Breaking the cycle: A novel eco-friendly strategy for poly(hexamethylene 2,5-furandicarboxylate) synthesis and recycling

The shift towards a circular economy in the plastic sector demands a holistic approach that prioritizes biobased feedstocks, benign synthetic routes and efficient end-of-life recycling. Herein, an integrated green strategy for the synthesis and recycling of poly(hexamethylene 2,5-furandicarboxylate) (PHF) is outlined. Cyclic oligoesters were prepared from biobased precursors via cyclodepolymerization (CDP) and subsequently converted into PHF through the entropically driven-ring opening polymerization (ED-ROP). To minimize processing steps the crude CDP product, containing cyclic and linear oligoesters, was used directly, with linear species acting as initiators. The ROP catalytic activity of non-toxic bismuth-based compounds was compared to traditional tin-based catalysts. Bismuth subsalicylate (BiSS) emerged as the most efficient choice, leading to high molecular weight PHF under mild conditions. These polymers were fully characterized by 1H NMR, FTIR, viscosimetry and XRD techniques and their thermal properties were studied using TGA, DSC, and DMTA methods. The so prepared PHF exhibited excellent thermal stability and high degree of crystallinity. Proof of concept experiments showed that PHF can be chemically recycled via CDP in a relatively short time frame. Altogether, these findings constitute a first step towards the development of a sustainable cradle-to-grave approach for PHF.