Mean permeability coefficients for CO 2 , O 2 , N 2 , and CH 4 in seven types of 6FDA polyimides with branched or extended diamine moieties were determined at 35.0°C (95.0°F) and at pressures up to 10.5 atm (155 psia). In addition, solubility coefficients for CO 2 , O 2 , N 2 , and CH 4 in six of these polyimides were determined at 35.0°C and at 6.8 atm (100 psia). Mean diffusion coefficients for the six gas/polyimide systems were calculated from the permeability and solubility data. The relationships between the chemical structure of the polyimides, some of their physical properties (glass transition temperature, mean interchain spacing, specific free volume), and their gas permeability, diffusivity, and solubility behavior are discussed. The 6FDA polyimides studied here exhibit a considerably lower selectivity for the CO 2 /CH 4 and O 2 /N 2 gas pairs than 6FDA polyimides with short and stiff aromatic diamines with comparable CO 2 and O 2 permeabilities.
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Stern et al. (1993) studied this question.
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