GAS SEPARATION PROPERTIES OF SPIROBIINDANE POLYCARBONATE

The permeability and solubility of various gases in spirobiindane polycarbonate (SBIPC) are compared to the properties of bisphenol-A polycarbonate (PC). SBIPC has high fractional free volume (FFV) and severe steric hindrance to torsional motion resulting from the presence of the spirobiindane ring in the chain backbone. These factors combine to produce oxygen permeabilities roughly four times higher in SBIPC than in PC, with slightly higher O2/N2 permselectivities. Although CO2 and He permeabilities are also roughly four times higher than in PC, markedly lower CO2/CH4 and He/CH4 permselectivities are observed for the SBIPC compared to PC. The causes of these trends are interpreted in terms of the component solubility and diffusivity contributions to overall selectivity. Also, the results for SBIPC are compared to earlier data for other polycarbonates with complex connector groups replacing the isopropylidene unit in standard polycarbonate.