Preparation of UV-cured polyurethane-urea acrylate coatings with high hardness and toughness

Polyurethane-urea acrylate (PUUA) has been used to develop mechanically robust materials, due to the urea-based bifurcated H-bond. However, the uncontrollable reaction rate between diamine and diisocyanate makes it difficult to prepare PUUA. Herein, we put forward a simple method to synthesize PUUA, which was then used to prepare UV-cured PUUA coatings with simultaneous high hardness and excellent toughness. In our strategy, a novel diol containing urea group has been designed, which was employed as chain extender to synthesize PUUA at a controllable polymerization rate. By adopting chain extenders with different molecular structures, two kinds of PUUA were synthesized. The molecular structures of diol containing urea group and PUUA were identified by Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance spectroscopy (1H NMR). Benefiting from the strong urea-based H-bond, the UV-cured PUUA films showed simultaneously enhanced mechanical strength and toughness. Specially, the optimal PUUA film exhibited high mechanical strength (19 MPa), high elongation at break (310 %), and high toughness (26.9 MJ m−3), which was 9.5, 2.8 and 19.2-fold increase compared with polyurethane acrylate (PUA) film without urea groups. Correspondingly, the UV-cured PUUA coatings exhibited higher impact resistance and higher hardness than PUA coating. This work provides a new avenue to develop PUUA for high-performance UV-curable coatings.