Elucidating the mechanism (s) of gas transport in poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes

Abstract Gas permeabilities in poly[1-(trimethylsilyl)-1-propyne] (PTMSP) are orders of magnitude larger than in other glassy polymers such gas polycarbonate. Based on solubility, permeability and other data, it is concluded that fast diffusion (and not a large solubility) is responsible; and that the polymer has ∼25 vol% of voids which may be linked through chain-to-chain gaps at least ∼3 A wide, suggesting that PTMSP may be“microporous”. Further evidence for the connectivity of microvoids in PTMSP is offered by mixture permeation results. The permeability of a light gas such as He or N 2 is drastically reduced by the co-permeation of a more strongly sorbing and/or more condensable species such as SF 6 . The extent of this light gas rejection is within the scope of mixture permeation under the pore transport model — via competitive adsorption/surface-diffusion and pore blocking — but appears to exceed expectations based on the dual-mode sorption model — which tacitly takes the microvoids to be not connected.

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