Polyurethane formulation for large scale casting

Claim 1

In a method of reacting an isocyanate compound with a compound containing active hydrogen capable of reacting with the isocyanate in the presence of a catalyst to form a polyurethane, wherein the catalyst is dissolved in the active hydrogen compound at a sufficient temperature to maintain the compound in a liquid phase, which compound is then mixed into the isocyanate at a sufficient temperature to prevent the compound from freezing out of solution, the improvement which comprises mixing the isocyanate into the active hydrogen compound in the absence of the catalyst at a sufficient temperature to maintain a homogeneous single-phase reaction solution, cooling the solution to a minimum temperature above the temperature at which the active hydrogen compound freezes out of the solution, which temperature is below the normal freezing point of the catalyst, and finally adding the catalyst.