On the Diffusion of Vapors through Polymers

Abstract

The rate of permeation of a gas through a polymer as a function of temperature may be represented as P = P₀e^−E/RT. All available data on the permeability of gases through polymers show that for a given gas there is a linear relation between log P₀ and E (the energy of activation for permeation). An explanation is offered for this apparent relationship. The effect of plasticization on permeation of water vapor is studied experimentally and it is shown that the lowering of the heat of solution is the predominant effect. From the data the entropy of solution may be calculated and interpreted as showing that water molecules dissolved in the unplasticized polymer exhibit much less freedom than when they are dissolved in plasticized polymer. Other calculations show (in agreement with Barrer) that a large number of degrees of freedom are simultaneously operative in the process of the diffusion of a gas molecule through a polymer.