Process for preparing polycarbonates using a catalyst system having a quarternary nitrogen compond and a quarternary phosphorous compound

A process for producing a polycarbonate, the process comprising:

• reacting one or more diaryl carbonates with one or more aromatic hydroxy compounds, wherein in the process a catalyst combination is employed which comprises:
• a first component comprising one or more quaternary nitrogen compounds;
• a second component comprising one or more quaternary phosphorus compounds;
• a third component comprising one or more alkali metal compounds;
• and
• a fourth component comprising one or more sulphur-containing organic compounds;
• a) transesterification of one or more diaryl carbonates with one or more aromatic hydroxy compounds in at least one transesterification reactor;
• b) pre-polycondensation of the reaction product of the transesterification in at least one pre-polycondensation reactor;
• and
• c) polycondensation of the reaction product of the pre-polycondensation in at least one polycondensation reactor,
• wherein the first component is added before or during the transesterification (step a)), the third component is added after step a) and before or during the pre-polycondensation (step b)) and the fourth component is added after step b) and before or during the polycondensation (step c)).