1. Field of the Invention
The present invention relates to isocyanurate-modified polyisocyanate compositions, to a process for the preparation thereof, and to microcellular foams prepared from said polyisocyanate compositions. More particularly, the invention relates to polyisocyanate compositions containing isocyanurate linkages prepared by reacting said polyisocyanate in the presence of an alkali metal organo-hydroxamate or the metal salt-free acid complex, hereinafter referred to as the "half-salt."
2. Description of the Prior Art
The prior art generally teaches the preparation of isocyanurate-modified isocyanate products, employing a variety of catalysts. U.S. Pat. No. 3,996,223 teaches a process for the preparation of polyurethane quasi-prepolymers containing isocyanurate structures by polymerization in the presence of catalytic quantities of a mixture of Mannich bases and carbamic acid esters from isocyanate and alcohols containing secondary alcohol groups. U.S. Pat. No. 3,645,979 teaches the polymerization of an aromatic polyisocyanate and an aliphatic polyisocyanate in the presence of an organic phosphine catalyst. U.S. Pat. No. 3,652,424 teaches a process for the preparation of polyisocyanate compositions containing 5 to 19 percent by weight of toluene diisocyanate trimer by employing as trimerization catalysts substituted guanidines and isobiguanidines.