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.