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 65wt% of PIL reached 17.9Barrer at 35°C, which was approximately ten times higher than that of the pristine PVC membrane (1.7Barrer). Upon utilizing a PVC-g-PIL/IL composite with 15wt% IL, the CO2 permeability increased to 137.6Barrer by approximately 7.7-fold with a moderate decrease of selectivity.
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In this work, PVC-g-PIL graft copolymers have been prepared via the ATRP method for potential applications as CO 2 separation membranes. A PVC backbone was used as a macroinitiator for the synthesis of PVC-g-PIL graft copolymers. Successful synthesis and grafting degree of the graft copolymers were confirmed by 1 H NMR and FT-IR spectroscopy. The XRD analysis showed that the randomness of the amorphous phase in graft copolymers was increased by grafting IL side chains, resulting in a perturbation of the long-range spacing between the chains. The presence of two distinct T g s in the DSC curves confirms that PVC-g-PIL graft copolymers are microphase-separated into PVC backbones and PIL side chains. The TEM and SAXS results reveal molecular self-assembled structures with bicontinuous morphologies that provide a good passage for gas molecules in the membranes. As the grafting degree increases, the domain spacing of the graft copolymer increased from 26.4 to 39.8 nm due to a stronger segregation of each domain. The microphase-separated structure gave the PVC-g-PIL graft copolymer membranes lower strength and greater elongation than PVC, as characterized by UTM measurements. When the grafting degree of PIL was 65 wt%, the CO 2 permeability and CO 2 /N 2 selectivity reached 17.9 and 24.7 Barrer, respectively. Further improvement of gas permeation properties was achieved via the introduction of small ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The CO 2 permeability was further increased to 137.6 Barrer by approximately 7.7-fold with a decrease of selectivity to 20.2 upon the introduction of 15 wt% IL. S.W. Kang acknowledges the support of a 2013 Research Grant from Sangmyung University.
This work was supported by the National Research Foundation (NRF) Grant funded by the Korean government (MEST) through the Korea CCS R&D Center, the Basic Science Research Program ( 2009–0072025 ) and the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) Grant funded by the Korea government Ministry of Knowledge Economy ( 20122010100040 ).
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry
- Filtration and Separation