Polyimide Ultrafiltration Membranes with High Thermal Stability and Chemical Durability

Asymmetric ultrafiltration membranes based on poly[(4,4'-oxydiphenylene)pyromelliteimide] were produced by wet technique from prepolymer casting solution, followed by solid-phase conversion of the prepolymer membranes into polyimide insoluble form at 200 degrees C. It was demonstrated that by adding benzimidazole to the casting solution and filling of prepolymer membrane pores with inert high-boiling oil prior to thermal treatment allow us to prepare asymmetric porous polyimide membranes. The main characteristics of the membranes obtained (permeability coefficients and molecular weight cut-off) match those typical to ultrafiltration membranes. It was found that the developed asymmetric ultrafiltration polyimide membranes have excellent thermal and chemical resistance. The membranes retain rigidity above Tg (360 degrees C) and are chemically stable at temperatures up to 400 degrees C. The developed membranes are resistant against swelling and dissolving in aggressive and organic media including amide solvents.