Toward controlled functional sequencing and hierarchical structuring in imidazolium ionenes

Abstract

This focused mini-review highlights recent advances related to the design and applications of imidazolium ionenes and forward-looking perspectives. Creative strategies which employ established synthetic approaches and utilize the modularity of the imidazole moiety unlock great potential for tailoring both functional and structural features arising from precise spacing of ionic groups within the polymer backbone. As imidazolium ionenes draw more interest, increased sophistication of chemical modifications and material processing is occurring, with a corresponding shift toward more demanding applications. Synthetic routes for placement and sequencing of ionic content are discussed, in addition to recent approaches to control structure and self-assembly or tune behaviors of imidazolium ionenes and composites.

Thiol‐yne photoclick polymerization as a method for preparing imidazolium‐containing ionene networks

“…Poly(ionic liquid)s or PILs are ion-containing polymers where the ionic liquid group is pendant to the backbone in the repeating unit 8,9 while ionenes have the ionic liquid group directly in the backbone of the polymer. [10][11][12] As the desire to create materials with highly tunable mechanical and conductive properties continues to increase, chemists and engineers must continuously investigate novel ways to incorporate ionic liquid groups into macromolecular architectures, decipher the often difficult relationships between ionic conductivity, morphology and polymer structure, and improve processability.…”

“…10 Examples have included using S N 2 Menshutkin, polyesterification or polyurethane chemistry while more recent efforts have focused on strategic placement of the IL moiety on the backbone in order to enhance conductivity. 7,[11][12][13][14][15][16][17] Regardless of the architectural methodology, PILs and ionenes act as single ion transporters since one of the ions (typically the cation) is covalently bound into the repeating unit. A number of key factors influence ionic conductivity, including polymer morphology, polymer chain relaxation (related to the glass transition temperature (T g )), and ion concentration and mobility.…”

Design and Gas Separation Performance of Imidazolium Poly(ILs) Containing Multivalent Imidazolium Fillers and Crosslinking Agents

“…Many polyelectrolytes and poly(ILs) (PILs) based upon imidazolium cations have been introduced, in conjunction with the development of imidazolium ionic liquid chemistries. Imidazolium polyelectrolytes and ILs are prevalent in the literature, due to the synthetic accessibility for the incorporation of the imidazolium group, in addition to important interactions for separation processes such as its affinity for CO 2 vs. other non-polar gases [ 13 , 14 , 15 ]. Many imidazolium polymers rely upon free-radical polymerization techniques to incorporate imidazolium groups pendant to the backbone, often utilizing vinyl- or styrenyl-imidazole monomers or linear/difunctional crosslinkers.…”

“…Contrary to imidazolium polyelectrolytes formed conventionally via free radical polymerization with charged features being pendant to the backbone, our group has reported several works related to the gas separation performance of polyimide and polyamide imidazolium ionenes, polymers formed via the Menshutkin reaction between a bis(imidazole) and α,ω-dihalide wherein the charged group is directly incorporated within the main chain alternating with other functional and structural features along the backbone [ 25 , 26 , 27 , 28 ] ( Figure 1 ). Our group has previously reviewed the synthetic pathways and applications of imidazolium ionenes, which are an extremely tunable platform which can further be modified by the integration of free IL or multivalent fillers to promote structuring within the polymeric ionene matrix [ 15 , 27 , 29 ]. These imidazolium ionene composites with IL yielded enhanced permeabilities, in comparison with their corresponding neat ionene counterparts, and high selectivities for CO 2 relative to N 2 and CH 4 .…”

Asking our early career researchers to envision the future

“…Furthermore, O'Harra et al describe the precise introduction of ionic sites in ionenes, wherein the charged sites are contained within the polymeric main chain, thus pointing to the importance of sequence control for designing a range of hierarchical structures. 8 Chidanguro et al continue to emphasize the importance of morphological order in macromolecular systems with a discussion of polymersomes wherein self-assembly generates novel structures in aqueous solutions. 9 Our early career leaders also point to the criticality of the interface of molecular sciences and mechanical engineering, and additive manufacturing is highlighted in this vision.…”