Preparation and properties of UV-curable diamine-based polyurethane acrylate hard coatings

Three polyurethane acrylate (PUA) branched compounds with different diamines (Norbornane dimethylamine, piperazine and ethylenediamine) were synthesized under the facile reaction condition. Coatings based on synthesized branched compounds were prepared under UV-irradiation, and used as hard coatings to protect the plastic surface. The structures of PUA branched compounds were characterised by proton nuclear magnetic resonance and gel permeation chromatography. The effect of rigid diamines on the properties of coatings was investigated regarding to the curing behaviour, dynamic mechanical property, mechanical property and coating surface property. The results indicate that the final double bond conversion is associated with the rigidity of the diamines and the viscosity of the prepared coating solution. The rigid diamine endows the coating with high Tg value, and leads to phase separation that creates rough coating surface. The tensile test shows that the coating with highest crosslinking and moderately rigid diamine possesses excellent mechanical property with 20.7 MPa in tensile strength and 6.8% in elongation at break. The pencil hardness of the prepared PUA-PZ coating can reach to 5H that is higher than the commercially available resin PUA-6, and this coating also shows good adhesion and flexibility, which has potential to be applied as protective coating to protect PC surface well. Moreover, all coatings exhibit good thermal properties.