Excellent water resistance and mechanically robust waterborne polyurethane-acrylate based on dithiol post-chain extension

There is a trade-off between water resistance and mechanical properties of the waterborne polyurethane film. Aiming to solve this problem, the waterborne polyurethane-acrylate (WPUBH) was prepared by post-chain extension of dithiol instead of diamine, which could improve the storage stability and reduce the water absorption rate due to the absence of urea groups, and by terminating with hydroxyethyl acrylate, which could reduce the water absorption rate and improve the mechanical properties at the same time deriving from the crosslinking of double bonds after heating. The rate of water absorption for WPUBH-2 film decreased down to 2.87%, and the tensile strength reached 8.5 MPa. The water resistance and the mechanical properties of WPUBH obtained a good balance compared with those of the carboxylate-based waterborne polyurethane-acrylate in the previous reports. They had excellent bonding properties for wood joints, and the tensile shear strength was up to 4.53 MPa.