmetric (stereoelective) polymerization and the factors influencing the magnitude of the choice (stereoelectivity) are discussed. Depending on the nature of monomers and the bulkiness of their substituents, different mechanisms of kinetic resolution of stereoisomeric mixtures are established leading generally to chiral polymers. With prochiral monomers, eg, cis-dimethylthiirane and cyclohexene oxide, enantiogenic processes with high regioselectivity were observed. Polymers of different structures (highly isotactic, predominantly syndiotactic) were obtained in the case of