Novel waterborne polymeric crosslinkers containing blocked isocyanate moieties and active epoxy groups for electrophoretic coatings

The epoxy intermediates with three hydroxyl groups were synthesized from 2-aminoethanol (ETA) with ethylene glycol diglycidyl ether (EGDE) or resorcinol diglycidyl ether (RDGE), followed by the neutralization of the inherent tertiary amine groups. The intermediate was then reacted with isophorone diisocyanate (IPDI) to produce polyurethane prepolymer, which was further chain-extended and modified by polyethylene glycol (PEG-1000) and polyethylene glycol monomethyl ether (MPEG-1200), respectively. Finally, methyl ethyl ketone oxime (MEKO) was used to block the residual isocyanate (NCO) group, leading to the achievement of the waterborne polymeric crosslinkers containing blocked NCO moieties and active epoxy groups. The structure of the crosslinkers was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectroscopy ( 1 H-NMR). TG and DTG profiles show that both crosslinkers can quickly crosslink and cure the resin at temperatures above 96 °C. The mechanical properties of the cured films obtained by applying crosslinkers to electrophoretic coatings were also studied. The results show that the coating prepared by the crosslinker of the RDGE system has the best adhesion and can reach a maximum of 0.66 MPa.