Unexpected performance of iron( iii )chloride in the polymerization of renewable 2,3-butanediol and the depolymerization of poly(ethylene terephthalate)

In this study, 2,3-butanediol (BDO), which can be obtained by fermentation, was used in a polycondensation reaction with renewable 2,5-furandicarboxylic acid (FDCA) to obtain a fully renewable polyester. Catalyst screening based on a deconvolution method was performed. 16 different, randomly chosen Lewis acids were screened with the aim to identify the most active catalyst. With iron(III)chloride, the most active catalyst also offering sustainability benefits, further investigations of a polycondensation in melt are presented. Further renewable dicarboxylic acids were (co)polymerized with BDO and FDCA to yield polyesters and copolyesters and to investigate whether FeCl$_3$ was also a suitable catalyst for other polycondensations. Full characterization of all polymers is provided, including $^1$H NMR and IR spectroscopy as well as differential scanning calorimetry (DSC), size-exclusion chromatography (SEC), and thermogravimetric analysis (TGA). Furthermore, depolymerization reactions of poly(ethylene terephthalate) (PET) materials are performed using the identified catalyst, iron(III)chloride, further demonstrating its versatility.