Gas permeability, diffusivity, and free volume of thermally rearranged polymers based on 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)

Nonequilibrium Lattice Fluid Modeling of Gas Solubility in HAB-6FDA Polyimide and Its Thermally Rearranged Analogues

“…As mentioned previously, the lack of solubility in organic solvents indicates a possibly crosslinked structure of TR polymers 6,7,8 . The NELF model does not account for the effects of polymer cross-linking, which tend to reduce the solubility of low molecular weight compounds in polymers 36 .…”

“…Three TR samples were considered, which were obtained by treating the polyimide precursor at different temperatures for a prescribed time 6,7,27 . The extent of thermal rearrangement increases in the following order: TR350-1h < TR400-1h < TR450-30min (cf., Table 2).…”

“…These materials, first reported by Park et al 2 , exhibit transport properties that, in some cases, surpass the upper bound defined by Robeson in 2008 3,4,5 . TR polymers are formed by chemically reacting solvent-soluble polyimides, via thermal treatment in the solid state, to insoluble, perhaps crosslinked polybenzoxazoles (PBOs) 2,6,7,8 . Since PBOs are insoluble in common organic solvents, it is not possible to exploit classic solution-casting procedures to obtain thin membranes.…”

“…The transport properties exhibited by TR polymers are ascribed to a favorable size and distribution of free volume elements 1,6,7,8 . For example, the increase in gas solubility with increasing extent of thermal conversion has been attributed to increases in excess fractional free volume 6 .…”

Polysulfone-ionic liquid based membranes for CO2/N2 separation with tunable porous surface features

“…Using the same set-up with mixed gas feed streams, gas permeability was measured with a constant volume, variable pressure method, by allowing the permeate gas to expand in a constant volume auxiliary cylinder [32]. Overall permeability of gases, P, is calculated from the rate of pressure (p 1 ) increase in a known downstream volume (V) at constant temperature (T) using the Ideal Gas law.…”