(640a) The Influence of Plasticization and Dual-Mode Competetive Effects On CO2 Transport in Thermally Rearranged (TR) Polymers

In this work, results of mixed-gas permeation tests involving CO₂ permeation in TR polymers derived from 3,3'-dihydroxy-4,4'-diamino-biphenyl (HAB) and 2,2'-bis-(3,4-dicarboxyphenyl) Hexafluoropropane Dianhydride (6FDA) are presented.  Polyimide HAB-6FDA films were converted to polybenzoxazole (PBO) to varying degrees by following different thermal treatment protocols.  Permeation tests with these films were conducted using CO₂-containing mixtures at temperatures from -15 to 70°C, and pressures up to 50 atm.  The bulk of the results are for 50% CO₂/CH₄ mixtures.  Preliminary results for CO₂/N₂ mixtures are presented as well, and exhibit trends similar to the CO₂/CH₄ results.  Mixed-gas results are compared against pure-gas measurements.  CO₂/CH₄ mixed-gas selectivity at 35°C was 20-30% higher than the simple ratio of pure-gas permeabilities.  Strong dual-mode competitive effects were responsible for a decrease in CH₄ and N₂ permeability in the presence of CO₂, with very little change to CO₂ permeability in the mixture.  Plasticization is not evident in the pure-gas CO₂ permeation data.  However, in the mixed-gas experiments, CH₄ permeability was found to increase gradually with increasing CO₂ pressure.  The degree of plasticization was found to decrease as the degree of thermal conversion to PBO increased.