Physical and mechanical properties of sulfonated aromatic copolyimide membranes

Abstract

Physical and mechanical properties of four series of chemically and thermally stable sulfonated copolyimides as ion-conducting ionomers for application in fuel cell membrane, depending on chemical structure of diamine monomers were studied. The physical and mechanical properties of solid polymer membranes including thermal stability, mechanical strength, water uptake, stability in water, crystallinity and morphology were evaluated. All the polymers were thermally stable. The XRD analysis and SEM micrograph revealed that the polymers were almost amorphous and hydrophobic-hydrophilic phase separation in polyimide did not occur. Use of flexible monomers such as 4,4'-oxydianiline (ODA) and 4,4'-(4-aminophenoxy) diphenylsulfone (APDS) in the hydrophobic sequences increased the plastic behavior compared to rigid polymers prepared from 4,4'-(5-amino-1-naphthoxy) diphenylsulfone (ANDS) and m-phenylenediamine (m-PDA). It was concluded that the properties of polymeric films were strictly dependent on chemical composition of monomers and molecular weight of copolymers.