In addition to the aa and β relaxation amorphous samples show a dielectric maximum at 120-130℃ due to the crystallization of the sample during temperature scanning. A dielectric method of characterizing the process of isothermal crystallization of PET in the temperature range of 97-113℃ has been demonstrated. During the primary stage of crystallization the change of e' with time obeys the Avrami equation

that is

ε'(t)- ε'(∞)/ε'(0)-ε'(∞) =" exp(-Ktn) with n - 2 in the temperature range studied. During secondary stage of crystallization the dielectric relaxation strength △ε determined from the Cole-Cole plote decreases while the Cole-Cole β parameter increases in the course of crystallization.