Improved oxalate-unit utilization in Sb-free melt polycondensation of hydrolytically degradable oxalate polyesters assisted by carboxylated MXene

High-molecular-weight poly(ethylene oxalate) (HMW-PEOx) is an attractive seawater-degradable polyester with high-barrier potential. However, its synthesis efficiency is limited by the generation and subsequent distillation of 1,4-dioxane-2,3‑dione during two-step polymerization, and its high crystallinity also leads to poor toughness, which restricts practical use. Here, we report a low-loading, antimony-free assisting strategy based on carboxyl-functionalized Ti 3 C 2 T x MXene for the melt synthesis of PEOx and PEOx-derived copolyesters with enhanced oxalate-unit retention. With only 300 ppm of MXene–COOH, PEOx achieved 78.9% oxalate utilization and M w of 87 kDa. This strategy was further extended to a series of PEOx copolyesters derived from primary diols of varying chain lengths, affording consistently high utilizations of 76.7–82.9%. Among them, PEH 15 Ox (H = 1,6-hexanediol) struck an optimal balance of tensile strength (∼28 MPa), elongation at break (209%), and barrier performance, exhibiting improvement factors of 32.7 (O 2 ), 81.8 (CO 2 ), and 37.5 (water vapor) relative to PBAT. Spectroscopic, microscopic, and DFT results suggest that carboxylated MXene interfaces contribute to improved oxalate retention by strengthening polymer–surface interactions and raising the energetic penalty for cyclic byproduct formation. This work provides a material-efficient Sb-free route to high-barrier degradable oxalate copolyesters.