Oligomeriser with improved mixing performance

A reactor for carrying out a melt transesterification reaction at a reactor temperature of 160 to 300° C. and a reactor pressure of 5 to 200, comprising:

• a cylindrical tank comprising a top, a side, and a bottom, wherein the bottom is convex, extending away from the top;
• a stirring shaft disposed within the cylindrical tank along an axis thereof so that it is rotatable from outside of the cylindrical tank;
• an impeller extending from the stirring shaft in the cylindrical tank and comprising a plurality of blades that are each independently at an angle α from an orthogonal of the axis;
• a reactant solution inlet;
• a reaction solution outlet;
• and
• an externally located heat exchanger in fluid communication with the cylindrical tank via a recirculation stream and a heated stream,
• wherein at least one of
• (i) the externally located heat exchanger is in fluid communication with an interior of the cylindrical tank via the recirculation stream and the heated stream, and
• (ii) the angle α of each of the plurality of blades independently is 25 to 65 degrees and the reactor is a vertical reactor.

A method of melt polymerizing a polycarbonate, comprising:

• adding a precursor solution comprising a polycarbonate precursor to a reactor for carrying out a melt transesterification reaction at a reactor temperature of 160 to 300° C. and a reactor pressure of 5 to 200 mbar, the reactor comprising:
• a cylindrical tank comprising a top, a side, and a bottom, wherein the bottom is convex, extending away from the top;
• a stirring shaft disposed within the cylindrical tank along an axis thereof so that it is rotatable from outside of the cylindrical tank;
• an impeller extending from the stirring shaft in the cylindrical tank and comprising a plurality of blades that are each independently at an angle α from an orthogonal of the axis;
• a reactant solution inlet;
• a reaction solution outlet;
• and
• an externally located heat exchanger in fluid communication with the cylindrical tank via a recirculation stream and a heated stream,
• wherein adding the precursor solution comprising the polycarbonate precursor to the reactor comprises adding the precursor solution comprising the polycarbonate precursor to the reactor through the reactant solution inlet;
• mixing and polymerizing the polycarbonate precursor at the reactor temperature of 160 to 300° C., and the reactor pressure of 5 to 200 mbar to form a polycarbonate oligomer;
• and
• withdrawing a mixed solution comprising the polycarbonate oligomer having a weight average molecular weight that is greater than that of the polycarbonate precursor from the reaction solution outlet.