Weijie Qiu, Xiaoyan Tang
Entropy-driven ring-opening polymerization (ED-ROP) of macrocyclic (thio)esters offers a promising platform for chemically recyclable polymers through intrinsically reversible ring-chain equilibria, yet its broader development remains constrained by low monomer reactivity, highly dilute depolymerization conditions, and the limited repolymerizability of recycled macrocyclic oligomers (MCOs). Here we report a 14-membered sulfur-containing macrocyclic di(ester-thioester), 14-DET, whose thioester linkages enhance monomer reactivity and enable controllable macrocycle-mediated recycling. Using efficient salen- or salan-based lanthanum catalysts, 14-DET undergoes rapid ED-ROP at ambient temperature to afford poly(ester-alt-thioester), P(14-DET), with number-average molar mass (Mn) up to 163 kDa and high sequence alternation (PAB H up to 0.97). Modulation of temperature, concentration, and time directs the reversible ring-chain system toward high-molar-mass polymer, MCOs, or the 28-membered cyclic dimer (14-DET)2, revealing distinct thermodynamic and kinetic regimes, including transient kinetically controlled polymer formation at 0°C before equilibration toward the precipitated cyclic dimer. Notably, both recovered (14-DET)2 and MCOs generated during monomer synthesis can be directly repolymerized to regenerate high-molar-mass P(14-DET), providing feedstock flexibility and improving overall material utilization. These results establish a closed-loop "monomer-dimer-polymer" cycle and demonstrate a macrocycle-mediated recycling paradigm in which the cyclic dimers and MCOs serve as valuable polymerizable feedstocks.