The instant invention relates to novel carbodiimidization catalysts consisting of a high molecular weight, insoluble matrix and low molecular weight carbodiimidization catalysts fixed to the matrix via ionic bonds. The novel high molecular weight catalysts are suitable for the preparation of storage stable, catalyst free, equilibrium mixtures of organic carbodiimides, uretone imines and isocyanates. Either the carbodiimide, or the uretone imine or both may contain isocyanate groups. Alternatively, mono and/or polyisocyanates free from carbodiimide and uretone imine groups may be added to the equilibrium mixture. The catalysts according to the invention are capable of bringing about selective carbodiimidization of individual isocyanates in a mixture of various isocyanates.