Space charge relaxation in polyetherimides by the electric modulus formalism

Dynamic electrical analysis shows that at high temperatures (above the glas s transition temperature), the electrical properties of polyetherimide are strongly influenced by space charge. In this article we have studied the re laxation of space charge in two commercial varieties of polyetherimide: Ult em 1000 and Ultem 5000. Their conductive properties were determined by dyna mic electrical analysis, using the electric modulus formalism. The complex part of the electric modulus was fitted to Coelho's model which considers o hmic conductivity and diffusion as the prevailing charge transport mechanis ms. The complex part of the electric modulus exhibits a peak in the low fre quency range that can be associated with space charge. A good agreement bet ween experimental and calculated data is observed after the fitting process to Coelho's model. Differences in the electrode behavior were required: bl ocking electrode conditions in the case of Ultem 5000 and partially blockin g electrode for Ultem 1000. In both cases the conductivity determined is th ermally activated and it increases with the temperature due to an increasin g mobility, as their carrier densities do not vary significantly in the tem perature range studied. (C) 2000 American Institute of Physics. [S0021- 897 9(00)03821-4].