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- (PC4VIX) were investigated using rheological and dielectric relaxation techniques to extract the role of counterions in the bulk polyelectrolyte system. All PC4VIX 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 PC4VIX with small BF4- or PF6- counterions was similar to that of electrically neutral polymers, in contrast to the master curves for PC4VITFSI, 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.