Preparation and characterization of UV-curable hyperbranched polyurethane acrylate

A series of UV-curable hyperbranched polyurethane acrylate (HBPUA) oligomers were synthesized with isophorone diisocyanate (IPDI), hyperbranched polyester Boltorn H20 (HBP) and hydroxy-ethyl acrylate (HEA). The structure of HBPUA oligomers was characterized by Fourier transform infrared (FTIR) spectroscopy, 1 H nuclear magnetic resonance ( 1 H-NMR) spectroscopy, and gel permeation chromatography (GPC). The UV-curing kinetics of HBPUA films with Darocur 1173 were investigated, and their heat resistance and mechanical properties (including hardness, adhesion force, flexibility, and impact strength) were measured. The results show that the HBPUA oligomers have superior photosensitivity and the percent conversion of C=C reaches 81% when radiation time is 43 s. The heat resistance of the cured films decreased slightly with the increase in the content of the urethane-acrylate terminal group. Moreover, the mechanical properties of the cured films were influenced by the content of the OH group in HBP that reacted with the first NCO group of IPDI. When the content was 60%, the cured film had excellent overall properties. The hardness, flexibility, adhesion force, and impact strength were 4 H, 2 mm, 0 grade, and 47 kg cm, respectively.