Molecular Dynamics and Charge Transport in Polymeric Polyisobutylene-Based Ionic Liquids

A homologous
series of 16 polymeric ionic liquids (PIL) are investigated
based on monovalent and bivalent telechelic polyisobutylene (PIB)
carrying the ionic liquid (IL)-like cationic headgroup (N,N,N-triethyl­ammonium or
1-methyl­pyrrolidinium) and Br, NTf2, OTf, or pTOS
as anions. Molecular dynamics, charge transport, and polarization
at mesoscopic scales are analyzed over a wide frequency (10–2–107 Hz) and temperature (200–400 K) range
by means of broadband dielectric spectroscopy (BDS); additionally,
differential scanning calorimetry (DSC) is employed. In detail, (i)
three molecular relaxation processes are observed including the dynamic
glass transition of the polymeric matrix, (ii) a conductivity relaxation
originating from charge transport in the IL-like moieties, and (iii)
a weak electrode polarization caused by the accumulation of mobile
charge carriers at the metal interfaces. The net conductivity of the
PIL as a whole is quantitatively described by an effective-medium
approximation (EMA) reflecting the microphase-separated character
of the PIL under study.