Influence of anion structure on thermal, mechanical and CO₂ solubility properties of uv-cross-linked poly(Ethylene glycol) diacrylate iongels

Iongel-based CO2 separation membranes were prepared by fast (< 1 min) UV-initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of different ionic liquids (ILs) with the [C2mim]⁺ cation and anions such as [TFSI]⁻, [FSI]⁻, [C(CN)3]⁻ and [B(CN)4]⁻. The four ILs were completely miscible with the non-ionic PEGDA network. Transparent and freestanding iongels containing between 60 and 90 %wt of IL were obtained and characterized by diverse techniques (FTIR, TGA, DSC, DMTA, SEM, CO2 solubility and pure gas permeability). The thermal and mechanical stability of the iongels, as well as CO2 solubility, were found to be strictly dependent on the IL content and the anion’s nature. The TGA results indicated that the iongels mostly follow the thermal profile of the respective neat ILs. The DMTA analysis revealed that the iongels based on fluorinated anions have higher storage modulus than those of cyano-functionalized anions. Conversely, the PEGDA–C(CN)3 iongels presented the highest CO2 solubility values ranging from 72 to 80 mmol/g. Single CO2 permeabilities of 583 ± 29 Barrer and ideal CO2/N2 selectivities of 66 ± 3 were obtained with the PEGDA–70 C(CN)3 iongel membrane. This work demonstrates that the combination of PEGDA with high contents of the best performing ILs is a promising and simple strategy, opening up new possibilities in the design of high-performance iongel membranes for CO2 separation.