Deep eutectic solvent-inspired supramolecular polymer networks: Unexpected absence of CO₂ affinity

Deep eutectic solvents (DESs) comprising a hydrogen bond donor (HBD, such as poly(ethylene glycol)) and a hydrogen bond acceptor (HBA, such as tetrabutylammonium bromide (TBAB)) have been demonstrated with enormous CO₂/CH₄ solubility selectivity because of the hydrogen-bonds (H-bonds). Inspired by them, we aimed to replicate these interactions in supramolecular polymer networks (SPNs) for membrane CO₂/gas separation. A series of SPNs were synthesized by photopolymerization of poly(ethylene glycol) methacrylate (PEGMA) containing –OH groups as an HBD with TBAB or methyltriphenylphosphonium bromide (MTPB) as an HBA. The polymer (pPEGMA) suppresses the crystallization of TBAB or MTPB because of the H-bonds, and adding 20 mass% TBAB decreases the glass transition temperature from −53 to −60 °C. However, adding TBAB or MTPB has a negligible effect on CO₂ solubility and CO₂/C₂H₆ solubility selectivity, indicating a lack of favorable interactions between the H-bonds in the polymers and CO₂, contrary to previous literature findings. Moreover, introducing TBAB or MTPB in pPEGMA scarcely affects CO₂ permeability and CO₂/N₂ and CO₂/CH₄ selectivity. The unexpected findings may prompt further investigation into the underlying interactions between CO₂ and H-bonds in DESs, and the derived mechanisms can be critical to designing advanced carbon capture membranes.