Diffusion of large penetrant molecules in amorphous polymers

A new version of the free‐volume theory of diffusion is modified to describe self‐diffusion phenomena in polymer + solvent systems for solvents which do not move as single units. The free‐volume equations are used to interpret data which appear to illustrate that some large solvent molecules do indeed move in a segmentwise manner. The dependence of the effective activation energy for diffusion on solvent size is examined, and the importance of energy effects on the diffusion process is considered.