Molecular dynamics simulation of gas transport in amorphous polypropylene

Molecular dynamics simulations are performed on polypropylene-penetrant systems with the penetrant being molecular hydrogen, molecular oxygen, and methane. Well equilibrated initial configurations of the amorphous polypropylene are generated by the method of Theodorou and Suter. At the qualitative level, a hopping motion is found to be the underlying mechanism for penetrant diffusion. Coefficients for the diffusion of the penetrant molecules in polypropylene are obtained from their mean-square displacements. The agreement with experimental results, where available, is satisfactory. A relation between the penetrant’s diffusion coefficient and its size frequently observed in experiments is confirmed by the present results.