A method of making polycarbonate comprises polymerizing, in a melt polymerization reaction, an aromatic dihydroxy compound and a diaryl carbonate in a presence of a polymerization catalyst and producing a by-product vapor stream comprising the dihydroxy compound, the diaryl carbonate and a diaryl carbonate by-product, adding a low vapor pressure compound to the by-product vapor stream to produce a modified by-product vapor stream, introducing the modified by-product vapor stream to a separation unit, removing the volatile diaryl carbonate by-product from the modified by-product vapor stream in the separation unit to form a treated by-product stream and returning the treated by-product stream to the polymerization reaction. Alternatively, the low vapor pressure compound can be added directly to the separation unit.