Linear polydimethylsiloxane-polyoxyalkylene block copolymers linked via Si-C groups and via carboxylic ester groups, a process for preparing them and their use

1. Linear polydimethylsiloxane-polyoxyalkylene block copolymers containing Si—C groups and carboxylic ester groups and having repeating (A 1 BA 2 B) units where A 1 and A 2 are two different polydimethyl-siloxane units of the general formula (I)

with a number of Si atoms N=(n+2) of 15≦N≦30 and N A1 ≠N A2

and B is a unit of the formula (II)

—CH 2 —CH 2 —(CH 2 ) a —CO[O—CH 2 —CH(R)] c —O-[D-O] e —[—CH(R)—CH 2 —O] d —OC—(CH 2 ) b —CH 2 —CH 2 —  (II)

where

R independently at each occurrence is H, —CH 3 or —C 2 H 5 ,

a and b independently of one another are 0 to 20,

c and d independently of one another are values≧1,

e is 0 or 1,

D is a hydrocarbon radical having 2 to 10 carbon atoms,

the overall molar weight of the unit of the formula II being from 600 to 10000 g/mol,

with the proviso that the average mixed molar weight of the polydimethylsiloxane units (A 1 +A 2 ) is from >1665 to <1998 g/mol and the fraction of [O—CH 2 —CH(R)] with R═H is >0% to ≦50% by weight, based on the overall weight of [O—CH 2 —CH(R)] in B.

2. Polydimethylsiloxane-polyoxyalkylene block copolymers according to claim 1 , characterized in that exclusively units A 1 with N≦20 and A 2 with N≧25 are present.

3. Polydimethylsiloxane-polyoxyalkylene block copolymers according to claim 2 characterized in that:

the unit of the formula II has an average molar mass of 2000 to 5000 g/mol;

the unit of the formula (II) has a fraction of [O—CH 2 —CH(R)] with R═H of 30% to ≦50% by weight, based on the overall weight of [O—CH 2 —CH(R)] in B; and

the polydimethylsiloxane-polyoxyalkylene block copolymer has an average number-averaged molecular weight M n of at least 10000 g/mol to approximately 100000 g/mol.

4. Polydimethylsiloxane-polyoxyalkylene block copolymers according to claim 1 , characterized in that the unit of the formula II has an average molar mass of 2000 to 5000 g/mol.

5. Polydimethylsiloxane-polyoxyalkylene block copolymers according to claim 1 , characterized in that the unit of the formula (II) has a fraction of [O—CH 2 —CH(R)] with R═H of 30% to ≦50% by weight, based on the overall weight of [O—CH 2 —CH(R)] in B.

6. Polydimethylsiloxane-polyoxyalkylene block copolymers according to claim 1 , characterized in that the polydimethylsiloxane-polyoxyalkylene block copolymer has an average number-averaged molecular weight M n of at least 10 000 g/mol to approximately 100 000 g/mol.

7. A method for stabilizing a polyurethane foam which comprises adding the SiC-linked, linear polydimethylsiloxane-polyoxyalkylene block copolymers according to claim 1 to a polyurethane foam.

8. The method of claim 7 , wherein the polyurethane foam is a polyurethane ether foam.

9. Process for preparing the linear poly-dimethylsiloxane-polyoxyalkylene block copolymers of claim 1 which comprises reacting at least two different linear α,ω-dihydropolydimethylsiloxanes A′ with at least one unsaturated polyetherdiol (B′) containing ester groups, in the presence of one or more noble metal compounds as catalyst, where

A′ is at least two different α,ω-dihydropolydimethylsiloxane compounds (A 1′ and A 2′ ) of the general formula (I′)

with a number of Si atoms N=(n+2) of 15≦N≦30 and N A1 ≠N A2 ,

B′ is

CH 2 ═CH—(CH 2 ) a —CO[O—CH 2 —CH(R)] c —O-[D-O] e —[—CH(R)—CH 2 —O] d —OC—(CH 2 ) b —CH═CH 2   (II′)

where

R at each occurrence is H, —CH 3 or —C 2 H 5 ,

a and b independently of one another are 0 to 20,

e is 0 or 1,

c and d independently of one another are values≧1 and

D is a hydrocarbon radical having 2 to 10 C atoms,

the overall molar weight of the polyether B′ being from 600 to 10000 g/mol,

with the provisos that the average mixed molar weight of the polydimethylsiloxane compounds (A 1′ +A 2′ ) is from >1665 to <1998 g/mol and that the fraction of [O—CH 2 —CH(R)] with R═H is >0% to ≦50% by weight, based on the overall polyether weight of [O—CH 2 —CH(R)] in B′.

10. The process according to claim 9 , characterized in that exclusively compounds A 1′ with N≦20 and A 2′ with N≧25 are used as compounds of the formula (I′).

11. The process according to claim 10 , characterized in that as component B′ a compound of the formula (II′) is used which has an average molar mass of 2000 to 5000 g/mol; and

that a compound of the formula (II′) is used which has a fraction of [O—CH 2 —CH(R)] with R═H of 30% to ≦50% by weight, based on the overall weight of [O—CH 2 —CH(R)] in B′.

12. The process according to claim 9 , characterized in that as component B′ a compound of the formula (II′) is used which has an average molar mass of 2000 to 5000 g/mol.

13. The process according to claim 9 , characterized in that a compound of the formula (II′) is used which has a fraction of [O—CH 2 —CH(R)] with R═H of 30% to ≦50% by weight, based on the overall weight of [O—CH 2 —CH(R)] in B′.