Diffusion of radioactively tagged 1,1-diphenylethane and n-hexadecane through rubbery polymers: Dependence on temperature and dilution with solvent

The diffusion of 1,1-diphenylethane in trace amounts through eight rubbery polymers has been studied by radioactive tagging of this penetrant with ¹⁴C. For several polymers, the dependence on temperature and on dilution (swelling) by untagged diphenylethane was investigated. In the diluted systems, tagged n-hexadecane was also used as a trace penetrant. The temperature and concentration dependences were interpreted rather successfully in terms of the free volume. In comparing different polymers, with a 4000-fold range of diffusion coefficients, the translatory friction coefficient of 1,1-diphenylethane was found to be proportional to that of n-hexadecane to the power 1.06. This is interpreted qualitatively by the free volume concept to indicate a slightly less efficient mobility mechanism for the diphenylethane.