Bayer Aktiengesellschaft

Horst Conrad

Kuno Wagner

Werner Dietrich

Georg Niederdellmann

Henning Klussmann

Karl-Josef Kraft

This invention relates to an improved process for the production of high molecular weight polyurethanes which are free from isocyanate groups and are soluble in organic solvent in reduced reaction times. The reactants, polyol and isocyanate, for example, are mixed together with solvent and the temperature is permitted to rise under the effect of the heat of reaction. The reaction mixture is then cooled with solvent addition in such a way that the viscosity of the reaction mixture remains constant until the optimum temperature for the polyurethane formation reaction ('specific reaction temperature') is reached. The mixture is then gradually cooled until there is no residual isocyanate present and the polymer is recovered from the reaction mixture.

Process for the production of soluble high molecular weight

A process is provided for the production of synthetic polyurethane plastics, particularly foam plastics, containing biuret groups by reacting polyisocyanates, polyhydroxyl and/or polycarboxyl compounds, flame inhibitors and, if desired, blowing agents, emulsifiers, activators and other additives which is characterized by using as the polyisocyanate solutions in monomeric polyisocyanates of from about 1 per cent to 85 per cent of polyisocyanates containing biuret groups and having the formula: ##EQU1## in which R is an aromatic, araliphatic or cycloaliphatic radical which may, if desired, be substituted and

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Dormagen, Germany

Horst Conrad