PIM-1, a glassy, spirobisindane-based ladder polymer is a novel intrinsically microporous membrane material. The pure- and mixed-gas permeation properties of PIM-1 are compared to those of highly permeable, microporous, linear chain, acetylene-based polymers, such as poly(1-trimethylsilyl-1-propyne) (PTMSP). PIM-1 exhibits very high permanent gas permeabilities coupled with moderate selectivities. For example, the oxygen permeability of PIM-1 at 25 degrees C is 1300 x 10(-10) cm(3) (STP) cm/cm(2) s cmHg combined with an oxygen/nitrogen selectivity of 3.8. Those values place PIM-1 above the Robeson trade-off curve for oxygen/nitrogen separation. Like microporous linear chain PTMSP, ladder-type PIM-1 is More permeable to large, condensable organic vapors, such as n-butane, than to small, permanent gases, such as methane. PIM-1 exhibits a mixed-gas n-butane/methane selectivity of up to 25, which is similar to that of PTMSP, the most permeable and selective polymer known for this separation. Because PIM-1 has significantly better solvent resistance than PTMSP, it could find applications as an advanced membrane material for the separation of organic vapor/permanent gas mixtures. (C) 2009 Elsevier B.V. All rights reserved