Curing behavior of a UV-curable coating based on urethane acrylate oligomer: the influence of reactive monomers

A hybrid organic-organic urethane acrylate oligomer was synthesized by the reaction of polypropyleneglycol (PPG),2,4-toluene diisocyanate (TDI) and 2-hydroxyethyl methacrylate (HEMA) using dibutyltin dilaurate (DBTDL) as a catalyst.The urethane acrylate oligomer’s structure was characterized by nuclear magnetic resonance (NMR) and Fourier transforminfrared spectroscopy (FT-IR). Two UV-curable coatings were prepared by blending the urethane acrylate oligomer, a reactivemonomer (1,6- hexanediol diacrylate (HDDA) or trimethylol propane triacrylate (TMPTA)) and a photoinitiator (2,2-dimethoxy-2-phenyl acetophenone). The UV curing process of such coatings was monitored by FT-IR and determination of thegel fraction. It was found that as the UV dose increased, the specific peaks at 1635 cm-1 and 810 cm-1, related to the carboncarbondouble (C=C) bond, decreased. Gel fraction of the cured coating film was found to increase with increasing radiationtime. Thermal properties of the cured coating were also investigated using differential scanning calorimetry (DSC) andthermal gravimetric analysis (TGA).