Molecular simulation of small molecule diffusion and solution in dense amorphous polysiloxanes and polyimides

Results of extensive molecular modeling investigations on the transport of different small molecules in flexible chain rubbery polysiloxanes and stiff chain glassy polyimides are discussed. Extended equilibration procedures were necessary to obtain reasonable packing models for the polyimides. The transition state Gusev–Suter Monte Carlo method was utilised to prove a reasonable coincidence between simulated and measured diffusivity and solubility values for the model structures. A comparison between the static structure and the dynamic behaviour of the free volume in the simulated flexible chain rubbery polymers and stiff chain glassy polymers reveals qualitative differences which are decisive for experimentally observable differences in the diffusion of small molecules in these materials.