Stereochemistry of ring opening polymerization of chiral monomers

Stereospecific polymerizations of racemic mixtures of chiral cyclic monomers have been shown to be stereoselective with non chiral initiators and stereoelective with some chiral initiators. The bulkiness of the ring substituents influences the interaction of monomer with initiator and this leads to various kinetic schemes for stereoelective reactions, that may give efficient kinetic resolution of the monomer. In some cases a very strong effect of optical purity of monomer is observed in non racemic systems. Monomers having two chiral groups in the ring may be polymerized by an asymmetric polymer synthesis, giving optically active polymers starting from meso compounds. An analysis of several stereoelective processes leads to the conclusion that the monomer enantiomers play a major part in determining the chirality of the active centres.