Gas transport in polymer membrane at temperatures above and below glass transition point

The processes of gas sorption and permeation in a polymer membrane at temperatures above and below the glass‐transition point were examined using poly‐4‐methylpentene‐1 (glass‐transition temperature reported to be 40°C) as a membrane material. The permeabilities to O 2 and N 2 were independent of applied gas pressure at every temperature; the mean permeability coefficient to CO 2 increased with increasing gas pressure. The logarithm of the mean permeability coefficient to CO 2 increased linearly with gas pressure due to the plasticization effect induced by sorbed CO 2 . From the sorption isotherms for CO 2 at 20 and 30°C it was judged that the glass transition was brought about by sorbed CO 2 at temperatures below the glass‐transition point of the pure polymer. © 1994 John Wiley & Sons, Inc.