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.

Network architectures reveal odd–even effects in existing PIL systems.

A series of acrylic polymerized ionic liquids (PILs) with imidazolium cations and bis­(trifluoromethylsulfonyl)­imide (TFSI) anions were synthesized via reversible addition–fragmentation chain-transfer polymerization. The absolute molecular weights (MWs) of PILs were determined from size exclusion chromatography with light scattering. The degree of polymerization (N) ranged from 15 to 254, and steady rotational rheology indicated the zero-shear viscosity (η0) measured at a constant distance above the glass transition scales as η0 ∼ N 1.0 for N < 92, in agreement with the theory for unentangled polymer melts. In the range from N = 92–254, we measured η0 ∼ N 2.3 which is interpreted as a transition region. The N 1.0 scaling in the unentangled regime is in contrast to the prior report of η0 ∼ N 1.7 in polyethylene-based PILs (Macromolecules, 2011, 44, 7719) but in agreement with a calculated η0 ∼ N 1.1 of acrylic ammonium TFSI PILs (Macromolecules, 2016, 49, 4557). Oscillatory shear rheology revealed that electrostatic interactions in this system were weak enough to have no impact on delaying the onset of flow, which was supported by a lack of ion aggregation in wide-angle X-ray scattering. The polymer nanostructure was also found to be minimally influenced by the degree of polymerization. Ionic conductivity slightly decreased as MW increased but overlapped when normalized to the calorimetric glass transition temperature.

Next‐generation material applications require electroactive materials for actuation which are light weight, operate at low voltages (<5 V), exhibit cyclability, and are compatible with a range of environments. Here, a class of network polymerized ionic liquid (n‐PIL) actuators is reported, synthesized via a facile step growth polymerization, which not only have comparable actuation strains (≈0.9%) to other state‐of‐the‐art ionic polymer systems at ±3 V, but also exhibit 85% performance preservation after 1000 testing cycles and operate with no additives such as solvent or free ionic liquid. Molecular engineering of the n‐PILs by controlling crosslinking density and linker polarity leads to an order‐of‐magnitude increase in tip displacement which provides insights on future materials development.