Diffusion of Methanol in Polydimethylsiloxane

The permeation and sorption of methanol in polydimethylsiloxane at 10 and 30°C. has been measured and the results analyzed to determine the concentration dependence of the steady‐state diffusion coefficient D which is found to decrease as the total concentration C is increased. An analysis of the isotherms indicates that clustering of the methanol occurs in the polymer, becoming more predominant as the concentration is increased. A polymerization model used to describe the shape of the D versus C curve for water in polydimethylsiloxane has been modified and applied with some success to describe the shape of the isotherm and the D versus C curve for methanol. The linearity of the permeation rate with relative pressure in this and a number of water—polymer systems is briefly commented on.