Preparation of well-defined hyper-branched polymers and the CO2 separation performance
2016
Taniguchi, Ikuo | Kinugasa, Kae | Egashira, Satsuki | Higa, Mitsuru
Polyoxyethylene (POE) exhibits great potential for selective CO2 permeation and is tethered onto poly(methyl methacrylate) (PMMA) or poly(styrene-r-acrylonitrile) (PSt-r-PAN) by atom transfer radical polymerization (ATRP) of POE methacrylate (POEM) to endow preferential CO2 permeability. The polymer backbones are first prepared from corresponding monomers and 4-(chloromethyl)styrene (Cl-St) with various mixture ratios by free radical polymerization. The POE grafting is then carried out by chain propagation of POEM from the Cl-St moiety by ATRP. The introduction of Cl-St to a polymer backbone is readily controlled when the monomer ratio was less than 2mol%, and thus the average distance of POE graft chains can be tuned along the polymer backbone. ATRP also defines the length of the POE graft chains. CO2 separation properties over N2 of the well-defined hyper-branched polymers are investigated by comparing permeability of CO2 and N2 pure gases. The gas permeabilities increase with increase of POE content, and the resulting CO2/N2 selectivity is also enhanced in comparison to the pristine polymers and 35 and 40 for PMMA-based and PSt-r-PAN-based hyper-branched copolymers, respectively. Higher POE content indeed gives higher diffusion coefficient for both of CO2 and N2, but the CO2 and N2 diffusivities are almost the same. Thus the gas permeation progresses under solubility control. The CO2 permeability is 135 Barrer with the CO2/N2 selectivity 42, when the POE content is 76wt% of PSt-r-PAN-based hyper-branched copolymer.
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