Modified cationic polymers, methods for their preparation and their use in papermaking

The invention relates to modified cationic polymers which can be obtained by reacting (a) water-soluble, polymeric compounds containing NH groups with (b) compounds which are at least bifunctional with regard to NH groups, which contain at least one alkyl radical or alkenyl radical having at least 8 C atoms, and which contain, as a functional group, a halohydrin, epoxide, carboxyl, chloroformate or isocyanate group or a halogen atom. The invention also relates to a method for producing the polymers by reacting the compounds of groups (a) and (b), and to the use of the modified cationic polymers during the production of paper as fixing agents for papermaking stock containing interfering substances.