Synthesis of recyclable polyesters via a <i>cis</i> -fused ring strategy

The development of chemically recyclable polymers is critical for addressing the environmental and resource limitations of the traditional linear plastic economy. Owing to its intrinsic reversibility, ring-opening polymerization (ROP) offers great potential for the development of recyclable polymers. However, achieving a balance between monomer polymerizability, polymer performance and recyclability remains a key challenge. This study explores the design and synthesis of a novel <i>cis</i>-fused cyclobutane-butyrolactone monomer (C4GBL) for use in ROP, leading to the formation of a polymer with 1,2-cyclobutane units in the main chain. C4GBL was synthesized using ethylene and bio-based maleic anhydride, and the resultant polymer exhibits high thermal stability (<i>T</i> _d,_5% = 380°C). Thermodynamic analysis of the ROP of C4GBL revealed a ceiling temperature (<i>T</i> _c) of -24°C, indicating that both polymerization and chemical recycling are feasible under appropriately tuned conditions. Density functional theory optimization reveals that the rigid fused cyclobutane forces the lactone segment of C4GBL into a near-eclipsed conformation, enhancing ring strain and polymerization reactivity. Collectively, this work establishes the <i>cis</i>-fused ring strategy as a new design principle for recyclable polyesters.