Permeability of polyglutamic acid ester membranes to benzene vapor

Abstract

AbstractPermeability of poly(γ‐methyl L‐glutamate) (PMLG), poly(γ‐hexahydrobenzyl L‐glutamate)‐(PHBLG), and poly(γ‐n‐amyl L‐glutamate) (PALG) membrane to benzene vapor was studied. Permeability coefficients of all the membranes were large, of the order of 10−9–10−6 cm3(STP) cm/cm2 sec cm Hg, and increased markedly with increasing relative vapor pressure and temperature. The large permeability was due to the large diffusion coefficient. The sorption behavior of the PALG–benzene system was interpreted in terms of the theory of the mixing of solvent with side chains. The Arrhenius plots of diffusion coefficients for PMLG and PHBLG showed a break at about 29 and 40°C, respectively, where the volume‐expansion curves of each polymer also showed a break, which is thought to be related to the side‐chain motion. The diffusivity data for PALG were examined in terms of Fujita's free‐volume theory, and it was found that the value of the average free‐volume fraction in the pure polymer for PALG was much larger than that for vinyl polymers. This means that the side‐chain motion of PALG is easy and is the reason that the diffusion coefficients for PALG are large. These results indicate that the diffusion of benzene in these polypeptides takes place in the side‐chain regions between helices.