Gas Transport Properties of Asymmetric Block Copolyimide Membranes

We have synthesized fluorinated block copolyimides with different block chain lengths by chemical imidization in a two-pot procedure and prepared the asymmetric coployimide membranes using the dry-wet phase inversion process. The gas transport properties of the asymmetric membranes were measured using a high vacuum apparatus equipped with a Baratron absolute pressure gauge at 76 cmHg and 35 degrees C. We demonstrated that the skin layer thicknesses and the gas transport properties of the asymmetric membranes depended on the copolyimide structures. The phase separation in the block copolyimide solution instantaneously occurred so that the skin layer of the asymmetric block copolyimide membrane became thinner than that of the asymmetric random copolyimide membrane and the gas permeance of the asymmetric block copolyimide membrane had a high value. The apparent skin layer thickness of the asymmetric block coployimide membrane was 230 nm. The asymmetric copolyimide membrane indicated an O-2 permeance of 2.7 x 10(-4) [cm(3) (STP) /(cm(2) sec cmHg)] (270 [GPU]) and an O-2/N-2 selectivity of 4.3.