Effects of some structural features of poly(dimethylsiloxane) on its unusually high gas permeabilities

Molecular dynamics simulations were carried out on poly(dimethylsiloxane) to elucidate the high permeabilities that have made it an extremely important polymer in gas separations and related processes involving diffusion. The results suggest that one important structural feature in this regard is the pronounced alternation in skeletal bond angles, which makes the low-energy conformation of the chain a closed polygon; this could increase free volumes by interfering with the efficient packing of the chains in the bulk state. Also important is the relatively large value of the Si-O bond length, which could increase chain flexibility and mobility by reducing intramolecular steric interactions.