Heteroatom Effect: Unraveling the Impact of Furan vs. Phenylene Ring Structures on the Gas Barrier Mechanism of Bio-Based Copolyester Elastomers

Abstract The bio-based monomer 2,5-furandicarboxylic acid (FDCA) endows thermoplastics such as poly(ethylene furanoate) with superior gas barrier properties. However, its application and mechanistic role in cross-linkable elastomers remain underexplored. To examine the possible contribution of the furan oxygen within this compositional framework, we synthesized partially bio-based, cross-linkable polyester elastomers with varied FDCA-to-isophthalic acid (IPA) ratios. IPA, sharing a similar nonlinear geometry but lacking the oxygen heteroatom, served as an internal reference. The synthesized elastomers exhibited high molecular weights (Mn ≥ 24,800 g/mol) and excellent thermal stability (Td,5% up to 359 °C). Dynamic mechanical analysis showed that increasing FDCA content was accompanied by suppressed β-relaxation; specifically, the IPA-based reference showed a β-relaxation peak area 1.8 times larger than that of the FDCA-rich elastomer. Correspondingly, the oxygen permeability coefficient decreased substantially from 1.99 to 0.81 Barrer as the FDCA content increased from 0 to 60 mol %. These results support an important contribution of the oxygen-containing furan unit to restricted local segmental dynamics and improved oxygen barrier performance in cross-linked copolyester elastomers. This work provides a composition-based design strategy for sustainable elastomers requiring both elasticity and gas barrier properties.