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Solubility (sorption) and transport measurements with water in solvent‐free poly (acrylonitrile)(PAN) (23) have been interpreted in terms of an extension of the “dual‐sorption” model for transport of small molecules in glassy polymers. Satisfactory agreement has been obtained between theory and experimental data. An earlier analysis of similar data for water in PAN containing 0.26 percent (by weight) of a residual solvent (1) has been compared with the present results in order to investigate the effects of residual solvent on the dual‐sorption and transport parameters for the water‐PAN system.

SynopsisSteady-state permeability coefficients have been measured for equimolar mixtures of C02-CzH4, C O Z -C~H~, and CzH4-C3H8, as well as for a mixture of 74.9 mol % C02 and 25.1 mol% C2H4 in polyethylene membranes. The measurements were made at 20,35, and 50°C and a t pressures of up to 28 atm. Each component of the permeating mixtures studied had the effect of increasing the permeability coefficient for the other component. Furthermore, at equal partial pressures and a t the same temperature, the component exhibiting the highest solubility in the polymer had the largest effect in increasing the permeability coefficient of the other component. This behavior is in agreement with the predictions of a free-volume model for the permeation of gas mixtures proposed by Fang, Stern, and Frisch. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the predicted values. The theoretical permeability coefficients can be estimated from the model by using parameters determined with the pure components only.

Solubility coefficients, S, and diffusion coefficients, D, have been determined for ethane and n‐butane in poly(n‐butyl methacrylate) (PnBMA) by the microbalance technique in the temperature range from −14 to 50°C, which encompasses the glass transition of the polymer (22–35°C). S and D for ethane were found to be independent of penetrant pressure and concentration at all temperatures studied No transition to “dual‐mode” sorption behavior, as reported for a number of penetrants in glassy polymers, was observed with ethane, even at the lowest experimental temperature. Plots of log S and log D versus 1‐T, the reciprocal absolute temperature, were linear for the ethane‐PnBMA system and did not exhibit discontinuities in the glass transition region. The above results suggest that the same mechanism of solution and transport of ethane in PnBMA is operative both above and below the glass transition of the polymer under the experimental conditions. This behavior is attributed to the low “excess” free volume of glassy PnBMA, as indicated by the small difference between the coefficients of thermal expansion of this polymer in its rubbery and glassy states. Possible conditions for the appearance of dual‐mode gas sorption are discussed. A similar study with the n‐butane‐PnBMA system showed that the polymer was plasticized by the penetrant below 20°C, due to the higher solubility of n‐butane compared with that of ethane in PnBMA.