Investigation of non-isocyanate urethane dimethacrylate reactive diluents for UV-curable polyurethane coatings

• Three urethane dimethacrylates were synthesized via a non-isocyanate method.
• PU coatings showed improvements in impact resistance and elongation-at-break.
• The coatings properties were dependent on the reactive diluents type and content.

Three non-isocyanate urethane dimethacrylate reactive diluents 2-(methacryloyloxy)ethyl 2-(methacryloyloxy)ethylcarbamate (EOAED), 2-(methacryloyloxy)ethyl 3-(methacryloyloxy)propylcarbamate (POAED), and 1-(methacryloyloxy)propan-2-yl 3-(methacryloyloxy)propylcarbamate (POAPD) were synthesized by the reaction of a cyclic carbonate with an amino alcohol followed by a second reaction with the methacrylic anhydride. These reactive diluents were formulated with an acrylated polyester (APE) oligomer and free radical photoinitiator to prepare UV-curable polyurethane coatings. For comparison with urethane dimethacrylate reactive diluents, ethylene glycol dimethacrylate (EGDMA) was also used. The effect of reactive diluent type and content on the viscosity of the APE oligomer was measured. After UV curing, the viscoelastic, tensile, and thermal properties of the cured films were evaluated as a function of the reactive diluent using dynamic mechanical thermal analysis (DMTA), tensile, differential scanning calorimeter (DSC), and thermal gravimetric analysis (TGA). In addition, coating properties such as pencil hardness, chemical resistance, impact resistance, and gloss were also investigated. It was found that crosslink density, storage and tensile modulus, pencil hardness, chemical resistance, gel content, total water absorption, and glass transition temperature (Tg) were directly proportional to the amount of the reactive diluent. The urethane dimethacrylate reactive diluents show significant improvements in impact resistance and elongation-at-break properties compared to the EGDMA. It was found that the optimum level of the urethane dimethacrylate reactive diluents concentration is between 10 and 20 wt%.