Rational design of waterborne biobased epoxy methacrylates using citric acid and epoxy soybean oil for UV-curable coatings

Waterborne biobased UV-curable coatings (WBUCs) with environmentally friendly, renewable and energy-saving characteristics have attracted increasing attention. However, waterborne epoxy soybean oil-based UV-curable resin is mainly synthesized by introducing a polyurethane acrylate segment, which involves the use of toxic isocyanates. It is highly desirable to develop a more environmentally friendly method to prepare waterborne epoxy soybean oil-based UV-curable coatings. In this work, a "green + green + green" method was provided to synthesize three kinds of epoxy methacrylates, in which a citric acid (CA)-derived functional precursor (GC) was used to modify epoxy soybean oil (ESO), hydrogenated bisphenol epoxy resin (HBPAEP), and bisphenol epoxy resin (BPAEP) via an epoxy ester reaction. After confirmation by FT-IR and 1H NMR, it was found that the obtained epoxy methacrylates contain abundant intrinsic hydroxyls and carboxyls and extrinsic hydroxyls by the epoxy ester reaction, thus endowing these epoxy methacrylates with excellent hydrophilicity, compatibility, and stability. Meanwhile, after UV curing, the obtained WBUCs exhibited superior adhesion and thermal and mechanical properties. Moreover, the differences in these performances were systematically studied for these WBUCs with different compositions. Our "green + green + green" method provides a novel and rational potential design for WBUCs with high biobased content and excellent performance.