Selective Synthesis and Polymerization of Methyl-1,4-dioxan-2-one toward Closed-Loop Recyclable Poly(ether- <i>alt</i> -ester) from Methyl Glycolate and Propylene Oxide

The global accumulation of plastic waste underscores the urgent need for sustainable polymers that combine commodity feedstocks, controlled synthesis, and closed-loop recyclability. Substituted six-membered lactones represent promising poly(ether-<i>alt</i>-ester) precursors owing to their tunable properties and inherent degradability, yet their structural diversity and recycling pathways remain limited. Here, we report a catalyst-modulated route to regioselectively synthesize methyl-substituted six-membered lactones from commodity methyl glycolate (MG) and propylene oxide (PO), which are subsequently polymerized into poly(ether-<i>alt</i>-ester)s capable of efficient chemical depolymerization. The choice of catalyst dictates both monomer structures and polymer microstructure, while thermal and stereochemical analyses reveal how subtle substitution patterns govern amorphous or semicrystalline behavior of the resulting polymers. Chemical depolymerization regenerates either mixed or pure lactones, demonstrating true closed-loop recycling. By integrating catalyst design, control over monomer regioisomer distribution, polymer microstructure and reversible polymerization, this work establishes a versatile platform for constructing recyclable poly(ether-<i>alt</i>-ester) systems, advancing circularity within polymer materials.