ASYMMETRIC RING-OPENING POLYMERIZATION

Different types of asymmetric polymerizations involving ring-opening o f racemic, scalemic or prochiral heterocyclic monomers (oxiranes, thii ranes, beta-lactones) in the presence of chiral or achiral initiators are described. The rules of chiral recognition in enantioasymmetric (s tereoelective) polymerization and the factors influencing the magnitud e of the choice (stereoelectivity) are discussed. Depending on the nat ure of monomers and the bulkiness of their substituents, different mec hanisms of kinetic resolution of stereoisomeric mixtures are establish ed leading generally to chiral polymers. With prochiral monomers, eg, cis-dimethylthiirane and cyclohexene oxide, enantiogenic processes wit h high regioselectivity were observed. Polymers of different structure s (highly isotactic, predominantly syndiotactic) were obtained in the case of