Process for preparing polysiloxane-polycarbonate block cocondensates

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

• in which
• R1 is H, Cl, Br or C1 to C4-alkyl,
• R2 and R3 are the same or different and each independently from one another selected from aryl, C1 to C10-alkyl and C1 to C10-alkylaryl,
• X is a single bond, —CO—, —O—, C1 to C6-alkylene, C2 to C5-alkylidene, C5 to C12-cycloalkylidene or C6 to C12-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 melt at temperatures of 280° C. to 400° C. and pressures of 0.001 mbar to 50 mbar;
• wherein the polycarbonate has at least one of the following structures (I) to (IV):
• wherein
• the phenyl rings are unsubstituted or independently mono- or disubstituted by C1 to C8-alkyl and/or halogen,
• X is a single bond, C1 to C6-alkylene, C2 to C5-alkylidene or C5 to C6-cycloalkylidene, and
• the linkages indicated by --- in the structural units (I) to (IV) are each part of a carboxylate group;
• wherein the amount of the structural units (I) to (IV) totals 50 to 2000 ppm (determined after hydrolysis, based on the polycarbonate), and wherein the polycarbonate has a weight-average molecular weight of 16 000 to 28 000 g/mol.