Gas-Transport Properties of Polyimides with Various Side Groups

Abstract

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 ≤ Тg ≤ 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).