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Ion transport in solid polymer electrolytes is crucial for applications like energy conversion and storage, as well as carbon dioxide capture. However, most of the materials studied in this area are petroleum-based. Natural materials (biopolymers) have the potential to act as alternatives to petroleum-based products and, when derived with ionic liquid (IL) functionalities, present a sustainable alternative for conductive materials by offering tunable morphological, thermal, and mechanical properties. In this study, a series of IL-functionalized cellulose derivatives with variations in pendant alkyl chain length, counteranions, and degrees of substitution were synthesized in order to explore structure-property relationships. Emphasis was placed on investigating morphological, thermal, and ionic conductivity changes, hypothesizing that materials synthesized with longer alkyl chains would exhibit increased backbone-to-backbone spacing, thereby lowering the glass transition temperature, and enhancing ionic conductivity. A variety of characterization techniques were used for this investigation, including nuclear magnetic resonance spectroscopy (NMR), elemental analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray scattering, and dielectric relaxation spectroscopy (DRS). The findings reveal a link between longer alkyl chain lengths, expanded backbone-backbone spacing, and side chain interdigitation. Within each set of samples, heightened ionic conductivity was observed with the introduction of bulkier, less coordinating anions, underscoring the significant influence of counteranion size. 

Abstract The synthesis and characterization of a series of polyurethane ionenes using a non‐isocyanate approach is disclosed. Imidazole‐capped, urethane‐containing prepolymers are prepared by first reacting carbonyl diimidazole (CDI) with several poly(propylene glycol) (PPG) diols with variable molecular weight, followed by subsequent reaction with 3‐aminopropylimidazole (API). Polymerization with 1,4‐dibromomethylbenzene followed by anion exchange resulted in the desired polyurethane ionenes bearing the [NTf₂] counteranion as a series of viscous liquids. NMR and FTIR spectroscopy are used to characterize the intermediates and final ionenes, including molecular weight determination by end‐group analysis. A single glass transition temperature (T_g), as determined by differential scanning calorimetry (DSC), is observed for each ionene (−38 to −64 °C) with theT_gdecreasing with increasing PPG molecular weight. Thermogravimetric analysis (TGA) indicated a two‐step decomposition for each ionene, with the first being degradation of the PPG segment, followed by the urethane/ionic segment. Microphase separation is observed from x‐ray scattering profiles with Bragg distances that increased with increasing PPG molecular weight. Ionic conductivity is found to be inversely dependent upon DSCT_gat lower temperatures (RT and below); however, at higher temperatures, conductivity appears to be more dependent upon the ability of ionic aggregates caused by phase separation to interact.