Exploring the Impact of Hydrogen Bonds on Poly(ethylene 2,5-furandicarboxylate) (PEF) Modification: Enhancing the PEF Properties through Copolymerization with 5-Hydroxyisophthalic Acid (5-HIPA)

Poly(ethylene 2,5-furandicarboxylate) (PEF) faces processing challenges due to structural rigidity, despite its superior barrier properties over polyethylene terephthalate (PET). This study demonstrates a hydrogen bonding-mediated strategy to enhance PEF’s performance through copolymerization with 5-hydroxyisophthalic acid (5-HIPA). A series of biobased copolyesters (named PEHIF–x: x denotes the molar ratio of 5-HIPA in the copolyester, x percent) were synthesized via polycondensation, where the phenolic hydroxyl groups of 5-HIPA introduced additional intermolecular hydrogen bonds while maintaining chain regularity. Structural characterization confirmed successful copolymer formation with composition-dependent properties. Remarkably, PEHIF–3 exhibited accelerated crystallization (22 to 15 min), while all PEHIFs showed ≥20 °C improvement in thermal decomposition temperatures and reduced melt index (94.96 to 55.84 g/10 min). Mechanical properties were significantly enhanced, with PEHIF–1 achieving 200% greater elongation at break than PEF. Crucially, the copolyesters retained PEF’s exceptional barrier performance, maintaining the advantages of 7-fold higher oxygen barrier, 10-fold higher carbon dioxide barrier, and 2-fold higher water vapor barrier compared to PET. This work establishes hydrogen bond engineering as an effective approach to simultaneously improve PEF’s processability, thermal stability, and mechanical properties without compromising its sustainable advantages, offering high-performance biobased packaging materials.