Crystalline elastomeric block copolymer/ionic liquid membranes with enhanced mechanical strength and gas separation properties

We report a high-performance, three-dimensional (3D) interconnected crystalline elastomeric membrane with enhanced mechanical strength and CO2 separation properties. The membranes were prepared using an amphiphilic crystalline block copolymer, poly(ethylene glycol) monomethyl ether-block-poly(acrylonitrile) (mPEG-b-PAN), synthesized via one-pot free-radical polymerization under environmental-friendly, mild conditions (in water at 50 °C). The strong interaction of the mPEG-b-PAN block copolymer with ionic liquid (IL) resulted in a microphase-separated, interconnected elastomeric structure in which the PAN crystallites acted as crosslinking junctions. Exceptionally high IL loadings of up to 300 wt % were efficiently confined in the crystalline network while maintaining outstanding mechanical properties. The mPEG-b-PAN/IL membrane with 250 wt % IL loading achieved the highest separation performance with a CO2 permeability of 456.4 barrer, CO2/N2 selectivity of 61.4, CO2/CH4 of 18.1 and CO2/H2 of 12.3. The CO2/N2 separation performance exceeds the Robeson upper bound (2008) and approached the upper bound (2019). Both the separation properties and mechanical strength of the mPEG-b-PAN/IL elastomeric membranes outperformed those of homopolymer PAN (H-PAN) and other membranes with ILs. Interestingly, the mPEG-b-PAN/IL membranes were effortlessly prepared regardless of the surface properties of the substrate and IL loading, in contrast to H-PAN/IL, indicating that the amphiphilic property of the polymer plays a pivotal role in turning the interface.