  It can be seen by Dynamic Electrical Analysis that the electrical properties
of polyetherimide at temperatures above the glass transition are strongly
influenced by space charge. We have studied space charge relaxation in two
commercial grades of polyetherimide, Ultem 1000 and Ultem 5000, using this
technique. The electric modulus formalism has been used to interpret their
conductive properties. In both grades of polyetherimide, asymmetric Argand
plots are observed, which are related to a sublinear power-law dependency
($\omega^{n}$ with $n<1$) in the real part of the conductivity. This behaviour
is attributed to correlated ion hopping. The imaginary part of the electric
modulus exhibits a peak in the low frequency range associated to conduction.
Modelling of this peak allows us to obtain the dependence, among other
parameters, of the conductivity ($\sigma_0$), the fractional exponent ($n$) and
the crossover frequency ($\omega_\mathrm{p}$) on the temperature. The $\alpha$
relaxation, that appears at higher frequencies, has also to be modelled since
it overlaps the conductivity relaxation. The study of the parameters in terms
of the temperature allows us to identify the ones that are thermally activated.
The difference between the conductivity relaxation time and the Maxwell
relaxation time indicates the presence of deep traps. The coupling model points
out that the correlation of the ionic motion diminishes with temperature,
probably due to increasing disorder due to thermal agitation.
