Process for preparing polysiloxane-polycarbonate block cocondensates using a salt of a weak acid

1. A process for preparing polysiloxane-polycarbonate block cocondensates, comprising reacting at least one hydroxyaryl-terminated siloxane of the formula (1)

in which

R 1 is H, Cl, Br or C 1 to C 4 -alkyl,

R 2 and R 3 are the same or different and each independently from one another selected from is aryl, C 1 to C 10 -alkyl and C 1 to C 10 -alkylaryl,

X is a single bond, —CO—, —O—, C 1 to C 6 -alkylene, C 2 to C 5 -alkylidene, C 5 to C 12 -cycloalkylidene or C 6 to C 12 -arylene which may optionally be fused to further aromatic rings containing heteroatoms,

n is a number from 10 to 100,

m is a number from 2 to 5, and

p is 0 or 1;

with at least one polycarbonate in the presence of an organic or inorganic sodium salt of a weak acid having a pK A value within the range of from 3 to 7 (25° C.) and polysiloxane-polycarbonate block cocondensate has a sodium content within the range of from 0.5 ppm to 100 ppm.

2. The process according to claim 1 , wherein the organic or inorganic salt is selected from the group consisting of alkali metal salts, earth alkaline metal salts, quaternary ammonium salts and quaternary phosphonium salts.

3. The process according to claim 1 , wherein the salt is derived from a carboxylic acid.

4. The process according to claim 1 , wherein the organic or inorganic salt is used in an amount of 0.5 to 1000 ppm, based on the total weight of the siloxane and the organic or inorganic salt.

5. The process according to claim 1 , wherein the hydroxyaryl-terminated siloxane has a weight-average molecular weight of 3000-20 000 g/mol.

6. The process according to claim 1 , wherein the hydroxyaryl-terminated siloxane is used in an amount of 2 to 20% by weight, based on the polycarbonate used.

7. The process according to claim 1 , wherein R 1 is H, p is 1 and X is isopropylidene.

8. The process according to claim 1 , wherein R 2 and R 3 are methyl.

9. The process according to claim 1 , wherein a phosphonium catalyst of the formula of the formula (5) is used during the reaction:

where

R a , R b , R c and R d may be identical or different C 1 -C 10 -alkyls, C 6 -C 14 -aryls, C 7 -C 15 -arylalkyls or C 5 -C 6 -cycloalkyls, and

Y— may be an anion selected from the group consisting of hydroxide, sulphate, hydrogensulphate, hydrogencarbonate, carbonate, halide or an alkoxide or aroxide of the formula —OR e where R e is C 6 -C 14 -aryl, C 7 -C 15 -arylalkyl or C 5 -C 6 -cycloalkyl.

10. The process according to claim 1 , wherein it is performed in the melt.

11. The process according to claim 1 , wherein the process is performed at temperatures of 280° C. to 400° C. and pressures of 0.001 mbar to 50 mbar.

12. The process according to claim 1 , wherein the polysiloxane-polycarbonate block cocondensate has a sodium content within the range of from 1.3 ppm to 5 ppm.