Coordination Ring-Opening Copolymerization of Naturally Renewable α-Methylene-γ-butyrolactone into Unsaturated Polyesters

Abstract

Reported herein is the first coordination–insertion ring-opening copolymerization of α-methylene-γ-butyrolactone (MBL) and e-caprolactone (e-CL) catalyzed by f-block lanthanide (Ln) catalysts, Ln[N(SiMe3)2]3, that produce exclusively an unsaturated copolyester PMBL-co-PCL without coproducing any homopolymer PMBL. Accomplishing such synthesis requires effective strategies to meet two key challenges: ring-opening of the γ-butyrolactone (γ-BL) ring in MBL—the five-membered lactone well recognized for its nonpolymerizability—and shutting down the vinyl-addition pathway via conjugate addition across the double bond—the exocyclic C═C moiety in MBL known for its high reactivity toward vinyl addition. Remarkably, the current Ln coordination catalyst system, coupled with judiciously chosen reaction conditions (relatively nonpolar solvent and low temperature, 0 or −20 °C), effectively copolymerizes MBL and e-CL to produce the ring-opening copolyester PMBL-co-PCL, with the MBL incorporation up to 40 mol % and withou...