Linear polydimethylsiloxane-polyoxyalkylene block copolymers of the structure type ABA

1. A process for producing trifluoromethanesulfonic acid-acidified equilibrated α,ω-diacetoxypolydimethylsiloxanes, wherein cyclic siloxanes comprising D 4 and/or D 5 , are reacted with acetic anhydride using trifluoromethanesulfonic acid as catalyst and with addition of acetic acid.

2. The process according to claim 1 , wherein the trifluoromethanesulfonic acid is employed in amounts of from 0.1 to 0.3 percent by mass based on the reaction matrix consisting of acetic anhydride and cyclic siloxanes.

3. The process according to claim 1 , wherein the reaction is performed in a temperature range of from 140° C. to 160° C. and over a period of from 4 to 8 hours.

4. The process according to claim 1 , wherein acetic acid is added in amounts of from 0.4 to 3.5 percent by weight, based on the reaction matrix consisting of acetic anhydride and cyclic siloxanes.

5. A trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxanes of general formula

where R=methyl,

which have an average chain length determined by 29 Si-NMR spectroscopy of 0≤X≤250 and contain from 0.1 to 0.3 percent by mass of trifluoromethanesulfonic acid and from 5 to 43 val % of free acetic anhydride based on the acetic anhydride equivalent chemically bonded in the α,ω-diacetoxypolydimethylsiloxane.

6. The trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxanes according to claim 5 , wherein they have an average chain length determined by 29 Si-NMR spectroscopy of 10<X<30.

7. A process for producing SiOC-bonded, linear polydimethylsiloxane-polyoxyalkylene block copolymers of the structure type ABA, wherein trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxane according to claim 5 is reacted with polyether monools in the presence of buffer mixtures, and optionally an additional condensation catalyst, and in the presence of an inert solvent.

8. The process according to claim 7 , wherein the amount of the base employed for treating the polyether monool in the buffer mixture is measured such that it corresponds at least to the stoichiometric equivalent, preferably at least to the 2-fold stoichiometric equivalent, of the trifluoromethanesulfonic acid present in the α,ω-diacetoxypolydimethylsiloxane.

9. The process according to claim 7 , wherein the polyether monool is initially treated with buffer mixtures and optionally an additional α,ω-diacetoxypolydimethylsiloxane,

and then using an azeotrope-forming solvent the liberated acetic acid 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.

10. The process according to claim 7 , wherein a condensation catalyst is used for reacting the equilibrated α,ω-diacetoxypolydimethylsiloxane with polyether monools,

wherein condensation catalysts employed are Brönsted acids,

wherein the condensation catalyst, in particular the trichloroacetic acid, is in the range from 0.1 to 0.7 percent by mass, based on the total amount of the reactants provided for the SiOC-bond forming reaction, namely α,ω-diacetoxypolydimethylsiloxane and polyether monool.

11. The process according to claim 7 , wherein the employed buffer mixtures contain at least proportions of the condensation catalyst and particularly preferably contain the condensation catalyst in the form of a salt.

12. The process according to claim 7 , wherein the buffer mixtures comprise sodium trichloroacetate and acetic acid or sodium acetate and acetic acid.

13. The process according to claim 7 , wherein solvents employed are aromatic, or in that the process is operated solventlessly.

14. The process according to claim 7 , wherein the 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 solvents by intimate mixing of the reactants with stirring at reaction temperatures of from 20° C. to 90° C. and from 30 minutes to 8 hours,

and/or,

in that the removal of the acetic acid liberated during the reaction between α,ω-diacetoxypolydimethylsiloxane and polyether monools and the acetic acid that may be present in the system is preferably effected by distillation at temperatures between 60° C. and 90° C. with application of an auxiliary vacuum.

15. The process according to claim 7 , 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.

16. The process according to claim 1 , wherein acetic acid is added in amounts of from 1.0 to 1.5 percent by weight, based on the reaction matrix consisting of acetic anhydride and cyclic siloxanes.

17. The trifluoromethanesulfonic acid-acidified, equilibrated α,ω-diacetoxypolydimethylsiloxanes according to claim 5 , wherein they have an average chain length determined by 29 Si-NMR spectroscopy of 10<X<20.

18. The process according to claim 7 , wherein a condensation catalyst is used for reacting the equilibrated α,ω-diacetoxypolydimethylsiloxane with polyether monools,

wherein condensation catalysts employed are acids selected from the group consisting of simple mineral acids and methanesulfonic acid, phosphoric acid, phosphonic acids and/or else acidic salt-like compounds such as triflate salts, bismuth triflate, and/or any Lewis-acidic compounds such as tin and organotin compounds, titanate esters, tetraalkoxy titanates, zinc acetylacetonate, zinc acetate, trispentafluorophenylborane and trichloroacetic acid,

wherein the condensation catalyst, in particular the trichloroacetic acid, is in the range from 0.2 to 0.5 percent by mass, based on the total amount of the reactants provided for the SiOC-bond forming reaction, namely α,ω-diacetoxypolydimethylsiloxane and polyether monool.