Sorption of Oxygen by Glassy Poly(Ethyl Methacrylate) at Low Temperatures

The solubility of molecular oxygen in glassy poly(ethyl methacrylate) at 160-308 K and a gas pres- sure from 50 kPa to 1.7 MPa is studied. The kinetics of desorption of molecules from films in vacuum at 175 K is investigated at various initial gas concentrations in the glass. It is shown that the dependences of con- centration of the dissolved oxygen on temperature and pressure may be described if the intermolecular cavi- ties in the glass are regarded as sorption sites and if the presence of distributions over the energies of insertion of the molecules into these sites are assumed. The same values of sorption-site concentrations and insertion- energy dispersions make it possible to describe both the solubility of the gas and the dependence of the desorption kinetics of oxygen on its initial concentration in the glass. The concentration of sites does not change with temperature throughout the studied temperature range and amounts to m -3 . The function of the distribution over energies is likewise independent of temperature and the concentration of oxygen in the glass up to m -3 (at 160 K). The dispersion of energies is kJ/mol. The tempera- ture independence of the concentration of sites is explained by the fact that the sizes of cavities in the glass change very weakly at temperatures below the glass-transition temperature.