Abstract: The instant invention is directed to a process for the production of isocyanate polyisocyanates containing at least 50%, by weight, of tris-isocyanatomonoisocyanurates and at most 3%, by weight, of isocyanurate-free diisocyanate. The process comprises catalytically trimerizing the organic diisocyanates free from isocyanurate groups and terminating the trimerization reaction by deactivation of the catalyst after 5 to 40% of the isocyanate groups of the isocyanurate-free diisocyanate have been trimerized. The unreacted isocyanurate-free diisocyanate is then distilled off in the presence of from 1 to 30%, by weight, based on the end product obtained as distillation residue, of an inert liquid distillation aid which boils at a temperature at least 50.degree. C. above the boiling point of the isocyanurate-free diisocyanate.The invention is also directed to the products produced by this process.

Abstract: This invention relates to a new process for the production, in inert organic solvents, of physiologically compatible polyisocyanates containing isocyanurate groups which have a monomeric diisocyanate content, based on solids, of at most 0.7%, by weight. The process uses Mannich bases as the trimerizing catalyst at temperatures below 60.degree. C and the reaction is terminated at the desired degree of trimerization by thermally decomposing the catalyst or by deactivating with a catalyst poison.

Abstract: Comparatively low viscosity biuret containing polyisocyanates are produced by reacting diisocyanates and biuretizing agents in proportions corresponding to a molar ratio of diisocyanate to monofunctional biuretizing agent of at least 11 : 1.