Preparation and properties of UV-curable hyperbranched polyurethane acrylate hard coatings

In order to efficiently protect plastic cover of 5G mobile phones, a novel hyperbranched polyurethane acrylate-based hard coating (HBPUA) having highly rigid hyperbranched cores was prepared and used as the protective film. For purpose of researching the structure and property relationship, two more hyperbranched cores (Hyper-6OH) and corresponding HBPUA oligomers were also synthesized. The structures of Hyper-6OH and HBPUA were characterised by proton nuclear magnetic resonance, and the molecular weight of HBPUA was confirmed by gel permeation chromatography. To further enhance the crosslinking and lower the internal stress, pentaerythritol tetra(3-mercaptopropionate) (PETMP) was introduced into the film system. The curing behaviours of the prepared HBPUA coatings were determined by Fourier-transform infrared spectroscopy. The results indicated that the double bond conversion was associated with the rigidity of the hyperbranched core and the content of thiol groups. The properties of HBPUA-based films were characterized by the test of gel content, swelling ratio and water absorption and as well as dynamic mechanical property, mechanical property, thermogravimetry and surface property. The results reveal that the pencil hardness of the prepared coatings reaches 5H that is higher than the commercially available resin PUA-6, enabling potential application in the protection of plastic cover. The rigidity of the hyperbranched cores and the introduction of PETMP remarkably affect the Tg value of the films, and the addition of thiol groups increases the gel content, swelling ratio, toughness and adhesion of coatings, but decreases the water absorption and tensile strength. Moreover, all coatings exhibit good thermal properties.