Sorption of carbon dioxide in fluorinated poyimides

Abstract

AbstractSorption isotherms of CO2 for ten fluorinated polyimides measured at 35°C and up to about 25 atm are analyzed according to the dual‐mode sorption model. Sorption properties for these polyimides are compared with those for other glassy Polymers including unfluorinated polyimides. The glassy polymers with higher glass transition temperatures Tg tend to show greater CO2 sorption. Introduction of a C (CF3)2 linkage into the repeat unit of the main chain increases the sorption by 20–80%. For glassy polymers, including the fluorinated and unfluorinated polyimides, the Langmuir affinity constant b and Henry's law solubility constant kD are correlated with the content of functional (carbonyl or sulfonyl) groups [FG], and composite parameter reflecting the magnitude of both [FG] and free‐space fraction VF, respectively, with some exceptions. The Langmuir capacity constant C′H is correlated with Tg, but there are two correlation lines; one for unfluorinated polyimides and a different one for other glassy polymers including fluorinated polyimides. The slope of the former group is smaller probably because of smaller differences in thermal probably because of smaller differences in thermal expansion coefficients in rubbery and glassy states. Most fluorinated polyimides show greater solubility of CO2 than unfluorinated polyimides and other glassy polymers, because of their larger C′H and kD. © 1993 John Wiley & Sons, Inc.