Synthesis of Phenyl-Substituted Poly(3-Hydroxybutyrates) with High and Tunable Glass Transition Temperatures via Sequential Catalytic Transformations

Atactic polystyrene is a commonplace transparent thermoplastic with a high glass transition temperature (T_g ∼ 100 °C), but its nondegradable backbone leads to detrimental environmental accumulation. Poly(hydroxyalkanoates) (PHAs) have emerged as biodegradable polyester alternatives to conventional olefinic plastics, but only a few PHAs possess the high T_g values (>100 °C) characteristic of polystyrene. Herein, we report the synthesis of phenyl-substituted poly(3-hydroxybutyrates) (PhPHBs) via sequential catalytic carbonylation and zinc-mediated ring-opening polymerization (ROP). Both cis and trans isomers of α-phenyl-β-butyrolactone (α-Ph-β-BL) were synthesized and polymerized to provide 13 distinct PhPHBs of varying trans incorporation and their resulting properties were systematically studied. The PhPHBs exhibit high and tunable T_g values (104-128 °C) and high thermal stability. We anticipate this work will inform the design of future high T_g PHAs as degradable alternatives to polystyrene.