Described is the use of dihydroxy fatty acids and/or dihydroxy polymers of fatty acids as a compound carrying an ionizable group and reactive towards isocyanates in the production of polyurethanes incorporating carboxy groups. The dihydroxy fatty acids can be obtained from naturally occuring raw materials and do not have the disadvantages of the hydroxycarboxylic acids used in the prior art. Their use also enables the properties of the polyurethane produced from them to be improved.
