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 CH4. 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 (PCO2 = 38.4 Barrer), while maintaining modest selectivities (αCO2/CH4 = 20.2, αCO2/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.
Highlights
Membrane-based gas separations have drawn significant research attention, serving as a more economic and less energy intensive alternative to conventional separation processes [1,2,3]
Robust polymeric films and ionic liquid (IL)-based materials are two of the primary material classes explored in leading membrane materials research, due to the stable and rigid nature of polymeric membranes and the tunable intermolecular interactions allowed by charged materials
A set of eight [C4vim][Tf2N]-based membranes were probed to confirm functional features, and pure gas permeation data revealed the structural effects of “free” ILs dispersed in the polymeric matrix versus integrated ionic crosslinks, which were shown to impact the permeability of CO2 through these thin films
Summary
Membrane-based gas separations have drawn significant research attention, serving as a more economic and less energy intensive alternative to conventional separation processes (i.e., cryogenic distillation, pressure swing absorption) [1,2,3]. We have explored the design of more sophisticated, multivalent ionic fillers as a means of altering the local ordering and structuring within an ionic polymeric matrix [27] These compositional concepts and structural fine tuning can be applied to poly(ILs) to ionene–IL composites, to better understand the how these charged fillers interact with the pendant ionic groups and probe the effects on structure, homogeneity, mechanical properties, and transport behaviors. The ([C4vim][Tf2N] matrix was manipulated with extended ionic crosslinkers designed from tri- and tetra(imidazolium benzene) cores synthetically modified to possess reactive (vinyl imidazolium) groups at the periphery The concept of such crosslinkers is a new approach in the design of PIL materials. Styrin-tahnedsisteotrfaD(iim-, iTdrai-z,oTleiutrma- baenndzHeneex)ac(oImreisdsayznotlhiuemtic)aBlleynmzeondeiIfLiesd to possess reactive (vinTyhl eimfoiduarzimoliudmaz)ogler-obuepnszeantethdeerpivearitpivheesryh.avTehebeceonncrepot rotfedsuinchthcerolsitselrinatkuerres, issyantnheewsiazpepdruoasicnhginsimthieladrecsoiugnploinfgPtIeLcmhnaitqeurieasls[3. 4T–h3e6s].tr1u,4c-tduiriaml iedffaezcotlseabnednzternane,s1p,o3r,5t-btreihimavidioarzsoo-f these composites were investigated, to gain an understanding of the structural–property relationships for these dispersed and crosslinked ionic composites and probe the influence of supplementary imidazolium moieties on the gas separation performance
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