The chief difficulty with any diffusion scenario is finding the diffusion coefficient, D. One approach is to follow a method approved by US and European regulatory bodies which provides a set of standard polymers and estimates D from the MWt of the molecule and the temperature, T (°K), for the specific scenario. The formula is:
C1=0.135, C2=0.003, C3=10454. A in turn depends on T and two polymer specific terms, A* and τ:
When you choose a polymer the A* and τ values are shown and from your given MWt and T, D is calculated
Although this formula is often used in food packaging applications, be aware that this app carries no guarantees that the calculated D values are correct. For example, the linear, branched and cyclic versions of a molecule with the same molecular weight will each have different D values; branched and cyclic molecules have lower D values than linear ones.