Sorption and permeation characteristics of CO2 and CH4 in phenolphthalein-based polysulfone (PSF-PPHA) were investigated. The incorporation of the bulky phthalide ring at the bridge carbon atom of bisphenol A results in an increase in T-g by 100 degrees C compared to that of bisphenol-A-based polysulfone (PSF). The increase in T-g leads to enhanced sorption characteristics for CO2 and CH4 in the Langmuir mode. The mobility of CO2 in the Langmuir mode has also been found to be higher than that in the case of PSF. Although the intersegmental chain spacing of PSF-PPHA is practically the same as that of PSF, the former polymer exhibits higher permeability for CO2 without a significant loss in selectivity with respect to CH4. The permeation study using a CO2:CH4 (55:45 mole ratio) mixture i indicates that the selectivity of PSF-PPHA is less susceptible to plasticization, at least in the pressure range 3-40 atm at 35.0 degrees C.