Fabrication of castor oil-based hyperbranched urethane acrylate UV-curable coatings via thiol-ene click reactions

Thiol-ene click reactions are more oxygen tolerant alternative to the conventional (meth)acrylate chemistry that is frequently used for the rapid production of photopolymerized networks with numerous desirable properties. To attain a high curing efficiency while maintaining the advantages of thiol-ene systems, a castor oil-based hyperbranched urethane acrylate was employed in this work as a primary oligomer for UV-curable coating formulation. Subsequently, a tetrathiol monomer (PETMP) was introduced into the coating formulation to obtain a thiol-ene system. The effects of PETMP loadings on the UV-curing kinetics and final polymer properties were systematically investigated. Consequently, thiol-ene based films with excellent flexibility and water resistance were obtained as a result of the high efficient thiol-ene photopolymerization. The double bond conversion of the thiol-ene system was found to increase with the addition of more PETMP. Impressively, with the incorporation of 5 wt% PETMP, the resultant UV-cured film had the best acid resistance and exhibited a double bond conversion of 93.6%, a pencil hardness of 6H, a water absorption of 0.76%. Additionally, all of the prepared films were completely transparent and possessed good microstructures. These thiol-ene based films may provide insight into the preparation of high-performance UV-curable coatings with excellent flexibility.