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Temperature- and frequency-dependent dielectric behaviour has been investigated for pristine, iodine-doped and annealed polyetherimide (PEI) in the temperature range 303–523 K at various frequencies (120 Hz, 1 kHz, 10 kHz and 100 kHz). In pristine PEI, the rapid decrease in the dielectric constant (e′) in the temperature range 303–373 K is governed by the Kirkwood model whereas the gradual decrease in e′ in the temperature range 373–473 K is governed by β-relaxation (dipolar) and αβ-relaxation (hybrid) processes. The occurrence of these relaxations is confirmed by the appearance of tan δ loss peaks at ca 403 and 443 K, respectively, in e″–T curves. The temperature-independence of e′ in the temperature range 473–523 K is mainly governed by the α-relaxation process associated with large segmental groups. The tan δ loss peak appearing at 503 K confirms this relaxation process. In iodine-doped samples, an overall increase in e′ is attributed to the formation of charge-transfer complexes in the polymer structure. The dominance of a new relaxation process due to interaction of iodine with ether linkages neutralizes the 1/T rule in the low-temperature region. A significant decrease in e′ in annealed samples below 393 K is due to the suppression of the dipolar relaxation process. The enhancement in e′ above 393 K is due to the dominance of the α-relaxation process. The shift in the high-temperature tan δ loss peak towards higher temperature with increasing frequency shows the distributive nature of relaxation time for this relaxation process. Copyright © 2011 Society of Chemical Industry |
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