AbstractThe diffusion coefficient of 1,1,2‐trichlorotrifluoroethane (TTE) in a liquid polybutene was determined at 25°C. as a function of concentration over the range 1.0–19.5 g. TTE/100 cc. The diffusion coefficient increase with increasing TTE concentration, rising continuously from 3 × 10−8cm.2/sec. at the lowest concentration to 15 × 10−8cm.2/sec. at the highest. The magnitudes of the diffusion coefficients indicate that the diffusion mechanism for small molecules in polymeric media must afford vastly greater opportunities for diffusion than the Stokes‐Einstein relation allows. Similarly, self‐diffusion coefficients for the liquid polymer are much lower than the observed mutual diffusion coefficients. An explanation for this behavio