A thermodynamic model for the compensation law and its physical significance for polymers

Abstract This paper describes how the compensation law can be explained by a linear relation between the activation entropy and enthalpy of a given process in a polymer. These two variables are related by the thermal expansion coefficient and a constant approximately equal to the Rao acoustical parameter. A relation between the activation free energy and some thermodynamic parameters is presented. The activated volumes for the α and β relaxations of polyethylene are shown to vary with temperature and cry-stallinity. The activated volume has also been calculated for some other polymers and is of the order of 1 to 6 molar volumes at 295 K.