Polyurethane modified epoxy acrylate resins containing ε-caprolactone unit

Epoxy acrylate resins modified by polyurethane with excellent mechanical properties play a crucial role in UV-curable coatings, but the high viscosity limits their further applications in 3D printing, electronic packaging material. In this work, a series of polyurethane modified epoxy acrylate resins containing various ε-caprolactone unit content were successfully synthesized to reduce the viscosity of polyurethane modified epoxy acrylate resins. The chemical structure and molecular weight of the prepared resins were characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC), respectively. The influences of ε-caprolactone unit on the viscosity of resins and double bond conversion of cured films were studied. The dynamic thermomechanical properties, mechanical properties, thermal stability and basic properties of UV curable coatings were also evaluated. The results show that the viscosity of resins is reduced by two orders of magnitude. As the ε-caprolactone unit content increased, the adhesive force increased from 0B to 5B according to ASTM D3359, while the glass transition temperatures (Tg) of films and pencil hardness were slightly lower than those of the conventional polyurethane modified epoxy acrylate resins. In summary the introduction of ε-caprolactone unit in the side chain enables the preparation of polyurethane modified epoxy acrylate resin with ultralow viscosity as well as a more comprehensive adhesive and impact force performance.