Physical aging of terephthalate-isosorbide co-polyesters

Isosorbide-based polyesters are emerging as sustainable alternatives to conventional polymers, yet their long-term stability remains underexplored. Here, we investigate the physical aging of three isosorbide copolyesters: poly(isosorbide butanediol terephthalate) (PIBT), poly(isosorbide-co-diethylene glycol terephthalate) (PIDT), and poly(isosorbide- co -1,4-cyclohexanedimethanol) (PICT) (∼50 mol% isosorbide) relative to PET and the high-Tg benchmark poly(1,4-cyclohexylenedimethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) (PCTT). Samples were aged up to 504 h near and below Tg, and enthalpy relaxation (via DSC) was correlated with mechanical changes. All polymers followed Arrhenius-type aging with activation energies of 162–260 kJ/mol, consistently higher for yield strength than enthalpy recovery. Despite comparable Tg values (∼108–109 °C), PIBT aged more rapidly than PCTT, underscoring the role of chemical structure beyond Tg in controlling aging kinetics. Physical aging also strongly suppressed stress relaxation across all materials. These results demonstrate how molecular design governs the thermal and mechanical stability of isosorbide-based polyesters, guiding the development of durable, sustainable alternatives to PET This study investigates the physical aging of three isosorbide copolyesters compared to native PET and the high-Tg benchmark PCTT. Samples were thermally aged up to 504 h below Tg, after which enthalpy relaxation was correlated with mechanical changes and effect on stress relaxation. The results show how molecular design governs the thermal and mechanical stability of isosorbide-based polyesters. • Physical aging of three isosorbide copolyesters: poly(isosorbide butanediol terephthalate) (PIBT), poly(isosorbide-co-diethylene glycol terephthalate) (PIDT), and poly(isosorbide- co -1,4-cyclohexanedimethanol) (PICT) (∼50 mol% isosorbide) were investigated relative to PET and the high-Tg benchmark poly(1,4-cyclohexylenedimethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) (PCTT). • Enthalpy relaxation was correlated with mechanical changes (aging at temperature near and below Tg for up to 504 h). • All polymers followed Arrhenius-type aging with activation energies of 162–260 kJ/mol, consistently higher for yield strength than enthalpy recovery. • PIBT aged more rapidly than PCTT, underscoring the role of chemical structure beyond Tg in controlling aging kinetics. • Physical aging also strongly suppressed stress relaxation across all materials, demonstrating structural governing the thermal and mechanical stability of isosorbide-based polyesters, and guiding the development of durable, sustainable alternatives to PET.