Gas permeation properties of thianthrene-5,5,10,10-tetraoxide-containing polyimides

A series of thianthrene-5,5,10,10-tetraoxide-containing polyimides with great chain stiffness were prepared and their gas permeation properties were investigated. TADATO/DSDA(1/1)–DDBT copolyimide, which was prepared from thianthrene-2,3,7,8-tetracarboxylic dianhydride-5,5,10,10-tetraoxide (TADATO), 3,3′,4,4′-diphenylsulfonyltetracarboxylic dianhydride (DSDA) and 3,7-diamino-2,8(6)-dimethyldibenzothiophene sulfone (DDBT), displayed much higher CO2 permeability coefficient (PCO2) than both DSDA–DDBT and TADATO–DDBT homopolyimides, but their ideal selectivity (PCO2/PN2) were similar. The higher CO2 permeability coefficient of TADATO/DSDA(1/1)–DDBT was attributed to the higher diffusion coefficient as well as a little higher solubility coefficient. The separation performance of TADATO/DSDA(1/1)–DDBT toward CO2/N2 fell above the “upper bound” line, indicating the highest separation performance among the glassy polymer membranes developed so far. Furthermore, this polyimide showed a significantly higher selectivity of CO2 over N2 for mixed gas permeation than for single gas permeation (single gas: PCO2/PN2=35, mixed gases: PCO2/PN2=49, at 35°C and 2 atm). The “dual-mode” model was used to describe gas sorption and transport behaviors in the membrane.