STUDY OF DIELECTRIC-RELAXATION OF AN EPOXIDE OLIGOMER BY A DIRECT-CURRENT TRANSIENT METHOD

Dielectric alpha-relaxation of a bisphenol-A type epoxide oligomer has been investigated in the vicinity of the glass transition temperature (T(g)) by the direct current (DC) transient method. The logarithm of the DC transient current for the oligomer was well approximated by the third order function of the logarithm of time. The complex dielectric constant was calculated through the Fourier transformation of that approximation function according to Simpson's integration rule in a frequency range of 10(-5) - 1 Hz. At the temperature around the T(g) (45-degrees-C), the dielectric alpha-relaxation process of the oligomer was found to be governed by the Havriliak-Negami equation. The relationship between the DC conductivity (sigma) and the dielectric relaxation time (tau), sigma . tau(m) = const, is valid near and above the T(g) of the oligomer. The DC transient current method combined with the DC conduction and the dielectric bridge measurements is considered to be a practical tool for analyzing the dielectric alpha-relaxation process of the epoxide oligomer over a wide frequency and temperature range.