Method for the preparation of cation-stabilised polyurethane dispersions comprising at least the following steps: a) preparation of a NCO-terminated polyurethane prepolymer wherein the preparation of the polyurethane prepolymer comprises at least the conversion of the following reagents: - at least a polyol A - at least an amino alcohol having the formula: having a tertiary amine group and in each case independently of each other: A= hydrocarbyl having 0 to 6 C-atoms B= hydrocarbyl having 0 to 6 C-atoms C and D= hydrocarbyl having 0 to 15 C-atoms at least a multifunctional isocyanate, wherein the NCO/OH+NH ratio of the reagents is 1.1: 1 to 2.5: 1 and the reaction is performed until a conversion of more than 80% of the sum of the hydroxyl-groups and the primary or the secondary amine-groups with the isocyanate groups; and wherein the tertiary amine-group is part of a side group of the carbon-carbon-chain and is bound via at least one -CH 2 - group to the carbon-carbon-chain, b) conversion of the NCO-terminated polyurethane prepolymer with one or more compounds for chain elongation, having at least one functional group, preferably at least two functional groups, selected from one or more members of the following groups: - a primary amino group - a secondary amino group, and - a hydroxyl group, until a NCO/OH+NH - ratio of 1: 1 to 1.2: 1 and the NCO/OH+NH - ratio is below that of step a), c) conversion of the tertiary amine group with one or more quarternising agents, including protonation with an acid to give ammonium salts, and d) dispersing in water. a) preparation of a NCO-terminated polyurethane prepolymer wherein the preparation of the polyurethane prepolymer comprises at least the conversion of the following reagents: - at least a polyol A - at least an amino alcohol having the formula: having a tertiary amine group and in each case independently of each other: A= hydrocarbyl having 0 to 6 C-atoms B= hydrocarbyl having 0 to 6 C-atoms C and D= hydrocarbyl having 0 to 15 C-atoms at least a multifunctional isocyanate, wherein the NCO/OH+NH ratio of the reagents is 1.1: 1 to 2.5: 1 and the reaction is performed until a conversion of more than 80% of the sum of the hydroxyl-groups and the primary or the secondary amine-groups with the isocyanate groups; and wherein the tertiary amine-group is part of a side group of the carbon-carbon-chain and is bound via at least one -CH 2 - group to the carbon-carbon-chain, - at least a polyol A - at least an amino alcohol having the formula: having a tertiary amine group and in each case independently of each other: A= hydrocarbyl having 0 to 6 C-atoms B= hydrocarbyl having 0 to 6 C-atoms C and D= hydrocarbyl having 0 to 15 C-atoms at least a multifunctional isocyanate, A= hydrocarbyl having 0 to 6 C-atoms B= hydrocarbyl having 0 to 6 C-atoms C and D= hydrocarbyl having 0 to 15 C-atoms b) conversion of the NCO-terminated polyurethane prepolymer with one or more compounds for chain elongation, having at least one functional group, preferably at least two functional groups, selected from one or more members of the following groups: - a primary amino group - a secondary amino group, and - a hydroxyl group, until a NCO/OH+NH - ratio of 1: 1 to 1.2: 1 and the NCO/OH+NH - ratio is below that of step a), - a primary amino group - a secondary amino group, and - a hydroxyl group, c) conversion of the tertiary amine group with one or more quarternising agents, including protonation with an acid to give ammonium salts, and d) dispersing in water.