Development of water-soluble, metal-based catalysts for poly- urethane coating applications

As regulatory changes continue to restrict the use of volatile organic compounds (VOCs) as well as traditionally used polyurethane catalysts, such as dibutyltin dilaurate (DBTL), in polyurethane (PU) coating applications the demand for the development of new two-component, waterborne polyurethane (2K WB PU) coating formulations and suitable waterborne PU catalysts has emerged. While the use of waterborne coating formulations may address many of the VOC concerns, the design of water-soluble, hydrolytically stable PU catalysts that exhibit performance matching that of DBTL in aqueous environments remains a challenge. The shortcomings of typical PU catalysts like DBTL in waterborne formulations, where factors such as temperature, relative humidity, hydrolytic stability, NCO/OH selectivity, and catalyst shelf life are of paramount importance, have become more evident as the usage of 2K WB PU coatings has increased. This work showcases several novel, water-soluble organotin-, Bi-, and Zn-based catalysts that exhibit excellent reactivity in several 2K waterborne and solventborne coating applications. The catalysts also demonstrate exceptional gloss/color, hardness, and chemical resistance development in addition to other related physical properties. Furthermore, WS-Sn 1 displays enhanced reactivity under high levels of relative humidity when compared to that of DBTL and a high level of selectivity towards the NCO/OH reaction over the undesired NCO/H 2 O side-reaction. Given the exceptional reactivity, selectivity, and stability that this series of water-soluble catalysts display, they offer promising alternatives to DBTL and other traditional PU catalysts in 2K WB PU coating applications.