Poly(1,4-Cyclohexanedimethylene Oxalate) as a Melt-Processable, Thermally Robust and Recyclable Oxalate Polyester

Poly(alkylene oxalate)s are attractive as potentially sustainable polyesters, but their broader development has been constrained by two persistent problems. Conventional linear oxalate monomers are readily evaporated under polymerization conditions because of their low boiling points, while most reported polyoxalates do not possess necessary thermal stability required for melt processing. Here, both above limitations were addressed using cyclic ethylene oxalate as a retained oxalate source and 1,4-cyclohexanedimethanol (CHDM) as a diol. A one-pot tandem polycondensation-depolymerization route afforded cyclic ethylene oxalate with the yield of 85% and purity of 98%, and ring-opening polycondensation with a series of diols produced poly(alkylene oxalate)s with molecular weights above 80 kDa with the oxalate retention of 94.0–96.7%. Among them, poly(1,4-cyclohexanedimethylene oxalate) showed the highest resistance to thermally induced mass loss, exhibiting only about 0.2% mass loss after 1 h at 20 °C above its melting temperature, consistent with experimental degradation analysis and calculated cracking barriers. This high melt-state stability enabled the fabrication of transparent films and tough injection-molded specimens and was accompanied by useful barrier performance, hydrolytic degradability, mild chemical depolymerization, and kilogram-scale preparation without loss of key material characteristics. These results identify poly(1,4-cyclohexanedimethylene oxalate) as a promising oxalate polyester for scalable applications.