Effect of soft chain length and generation number on properties of flexible hyperbranched polyurethane acrylate and its UV-cured film

A series of UV-curable flexible hyperbranched polyurethane acrylate (F-HBPUA) with various generation numbers and soft chains are successfully developed by modifying different generations of hydroxyl terminated hyperbranched polyurethane (HBPU-OH) with diverse soft chains contained semiadduct urethane monoacrylate. The influence of generation number and soft chain on the performances of F-HBPUA and its UV-cured freestanding film is studied. The degree of branching of F-HBPUA from the second to the fifth generation is proved to be 0.74, 0.79, 0.82 and 0.94, respectively. The glass transition temperature of F-HBPUA increases with increasing generation number but it decreases with the increase of soft chain length. The thermal stability of F-HBPUA improveswith higher generations while the longer soft chain is only beneficial to the heat resistance at below 300   °C. As the increase of generation number and chain length, the UV-curing time of F-HBPUA film is significantly shortened from 12   s to 3   s, the flexibility of the UV-cured film is greatly increased from 4   mm to 1   mm, adhesion is improved to 3 grades. This novel flexible hyperbranched polyurethane acrylates can be applied to coatings, membranes and 3D print parts with excellent flexibility.