A strategy to enhance CO2 permeability of well-defined hyper-branched polymers with dense polyoxyethylene comb graft

Hyper-branched polymers comprised of dense polyoxyethylene (POE) comb graft and poly(methyl methacrylate) (PMMA) backbone are prepared with a well-defined chemical structure and the gas transportation properties are investigated. The CO2 permeation is strongly dependent on the POE weight fraction. To enhance the CO2 permeability, a thin film layer of the hyper-branched polymers is formed on a polydimethylsiloxane (PDMS) support with thickness less than 60 mu m, where poly(vinyl alcohol) (PVA) is blended to improve the membrane formability. The CO2 permeability is increased by decreasing the thickness of the CO2-selective layer. The permeability coefficient of the resulting thin film composite (TFC) membranes exceeds 1000 barrer with 40.5 wt % of POE methacrylate (POEM) fraction, when the thickness of the selective layer is smaller than 25 mu m. It reaches a maximum of 1470 barrer for 15 mu m selective layer thickness with a CO2/N-2 selectivity of 24.5. The permeability coefficient of the selective layer alone is 490 barrer, with CO2 selectivity of > 30. Formation of a POE-rich domain upon microphase separation is confirmed by DSC and SAXS, and this is deemed crucial to enhance CO2 permeability, due to improved CO2 solubility in the selective layer. A dense POE comb architecture on the graft chain results in higher CO2 permeability than that on the polymer backbone.