Dielectric Relaxation and Viscoelastic Behavior of Polymerized Ionic Liquids with Various Counteranions

The macro and micro dynamics of poly(1-butyl-3-vinylimidazolium)-based polymerized ionic liquids with various counterions X – (PC 4 VIX) were investigated using rheological and dielectric relaxation techniques to extract the role of counterions in the bulk polyelectrolyte system. All PC 4 VIX species studied showed two dielectric relaxation modes. The faster dielectric relaxation mode, side-chain motions, arose at the determined temperature if X – was not bulky. The slower mode, ion-pair motions, showed good cooperativity with direct current conductivity irrespective of the X – species. The viscoelastic behavior of PC 4 VIX with small BF 4 – or PF 6 – counterions was similar to that of electrically neutral polymers, in contrast to the master curves for PC 4 VITFSI, which possess the large TFSI – counterion and showed additional shoulders in the glass-to-rubber transition region. The additional shoulders were due to rotational motion of the nonspherical TFSI – ions. The classical Rouse segmental motion depends only on the glass transition behavior, as is the case for electrically neutral polymers; it is independent of the X – species.