Lower critical solution behavior in binary blends of hydrophobic polyethers with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf 2 N]) exhibited a difference in lower critical solution temperature (LCST) greater than 80 °C between structurally homologous poly(isopropyl glycidyl ether) (PiPGE) and poly(n-butyl glycidyl ether) (PnBGE). Replacement of the acidic hydrogen on the imidazolium ring with a methyl group (i.e., 2,3-dimethyl-1-hexylimidazolium bis(trifluoromethylsulfonyl)imide ([hmmim][Tf 2 N])) significantly reduced the LCST of both the PnBGE/ionic liquid (IL) mixture and the PiPGE/IL mixture. Differing degrees of hydrogen bonding between the polymer and the cation cannot alone explain the observed behavior. Similar hydrogen bonding between the [hmim] + cation and both polymers from molecular dynamics simulations was consistent with this conclusion. However, stronger [hmim] + cation tail/polymer alkyl side-chain interactions for PnBGE, with consequently stronger cation/anion interactions, point to solvophobic interactions as the basis for the large LCST difference between the PnBGE/[hmim][Tf 2 N] and PiPGE/[hmim][Tf 2 N] blends.

The addition of a diglycidyl-ether to a mono(μ-alkoxo)bis-(alkylaluminum)-initiated epoxide polymerization presents a strategy for amorphous polyether-based membrane synthesis. In situ kinetic 1 H NMR spectroscopy was used to monitor model network copolymerizations of epichlorohydrin (ECH) with 1,4butanediol-diglycidyl ether (Butyl-dGE) or poly(ethylene oxide)-diglycidyl ether (PEO-dGE). Reactivity ratios were extracted from the evolution of polymer composition from the monomer feed during copolymerization. Quantitative conversion and nearly random comonomer incorporation was achieved. The generality of this synthetic technique was supported by the polymerization of Butyl-dGE and a range of epoxide monomers such as n-butyl glycidyl ether (nBGE), allyl glycidyl ether, ECH, and glycidol. The copolymerizations produced optically clear, flexible films in all cases. We investigated the potential for this synthetic platform to provide compositional control of structure−property relationships within the context of industrially relevant membrane separations for CO 2 . Given the affinity of PEO for CO 2 and water, we explored using nBGE as a hydrophobic diluent, which was copolymerized with varying incorporations of PEO-dGE. The resultant cross-linked polyether membranes exhibited high CO 2 permeabilities (150−300 barrer) and selectivity over N 2 (α CO 2 /N 2 = 20−30) and H 2 (α CO 2 /H 2 ≈ 6). CO 2 sorption isotherms could be described by Henry's law and did not vary across the series of nBGE/PEO-dGE films. The similar sorption coefficients suggested that differences in permeability among these samples were driven by differences in diffusion coefficients. The diffusivity of CO 2 increased with cross-link density, and permeability was unaffected by humidity for this series of hydrophobic cross-linked polyether membranes.

The solubility of CO 2 in poly(ethylene oxide), poly(ethyl glycidyl ether), poly(iso-propyl glycidyl ether), poly(allyl glycidyl ether), poly(n-butyl glycidyl ether), and poly(ethyl vinyl ether) was measured at room temperature and 333.15 K and pressures up to 15 bar. CO 2 solubility, expressed as mole fraction in terms of molecular weight of the polymer repeat unit, was directly related to polymer repeat unit molecular weight regardless of pendant chain structure or ether oxygen placement in the backbone. The molality of CO 2 was highest in poly(ethyl vinyl ether) and was equal in all the poly(glycidyl ethers) and poly(ethylene oxide). The standard enthalpies and entropies of CO 2 absorption in poly(ethylene oxide), poly(ethyl glycidyl ether), and poly(ethyl vinyl ether) were calculated from the Henry's constants obtained from three isotherms. CO 2 dissolution was slightly more favorable enthalpically in poly(ethylene oxide). However, the entropic penalty for absorption was lower in poly(ethyl glycidyl ether) and poly(ethyl vinyl ether). These results suggest that poly(glycidyl ethers) and poly(ethyl vinyl ether) are promising alternatives to poly(ethylene oxide) for CO 2 separation by absorption or membrane separation because they have similar CO 2 uptake capacity, low glass transition temperatures, are amorphous, and are more hydrophobic than poly(ethylene oxide).

The transport properties, thermal properties, and CO2 solubility for several ionic liquids (ILs) with triethyl­(octyl)­phosphonium cations and a variety of CO2-reactive aprotic N-heterocyclic anions (AHAs) are reported in this work. Eleven new ILs were designed and synthesized. They were characterized in terms of their melting points, glass transition temperatures, decomposition temperatures, viscosities and densities (where possible), as well as their CO2 capacity as a function of pressure. Of the 11, 3 were solid at room temperature, 1 was a room-temperature liquid which remained liquid upon reaction with CO2, and 7 others were liquids that crystallized at room temperature upon reaction with CO2, so experimentation at elevated temperatures was required. The CO2 uptake isotherms for seven of the ILs, at temperatures ranging from 49 to 64 °C and pressures from 0 to 80 kPa, were fit to a Langmuir model. The CO2 solubility for several of these ILs was among the highest reported at these temperatures and pressures for AHA ILs in the literature, but they have lower thermal stability and higher viscosity than other promising AHA ILs.

Ionic liquids (ILs) have been evaluated extensively as post-combustion CO2 capture solvents, with CO2 solubility data available for a large number of ILs. However, data for the solubility of the less-soluble gas component, N2, are sparse. Therefore, the solubility of N2 was measured gravimetrically at pressures up to 140 bar in 12 ILs containing imidazolium, ammonium, pyrrolidinium, and phosphonium cations paired with bis(trifluoromethanesulfonyl)imide ([TFSI]−), dicyanamide ([DCA]−), methanesulfonate ([MeSO3]−), tetrafluoroborate [BF4]−), and triflate ([TfO]−) anions. Increasing the alkyl chain length from ethyl to hexyl to decyl in alkylimidazolium bis(trifluoromethanesulfonyl)imide ILs increased the N2 solubility. The same effect was observed with phosphonium cations paired with the bis(trifluoromethylsulfonyl)imide anion. Nitrogen solubility in ILs with the 1-ethyl-3-methylimidazolium cation followed the order [DCA]− < [MeSO3]− < [BF4]− < [TfO]− < [TFSI]−. Generally, regardless of the IL structure, the N2 solubility increased with increasing IL molar volume. For ILs with similar chemical composition and molar volume (i.e., ILs with tetraalkylammonium and pyrrolidinium cations), N2 was less soluble in the IL with the cyclic cation. The absorption of N2 in bis(trifluoromethylsulfonyl)imide ILs did not depend significantly on temperature. However, [emim][BF4] had a significant positive enthalpy of N2 absorption. These N2 solubility data, along with the readily available CO2 solubilities in ILs, is critical to evaluating ILs for post-combustion carbon capture processes.