摘要 |
PURPOSE:To enhance separation property without lowering a permeation speed, in preparing a membrane, by adding a definite amount of a specific aliphatic carboxylic acid compound in a dope consisting of polyimide and a phenolic compound. CONSTITUTION:A polymer used as a membrane comprises aromatic polyimide having 90% or more of a repeating unit represented by formula in its main chain. This polymer is dissolved in a phenolic solvent, especially, halogenated phenol with a b.p. of 300 deg.C or less to prepare a dope to which specific aliphatic carboxylic acid such as undecanoic acid, lauric acid or oleic acid is, in turn, added in an amount of 5-40%wt. of polyimide. A membrane with a thickness of 10-500mum is formed from this dope and immersed in a coagulation bath consisting of an org. liquid freely mixed with the phenolic solvent and water to be coagulated. |