Flexible Furfural-Based Barrier Polyester from a Self-Condensable Monomer

A novel biobased sulfur-bridged polyester, with high oxygen barrier properties, was synthesized via self-condensation of a new AB-type furfural-based monomer, i.e., methyl 5-[(2-hydroxyethyl)sulfanyl]furan-2-carboxylate (MSF). The novel MSF-based polyester (pMSF) showed a 15× higher barrier improvement factor compared to amorphous poly(ethylene terephthalate) (PET) and good UV light filtering, with a cutoff wavelength of ca. 340 nm, thanks to the introduced sulfur heteroatom. Interestingly, pMSF offers a circular life cycle, with excellent chemical recyclability. Furthermore, the new self-condensable monomer, MSF, was utilized as a comonomer to improve the O2 barrier performance of poly(ethylene furanoate) (PEF) and poly(ethylene bifuranoate) (PEBF). The new copolymers, i.e., PEF80MSF20 and PEBF80MSF20, have been characterized by structural, thermal, mechanical, and barrier measurements. The results clearly show that the novel monomer, MSF, is a promising precursor for sustainable biobased packaging materials with benefits of high O2 barrier, UV light filtering, flexibility, and chemical recyclability.