Enabling Closed‐Loop Circularity of “Non‐Polymerizable” α, β‐Conjugated Lactone Towards High‐Performance Polyester with the Assistance of Cyclopentadiene

Chemical recycling of polymers to monomers presents a promising solution to the escalating crisis associated with plastic waste. Despite considerable progress made in this field, the primary efforts have been focused on redesigning new monomers to produce readily recyclable polymers. In contrast, limited research into the potential of seemingly “non‐polymerizable” monomers has been conducted. Herein, we propose a paradigm that leverages a “chaperone”‐assisted strategy to establish closed‐loop circularity for a “non‐polymerizable” α, β‐conjugated lactone, 5,6‐dihydro‐2H‐pyran‐2‐one (DPO). The resulting PDPO, a structural analogue of poly(δ‐valerolactone) (PVL), exhibits enhanced thermal properties with a melting point (Tm) of 114 °C and a decomposition temperature (Td,5%) of 305 °C. Notably, owing to the structural similarity between DPO and δ‐VL, the copolymerization generates semi‐crystalline P(DPO‐co‐VL)s irrespective of the DPO incorporation ratio. Intriguingly, the inherent C=C bonds in P(DPO‐co‐VL)s enable their convenient post‐functionalization via Michael‐addition reaction. Lastly, PDPO was demonstrated to be chemically recyclable via ring‐closing metathesis (RCM), representing a significant step towards the pursuit of enabling the closed‐loop circularity of “non‐polymerizable” lactones without altering the ultimate polymer structure. For “non‐polymerizable” α, β‐conjugated lactone, 5,6‐dihydro‐2H‐pyran‐2‐one (DPO), cyclopentadiene is used as the “chaperone” to assist the polymerization of the monomer via simple Diels–Alder reaction and its retro reaction. The exclusive presence of trans C=C double bond make the polymer PDPO exhibit enhanced thermal properties, with much higher Tm value and thermal stability than its structural anologue, PVL. Finally, the polymer PDPO undergoes ring‐closing metathesis and recycles back to its original monomer, enabling the closed‐loop circularity of “non‐polymerizable” DPO.