Polyimide membranes derived from poly(amic acid) salt precursor polymers. 2. Composite membrane preparation

A novel two-step process for fabrication of composite polyimide hollow fiber membranes using poly(amic acid) tertiary amine salts, PAAS, is described. In the first step, a precursor membrane is formed by depositing a thin PAAS polymer layer from an alcohol-based solution onto a porous hollow fiber substrate. In the second step, the final composite polyimide membrane is obtained upon thermal treatment of the precursor composite PAAS membrane at 150 degreesC. The novel process was demonstrated by preparing a composite polyimide membrane on a polysulfone hollow fiber substrate from the PAAS polymer (6FDA-ODA/Et3N) derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 4,4'-oxydianiline (ODA), and triethylamine. The surface layer and cross section of the precursor composite PAAS membrane and the final polyimide membrane were studied by SEM. The quantitative transformation of PAAS prepolymer into the respective polyimide by heat treatment at 150 degreesC was confirmed by ATR FT-IR analyses. Gas permeation characteristics of composite PAAS and polyimide membranes were measured and are reported.