Metal-catalyzed synthesis of stereoregular polyketones, polyesters, and polycarbonates

Stereocontrol of the stereogenic centers in the main chain during the synthesis of polyketones, polyesters, and polycarbonates has been reviewed. The examples described may be classified in the following ways. Retention of the configuration which exists in the monomer: as described in the ring opening polymerization of (S,S)-lactide and (R)-β-butyrolactone to give poly[(S)-lactic acid] (PSLA) and poly[(R)-3-hydroxybutyrate] (PRHB), respectively. Enantiomer selection either by the catalyst or by the chain-end: presented examples are the synthesis of heterotactic and isotactic PLAs from racemic lactide and the preparation of syndiotactic and isotactic PHBs from a racemic mixture of β-butyrolactone. Selection of enantiotopic sites of a meso monomer by the catalyst or by the chain-end: syndiotactic and heterotactic PLAs from meso-lactide and isotactic poly(epoxide-alt-CO2) from meso-epoxide are the examples described here. Creation of a new stereogenic center upon polymerization starting from prochiral monomers. The catalyst or the chain-end selects one of the two enantiofaces of an α-olefin in the olefin/CO alternating copolymerization to give either isotactic or syndiotactic polyketones. Thus, a variety of stereoregular polymers are now available owing to the remarkable achievements of precise design and synthesis of single-site catalysts.