LONG-TERM PERMEATION PROPERTIES OF POLY(1-TRIMETHYLSILYL-1-PROPYNE) MEMBRANES IN HYDROCARBON-VAPOR ENVIRONMENT

Poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free-volume glassy di substituted polyacetylene, has the highest gas permeabilities of all k nown polymers. The high gas permeabilities in PTMSP result from its ve ry high excess free volume and connectivity of free volume elements. P ermeability coefficients of permanent gases in PTMSP decrease dramatic ally over time due to loss of excess free volume. The effects of aging on gas permeability and selectivity of PTMSP membranes continuously e xposed to a 2 mol % n-butane/98 mol % hydrogen mixture over a period o f 47 days are reported. The permeation properties of PTMSP membranes a re quite stable when the polymer is continuously exposed to a gas mixt ure containing a highly sorbing organic vapor such as n-butane. The n- butane/hydrogen selectivity was essentially constant for the 47-day te st period at a value of 29, or 88% of the initial value of the as-cast film of 33. Condensable gases such as n-butane may serve as a ''fille r'' in the nonequilibrium free volume of the polymer, thereby preservi ng the high level of excess free volume. (C) 1997 John Wiley & Sons, I nc.