Synthesis of polyrosin-based epoxy resins catalyzed by Lewis-acidic deep eutectic solvents

Abstract

The preparation of bio-based epoxy resins has attracted considerable attention. Using natural and renewable rosin as the raw material and an environmentally friendly deep eutectic solvent (DES) as the catalyst, an epoxy resin modified with polymerized rosin was synthesized. The resin had good oxidation resistance, rigidity, and resistance to heat and weather. Three key reactions for synthesizing polyrosin-based epoxy resins were studied in detail: polymerization of rosin, ring-opening esterification of epichlorohydrin with polymerized rosin, and ring-closing of the esterification product. The catalysts used in the first two reactions were Lewis-acidic DESs, which showed good catalytic activity, recovery, and recyclability. The optimal DES catalyst, [AlCl₃·6H₂O][ChCl]₄ synthesized from aluminum trichloride hexahydrate (AlCl₃·6H₂O) and choline chloride (ChCl), could catalyze both the polymerization of rosin and the ring-opening esterification of epichlorohydrin, thus realizing one-pot catalytic synthesis of polyrosin-based epoxy resins. In addition, [AlCl₃·6H₂O][ChCl]₄ exhibited good recycling performance. The new synthesis method produced the polyrosin-based epoxy resin with the highest epoxy value of 0.219 mol 100 g⁻¹, an acid value of 1.56 mg KOH g⁻¹, and a peak-average molecular weight of 1092 g mol⁻¹. Thermogravimetric tests showed that the resin exhibited good thermal stability. This study provides an efficient, economical, and environmentally friendly method for synthesizing bio-based epoxy resins, which have excellent prospects for industrial applications.