Four polymerized ionic liquids (PILs)
were systematically designed
to study the effect of polymer architecture and linker polarity on
ion aggregation and transport. Specifically, linear and network PILs
with the same ammonium cations (Am) and bis(trifluoromethane)sulfonimide
(TFSI) anions were prepared by step-growth polymerization, and polarity
was tuned by incorporating two precise linkers, either polar tetra(ethylene
oxide) (4EO) linker or nonpolar undecyl (C11) linker. The glass transition
temperature (T
g) substantially increased
with the nonpolar C11 linker or upon cross-linking to form a network.
The low wave-vector (q) ion aggregation peak from
wide-angle X-ray scattering (WAXS) was not observable in the linear
4EO PIL, while it was most pronounced in the network C11 PIL. The
network C11 PIL exhibited the strongest decoupling, where the ionic
conductivity at T
g is greater than 1 order
of magnitude higher than the other PILs. This systematic comparison
suggests that network structure and nonpolar linkers can promote both
ion aggregation and ionic conductivity close to T
g.
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