In this report, fully-zwitterionic (ZI) copolymer scaffolds for ionogel electrolytes have been synthesized via in situ photopolymerization using various molar ratios of 2-methacryloyloxyethyl phosphorylcholine (MPC) and sulfobetaine vinylimidazole (SBVI) within the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI). Depending on the chemical composition of the ZI scaffold, ionogel room temperature ionic conductivities are found to vary between 2.5 and 6.7 mS cm at a fixed 20 mol % total polymer content. Compressive elastic moduli also exhibit a strong dependence on the co-monomer ratio, with values between 23 kPa and 11 MPa observed because of different degrees of ZI physical cross-linking. These results, together with NMR chemical shift analysis, suggest that the phosphorylcholine ZI group of MPC interacts more strongly with EMI TFSI, while SBVI prefers to self-aggregate and form dipole-dipole cross-links in the ionic liquid (IL). Self-diffusivity measurements of the EMI cations and TFSI anions in both ionogel and ZI solution samples confirm that slower ion diffusion in MPC-containing systems is due to attractive zwitterion/IL interactions, and not merely reduced mobility in the presence of a polymeric scaffold. This work highlights the importance of relative zwitterion/IL and ZI dipole-dipole interactions on the properties of a novel class of fully-ZI polymer-supported ionogel electrolytes containing a hydrophobic IL suitable for future electrical energy storage applications.

A series of polyzwitterion-supported gels featuring two classes of lithium-containing ionic liquid (IL) electrolytes have been created to examine the impact of different zwitterionic (ZI) group chemistries on lithium ion conductivity in these nonvolatile electrolytes. ZI homopolymer-supported gels containing poly­(carboxybetaine methacrylate) (pCBMA), poly­(2-methacryl­oyloxyethyl­phosphorylcholine) (pMPC), poly­(sulfobetaine vinylimidazole) (pSBVI), and poly­(sulfobetaine 2-vinylpyridine) (pSB2VP) were realized by rapid, in situ UV photopolymerization. Within a 1 M solution of lithium bis­(trifluoro­methyl­sulfonyl)­imide (LiTFSI) in a conventional IL, strong Coulombic interactions between ZI moieties and Li+ cations promoted higher ion self-diffusivities for all zwitterion types and generated improved Li+ conductivities. In particular, the pCBMA and pMPC gels exhibited improved lithium transference numbers of 0.37 and 0.38, respectively, compared to 0.23 for the IL solution. In the solvate ionic liquid (SIL) prepared from an equimolar mixture of LiTFSI and tetraglyme, the pCBMA scaffold resulted in the largest room temperature Li+ conductivity achieved, 0.44 mS cm–1 (vs 0.23 mS cm–1 in the neat SIL). The carboxybetaine ZI motif yielded the largest boost in Li+ conductivity in both IL electrolyte types, which was found to be correlated to this monomer generating the largest downfield 7Li NMR chemical shift in solution. This study illustrates the great potential of polyzwitterions for future application in lithium ion batteries and reveals the importance of zwitterion chemistry when selecting materials for nonaqueous ionogel electrolytes.

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Zwitterionic polymers are a distinctive class of materials with unique physical and chemical properties. In this study, the synthesis of fully zwitterionic ABA triblock copolymers was achieved by controlled radical polymerization using two different zwitterionic monomers, sulfobetaine methacrylate (SBMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC). Due to the strong tendency of the sulfobetaine groups to aggregate, the fully zwitterionic triblock copolymers demonstrated self-assembly as well as salt and thermal responsiveness in solution.

The glass-forming ability of a series of specially synthesized polyzwitterions was studied using fast scanning calorimetry (FSC). Polyzwitterions include those based on the sulfobetaine moiety: sulfobetaine acrylate, ethyl sulfobetaine methacrylate, sulfobetaine vinylimidazole, sulfobetaine 4-vinylpyridine, sulfobetaine methacrylate, and sulfobetaine methacrylamide. FSC was used to investigate the dynamic fragility over a large range of cooling rates, 10−4000 K/s, minimizing thermal degradation of the polyzwitterions. The rate dependence of the limiting fictive temperatures (T f ) was measured and fit to the Williams−Landel−Ferry model, from which the polyzwitterion dynamic fragility was determined for the first time. Dynamic fragility was low, ranging from 41 to 110, depending on the underlying chemical structure, which allows classification of this series of polyzwitterions as moderate to relatively strong polymeric glass formers. Their high glass transition temperatures combined with low fragilities indicates that polyzwitterions are unique among polymeric glass formers. This behavior arises from the formation of interand intrachain dipole−dipole cross-links which causes more dense molecular packing and cohesion.

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