Linear polydimethylsiloxane-polyoxyalkylene block copolymers of the structure type ABA

1. The process for producing SiOC-bonded, linear polydimethylsiloxane-polyoxyalkylene block copolymers of the structure type ABA, wherein trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxane, having a general formula of

where R=methyl,

which have an average chain length determined by 29 Si-NMR spectroscopy of 0≤X≤250 and contains from 0.1 to 0.3 percent by mass of trifluoromethanesulfonic acid and 5 to 43 val % of free acetic anhydride based on the acetic anhydride equivalent chemically bonded in the α,ω-diacetoxypolydimethylsiloxane, is reacted with polyether monools in the presence of bases and optionally in the presence of an inert solvent.

2. The process according to claim 1 , wherein an acetic acid liberated during the reaction and the acetic acid that may be present in a system is precipitated and filtered off in the form of acetate salts and the SiOC-bonded, linear polydimethylsiloxane-polyoxyalkylene block copolymer is isolated after optionally distillative removal of the solvent and optionally end-stabilization.

3. The process according to claim 1 , wherein the polyether monool is initially treated with bases optionally in the presence of an inert solvent and then admixed with trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxane and a condensation catalyst and then using an azeotrope-forming solvent the liberated acetic acid liberated and the acetic acid that may be present in the system is thermally removed together with the solvent and the obtained SiOC-bonded, linear polydimethylsiloxane-polyoxyalkylene block copolymer is neutralized by addition of an auxiliary base, filtered and end-stabilized.

4. The process according to claim 1 , wherein solid, liquid or gaseous base is introduced into a reaction system at temperatures of T<30° C. at least in an amount such that it is sufficient not only for the neutralization of the trifluoromethanesulfonic acid present in the system but also for a salt precipitation of acetate groups bonded to the α,ω-diacetoxypolydimethylsiloxane and the precipitation of any acetic anhydride still present in the reaction system and any free acetic acid.

5. The process according to claim 1 , wherein replacement of the acetoxy groups bonded to the α,ω-diacetoxypolydimethylsiloxane by reaction with polyether monools to afford SiOC-bonded, linear polyether siloxanes is effected in the presence of the inert solvent or without the inert solvent by intimate mixing of reactants with stirring at reaction temperatures of from 20° C. to 90° C.

6. The process according to claim 3 , wherein the amount of the base used for treatment of the polyether monool is measured such that it corresponds at least to a stoichiometric equivalent of base and polyether monool.

7. The process according to claim 5 , wherein a Brönsted acid condensation catalyst is employed for reaction of the equilibrated α,ω-diacetoxypolydimethylsiloxane with polyether monools.

8. The process according to claim 1 , wherein solvents employed are aromatic.

9. The process according to claim 1 , wherein the molar ratio of the reactants is measured such that at least 1 mol of polyether-bonded OH functionality is employed per mol of acetoxy group of the α,ω-diacetoxypolydimethylsiloxane.

10. The process according to claim 3 , wherein the amount of the base used for treatment of the polyether monool is at least to a 2- to 3-fold stoichiometric equivalent of the trifluoromethanesulfonic acid present in the α,ω-diacetoxypolydimethylsiloxane.

11. The process according to claim 1 , wherein the solvent employed is toluene.

12. The process according to claim 1 , wherein the molar ratio of the reactants is measured such that from 1.1 to 1.6 mol of polyether-bonded OH functionality is employed per mol of acetoxy group of the α,ω-diacetoxypolydimethylsiloxane.