Imidazole-functionalized hydrophilic rubbery comb copolymers: Microphase-separation and good gas separation properties

Imidazole groups have attracted considerable attention owing to their potential to be modified into ionic liquids, metal complexes, and biomimetic products. Herein, we report the synthesis of an imidazole-functionalized comb copolymer, i.e., poly(vinyl imidazole)-poly(oxyethylene methacrylate) (PVIm-POEM), via free-radical polymerization for a CO₂ capture membrane. The imidazole group in PVIm-POEM exhibits a good interaction with the ethylene oxide groups of the POEM domain to cover the severe structural defects of PVIm domains. The selectivities of PVIm-POEM comb copolymer membranes were far greater than those of PVIm and POEM homopolymers. The PVIm domain not only provided a good physical property for generating a defect-free membrane but also generated an effective CO₂-philic pathway via microphase separation and interactions with ethylene oxide groups. The highest performance was exhibited by PVIm-POEM37 (with a volumetric ratio of 3:7): the CO₂ permeability reached 148.6 Barrer, and the CO₂/N₂ and CO₂/CH₄ selectivities reached 65.3 and 35.0, respectively, which represents one of the highest values for water/alcohol-soluble polymeric membranes without additives. The results suggest that the imidazole group-based copolymer provides avenues for future research through various types of reformation.