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The preparation of polyurethane foams or film and varnish coatings from multi-component reaction systems sometimes necessitates selective monitoring of the individual stages in the reaction depending on the technological nature of the process. Accordingly various additives are introduced into the reaction mixtures to accelerate or inhibit the interaction of aocyanates with certain compounds having a labile hydrogen atom. Information has been published regarding the way in which a mixture of amine and organotin catalysts led to the discovery of the synergetic effect during the interaction of isocyanates with alcohols and water [1,2]. The reaction of phenylisocyanate with n-butyl alcohol in the presence of a mixed catalyst took place at a much higher rate than would have been expected in view of the rates of these reactions in the presence of each of the catalysts used by itself.

The mechanism of the catalyzed linear polyurethane formation in the presence of dibutyltin dilaurate, copper acetylacetonate, and similar catalysts was investigated. It was found that the central ion coordinates with the isocyanate group. The second reacting component may be coordinated by the organic substituent or ligand groups near the central ion. It was concluded that the catalytic mechanism would vary depending on such reaction conditions as temperature, solvent, and the nature of the ligands near the central ion.