Abstract: The invention relates to a process for the preparation of SiOC-linked, linear polydimethylsiloxane-polyoxyalkylene block copolymers having (AB) repeat units, via reaction by methods known per se of polyetherdiols with a stoichiometric excess of ?,?-dihydropolydimethylsiloxanes, in the presence of one or more compounds of elements of main group 13 and/or of transition group 3 as catalyst, which comprises, after completed reaction of the alcohol component, continuing the reaction until no remaining ?Si(H) groups are detectable by a gas-volumetric method, and also to the compounds thus prepared, and to their use as surfactant additives for the production of polyurethane ether foams.

Abstract: The invention provides a process for preparing SiOC-bonded polyorganosiloxanes by reacting, by processes known per se, hydroxyl-containing compounds with a stoichiometric excess of polyorganosiloxanes which contain —Si(H) units and are of the general formula (I) in the presence of one or more element compounds of main group III and/or of transition group 3 as a catalyst, wherein the reaction, on completion of conversion of the compounds containing hydroxyl groups, is continued until no further ?Si—H groups are detectable by gas volumetric means, and also the compounds prepared in this way and their use.