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

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 [C(4)vim][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 (similar to 20-40 Barrer), a 4-7x increase relative to corresponding neat PIL, with excellent selectivities against N-2 or CH4. The addition of imidazolium-benzene fillers with increased imidazolium content were shown to correspondingly enhance CO2 solubility (di- < tri- < tetra- < hexa-), with the [C(4)vim][Tf2N]: [Hexa(Im(+))Benz][Tf2N] composite showing the highest CO2 permeability (P-CO2 = 38.4 Barrer), while maintaining modest selectivities (alpha(CO2/CH4) = 20.2, alpha(CO2/N2) = 23.6). Additionally, these metrics were similarly improved with the integration of more ionic content bonded to the polymeric matrix; increased PCO2 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.

Automated summary

This study introduces a series of vinyl-imidazolium-based polyelectrolyte composites modified with multivalent imidazolium-benzene ionic liquids or crosslinked with novel cationic crosslinkers. The composites exhibited enhanced CO2 permeabilities and selectivities against N-2 or CH4, demonstrating the potential for tuning the properties and transport behaviors of ionic polymers using ionic liquid-inspired small molecules.