Dielectric Relaxations in Poly(γ-n-alkyl L-glutamate)s I. Study of the Relaxations above Room Temperature Using the Direct-Current Technique

Abstract

Time and temperature dependences of the absorption and conduction currents in poly(γ-n-alkyl L-glutamate)s, having methyl, ethyl, n-propyl, and n-butyl groups, have been investigated at temperatures ranging from −15 to 80°C and in the time range from 10 to 900 s. The data on the DC current have been analyzed by the Hamon approximation and the method of reduced variables and converted into the loss permittivity master curves. The master curve is composed of the contribution from a relaxation and that from a conduction current. The former is a new relaxation named α-relaxation and characterized by the relaxation spectrum whose shape is independent of the side-chain length and much sharper than that of the spectrum for the side-chain relaxation called β-relaxation. The shift factor is common to the α-relaxation and conduction process, obeying the WLF equation with parameters proper to each sample. The glass transition temperature for each sample was determined as the temperature at which the shift factor deviates from the WLF equation. It decreases with an increase of the side-chain length, while the thermal expansion coefficient of the free volume fraction determined from the WLF parameters shows the opposite tendency. The nature of the dielectric α-relaxation is discussed briefly.