Process for preparing a branched polycarbonate

Claim 1

A process for preparing a thermoplastic randomly branched aromatic polycarbonate having improved resistance to thermal oxidation and having excellent blow molding properties which process comprises reacting at least 20 weight percent of a stoichiometric quantity of a carbonate precursor with a mixture of a dihydric phenol and at least 0.05 mole percent of a polyfunctional aromatic compound in a medium of water and an inert organic solvent for the polycarbonate having present therein at least 1.2 mole percent of a polymerization catalyst, a molecular weight regulator, and an inert organic solvent for the polycarbonate while concomitantly adding to the reaction medium sufficient alkali metal hydroxide to maintain a pH range of about 3.0 to about 6.0, and then adding sufficient alkali metal hydroxide to raise the pH to at least 9.0 but less than about 12.0 while reacting the remaining amount of the stoichiometric quantity of the carbonate precursor; said polyfunctional aromatic compound containing at least three functional groups selected from the group consisting of carboxyl, carboxylic anhydride and haloformyl or mixtures thereof.