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Carbonized hollow fiber membranes were prepared by pyrolyzing an asymmetric hollow fiber membrane of a polyimide from 3,3‘,4,4‘-biphenyltetracarboxylic dianhydride and aromatic diamines at temperatures of 500−700 °C under a nitrogen stream. The precursor membrane was treated in air at 400 °C for 0.5 h before the pyrolysis. This pretreatment was effective for improvement of gas permeance of the carbonized membranes. The carbonized membranes had an asymmetric structure with a skin layer of around 200 nm in thickness. They had the characteristics of larger permeance and lower permselectivity for inorganic gas pairs such as O2/N2, but this was rather preferable to the separation of olefin/paraffin. The membranes pyrolyzed at 600−630 °C displayed good stability and excellent performances of propylene/propane and 1,3-butadiene/n-butane separation based on the molecular sieving.

Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual‐mode sorption and transport type, (3) dual‐mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual‐mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and dimethyl‐3,7‐diaminodibenzothiophene‐5, 5‐dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′‐oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF3)2 groups. © 1992 John Wiley & Sons, Inc.

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