Processes are described for purifying acidic, preferably superacidic, in particular trifluoromethanesulfonic acid-acidified, end-equilibrated acetoxysiloxanes, wherein the acidic, preferably superacidic, in particular trifluoromethanesulfonic acid-acidified, acetic anhydride-containing and optionally acetic acid-containing equilibrated, preferably end-equilibrated acetoxysiloxane, which is optionally dissolved in an inert solvent, is contacted with a base, the precipitate is filtered off thereafter and then the filtrate obtained is optionally purified by distillation.

Described is a process for producing SiOC-bonded polyether siloxanes branched in the siloxane portion from cyclic branched siloxanes of the D/T type, wherein said process comprises in a first step reacting the mixtures of cyclic branched siloxanes of the D/T type with acetic anhydride optionally in admixture with simple siloxane cycles under acid catalysis to afford acetoxy-bearing branched siloxanes, in a second step performing the equilibration of the acetoxy-modified branched siloxane with superacid, preferably with addition of acetic acid and in a third step reacting the superacid-treated acetoxysiloxane with polyetherols optionally in the presence of bases and optionally in the presence of an inert solvent.

Reaction system for preparing acetoxy function-bearing siloxanes having chain lengths of more than 3 silicon atoms, comprising silanes and/or siloxanes bearing alkoxy groups, silanes and/or siloxanes bearing acetoxy groups, silanes and/or siloxanes bearing hydroxy groups and/or simple siloxane cycles and/or DT cycles, and also a reaction medium comprising acetic anhydride, Brnsted acid and acetic acid, wherein Brnsted acids having a pKa 1.30 are used, and wherein the acetic acid is present in the reaction system in amounts of 0.4 to 15.0 percent by weight, based on the reaction system, wherein the molar ratio of Brnsted acid used to acetic acid is in a defined range, with the proviso that either the sole use of trifluoromethanesulfonic acid and also of trifluoromethanesulfonic acid and acetic acid is excluded, and/or that the Brnsted acid used at least in part has a pKa between 1.3 and >13.5.

Reaction system for preparing acetoxy function-bearing siloxanes having chain lengths of more than 3 silicon atoms, comprising silanes and/or siloxanes bearing alkoxy groups, silanes and/or siloxanes bearing acetoxy groups, silanes and/or siloxanes bearing hydroxy groups and/or simple siloxane cycles and/or DT cycles, and also a reaction medium comprising acetic anhydride, Brnsted acid and acetic acid, wherein Brnsted acids having a pKa 1.30 are used, and wherein the acetic acid is present in the reaction system in amounts of 0.4 to 15.0 percent by weight, based on the reaction system, wherein the molar ratio of Brnsted acid used to acetic acid is in a defined range, with the proviso that either the sole use of trifluoromethanesulfonic acid and also of trifluoromethanesulfonic acid and acetic acid is excluded, and/or that the Brnsted acid used at least in part has a pKa between 1.3 and >13.5.

SiOC-linked, linear polydimethylsiloxane-polyoxyalkylene block copolymers of formula (I) CB-(AB).sub.aC1 are produced by reaction of end-equilibrated ,-diacetoxypolydimethylsiloxanes with a mixture including at least one polyether polyol, preferably a polyether diol, and at least one polyether monool or at least one monohydric alcohol.

Branched SiOC-linked polyethersiloxanes have the following formula (I)

##STR00001##

where R.sup.1 is an alkyl radical having 1 to 4 carbon atoms or a phenyl radical, but preferably 90% of the radicals R.sup.1 are methyl radicals; b has a value of from 1 to 10; a has a value of from 1 to 200, preferably 10 to 100, a value of from 3 to 70 when b is 1 and 4, or a value of from 3 to 30 when b is >4; and R.sup.2 denotes identical or different polyether radicals, but at least one radical R.sup.2 is a structural element radical of formula (II):

##STR00002##

where p=at least 2, preferably p=2-6, particularly preferably p=3.

Mixtures of cyclic branched siloxanes having exclusively D and T units, with the proviso that the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by .sup.29Si NMR spectroscopy, is less than 2.0 and preferably less than 1.0 mole percent, are described, as are branched organomodified siloxanes obtainable therefrom.

Mixtures of cyclic branched siloxanes having exclusively D and T units, with the proviso that the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by .sup.29Si NMR spectroscopy, is less than 2.0 and preferably less than 1.0 mole percent, are described, as are branched organomodified siloxanes obtainable therefrom.

Mixtures of cyclic branched siloxanes having exclusively D and T units and having no functional groups, with the proviso that the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by .sup.29Si NMR spectroscopy, is 2 mole percent, are described, as are branched organo-modified siloxanes obtainable therefrom.

Mixtures of cyclic branched siloxanes having exclusively D and T units and having no functional groups, with the proviso that the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by .sup.29Si NMR spectroscopy, is 2 mole percent, are described, as are branched organo-modified siloxanes obtainable therefrom.