Abstract
Relaxations in poly(etherimide) PEI Ultem 1000 have been analysed by differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization current (TSDC) measurements. DMTA and DRS results show three distinct relaxations γ, β and α in the temperature range -140 to 250°C. The first one depends strongly on the water content in the sample as will be discussed in more detail in the second paper of this series. These results are in good agreement with those observed by TSDC of conventionally polarized electrets. In addition to these three relaxations, TSDC measurements show: (1) a peak (ρ) at which is attributed to space charge temperatures above the α relaxation, (2) indications of structure in the β relaxation zone. In the case of electrets formed by the windowing polarization method, the resulting TSDC spectra allow us to discern the fine structure of the β relaxation, which is formed by three sub-relaxations. In this work, the activation energies calculated by the different techniques are compared, and a molecular origin for each relaxation is proposed. © 1998 SCI.
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