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.