Synthesis, structure and gas permeation of polymerized ionic liquid graft copolymer membranes

Amphiphilic graft copolymers consisting of poly(vinyl chloride) (PVC) main chains and polymerized ionic liquid (PIL) side chains were synthesized via atom transfer radical polymerization (ATRP). Successful synthesis of the graft copolymers was confirmed using 1H nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) analysis. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) analysis revealed well-defined microphase-separated structures in the hydrophobic PVC and the hydrophilic PIL domains. Thus, the PVC-g-PIL graft copolymer membranes maintained good mechanical properties (i.e. a lower strength and greater elongation than PVC) without losing separation properties, as confirmed by universal tensile machine (UTM) and mixture gas permeation tests of CO2/N2 (50/50) at 35 °C. As the content of PIL increased, the CO2 permeability increased with a slight decrease of selectivity. The CO2 permeability of PVC-g-PIL membrane with 65 wt% of PIL reached 17.9 Barrer at 35 °C, which was approximately ten times higher than that of the pristine PVC membrane (1.7 Barrer). Upon utilizing a PVC-g-PIL/IL composite with 15 wt% IL, the CO2 permeability increased to 137.6 Barrer by approximately 7.7-fold with a moderate decrease of selectivity.