(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.