Discrete Metal Catalysts for Stereoselective Ring-Opening Polymerization of Chiral Racemic β-Lactones

Poly(beta-hydroxyalkanoate)s (PHAs) are a class of aliphatic polyesters that can be efficiently synthesized by ring-opening polymerization (ROP) of beta-lactones. The case of chiral racemic beta-substituted beta-lactones is particularly appealing since these monomers open the way to original tacticities and materials different from those biotechnologically produced. In this overview, after briefly surveying general considerations associated to the ROP of beta-lactones and metal-based catalysts used in stereoselective ROP of racemic beta-butyrolactone, special emphasis is given to discrete rare earth catalysts that have allowed the preparation of highly syndiotactic poly(3-hydroxybutyrate)s. Recent developments such as preparation of stereo-controlled PHAs with pendant structural groups via (co)polymerization of functional beta-substituted beta-lactones, and highly alternating copolymers obtained by ROP of mixtures of enantiomerically pure but different monomers - are also discussed.