Patent ID: 7485694

Claim:
A method for preparing polycarbonate wherein the method comprises the steps of, (i) introducing to an extruder through one or more feed sections, a plurality of reaction components comprising an activated carbonate, a dihydroxy compound, an activated carbonate residue, and a transesterification catalyst, wherein the extruder comprises: (a) a first feed section; (b) a polycarbonate exit section; and (c) a reaction section, disposed between the first feed section and the polycarbonate exit section, the reaction section comprising at least one conveying section having a screw element configuration consisting of one or more conveying elements, a plurality of kneading sections wherein each kneading section has a screw element configuration comprising a kneading element, and a plurality of venting sections, wherein: a venting section is disposed between each of the plurality kneading sections and the conveying section and a final venting section is disposed between the final kneading section and the polycarbonate exit section, and the plurality of kneading sections and the plurality of venting sections are selected such that the number of venting sections minus the number of kneading sections is greater than or equal to one, and (ii) extruding the plurality of 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 plurality of venting sections, and polycarbonate is removed through the polycarbonate exit section.