Relationship between the gas transport properties and the refractive index in high-free-volume fluorine-containing polyimide membranes

Abstract

The refractive index and gas transport properties (i.e., permeability, diffusivity, and solubility) in the 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)-based polyimides were systematically investigated in terms of their polymer fractional free volumes (FFVs). The permeability and diffusion coefficients of the 6FDA-based polyimide membranes to hydrogen, oxygen, nitrogen, methane, and carbon dioxide were correlated with their FFVs, which were estimated with van Krevelen's group contribution method. Linear correlations were also observed between the gas transport properties and the refractive index of these polyimides. We described FFV as a function of the refractive index..