Synthesis and characterization of water-borne diisocyanate crosslinkers from methyl ethyl ketoxime/2-methylimidazole-blocked aromatic isocyanates

Water-borne blocked isocyanates (WBIs) were synthesized using toluene 2,4-diisocyanate (TDI), trimethylolpropane, dimethylolpropionic acid, 2-methylimidazole (2-MI), and methyl ethyl ketoxime (MEKO). The particle size, viscosity, pH, and storage stability of the WBI dispersions were studied and compared. De-blocking temperatures of the WBIs were characterized by Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), and thermo-gravimetric analysis (TGA) techniques. The thermal analysis revealed that MEKO-blocked TDI adducts and 2-MI-blocked TDI adducts started to de-block at about 70.7 and 125.2 °C, respectively. The storage stability results showed that all dispersions prepared were stable for more than 6 months. The dispersions prepared were all in liquid form and miscible (compatible) with acrylic dispersion. Gelation test results confirmed that MEKO-blocked isocyanate adducts dispersions de-block at higher temperatures and cure at faster rates than 2-MI-blocked isocyanate adducts dispersions. These anionically modified blocked isocyanate adducts can be used as potential crosslinkers.