Synthesis and characterization of porous PMDA-ODA polyimide asymmetric membranes with low dielectric constant

Abstract

A solvent resistant porous PMDA-ODA polyimide asymmetric membrane have been fabricated via thermal imidization of poly(amic acid prepared by immersion precipitation method. We investigate on the liquid-liquid demixing process using different types of nonvolatile solvents such as N-Methyl2-pyrrolidone(NMP), γ-butyrolactone(GBL). The effect of coagulation media for the membrane morphology change is discussed. The membrane structure was variable by changing the ratio of nonvolatile solvents(NMP,GBL). It is important that membrane structure can be changed from macroporous structures to sponge like structure based on the ratio of NMP/GBL. Using the toluene, we obtain uniform poresize distribution in the membrane structure. In case of water, macroporous membrane structure was obtained. These results might be related to different solubility parameters of NMP/GBL for water, toluene. The dielectric properties of asymmetric membranes were measured from 1 kHz to 1MHz by impedance analyzer.