Gas-Transport Properties of Polyimides with Various Side Groups

Using one-step high-temperature polycyclocondensation organosoluble homo- and copolyimides containing various side groups, such as CF₃‒, СOOН‒, Cl‒, and fluorene, and their certain combinations, are synthesized, and their effect on O₂, N₂, CO₂, He, and CH₄ permeability coefficients of films is studied. The synthesized polymers with a inherent viscosity of 0.41–0.76 dL/g are characterized by a high heat resistance (230°C ≤ Т_g ≤ 380°C) and form strong films (60 MPa ≤ σ ≤ 140 MPa; 0.9 GPa ≤ E ≤ 1.6 GPa). It is shown that depending on the nature of side groups the polyimides under consideration demonstrate different gas-transport behavior. For example, for one of the polymers the selectivity factor for He/CH₄ separation is 315 (a He permeability coefficient of 9.5 Barrer), while for another polymer the selectivity factor for CO₂/CH₄ separation is 34 (at a CO₂ permeability coefficient of 37.3 Barrer). For crosslinked polyimide films the selectivity factor for He/CH₄ separation attains 125 (at a He permeability coefficient of 19.7 Barrer) and the selectivity factor for CO₂/CH₄ separation is 43 (at a CO₂ permeability coefficient of 7.0 Barrer).