Siloxane copolymers producible by (a) reacting organopolysiloxanes (1) having a Si-bound hydrogen atom with linear oligomeric or polymeric compounds (2) of the general formula R1-(A-CnH2n)m-A1-H (I), (b) reacting the resultant H-A1 group-bearing intermediates (4) with organic compounds (5) having at least two isocyanate groups in the presence of further organic compounds (6) and (7) which are reactive toward isocyanate groups, wherein the compounds (6) contain at least one tertiary amine group and the compounds (7) can be eliminated from the siloxane copolymer in a temperature range from 50° C. to 250° C., wherein free isocyanate groups are formed in the siloxane copolymer, and (c) partially or completely quaternizing the amine-containing intermediates (8) from step (b) with an alkylating agent (9).