Dielectric constant and loss investigations of pristine, iodine‐doped and annealed polyetherimide film

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 (ε′) in the temperature range 303–373 K is governed by the Kirkwood model whereas the gradual decrease in ε′ 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 ε″– T curves. The temperature‐independence of ε′ 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 ε′ 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 ε′ in annealed samples below 393 K is due to the suppression of the dipolar relaxation process. The enhancement in ε′ 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