Chemical Synthesis of Polyhydroxyalkanoates via Metal-Catalyzed Ring-Opening Polymerization of Cyclic Esters

Polyhydroxyalkanoates (PHAs), an important class of biodegradable and/or biocompatible linear aliphatic polyesters with thermal and mechanical properties spanning in a wide range, are ideal alternatives to petroleum-based plastics. Although more than 150 different congeners of PHAs via biosynthesis method have been reported, the high cost and low volume of microbial fermentation pathway limited their applications. Therefore, the development of efficient chemical synthesis routes to PHAs is highly pursued in recent years. The synthetic efforts for stereospecific P3HB could trace back to 1960s, and after over 60 years’ efforts made by scientists, two main strategies have been developed: (1) ring-opening polymerization (ROP) of four-membered lactones, such as β-butyrolactone (β-BL), and (2) ROP of eight-membered cyclic diolides (8DL). This chapter will highlight stereoselective ROP of cyclic esters by metal catalysts to produce PHAs, especially the most widely studied member – poly(3-hydroxybutyrate) (P3HB), and present the relation between the structures of catalysts and the stereoselectivity of the polymerizations.