One-pot and solvent-free synthesis of castor oil-based polyurethane acrylate oligomers for UV-curable coatings applications

Due to the complex chemical modification, harsh synthesis conditions and imperative post-treatment, the industrial products of vegetable oil-based polymers are very rare. In this study, castor oil-based polyurethane acrylic resin (COPUA) was synthesizled by one-pot method from castor oil (CO), isophorone diisocyanate (IPDI), hydroxyethyl acrylate (HEA) and isobbornyl acrylate (IBOA). 1H NMR and FT-IR measurements were employed to verify the successful preparation of COPUA. Various UV curable films were prepared by mixing non-treated COPUA, photoinitiator (PI-1173), mono-functional active diluent hydroxyethyl methacrylate (HEMA) or bifunctional active diluent tripropylene glycol diacrylate (TPGDA). The mechanical performances of the cured films were studied. Besides, DMA and TGA analyses were used to determine the dynamic thermodynamic performances and the thermal stability of the cured films. As a result, the pure COPUA cured film exhibited excellent thermal stability, storage modulus (421 MPa at 25 °C), tensile strength (9.87 MPa) and high glass transition temperature (60.3 °C). The cross-linking density of films improved with increasing the content of active diluent, resulting in excellent overall performances. In addition, all films possessed excellent hardness, adhesion, solvent resistance and flexibility. In this study, it provides a green and environmentally friendly strategy for the synthesis of vegetable oil-based polymers, reducing our chemical dependence on petrochemical energy.