The above-described and other deficiencies of the art are met by a method of making a polycarbonate polymer comprising isosorbide carbonate units, comprising melt reacting a dihydroxy compound comprising an isosorbide of the general formula (2a): ##STR00001## and an activated carbonate, in the presence of a catalyst consisting essentially of a sodium salt capable of providing a hydroxide ion, wherein the polycarbonate polymer comprises greater than or equal to 50 mol % isosorbide carbonate units, and wherein the polycarbonate polymer has a Mw of greater than or equal to about 40,000 g/mol as determined by gel-permeation chromatography relative to polystyrene standards. Polycarbonates comprising the isosorbide carbonate unit, including isosorbide homopolycarbonate and an isosorbide-based polyester-polycarbonate, are also disclosed, as are a thermoplastic composition and an article including the isosorbide-based polycarbonate polymer.