Ideal CO₂/Light Gas Separation Performance of Poly(vinylimidazolium) Membranes and Poly(vinylimidazolium)-Ionic Liquid Composite Films

Six vinyl-based, imidazolium room-temperature ionic liquid (RTIL) monomers were synthesized and photopolymerized to form dense poly­(RTIL) membranes. The effect of polymer backbone (i.e., poly­(ethylene), poly­(styrene), and poly­(acrylate)) and functional cationic substituent (e.g., alkyl, fluoroalkyl, oligo­(ethylene glycol), and disiloxane) on ideal CO₂/N₂ and CO₂/CH₄ membrane separation performance was investigated. The vinyl-based poly­(RTIL)­s were found to be generally less CO₂-selective compared to analogous styrene- and acrylate-based poly­(RTIL)­s. The CO₂ permeability of <i>n</i>-hexyl- (69 barrers) and disiloxane- (130 barrers) substituted vinyl-based poly­(RTIL)­s were found to be exceptionally larger than that of previously studied styrene and acrylate poly­(RTIL)­s. The CO₂ selectivity of oligo­(ethylene glycol)-functionalized vinyl poly­(RTIL)­s was enhanced, and the CO₂ permeability was reduced when compared to the <i>n</i>-hexyl-substituted vinyl-based poly­(RTIL). Nominal improvement in CO₂/CH₄ selectivity was observed upon fluorination of the <i>n</i>-hexyl vinyl-based poly­(RTIL), with no observed change in CO₂ permeability. However, rather dramatic improvements in both CO₂ permeability <i>and</i> selectivity were observed upon blending 20 mol % RTIL (emim Tf₂N) into the <i>n</i>-hexyl- and disiloxane-functionalized vinyl poly­(RTIL)­s to form solid–liquid composite films

Morphological Phase Behavior of Poly(RTIL)-Containing Diblock Copolymer Melts

The development of nanostructured polymeric systems containing directionally continuous poly­(ionic liquid) (poly­(IL)) domains has considerable implications toward a range of transport-dependent, energy-based technology applications. The controlled, synthetic integration of poly­(IL)­s into block copolymer (BCP) architectures provides a promising means to this end, based on their inherent ability to self-assemble into a range of defined, periodic morphologies. In this work, we report the melt-state phase behavior of an imidazolium-containing alkyl–ionic BCP system, derived from the sequential ring-opening metathesis polymerization (ROMP) of imidazolium- and alkyl-substituted norbornene monomer derivatives. A series of 16 BCP samples were synthesized, varying both the relative volume fraction of the poly­(norbornene dodecyl ester) block (<i>f</i>_DOD = 0.42–0.96) and the overall molecular weights of the block copolymers (<i>M</i>_n values from 5000–20 100 g mol^–1). Through a combination of small-angle X-ray scattering (SAXS) and dynamic rheology, we were able to delineate clear compositional phase boundaries for each of the classic BCP phases, including lamellae (Lam), hexagonally packed cylinders (Hex), and spheres on a body-centered-cubic lattice (S_BCC). Additionally, a liquid-like packing (LLP) of spheres was found for samples located in the extreme asymmetric region of the phase diagram, and a persistent coexistence of Lam and Hex domains was found in lieu of the bicontinuous cubic gyroid phase for samples located at the intersection of Hex and Lam regions. Thermal disordering was opposed even in very low molecular weight samples, detected only when the composition was highly asymmetric (<i>f</i>_DOD = 0.96). Annealing experiments on samples exhibiting Lam and Hex coexistence revealed the presence of extremely slow transition kinetics, ultimately selective for one or the other but not the more complex gyroid phase. In fact, no evidence of the bicontinuous network was detected over a 2 month annealing period. The ramifications of these results for transport-dependent applications targeting the use of highly segregated poly­(IL)-containing BCP systems are carefully considered