| abstract |
The disclosed process for making a high % solids, one-part, curable, essentially flowable or pumpable, high equivalent weight polyurethane (i.e., polyol-polyisocyanate adduct) prepolymer composition involves de-watering the polyol component of the reaction mixture with an alkaline earth metal oxide, preferably calcium oxide; adding the minimum acceptable level of catalyst for the NCO/polyol reaction; exothermically reacting a partially hindered aliphatic polyisocyanate such as isophorone diisocyanate (IPDI) and a partially hindered aromatic polyisocyanate such as 2,4-tolylene diisocyanate seriatim, so that at least about one-fourth of the IPDI reacts before the 2,4-TDI is added; and then adding more catalyst for the curing (e.g. moisture cure) reaction. Careful control over the amounts and selection of raw materials, proper selection of sequences of addition of these amounts and materials, careful de-watering of the reaction mixture, and proper adjustment or selection of isocyanate functionality minimizes random and undesired reactions and side reactions (e.g. chain extension) during prepolymer formation and insures good elastomeric properties in the ultimately cured product. As a result, this well-controlled prepolymer composition can be made efficiently with simple mixing equipment. One of the preferred coating or sealant uses for the prepolymer product is cured elastomeric coatings for the building industry, e.g. as a primary seal in roofing. |