Synthesis and properties of hyperbranched polyurethane acrylate used for UV curing coatings

The hyperbranched polyurethane acrylate (HPUA) was synthesized through the addition of hyperbranched polyurethane endcapped by hydroxyl groups (HPU-OH), with the semiadduct urethane monoacrylate (IPDI-HEA). The HPU-OH was prepared by the amidation reaction of diethanolamine with isophorone diisocyanate. The molecular structure of HPUA was characterized by FTIR and 1H NMR analyses. The number average molecular weight and its polydispersity index were measured by GPC to be 7714 g mol−1 and 1.24, respectively. The HPUA was blended with epoxy acrylate EB600 and difunctional monomer TPGDA in different ratios, and exposed to a UV lamp for photopolymerization in the presence of Runtecure 1104 as a photoinitiator at room temperature. The photopolymerization rate and final unsaturation conversion reached to the highest values with only 5 wt% HPUA addition, whereas decreased as further added. The tensile strength of UV-cured films was improved by adding less than 10 wt% HPUA without damaging the modulus, having the value of 62.56 MPa for EB90HPUA10 film. Besides, the elongation at break increased continuously with the addition of HPUA, reaching to 130% for EB70HPUA30 film. Moreover, the impact strength was greatly enhanced by the addition of HPUA, possessing nearly two times high for EB70HPUA30 film compared with pure EB600 film. However, the Tg decreased as HPUA was added from the DMTA measurements. According to the ratios of Ts/Tg the HPUA has good compatibility with EB600/TPGDA resin.