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 PU coating applications, the demand for the development of new two-component, waterborne polyurethane (2K WB PU) coating formulations and suitable water-borne PU catalysts has emerged. While the use of waterborne systems may address many of the VOC concerns, the design of water-soluble, hydrolytically stable PU catalysts that exhibit performance similar to that of DBTL in aqueous environments has been a challenge. Reaxis believes that the shortcomings of typical PU catalysts like DBTL in waterborne formulations, where factors such as temperature, relative humidity, hydrolytic stability, polyol/isocyanate (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 (C333W50, C739W50, and C622W78, respectively) that we think exhibit excellent reactivity in several 2K waterborne and solventborne coating applications. The catalysts also provide exceptional gloss/color, hardness, and chemical resistance development in addition to other related physical properties. Furthermore, C333W50 exhibited enhanced reactivity under high levels of relative humidity when compared to that of DBTL and a high level of selectivity (Krel = 6.7) towards the polyol/isocyanate reaction over the undesired water/isocyanate (NCO/H2O) side-reaction.
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