Synthesis and Performance of Aromatic Polyamide Ionenes as Gas Separation Membranes

Abstract

Here, we report the synthesis and thermophysical properties of seven primarily aromatic, imidazolium-based polyamide ionenes. The effects of varied para-, meta-, and ortho-connectivity, and spacing of ionic and amide functional groups, on structural and thermophysical properties were analyzed. Suitable, robust derivatives were cast into thin films, neat, or with stoichiometric equivalents of the ionic liquid (IL) 1-benzy-3-methylimidazolium bistriflimide ([Bnmim][Tf2N]), and the gas transport properties of these membranes were measured. Pure gas permeabilities and permselectivities for N2, CH4, and CO2 are reported. Consistent para-connectivity in the backbone was shown to yield the highest CO2 permeability and suitability for casting as a very thin, flexible film. Derivatives containing terephthalamide segments exhibited the highest CO2/CH4 and CO2/N2 selectivities, yet CO2 permeability decreased with further deviation from consistent para-linkages.

Designing Imidazolium Poly(amide-amide) and Poly(amide-imide) Ionenes and Their Interactions with Mono- and Tris(imidazolium) Ionic Liquids

“…There have been abundant research efforts in recent decades dedicated to the design and applications surrounding polyelectrolytes and ionomers which contain charged features pendant to the main chain, highlighted in several reviews [1][2][3][4][5][6]. The design of ionic liquids (ILs) undoubtably serves as an influential synthetic inspiration for polyelectrolytes, which possess essentially The utility of ionenes has been demonstrated in separations and CO2 capture [8][9][10][11][12][13], ionexchange or conducting membranes [14], antimicrobial coatings [15][16][17][18], batteries [19][20][21], electrochromic devices [22], hydrogels and gelators [23][24][25], water treatment [26], and fiber applications [12,27,28]. Nearly all known ionenes bear cationic moieties such as ammonium, phosphonium, pyrrolidinium, pyridinium, triazolium, and imidazolium groups [8,14,20,22,23,[29][30][31][32][33][34].…”

“…Long's group has emphasized the progress and versatile applicability of ammonium, imidazolium, and phosphonium ionenes [32,38,39]. Previous literature by Bara and coworkers has demonstrated the expansive possibilities of imidazolium ionenes, shifting toward more "high-performance" materials and exploring the effects of introducing imidazolium ILs into the ionene matrix [9,10,13,28,36,40,41]. We have demonstrated the suitability of imidazolium ionenes applied as CO 2 -selective gas separation membranes, self-healing and shape memory materials, 3D printing feedstocks, and as fibers [9][10][11][12][13]27,28].…”

“…Previous literature by Bara and coworkers has demonstrated the expansive possibilities of imidazolium ionenes, shifting toward more "high-performance" materials and exploring the effects of introducing imidazolium ILs into the ionene matrix [9,10,13,28,36,40,41]. We have demonstrated the suitability of imidazolium ionenes applied as CO 2 -selective gas separation membranes, self-healing and shape memory materials, 3D printing feedstocks, and as fibers [9][10][11][12][13]27,28]. The tailorability of this imidazolium platform is vast, when creative chemistries are employed to probe the effects of structural or connective variation of the cyclic cation, substitution, charge density, functionality, and modification of properties via addition of ILs.…”

“…Only a few examples of polyamide (PA) ionenes have been demonstrated in literature, typically containing ammonium, pyridinium, and imidazolium cations. Our group has introduced aliphatic and aromatic imidazolium-based PA ionenes used as gas separation membranes or self-healing elastomers [10,12,27,28]. We have also recently demonstrated that some of the key monomers for these PA ionenes can be derived from poly(ethylene terephthalate) (PET).…”

“…These methods allow for the controlled sequencing and spacing of functionality using only two monomers, with distributed ionic groups located between these features. In our previous work, we have introduced multiple series of PA and PI ionenes, and reported that these ionene systems undergo ordering when "free" imidazolium IL is present [9][10][11][12]27,28,36]. This free IL serves as a non-covalent crosslink between ionene chains.…”