Novel organosilicon-modified polyisocyanate crosslinkers for curing of waterborne hydroxyl acrylic resin

The organosilicon intermediate with three hydroxyl groups was synthesized from isopropanol amine (MIPA) and (3-glycidoxypropyl) trimethoxy silane. Meanwhile, a polyurethane prepolymer, prepared by the polymerization of isophorone diisocyanate with 2, 2-bis(hydroxymethyl) propionic acid and polyethylene glycol (PEG-600) in sequence, was chain extended by the intermediate. Ultimately, methyl ethyl ketone oxime, a conventional isocyanate (NCO) blocking agent, was chosen to inactivate the branched polymers. Thus, a waterborne blocked crosslinker containing siloxane groups was achieved, which was further treated by a mixture of alcohol and water to obtain its hydrolyzed product, i.e., a crosslinker containing silanol groups. The structure and thermal properties of crosslinkers were analyzed by means of 1 H-NMR, FTIR, TG, and DTG, respectively. The gel content, hardness, and adhesion of the cured coatings were also investigated. The results confirm the crosslinker system containing silanol groups performs much better, and when the hardness reaches 0.64 or above, the adhesion can still be maintained above 1.2 MPa.