Polyoxyalkylene-polysiloxane block copolymers, a process for their preparation and their use as defoamers in aqueous dispersions

The invention polyoxyalkylene-polysiloxane block polymers of the general formula (I) CB (AB) wherein mean A = is a polyoxyalkylene block of the general formula - (C B = a polysiloxane of the general formula - (SiR C, C R = identical or different C R Z = an alkyl, alkylene, aryl or alkylaryl, a = 1 to 20, preferably 2 to 10, b = an average value from 10 to 130, preferably 20 to 100, c = 3 to 100, preferably 10 to 80, d = independently of one another in C / C n = 2 to 12 with an average numerical value from 2.7 to 4.0 and a process for their preparation and their use as defoamers in aqueous dispersions.