Gas permeability of the racemic form of poly(γ‐benzyl glutamate)

Abstract

AbstractSorption of carbon dioxide gas by a film of the racemic form of poly(γ‐benzyl glutamate) was observed over the temperature range from 10 to 40°C and the permeability coefficient of carbon dioxide gas through the film was measured over the temperature range from 30 to 120°C. Different sorption isotherms were obtained in the ranges above and below the glass‐like transition temperature, respectively. The result indicates that the sorption behavior is influenced by the side chain mobility. The amount of sorption by the racemic form of poly(γ‐benzyl glutamate) does not vary with the intermolecular benzene ring stacking, but is similar to that of the form C of poly(γ‐benzyl‐L‐glutamate) which contains no stacking. The breakdown of the intermolecular benzene ring stacking, which was confirmed by X‐ray diffraction analysis and differential scanning calorimetry, results in an abrupt increase of the permeability and the diffusion coefficients, and conversely the formation of the stacking leads to an abrupt decrease in the permeability and the diffusion coefficients. Below the transition temperature, the permeability coefficient of the racemic form of poly(γ‐benzyl glutamate) is smaller than that of the forms A, B, and C of poly(γ‐benzyl‐L‐glutamate), related to the benzene ring stacking. The diffusion coefficient was estimated from the free volume theory, and the calculated value was compared with the value obtained from the permeability and the solubility coefficients. The fractional free volume was estimated to be about 0,068, when the best fit between the experimental and the calculated diffusion coefficients was obtained by a trial and error method.