Polyurethane carboxylate ionomers based on poly(ethylene glycol) (M n = 600) with sodium and various ammonium, phosphonium and imidazolium cations are synthesized for systematic comparison of different cationic counterions. Generally, larger cations act as plasticizers, lowering T g because of weaker Coulombic force for ion associations (acting as physical cross-links). T g can be reduced from 47 °C to -6 °C when replacing Na þ with large ether-oxygen containing ammonium without changing polymer composition and the lower T g can enhance ionic conductivity by 5 orders of magnitude. Ionic conductivity has a stronger correlation with segmental relaxation than T g , suggesting that counterion motion is coupled to the poly(ethylene oxide) local motions. An electrode polarization model is used to quantify the conducting ion concentration and mobility. All cation mobility follows VFT behavior, whereas conducting ion concentration has an Arrhenius temperature dependence, with slope providing activation energy and intercept determining the fraction of counterions available to participate in ionic conduction. Sodium counterions are mostly trapped by pPDI-carboxylate-pPDI segments, whereas the larger counterions are less trapped. Cation species and methoxyalkyl tails were found to impact both conducting ion concentration and their mobility but T g and R-relaxation time are the key factors for ionic conductivity at a given temperature.

Conventional sodium cations (Na+) in sulfonated polyester ionomers were replaced with ammonium-based ionic liquid counterions. Counterion dynamics were measured by dielectric spectroscopy and linear viscoelastic response via oscillatory shear. Ion exchange from sodium counterions to ionic liquid counterions such as tetramethylammonium and tetrabutylammonium showed an order of 104 increase in conductivity compared with sodium counterions, primarily attributed to weaker ionic interactions that lower the glass transition temperature. Electrode polarization was used in conjunction with the 1953 Macdonald model to determine the number density of conducting counterions and their mobility. Conductivity and mobility exhibit Vogel−Fulcher−Tammann (VFT) temperature dependences and both increased with counterion size. Conducting counterion concentrations showed Arrhenius temperature dependences, with activation energy reduced as counterion size increased. When ether−oxygen was incorporated into the mobile cation structure, self-solvating ability notably increased the conducting ion concentration. Weakened ion pairing interactions prove favorable for fundamental design of single-ion conductors for actuators, as ionic liquid counterions can provide both larger and faster strains, required by such electro-active devices.

Novel polyurethane (PU) cationomers are synthesized using an imidazolium diol‐based ionic liquid (IL) chain extender. A systematic comparison with a non‐ionic PU analogue reveals effect of the imidazolium cation on physical properties, hydrogen bonding, and morphology of segmented PU. Casting resulting PU solutions with various contents of IL generates novel membranes. Thermal study reveals that IL‐containing PU membranes exhibit a constant soft segment Tg at −81 °C; however, the Tg of imidazolium hard segments systematically shifts to lower temperatures with increasing IL content. This suggests that IL preferentially locates into the imidazolium ionic hard domains, which is also evident in small‐angle X‐ray scattering. Moreover, dielectric relaxation spectroscopy demonstrates increased ionic conductivity of PU membranes by 5 orders of magnitude upon incorporation of 30 wt% IL.

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PEO-based polyurethane sulfonate ionomers with various PEO chain lengths and sodium counterions were synthesized and characterized by both linear viscoelasticity (LVE) and dielectric relaxation spectroscopy (DRS). Since p-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC T g which increases with both ion content and hard segment content. An electrode polarization model was used to simultaneously determine the temperature dependence of conducting ion concentration and their mobility, which show Arrhenius and Vogel–Fulcher–Tammann (VFT) temperature dependences, respectively. The polymer dipole relaxation probed by DRS was found to be between 103 and 106 times faster than the mechanical segmental relaxation observed in LVE data near T g, suggesting that most polymer modes need to wait for the ions to rearrange. The dielectric relaxation, mechanical relaxation, and ionic conductivity all show good correlation with DSC T g and are related to ion rearrangement. Lower ion content creates lower T g, lower activation energy for conducting ions, and higher ion mobility, as sodium cations interact strongly with both PEO and the urethane linkage.