Gas transport characteristics of supramolecular networks of metal-coordinated highly branched Poly(ethylene oxide)

Model systems are developed and investigated to better understand the effect of polyether-metal ion interactions on gas separation characteristics. These systems help answer current questions raised by the substantial body of research on metal-organic frameworks (MOFs) dispersed in polyethers to improve gas separation performance, where favorable interactions between the metal centers and polyethers are preferred to improve interfacial compatibility. Specifically, we investigate CO2/gas transport properties of supramolecular networks comprising cross-linked poly(ethylene oxide) (XLPEO) and dissociable salts, including LiClO4, Ni(BF4)2, and Cu(BF4)2. Increasing the salt content increases the glass transition temperature (Tg) and generally decreases gas diffusivity and permeability, which can be successfully described using a Tg-integrated free volume model with an expression similar to the Vogel-Tammann-Fulcher (VTF) equation. Surprisingly, low loadings of LiClO4 and Cu(BF4)2 (2 mass% or less) can increase gas permeability by 30%–70% without affecting the CO2/gas selectivity. This increase correlates with polyether-metal ion dynamics as measured by dielectric spectroscopy. Understanding how interaction-mediated dynamics affect gas transport will be instrumental to designing MOF-based mixed matrix materials for gas separations. [Display omitted] •Dissociated salts in cross-linked PEO increase Tg and decrease free volume.•Introduction of the salts generally decreases gas permeability.•Low loadings of LiClO4 and Cu(BF4)2 unexpectedly increase gas permeability.•Effect of the salt doping on gas diffusivity is described using a free volume model.