Sustainable\nTerephthalic Polyesters with Medium/Long\nMethylene Sequence: Structure–Property Relationships and Closed-Loop\nChemical Recycling

Traditional\nshort-chain terephthalic polyesters such as poly(ethylene\nterephthalate) (PET) are among the most produced plastics in today’s\npolymer industry, while their large-scale chemical recycling has been\na long-standing challenge. The long-chain polyesters have shown good\nrecyclability under mild conditions, whereas the structure–property\nrelationships and chemical recycling performance of long-chain terephthalic\npolyesters are still unclear. Herein, we synthesized a series of medium/long-chain\nterephthalic polyesters with different methylene sequence lengths\n(CH<sub>2</sub> number in diol monomer <i>n</i><sub>CH<sub>2</sub></sub> = 6, 8, 10, 12) and investigated their thermal properties,\ncrystallization behavior, mechanical properties, and chemical recycling\nperformance. All terephthalic polyesters show good crystallizability;\ntheir melting temperature decreases, and melting enthalpy increases\ngradually as <i>n</i><sub>CH<sub>2</sub></sub> increases\nfrom 2 to 12. All polyesters adopt a triclinic crystal lattice while\nslightly different crystalline lamellar structures. The medium/long-chain\nterephthalic polyesters exhibit improved ductility and good melt processability,\nenabling them to be used as three-dimensional (3D) printing materials.\nIn addition, the medium- and long-chain terephthalic polyesters are\nchemically recyclable and can depolymerize under mild conditions (e.g.,\n140 °C in methanol). The monomers obtained by depolymerization\ncan be reused to synthesize again the according polyesters. This study\nprovides new inspiration for developing sustainable high-performance\npolyesters with great industrial potential.