Controlled Ring-Opening Polymerization of 5-Phenyl-1,4-dioxan-2-one toward Stereochemically Tunable and Closed-Loop Recyclable Polyesters

Abstract The practical applications of closed-loop recyclable polymers demand monomers that are readily accessible from simple feedstocks while enabling controlled polymerization and tunable physical properties. Herein, we report a one-pot synthesis of 5-phenyl-1,4-dioxan-2-one (PhDO) from methyl glycolate and styrene oxide via acid-catalyzed epoxide ring opening followed by intramolecular cyclization. The H2SO4-catalyzed route afforded pure PhDO in 62% isolated yield. At –40 °C and [M]0 = 2.0 M, MeAl[salen] (Al-1) enabled controlled ring-opening polymerization (ROP) of PhDO, affording poly(5-phenyl-1,4-dioxan-2-one) (PPhDO) with number-average molecular weights (Mn) up to 81.1 kDa and narrow dispersity. Polymerization of PhDO monomers with different enantiomeric compositions provided PPhDO samples with stereostructures ranging from essentially atactic to isotactic. Individual PPhDO samples were amorphous, whereas the complementary enantiomeric polymers formed a crystalline phase with a melting temperature of 141.6 °C and an estimated WAXS crystallinity of 72.3%, consistent with stereocomplexation. A representative high-molecular-weight P(rac-PhDO) showed appreciable tensile strength and moderate ductility. Importantly, P(rac-PhDO) underwent catalytic bulk depolymerization to regenerate rac-PhDO in 83% isolated yield. Together, these results establish a PhDO-based route to phenyl-substituted, closed-loop recyclable polyesters that integrates accessible monomer synthesis, controlled ROP, stereochemical transfer, stereocomplexation behavior, and catalytic monomer recovery.