(250a) Invited Talk: Gas Sorption and Permeation in Thin Films of High Free Volume Polymers

Separation of gases by polymer membranes has become a well established industrial practice.  To achieve high productivity, or high fluxes of gas permeation, the active portion of these membranes must be very thin, of the order of 100 nanometers.  In most cases, the preferred polymers are in the glassy state where properties depend on prior history.  A great deal of research over the past decade has shown that thin films (< 1,000 nm) show much more rapid physical aging than observed in bulk, and generally thin films can have different permeation properties than thick films (10’s of microns).  There has been much interest in identifying new polymers for membrane applications that provide a more advantageous combination of permeability and selectivity than those currently used commercially.  One direction of this research has been to develop high free volume polymers that have exceptionally high gas permeabilities and very high glass transitions.  We have examined the gas permeation behavior of a number of these high free volume polymers in both thick and thin films forms and have compared their physical aging rates. The materials examined include polyimides, poly[1-(trimethylsilyl)-1-propyne], PTMSP; PIM-1 (PIM = “polymers of intrinsic microporosity); amorphous Teflons; and a polybenzoxazole made by thermal rearrangement (TR).  The thin films showed much lower permeabilities than thick films especially for PTMSP and PIM-1. For a wide range of polymers, including those mentioned above, the physical aging rate was found to increase strongly with the glass transition temperature of the polymer  relative to the temperature of observation.