Comparative study of Poly(n-butyl methacrylate) by thermo-stimulated currents and dynamic dielectric spectroscopy

Abstract

The dielectric behaviour of Poly(n-butyl methacrylate) (PnBMA) has been studied by thermo-stimulated currents (TSC) and dynamic dielectric spectroscopy (DDS). The analysis of the TSC complex spectrum shows the existence of three dipolar relaxations around the glass transition. The first one, labelled β, near -25°, has been assigned to a secondary relaxation mode. The second one, α, at 30°, has been associated with the glass relaxation. The third one, above Tg at 90°, might be assigned to the dielectric manifestation of the liquid-liquid transition. The use of fractional polarizations allows us to determine the fine structure of these three modes. The relaxation times of the β and α modes are widely distributed and they follow an Arrhenius equation. We also report a compensation phenomenon for the α mode. As for the α' mode, the relaxation times are narrowly distributed and they obey a Vogel equation. By using a blocking electrode, the study by DDS exhibits three relaxational phenomena: the β and α modes which merge approximately at 104 Hz and lead to an (αβ) mode, and an additional α' phenomenon. By using the Havriliak-Negami parameters, we characterize the shift of their maxima with frequency and temperature. The consistent set of data obtained from TSC and DDS allows us to follow the relaxation modes of PnBMA in a very broad temperature and frequency range. They significantly improve the knowledge of molecular mobility/dynamic structure relationships.