AbstractConsiderable deviations of molar refraction from the additivity in the solutions containing polycarbonate and its antiplasticizers symmetrical trinitrotoluene and 1,1‐bis(4‐hydroxy‐3, 5‐dichlorophenyl)2,2,2‐trichloroethane diacetate are reported. In contrast to this, the solutions of polycarbonate with plasticizer di‐n‐butyl phthalate and the solutions of antiplasticizers in pure solvent show only insignificant deviation from the additivity. The calorimetric studies showed the differences in the heats of solution of the used antiplasticizers in pure solvent and in the solvent containing a constant amount of polymer, whereas there was no noticeable difference in the polycarbonate–plasticizer (di‐n‐butyl phthalate) system. Both deviations of the molar refraction from the additivity and differences of the heats of solution prove the existence of strong interactions between the molecules of polycarbonate and