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

Kathryn E O'Harra; Emily M DeVriese; Erika M Turflinger; Danielle M Noll; Jason E Bara

doi:10.3390/polym13091388

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

Polymers (Basel). 2021 Apr 24;13(9):1388. doi: 10.3390/polym13091388.

Authors

Kathryn E O'Harra¹, Emily M DeVriese¹, Erika M Turflinger¹, Danielle M Noll¹, Jason E Bara¹

Affiliation

¹ Department of Chemical & Biological Engineering, University of Alabama, Tuscaloosa, AL 35487-0203, USA.

Abstract

This work introduces a series of vinyl-imidazolium-based polyelectrolyte composites, which were structurally modified via impregnation with multivalent imidazolium-benzene ionic liquids (ILs) or crosslinked with novel cationic crosslinkers which possess internal imidazolium cations and vinylimidazolium cations at the periphery. A set of eight [C₄vim][Tf₂N]-based membranes were prepared via UV-initiated free radical polymerization, including four composites containing di-, tri-, tetra-, and hexa-imidazolium benzene ILs and four crosslinked derivatives which utilized tri- and tetra- vinylimidazolium benzene crosslinking agents. Structural and functional characterizations were performed, and pure gas permeation data were collected to better understand the effects of "free" ILs dispersed in the polymeric matrix versus integrated ionic crosslinks on the transport behaviors of these thin films. These imidazolium PIL:IL composites exhibited moderately high CO₂ permeabilities (~20-40 Barrer), a 4-7× increase relative to corresponding neat PIL, with excellent selectivities against N₂ or CH_4. The addition of imidazolium-benzene fillers with increased imidazolium content were shown to correspondingly enhance CO₂ solubility (di- < tri- < tetra- < hexa-), with the [C₄vim][Tf₂N]: [Hexa(Im⁺)Benz ][Tf₂N] composite showing the highest CO₂ permeability (P_CO2 = 38.4 Barrer), while maintaining modest selectivities (α_CO2/CH4 = 20.2, α_CO2/N2 = 23.6). Additionally, these metrics were similarly improved with the integration of more ionic content bonded to the polymeric matrix; increased P_CO2 with increased wt% of the tri- and tetra-vinylimidazolium benzene crosslinking agent was observed. This study demonstrates the intriguing interactions and effects of ionic additives or crosslinkers within a PIL matrix, revealing the potential for the tuning of the properties and transport behaviors of ionic polymers using ionic liquid-inspired small molecules.

Keywords: crosslinkers; gas separation; imidazolium; ionic liquids; membranes; polyelectrolytes.

Abstract

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