Patent ID: 7534851

Claim:
An improved method for preparing polycarbonate by an interfacial, polycondensation reaction with the steps of: (a) reacting phosgene and a bisphenol using a two-phase reaction mixture to form carbonate oligomers; the reaction mixture comprising an aqueous, alkaline phase and an immiscible organic phase, with the phosgene being dissolved in the organic phase and the bisphenol dissolved as a salt in the aqueous phase; (b) subsequently reacting the carbonate oligomers in the presence of a coupling catalyst to form a polycarbonate; (c) separating the aqueous and organic phases; the aqueous phase containing salts formed as by-products of the reaction of bisphenol and phosgene as well as organic liquid and one or more phenolic material(s), including water soluble polycarbonate oligomers and polycarbonate particles, and the organic phase containing the coupling catalyst and polycarbonate product; (d) treating the separated organic phase with an acidic wash water solution to remove amine coupling agent and then with aqueous liquid to remove inorganic impurities; (e) recovering the polycarbonate product; wherein the improvement comprises (i) treating either or both the separated aqueous phase obtained in step (c) and/or the wash water obtained in step (d) with an organic solution of the coupling catalyst in a halogenated organic liquid to extract the phenolic materials; and (ii) steam stripping the aqueous solutions treated in step (i) to remove the organic liquid and coupling catalyst.