Thermally Rearranged Ortho-Functional Polyimides for Gas Separations

Thermally rearranged ortho-functional polyimides (TR polymers) have shown promising separation characteristics for several common gas separation applications. The mechanism by which these separations occur, however, is largely unknown. This report will analyze one class of TR polymers, derived from 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 3,3'-dihydroxy-4,4'-diamino-biphenyl (6FDA-HAB). A description of chemical synthesis, film preparation, testing procedures will be described. Transport properties in these polymers, as they relate to the solution-diffusion model, will also be analyzed. The changes in permeability, solubility, and diffusivity are reported for H2, N2, O2, CO2, and CH4 as they relate to the degree of TR conversion. It is shown that the dramatic increases in permeability for TR polymers compared to their precursor polyimides is largely related to increases in gas diffusivity. Furthermore, increases in fractional free volume, correlated from a group contribution method, dual-mode sorption parameters, and positron annihilation lifetime spectroscopy, will be reported.