Preparation And Properties Of Thiol Post-chain-extended Waterborne Polyurethane-acrylate

Waterborne polyurethane(WPU)is usually prepared by the reaction of polyisocyanate with polymer polyol and diol containing carboxyl or sulfonic acid groups,the post-chain extension of diamine or diol,and the emulsification in a water medium.Compared with the solvent-based polyurethane,WPU possesses unique advantages in environmental protection,processing,transportation,etc.But its water resistance,mechanical properties,and storage stability are relatively poor,which limits the range of application of WPU.In our group's previous works,dithiol instead of diamine was used as a post-chain extender to prepare the carboxylate-based WPUB,achieving the improvement of storage stability of WPU.In order to further solve the contradiction between the mechanical properties and the water resistance of WPU film,the waterborne polyurethane acrylate emulsion(WPUBH)with a high solid content(42%)was prepared with dithiol as a post-chain extender and hydroxyethyl acrylate as a capping agent.The stability of emulsion was studied by the gel transition temperature deriving from rheometer.The effects of the dithiol/hydroxyethyl acrylate molar ratio on the mechanical properties,water resistance and bonding strength of WPUBH film were explored.Compared with WPUB prepared from dithiol as the post-chain extender alone,it was found that the dithiol post-chain extended and hydroxyethyl acrylate terminated WPUBH film had a certain extent improvement in the water resistance and the mechanical properties,and the emulsion had also good storage stability.To further improve the mechanical properties and water resistance of WPU film,the WPUDBM and WPUBDM emulsions were successfully prepared with hydroxyethyl methacrylate instead of hydroxyethyl acrylate.The stability of emulsions was investigated by testing pH value,particle size,zeta potential,viscosity and centrifugal experiments.Meanwhile,the possibility and temperature of thermal curing for WPU film were explored by the variable temperature infrared spectroscopy.Lastly,the effects of the order of addition and the ratio on the performances of WPU were explored.