Dielectric spectroscopy was used to determine the static dielectric constants (ε s ) of imidazolium acrylates and methacrylates and their ionomers, with different imidazolium pendant structures containing a combination of alkylene [(CH 2 ) n , n = 5 or 10] and ethyleneoxy [(CH 2 CH 2 O) n , n = 4 or 7.3 (the average of a mixture of n = 1 to 20)] units as spacers between the backbone and the imidazolium cation. All monomers and polymers exhibited two dipolar relaxations, assigned to the usual segmental motion (α) associated with the glass transition and a lower frequency relaxation (α 2 ), attributed to ions rearranging. From the analysis of the static dielectric constants using the Kirkwood g correlation factor, the dipoles in conventional (smaller) ionic liquids prefer antiparallel alignment (g ≈ 0.1), lowering ε s values (≤30), because their polarizability volumes V p strongly overlap, whereas the dipoles in the larger ionic liquid monomers display g of order unity and 50 ≤ ε s ≤ 110. A longer spacer leads to higher static dielectric constant, owing to a significant increase of the relaxation strength of the α 2 process, which is directly reflected through an unanticipated increase of the static dielectric constant with ionic liquid molecular volume V m . The glass transition temperature of polymerized imidazolium ionic liquids with various counterions is also shown to simply be a monotonically decreasing function of V m . Furthermore, the ionomers consistently exhibit 1.5−2.3 times higher static dielectric constants (ε s up to ∼140 at room temperature) than the monomers from which they were synthesized, suggesting that polymerization encourages the observed synergistic dipole alignment (g > 1).

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New bis(ω‐hydroxyalkyl)imidazolium and 1,2‐bis[N‐(ω‐hydroxyalkyl)imidazolium]ethane salts are synthesized and characterized; most of the salts are room temperature ionic liquids. These hydroxyl end‐functionalized ionic liquids are polymerized with diacid chlorides, yielding polyesters containing imidazolium cations embedded in the main chain. By X‐ray scattering, four polyesters are found to be semicrystalline at room temperature: mono‐imidazolium‐C11‐sebacate‐C6 (4e), mono‐imidazolium‐C11‐sebacate‐C11 (4c), bis(imidazolium)ethane‐C6‐sebacate‐C6 (5a), and bis(imidazolium)ethane‐C11‐sebacate‐C11 (5c), all with hexafluorophosphate counterions. The other imidazolium polyesters, including all those with bis(trifluoromethanesulfonyl)imide (TFSI−) counterions, are amorphous at room temperature. Room temperature ionic conductivities of the mono‐imidazolium polyesters (4 × 10−6 to 3 × 10−5 S cm−1) are higher than those of the corresponding bis‐imidazolium polyesters (4 × 10−9 to 8 × 10−6 S cm−1), even though the bis‐imidazolium polyesters have higher ion concentrations. Counterions affect ionic conduction significantly; all polymers with TFSI− counterions have higher ionic conductivities than the hexafluorophosphate analogs. Interestingly, the hexafluorophosphate polyester, 1,2‐bis(imidazolium)ethane‐C11‐sebacate‐C11 (5c), displays almost 400‐fold higher room temperature ionic conductivity (1.6 × 10−6 S cm−1) than the 1,2‐bis(imidazolium)ethane‐C6‐sebacate‐C6 analog (5a, 4.3 × 10−9 S cm−1), attributable to the differences in the semicrystalline structure in 5c as compared to 5a. These results indicate that semicrystalline polymers may result in high ionic conductivity in a soft (low glass tranition temperature, Tg) amorphous phase and good mechanical properties of the crystalline phase.

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