Ring-Opening Polymerization and Closed-Loop Recycling of 3,6-Dialkylated Morpholine-2,5-dione Monomers

The design and synthesis of closed-loop recyclable polymers offer an effective solution to environmental pollution caused by disposable plastics and the associated significant economic losses. In this study, we synthesized a series of 3-substituted morpholino-2,5-dione monomers (MDs) and successfully achieved ring-opening polymerization (ROP) using a 1,8-diazabicyclo[5.4.0]-undec-7-ene/thiourea (DBU/TU) catalytic system. The resulting poly(ester amide)s (PEAs) exhibited a high molecular weight of up to 123.9 kg/mol with a narrow molecular weight distribution of only 1.20. By reducing the upper limit temperature of the polymer, we successfully depolymerized the polymer back into MDs, demonstrating the end-of-polymer depolymerization mechanism under these conditions. By changing the side-chain types, the thermal and mechanical properties of the polymer could be directly adjusted, highlighting the immense application potential of PEAs and their prospects as the next generation of sustainable polymers.