Novel epoxy-benzoxazine water-based emulsions with reactive benzoxazine surfactants for coatings

Novel epoxy-benzoxazine emulsions designed for water-based coatings were prepared and investigated. Bisphe- nol#A-based epoxy resins with molar weights of 340, 377 and 1750 g/mol along with epoxidized soybean oil were emulsi- fied using mono- and bi-functional benzoxazine surfactants, which are able to react with epoxy resins at their cure temperature. The structure of synthesized surfactants carrying one or two polyether chains was confirmed using Fourier transform infrared spectroscopy, 1 H nuclear magnetic resonance and differential scanning calorimetry. Stability of emul- sions was verified by particle diameters measurements. Coatings, made directly from emulsions, were dried and cured at elevated temperature using 3,3$-dimetoxybenzidine as curing agent to ensure a highly cross-linked structure of thermoset- ting films. Curing process, thermal properties and hardness of cured films were investigated. It was found that benzoxazine molecules were well incorporated into the epoxy network upon curing, which ensures no void structure of cured copolymer and enhanced coating properties.