The diffusion of small molecules through amorphous polymers proceeds by the thermally activated jumps whose rate changes from one region to another due to polymer heterogeneity. Little is known at present about the origin of diffusion heterogeneity. The oxidation of triplet nitrene and quenching of phenanthrene phosphorescence have been used to study the movement of molecular oxygen on a nanometer length scale in glassy poly(ethyl methacrylate) and poly(n-butyl methacrylate) far below the glass transition temperature. It has been found that, as temperature increases, the jump rates in all regions increase by the same factor. This finding points to the equality of the activation energies of oxygen jumps in different regions of the polymers. We conclude that the correlated elastic displacements of polymer chains inside regions about several nanometers in size provide molecules jumps. Due to the large size of these regions, the activation energy of jump does not depend on local polymer structure. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019