Oxygen Separation Properties of Bis(phenyl)fluorene-based Cardo Polymer Membranes

Abstract

Oxygen separation properties of cardo polymers, i.e. polyamide, polycarbonate, polyimide and polysulfone, were investigated. These cardo polymers contain bis(phenyl)fluorene moiety as the cardo unit. Further, a variety of cardo polyimides were prepared from various dianhydrides to study the relationship between chemical structure and the gas transport properties. In the relationship between O2/N2 selectivity and O2 permeability, the most rigid polyimide showed the largest O2 permeability coefficient of 18 Barrers (1 Barrer = 7.5 × 10−18 m3(STP)m m−2 s−1 Pa−1), with large permselectivity, PO2/PN2, of 4.8. On the other hand, the most flexible polyimide showed the largest permselectivity of 9.2. O2 permeability, diffusivity and solubility of the cardo polyimides were well correlated to their fractional free volume (FFV). The rigid polyimide showed a large FFV, and consequently showed large gas permeability, diffusivity and solubility. On the other hand, polyamide, which has hydrogen bond, deviates from the diffusivity-FFV correlation of polyimides. The magnitude of gas permeability was mainly attributed to that of gas diffusivity, and also the magnitude of permselectivity of oxygen over nitrogen was attributed to that of mobility selectivity.