Permeability of Dry Gases and Those Dissolved in Water through Hydrophobic High Free-Volume Silicon- or Fluorine-Containing Nonporous Glassy Polymer Membranes

This study systematically investigates the oxygen and carbon dioxide permeability of dry gases and those dissolved in water through hydrophobic high free-volume silicon- or fluorine-containing nonporous glassy polymers including poly(trimethylsilylmethylmethacrylate) (PTMSMMA), poly(1-trimethylsilyl-1-propyne), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride-4,4′-(9-fluorenylidene) dianiline, and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylene-diamine. The dry state gas permeability coefficient was almost higher than that of the wet state because the effect of the boundary layer, which is the water resistant layer, on the membrane surface depends on the gas permeability in the wet state. In addition, the gas permeability difference between the dry and wet states depends on the combination of competitive sorption between water and gas species and plasticization by water. Carbon dioxide/oxygen permselectivity increased with the decrease in gas permeability, except for PTMSMMA. The gas permeability in the wet state of PTMSMMA with low glass transition temperature was approximately equal to that in the dry state because plasticization by water increased in the wet state. Therefore, the mobility of the polymer segment depends on the plasticization by water.