Conductivity and high-temperature relaxation of tyrosine-derived polyarylates measured with thermal stimulated currents

Thermal-stimulated polarization and depolarization experiments without bloc king electrodes are performed on tyrosine-derived polyarylates with differe nt backbone lengths. The experiments on the different samples are carried o ut using the same thermal history throughout the entire characterization pr ocess. The high-temperature current rise caused by the conductivity of the samples is studied with a simple model that utilizes an approximation of th e Williams-Landel-Ferry (WLF) relaxation time. The conductivity data is wel l reproduced except for temperatures well below the glass-transition temper ature and for small currents. The glass-transition peak is modeled with a p henomenological expression valid near T-g, which is able to describe the gl ass relaxation with a minimum number of parameters. The conduction and the glass-transition relaxation are studied versus the structural changes for t he different samples. It is found that the conductivity and the glass-trans ition temperature shift to lower temperatures as the methylene groups in th e backbone increase. Furthermore, if the experimental data is presented as a function of the reduced temperature, the shape of the glass-transition re laxation for the different samples is independent of the polymer backbone l ength. (C) 1999 John Wiley & Sons, Inc.