Crystalline Stereoregular Poly(ether-ester) via MeAl[Salen]-Catalyzed Well-Controlled Ring-Opening Polymerization of Enantiopure Cyclic Ether-Ester Monomer

The development of chemically recyclable polymers with closed-loop life cycles is believed to be the most attractive strategy in creating the circular plastic economy. Here, we successfully prepared a pair of enantiopure O-heterocyclic lactones bearing with pendent phenyl substituent, which are named (2S,7R)-7-methyl-2-phenyl-1,4-dioxepan-5-one (SR-M1) and (2R,7R)-7-methyl-2-phenyl-1,4-dioxepan-5-one (RR-M2), respectively, by using the methanolysis product of poly(3-hydroxybutyrate) (P3HB) as the raw material. The well-controlled ring-opening polymerizations of SR-M1 and RR-M2 were achieved in the presence of MeAl[salen] as the catalyst to produce poly(ether-ester)s with controlled molecular weights, narrow dispersities, and well-defined terminal groups. The monomer stereoconfiguration has a big impact on their polymerization kinetics and thermodynamics as well as the thermal and mechanical properties of resultant polyesters. Both the resultant P(SR-M1) and P(RR-M2) exhibited closed-loop recyclability. The depolymerization of resultant polyesters back to pristine monomers can be easily realized using stannous octoate as the catalyst in solution.