CO₂-philic PBEM-g-POEM comb copolymer membranes: Synthesis, characterization and CO₂/N₂ separation

We report a high performance, CO₂-philic, alcohol-soluble, comb copolymer consisting of poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl] ethyl methacrylate) (PBEM) and poly(oxyethylene methacryalate) (POEM) for use in composite membranes for CO₂/N₂ separation. The PBEM-g-POEM comb copolymer was synthesized via facile free radical polymerization, and the structure was confirmed by using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). The bimodal nanostructural morphology and amorphous structure of the comb copolymers were observed using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and atomic force microscopy (AFM). When the PBEM content in the copolymer was below 20wt%, the CO₂/N₂ selectivity was <4 and the CO₂ permeance increased linearly with pressure due to the liquid-like rubbery nature of the POEM chains. When the PBEM content was above 20wt%, the CO₂ permeance did not change much with pressure, indicating resistance to plasticization. The best performance was obtained from a membrane with a PBEM:POEM ratio of 20:80wt%, in which the CO₂ permeance and CO₂/N₂ selectivity were 29.3GPU (1GPU=10^-6cm³(STP)/(scm²cmHg)) and 73.3, respectively. This performance was much better than that of the composite membrane prepared using commercially available PEBAX (CO₂ permeance: 22.9 GPU, CO₂/N₂ selectivity: 21.8).