Contributions from interfacial polarization, conductivity and polymer relaxations to the complex permittivity of a film of poly[(5-ethyl-1,3-dioxan-5-yl)methyl acrylate] containing ionic impurities

Abstract

The complex permittivity of a film of the polymer poly[(5-ethyl-1,3-dioxan-5-yl)methyl acrylate] of width 0.4 mm and containing very small amounts of ionic impurities has been studied at a range of frequencies from 0.01 Hz to 100 kHz and at a range of temperatures from −135 to +140 °C. Some mechanical determinations of the complex Young modulus have also been performed for the same polymer. To separate the surface polarisation effects and the conductivity effects from the dielectric relaxations of the polymer chains and side-chains we have used the same theoretical methods as earlier described for a film of a copolymer of vinylidene cyanide and vinyl acetate and for a film of poly[4-(acryloxy)phenyl-(4-chlorophenyl)methanone]. The diffusion coefficient of the most rapidly diffusing ion is studied as a function of temperature. The diffusion coefficient follows a non-Arrhenius Vogel relation with the same Vogel temperature as the α-relaxation (glass–rubber). Both phenomena may be interpreted using the Cohen–Turnbull theory of free volume as has previously been done for the diffusion of oxygen through poly(cyclohexyl acrylate). The fractional free volume at the glass transition temperature (ca. 36 °C) is found to be 0.031, close to the range normally found (0.025 ± 0.005). A β-relaxation is also found at higher frequencies and lower temperatures. This relaxation shows Arrhenius behaviour with an activation energy E ^‡ /R = 5780 K. The α- and β-relaxations seem to merge at ca. 100 °C and in addition a relaxation more slow than the α-relaxation is found at even higher temperatures. This relaxation can only be seen after correction of the dielectric loss for conductivity. The mean activation energy of this relaxation in the temperature range 90–140 °C is practically identical with the mean activation energy of the α-relaxation in the same range of temperatures (E ^‡ /R ≈ 15000 K). The slow relaxation is probably connected with the motion of the polymer molecule as a whole in the ‘virtual tubes’ of long-range, topological entanglements, for example by ‘reptation’. At very high frequencies (50–100 kHz), isochronous graphs of dielectric loss vs. temperature exhibit a splitting of the α-peak into two peaks.