A molecular-level understanding of dynamics in imidazolium-based ionomers with different counterions and side chain lengths was investigated using X-ray scattering, oscillatory shear, and dielectric relaxation spectroscopy (DRS). Variations of the counterion size and side chain length lead to changes in glass transition temperature (T g ), extent of ionic aggregation, and dielectric constant, with consequences for ion transport. A physical model of electrode polarization is used to determine the number density of simultaneously conducting ions and their mobility. Imidazolium-based ionomers with larger counterion and longer side chain have lower T g , resulting in higher ionic conductivity and mobility. The ionic mobility is coupled to ion motions that are directly measured as a second segmental process in DRS, as these are observed to share the same Vogel temperature. Time−temperature superposition (tTS) was applied to create linear viscoelasticity master curves and to investigate the delay in chain motion related to ionic associations. tTS works well for these materials, and the terminal relaxation time increases with decreasing side chain length and smaller counterion size. X-ray scattering confirms the extent of ionic aggregation and helps to rationalize the observed dielectric constants. Larger counterions or longer side chains diminish ionic aggregation, and their ionomers have higher dielectric constants, which agree reasonably with the Onsager prediction at all temperatures studied. Smaller counterions or shorter side chains promote ionic aggregation, and their ionomers have lower dielectric constants, which are directly reflected in the lower content of simultaneously conducting ions.

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We thoroughly investigate and quantify the chemical stability of an imidazolium-based alkaline anion exchange polymerized ionic liquid (PIL), poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium hydroxide) (poly(MEBIm-OH), over a broad range of humidities, temperatures, and alkaline concentrations using the combined techniques of electrochemical impedance spectroscopy and nuclear magnetic resonance spectroscopy. High chemical stability was observed under dry conditions (10% RH) at 30 °C, humid and saturated conditions up to 80 °C, and even in mild alkaline conditions ([KOH] < 1 M) at 25 °C. Degradation was only observed under more vigorous conditions: dry conditions (10% RH) at 80 °C or at higher alkaline concentrations ([KOH] > 1 M). Under these conditions, we suggest an imidazolium ring-opening mechanism as the primary degradation pathway, based on a detailed analysis of the 1 H NMR spectra. Similar to poly(MEBIm-OH), other alkaline anion (carbonate (CO 3 2À) and bicarbonate (HCO 3 À )) exchange PILs were also synthesized in this study via salt metathesis of the PIL precursor, poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bromide) (poly(MEBIm-Br)). The thermal and ion conductive properties of each PIL in this study were characterized. The ionic conductivity of the hydroxide conducting PIL, poly(MEBIm-OH), was the highest of these PILs investigated at 9.6 mS cm À1 at 90% RH and 30 °C with an Arrhenius activation energy of 17.1 kJ mol À1 at 90% RH.

A series of strongly microphase-separated polymerized ionic liquid (PIL) diblock copolymers, poly(styrene-b-1-((2-acryloyloxy)ethyl)-3-butylimidazolium bis(trifluoromethanesulfonyl)imide) (poly(S-b-AEBIm-TFSI)), were synthesized to explore relationships between morphology and ionic conductivity. Using small-angle X-ray scattering and transmission electron microscopy, a variety of self-assembled nanostructures including hexagonally packed cylinders, lamellae, and coexisting lamellae and network morphologies were observed by varying PIL composition (6.6–23.6 PIL mol %). At comparable PIL composition, this acrylate-based PIL block copolymer with strong microphase separation exhibited ∼1.5–2 orders of magnitude higher ionic conductivity than a methacrylate-based PIL block copolymer with weak microphase separation. Remarkably, we achieved high ionic conductivity (0.88 mS cm–1 at 150 °C) and a morphology factor (normalized ionic conductivity, f) of ∼1 through the morphological transition from lamellar to a coexistence of lamellar and three-dimensional network morphologies with increasing PIL composition in anhydrous single-ion conducting PIL block copolymers, which highlights a good agreement with the model predictions. In addition to strong microphase separation and the connectivity of conducting microdomains, the orientation of conducting microdomains and the compatibility between polymer backbone and IL moiety of PIL also significantly affect the ionic conductivity. This study provides avenues to controlling the extent of microphase separation, morphology, and ion transport properties in PIL block copolymers for energy conversion and storage applications.

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