Catalyst-free synthesis of poly(furfuryl alcohol) using deep eutectic solvents

We report a catalyst-free pathway for the polymerization of furfuryl alcohol (FA) into poly(furfuryl alcohol) (PFA) using a deep eutectic solvent (DES) system. The DES prepared by mixing choline chloride (ChCl) and zinc chloride (ZnCl2) to polymerize FA in high yield under comparatively moderate reaction conditions. The FA conversion was found to increase with increasing reaction temperature and weight ratio of DES/FA. The highest yield of PFA (92.5%) was achieved at 80 °C in 4 h using a weight ratio of DES : FA of 10. FT-IR, 1H and 13C NMR, TGA, XRD and DSC analytical techniques were used to elucidate the structure and thermal behavior of the end product to confirm the successful formation of PFA. Moreover, we investigated the kinetics and calculated the activation energy for the reaction. A plausible mechanism for the reaction was proposed, focusing on the important role of the Ch+ cation to initiate the polymerization process. The main advantage of this work is the exploitation of DES systems as a recyclable medium that can efficiently catalyze FA polymerization without using any external solvent and catalyst.