Block copolyestercarbonates substantially free of anhydride linkages linking at least two mers of the polymer chain may be prepared by a method which comprises the steps of: (A) preparing a hydroxy-terminated polyester intermediate in a molten reaction mixture comprising at least one 1,3-dihydroxybenzene moiety and at least one aromatic dicarboxylic acid diarylester under transesterification conditions, said polyester intermediate having a degree of polymerization of at least 4; and (B) conducting a reaction of said polyester intermediate with a carbonate precursor in a two-phase system comprising an aqueous phase and a water-immiscible organic solvent. Articles comprising the copolyestercarbonates are another aspect of the invention.