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

Gleason, K. L., The University of Texas at Austin
Smith, Z. P., The University of Texas at Austin
Liu, Q., The University of Texas at Austin
Paul, D. R., The University of Texas at Austin
Freeman, B. D., University of Texas at Austin

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.