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 H-1 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 EB(90)HPUA(10) film. Besides, the elongation at break increased continuously with the addition of HPUA, reaching to 130% for EB(70)HPUA(30) film. Moreover, the impact strength was greatly enhanced by the addition of HPUA, possessing nearly two times high for EB(70)HPUA(30) film compared with pure EB600 film. However, the T-g decreased as HPUA was added from the DMTA measurements. According to the ratios of T-s/T-g the HPUA has good compatibility with EB600/TPGDA resin. (C) 2010 Elsevier B.V. All rights reserved.