Influence of anion and ionization ratio on CO2 sorption of poly(ionic liquid)s with imidazolium cations derived from polyepichlorohydrin: a multi-scale analysis

Abstract

Aiming at developing new polymer absorbents for the physical CO₂ capture, this work reports the synthesis and multi-scale characterization of two new families of poly(ionic liquid)s (PILs) obtained from polyepichlorohydrin (polyECH). PolyECH was quaternized with 1-methylimidazole quasi-quantitatively and the Cl anions were then exchanged by different salts to introduce BF₄, AcO and TFSI anions for the first series of PILs. The second series was then obtained by varying the amount of 1-methylimidazole, leading to new PILs with TFSI anions and ionization ratios increasing from 0 to 94.6%. The chemical structure of the different PILs was characterized by different NMR techniques (¹H, ¹³C, 2D ¹H/¹³C HSQC, APT ¹³C). Their physical properties and morphology were investigated by DSC, rheology and SAXS/WAXS. The CO₂ sorption properties were then assessed with a magnetic suspension balance (MSB) and discussed based on structure-morphology-properties relationships. The best CO₂ sorption properties (159.3 mg CO₂/g PIL at 10 bar and 35°C) were obtained with the PIL having TFSI anions and the highest ionization ratio (IR = 94.6%). The particularly high CO₂ sorption of this PIL was related to its highest interchain d-spacing, inducing better accessibility to the CO₂-philic ionic sites.