AbstractBlends of polycarbonate of bisphenol A (PC) and a polyarylate of bisphenol A (PAr) are susceptible to showing interchange reactions in the melt state. The control of these reactions was carried out by means of the observation of the torque required to turn the Brabender and of its increase against the time due to copolymer formation in the processing equipment. Based on this variation and on glass transition temperature (Tg) measurements, the possibility of an exchange reaction in two steps in this blend was suggested.Tgmeasurements in melt‐ and solvent‐cast blends also showed that this mixture is immiscible at all compositions and that, by copolymer evolution, a singleTgintermediate between those of the individual constituents can be found in all compositions. The influence of immiscibility on the mechanical properties of the blends was shown by the appearance of a minimum in large‐strain properties at about 25 PAr. The behavior of the transesterified blends was very different showing a clear improvement of the tensile properties compared with those of the corresponding b
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