| abstract |
The invention provides 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 polydimethylsiloxane units of the general formula (I) n n n n n n n n n n n n 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 2 —CH(R)—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, n n n c and d independently of one another are values ≧1, e is 0 or 1 and D is a hydrocarbon radical having 2 to 10 C 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, a process for preparing them and their use. |