Gas Transport Coefficients of Phthalide-Containing High-Tg Glassy Polymers Determined by Gas-Flux and NMR Measurements

The synthesis of three aromatic polymers containing phthalide cardo groups having high inherent viscosities is described. Polyimides PIC-6F and PIC-TB were prepared from a cardo diamine and two different dianhydrides, and poly(phthalidylidenearylene) (PPDAr) was prepared by a precipitative Friedel-Crafts homopolycondensation of 3-(4-biphenylyl)-3-chlorophthalide. All polymers presented high glass transition temperatures varying between 600 and 690 K. Dense membranes prepared by casting from N,N-dimethylacetamide solutions exhibited good mechanical properties and decomposition temperatures over 770 K under a N-2 atmosphere. Results of gas transport measurements of O-2, N-2, and CO2 were comparatively analyzed based on the chemical structure of the polymers. Additionally, the solubility, diffusion, and permeability coefficients of [C-13]O-2 in these membranes were determined by C-13 NMR spectroscopy and pulsed-field gradient NMR measurements, and the results were in good agreement with those determined with pressure-driven measurements. It was found that membranes of PPDAr exhibited the highest permeability and CO2/N-2 and CO2/O-2 permselectivities.