Configurational rules governing the stereochemical control of chiral initiators in ring-opening polymerizations of heterocyclic monomers

Configuration rules were established for the polymerization of cyclic monomers with chiral initiators. The latter recognize in the monomer an asymmetric carbon of homochiral configuration. The chirality of the initiator is defined by the “local” asymmetry of the ligand and by the overall asymmetry of the particular arrangement of catalytic aggregates. Two types of process called “homosteric” and “antisteric,” which apply to the polymerization of resolvable monomers and achiral monomers of meso structure, are defined. These configurational rules have a general character and are verified in many examples of differently substituted three- or four-membered cyclic monomers (oxiranes, thiiranes, β-lactones). Stereoelective polymerization appears to be an original method for the determination of the absolute configuration of some monomers of unknown chirality.