Chiral polymer synthesis by means of repeated asymmetric reaction

Chiral polymers are important in a variety of applications, including the separation of racemic compounds and polymeric catalysts in asymmetric syntheses. Although various methods have been developed to synthesize chiral polymers, we focus on repetitive asymmetric reaction between prochiral monomers using a chiral catalyst. Asymmetric polymerization by means of repetitive asymmetric C-C bond forming reactions in the presence of a chiral catalyst gives optically active polymers having main-chain configurational chirality. Novel optically active polymers have been prepared by asymmetric polymerization methods based on asymmetric reactions, such as an asymmetric Diels-Alder reaction, asymmetric addition of allylsilane to aldehyde, and an asymmetric Mukaiyama aldol reaction. Precise model reaction studies indicate that an asymmetric polymerization should occur in a stereoselective manner. Degradation of optically active polymers synthesized by asymmetric polymerization, followed by chiral HPLC analysis of the degraded products, revealed the degree of asymmetric induction during the asymmetric polymerization. Alternatively, NMR analysis after chemical modification of the optically active polymers with chiral derivatizing agents is also an efficient method to evaluate the optical purity of a chiral polymer without decomposition of the polymer main chain. Asymmetric polymerization is now becoming a powerful method to obtain chiral polymers with main-chain chirality.