Effect of structure on the temperature dependence of gas transport and sorption in a series of polycarbonates

The permeabilities and solubilities of five gases are reported for bisphenol-A polycarbonate (PC), tetramethyl polycarbonate (TMPC), and tetramethyl hexafluoro polycarbonate (TMHFPC) at temperatures up to 200°C. The temperature dependence of permselectivity is discussed in terms of solubility and diffusivity selectivity changes with temperature for CO₂/CH₄ and He/N₂ gas separations. The activation energies for permeation and diffusion and the heats of sorption are also reported for each gas in the three polycarbonates. Analysis of these values provides a better fundamental understanding of the effect of polymer-penetrant interactions and polymer backbone structure on the temperature dependence of the transport and sorption properties of gases in membrane separation processes. Important factors affecting the solubility and diffusivity selectivity losses or gains with increased temperature are also identified through correlation of these data with physical properties of the gases and polymers. These conclusions provide a framework for choosing the most promising membrane materials for particular gas separations at elevated temperatures. © 1994 John Wiley & Sons, Inc.