| Abstract: | The permeability of isotactic poly(phenyl silsesquioxane) (PPSQ) to O2 and N2 at 25.0°C and to CO2 and CH4 at 35.0°C was measured at low pressures by the “time-lag” method. PPSQ is a glassy silicone polymer with an 8-atom ring structure of alternating Si and O atoms. The CO2/CH4 selectivity of PPSQ is markedly higher than that of other silicone polymers, whereas its O2/N2 selectivity appears to be only slightly higher. PPSQ is not as effective a “molecular sieve” as would be expected from its ring structure, possibly because its relatively large mean interchain distance suggests that this polymer has a large mean free volume. |
