Mahmoud A Abdulhamid and Ingo Pinnau
King Abdullah University of Science and Technology, Saudi Arabia
Posters & Accepted Abstracts: J Chromatogr Sep Tech
Three novel polyimides were synthesized from a 9,10-dimethyl-2,6(7)-diaminotriptycene (T) with a commercially available bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BC) and its halogenated derivatives. The non-halogenated T-BC polyimide derivative was made as a reference material to evaluate the effect of the halogen groups in T-BCCl4 and T-BCBr4 on its gas transport properties. Pure-gas permeability coefficients of He, H2, N2, O2, CH4, and CO2 were measured at 35 ├?┬░C and 2 atm. The BET surface area based on nitrogen adsorption at 77 K of T-BC was 570 m2 g-1 while those of tetrachlorofunctionalized T-BCCl4 and tetrabromo-functionalized polyimide T-BCBr4 were reduced significantly to 340 and 30 m2 g-1, respectively. The decrease in BET surface area in the halogenated polyimides resulted from reduction in their pore volumes relative to that of T-BC due to occupation of free volume space by the halogens. The freshly prepared T-BC membrane had a pure-gas O2 permeability of 66 Barrer and O2/N2 selectivity of five. The permeability decreased significantly by replacing the hydrogen groups by the chloro- or bromo groups in the cycloaliphatic dianhydride building block. For example, the permeability of O2 decreased by 3-fold from 66 in T-BC to 20 Barrer in T-BCBr4, while the permeability of nitrogen was reduced from 13 to 3.4 Barrer. As expected for lower permeability polymers, the O2/N2 selectivity increased concurrently from 5 in T-BC to 6 in T-BCBr4. Long-term testing over 365 days resulted in only ~ 15% loss in gas permeability├ó┬?┬?s and without significant changes in selectivity├ó┬?┬?s, which demonstrated that these polyimides were resistant to physical aging. These combined results suggest that BC-based polyimides are promising candidate membrane materials for gas separation applications.