It is highly desirable to integrate the CO 2 solubility benefits of ionic liquids (ILs) in polymeric membrane systems for effective CO 2 separations. Herein, we are exclusively exploring a series of four novel imidazolium-mediated Tröger’s base (TB)-containing ionene polymers for enhanced CO 2 separation. The two diimidazole-functionalized Tröger’s base monomers synthesized from “ortho”- and “para”-substituted imidazole anilines were polymerized with equimolar amounts of two different aromatic and aliphatic comonomers (α,α′-dichloro- p -xylene and 1,10-dibromodecane, respectively) via Menshutkin reactions to obtain four respective ionene polymers ([Im-TB( o & p )-Xy][Cl] and ([Im-TB( o & p )-C 10 ][Br], respectively). The resulting ionene polymers having halide anions were exchanged with [Tf 2 N] − anions, yielding a novel Tröger’s base material [Im-TB(x)-R][Tf 2 N] or “Im-TB-Ionenes”. The structural and physical properties as well as the gas separation behaviors of the copolymers of aromatic and aliphatic Im-TB-Ionenes have been extensively investigated with respect to the regiochemistry of imidazolium groups at the ortho and para positions of the TB unit. The imidazolium-mediated TB-Ionenes showed high CO 2 solubility and hence an excellent CO 2 /CH 4 permselectivity of 82.5. The Im-TB-Ionenes also displayed good thermal and mechanical stabilities.
Three new isomeric 6FDA-based polyimide-ionenes, with imidazolium moieties and varying regiochemistry (para-, meta-, and ortho- connectivity), and composites with three different ionic liquids (ILs) have been developed as gas separation membranes. The structural-property relationships and gas separation behaviors of the newly developed 6FDA polyimide-ionene + IL composites have been extensively studied. All the 6FDA-based polyimide-ionenes exhibited good compatibility with the ILs and produced homogeneous hybrid membranes with the high thermal stability of ~380 °C. Particularly, [6FDA I4A pXy][Tf2N] ionene + IL hybrids having [C4mim][Tf2N] and [Bnmim][Tf2N] ILs offered mechanically stable matrixes with high CO2 affinity. The permeability of CO2 was increased by factors of 2 and 3 for C4mim and Bnmim hybrids (2.15 to 6.32 barrers), respectively, compared to the neat [6FDA I4A pXy][Tf2N] without sacrificing their permselectivity for CO2/CH4 and CO2/N2 gas pairs.
Polymeric membranes either containing, or built from, ionic liquids (ILs) are of great interest for enhanced CO 2 /light gas separation due to the stronger affinity of ILs toward quadrupolar CO 2 molecules, and hence, high CO 2 solubility selectivity. Herein, we report the development of a series of four novel anionic poly(IL)-IL composite membranes via a photopolymerization method for effective CO 2 separation. Interestingly, these are the first examples of anionic poly(IL)-IL composite systems, in which the poly(IL) component has delocalized sulfonimide anions pendant from the polymer backbone with imidazolium cations as "free" counterions. Two types of photopolymerizable methacryloxy-based IL monomers (MILs) with highly delocalized anions (-SO 2 -N (-) -SO 2 -CF 3 and -SO 2 -N (-) -SO 2 -C 7 H 7 ) and mobile imidazolium ([C 2 mim] + ) counter cations were successfully synthesized and photopolymerized with two distinct amounts of free IL containing the same structural cation ([C 2 mim][Tf 2 N]) and 20 wt% PEGDA crosslinker, to serve as a composite matrix. The structure-property relationships of the four newly developed anionic poly(IL)-IL composite membranes were extensively characterized by TGA, DSC, and XRD analysis. All of the newly developed anionic poly(IL)-IL composite membranes exhibited superior CO 2 /CH 4 and CO 2 /N 2 selectivities together with moderate CO 2 /H 2 selectivity and reasonable CO 2 permeabilities. The membrane with an optimal composition and polymer architecture (MIL-C 7 H 7 /PEGDA (20%) /IL (1eq.) ) reaches the 2008 Robeson upper bound limit of CO 2 /CH 4 , due to the simultaneous improvement in permeability and selectivity (CO 2 permeability ~ 20 barrer and αCO 2 /CH 4 ~119). This study provides a promising strategy to explore the benefits of anionic poly(IL)-IL composites to separate CO 2 from flue gas, natural gas, and syngas streams and open up new possibilities in the polymer membrane design with strong candidate materials for practical applications.
A new series of six imidazolium-based ionenes containing aromatic amide linkages has been developed. These ionene-polyamides are all constitutional isomers varying in the regiochemistry of the amide linkages (para, meta) and xylyl linkages (ortho, meta, para) along the polymer backbone. The physical properties as well as the gas separation behaviors of the corresponding membranes have been extensively studied. These ionene-polyamide membranes show excellent thermal and mechanical stabilities, together with self-healing and shape memory characteristics. , terephthaloyl chloride; API, 1-(3-aminopropyl)imidazole; Xy, xylyl; Tf 2 N, bis(trifluoromethylsulfonyl) imide; IC, isophthaloyl chloride), where the amide and xylyl linkages are attached at para and meta positions, exhibit superior selectivity for CO 2 /CH 4 and CO 2 /N 2 gas pairs. We also demonstrate the transport properties and diverse applicability of our newly developed ionene-polyamides, particularly [TC-API(p)-Xy][Tf 2 N], for various industrial applications. Most importantly, [TC-API(p)-Xy][Tf 2 N] and [IC-API(m)-Xy][Tf 2 N] membranes (TC
The anionic ring-opening copolymerization of N-(p-tolylsulfonyl)azetidine ( pTsAzet) and N-(o-tolylsulfonyl)azetidine ( oTsAzet) produces poly(pTsAzet-co-oTsAzet) as a statistical copolymer. The pTsAzet/ oTsAzet copolymerization is living and allows for the synthesis of poly(sulfonylazetidine) of target molecular weights with narrow dispersities. 1H NMR spectroscopy was used to monitor the kinetics of the polymerization and estimate the monomer reactivity ratios. It was found that the reactivity ratios for oTsAzet and pTsAzet at 180 °C are 1.66 and 0.60, respectively. The tosyl groups of p(pTsAzet-co-oTsAzet) were reductively removed to produce linear poly(trimethylenimine) (LPTMI). This represents the first route to LPTMI of controlled molecular weight and low dispersity. Finally, the slow kinetics of the sulfonylazetidine polymerization facilitated the synthesis of a block copolymer without requiring the sequential addition of monomer. Specifically, pTsAzet, oTsAzet, and (N-p-toluenesulfonyl-2-methylaziridine) ( pTsMAz) were combined in solution. pTsMAz selectively polymerizes to form the first block at moderate temperature. After consumption of pTsMAz, the temperature was increased to copolymerize pTsAzet and oTsAzet and produce the block copolymer p(pTsMAz)-b-p(pTsAzet-co-oTsAzet).
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