Complex permittivity of a film of poly[4-(acryloxy)phenyl-(4-chlorophenyl)methanone] containing free ion impurities and the separation of the contributions from interfacial polarization, Maxwell–Wagner–Sillars effects and dielectric relaxations of the polymer chains

Abstract

The previous theoretical study of measured complex permittivities of the amorphous copolymer of vinylidene cyanide and vinyl acetate (T. S. Sørensen and V. Compañ, J. Chem. Soc., Faraday Trans., 1995, 91, 4235) is refined and used to explain measurements of the complex permittivity of the amorphous polymer poly[4-(acryloxy)phenyl(4-chlorophenyl)methanone] at different temperatures and frequencies. Throughout the paper we stress the use of physical models rather than the traditional use of equivalent circuits without much informational content. The data exhibit a maximum in the loss tangent at low frequencies (below 0.1 Hz) which can be explained by interfacial polarization near the two condensor plates, and from which information concerning the diffusion and the concentration of free charge (mobile ion) carriers may be estimated. The diffusion coefficient for the fast ion varies from 1.9 × 10^–14 m² s^–1 at 120 °C to 1.8 × 10^–13 m² s^–1 at 140 °C. The activation energy for diffusion is E_a/R≈ 12 800 K. At frequencies in the range 0.1–10 Hz, the Maxwell–Wagner–Sillars contribution dominates. This contribution is due to the bulk conductivity of the free charge carriers. From the value of this conductivity and the information obtained from the interfacial polarization, the value of the static permittivity of the polymer may be found. Experimentally, this value is completely obscured by the effects of the free charge carriers. At higher frequencies, the dielectric relaxations connected with the motion of segments of the polymer chains are seen if corrections are made for conductivity. Two dielectric loss peaks are observed moving towards higher frequencies when the temperature increases. The low frequency relaxation has an activation energy E_a/R≈ 11 200 K. For the high frequency relaxation E_a/R≈ 24 500 K. The approximate identity of the activation energy of the low frequency relaxation and the activation energy of diffusion might indicate that the same molecular reorientation is involved in both cases.