Syndioselective Ring-Opening Polymerization of β-Lactones Enabled by Dimethylbiphenyl-Salen Yttrium Complexes.

Polyhydroxyalkanoates (PHAs) have served as promising alternatives to traditional petroleum-based plastics. Chemical synthesis of stereoregular PHAs via stereocontrolled ring-opening polymerization (ROP) of racemic β-lactones was a desired strategy with a formidable challenge. Herein, we developed a class of DiMeBiPh-salen yttrium complexes that adopted a -α configuration for stereoselective ROP of -β-butyrolactones (-BBL) and -β-valerolactone (-BVL). Notably, catalyst promoted robust polymerization with TOF up to 10 h and furnished syndiotactic P3HB, P3HV, and P(3HB)--P(3HV) copolymers with values of up to 0.95. Varying the compositions in P(3HB)--P(3HV) copolymers offered an intriguing opportunity to fine tune the thermal properties. Our kinetic study supported a polymeryl exchange mechanism. This work demonstrated that the DiMeBiPh-salen system could serve as a new catalytic framework for the stereoselective ROP of β-lactones, which leverages the catalyst design for stereoselective polymerization.