Polycarbonate is prepared by reactive extrusion on a reactive extruder. A method incorporates the steps of introducing a polycarbonate oligomer, an activated carbonate residue, and a transesterification catalyst to the extruder through a feed section. The extruder has the feed section, a polycarbonate exit section, and a reaction section between the feed section and the polycarbonate exit section. The reaction section is made up of at least one conveying section, kneading sections, and venting sections. The configuration of the reaction section requires that at least one venting section be disposed between each pair of kneading sections, and that the kneading sections and venting sections are selected such that the number of venting sections minus the number of kneading sections is greater than or equal to one. The method further contains the step of extruding the reaction components at a temperature in a range between 100° C. and 500° C., wherein during the extrusion of the reaction components, activated carbonate residue is removed through the venting sections.