Hybrid membranes of nanostructrual copolymer and ionic liquid for carbon dioxide capture

Efficient CO₂ capture membranes were prepared using a hybrid comprising the poly(styrene-block-butadiene-block-styrene)-graft-poly(oxyethylene methacrylate) (SBS-g-POEM) nanostructural copolymer and the ionic liquid (IL) 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCA). The SBS-g-POEM copolymer was synthesized via a mass-producible, cheap, free-radical polymerization process. The specific interaction of SBS-g-POEM with EMIMDCA and the good miscibility of these species were confirmed by Fourier transform infrared spectroscopy (FT–IR) and wide angle X-ray scattering (WAXS) and by using a universal testing machine (UTM). The microphase-separated nanostructure of the membranes and uniform distribution of EMIMDCA were also observed using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The neat SBS membrane exhibited a CO₂ permeability of 372 Barrer (1 Barrer = 10⁻¹⁰ cm³(STP)·cm/(cm²·s·cmHg) and CO₂/N₂ selectivity of 16.4; these values increased to 407 Barrer and 21.6, respectively, for the SBS-g-POEM membrane due to the high CO₂ affinity of the polar POEM side chains. Upon incorporation of EMIMDCA, the CO₂ permeability increased to 514 Barrer without a large sacrifice of the selectivity. In contrast, the blend of neat SBS and EMIMDCA did not show any gas separation ability due to the inhomogeneity and poor mechanical properties, indicating the importance of grafting POEM to the SBS main chains.