Synthesis and characterization of sulfonated homo- and co-polyimides based on 2,4 and 2,5-diaminobenzenesulfonic acid for proton exchange membranes

• Published in: Polymers for advanced technologies Vol. 19; no. 12; pp. 1792 - 1802
• Main Authors: Deligöz, Hüseyin, Vatansever, Sibel, Öksüzömer, Faruk, Koç, S. Naci, Özgümüş, Saadet, Gürkaynak, M. Ali
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-12-2008
• Subjects: conductivity; ionomers; membranes; PEM fuel cell; sulfonated polyimides
• ISSN: 1042-7147; 1099-1581
• DOI: 10.1002/pat.1196

A series of sulfonated homo‐ and random co‐polyimides (co‐SPI) based on 2,4‐diaminobenzenesulfonic acid (2,4‐DABS) and 2,5‐diaminobenzenesulfonic acid (2,5‐DABS) has been synthesized via conventional two‐step polyimidization method. 2,4‐DABS and 2,5‐DABS were used as sulfonated diamine compounds, 4,4′‐oxydianiline (ODA) and 4,4′‐diaminodiphenyl sulfone (DDS) were used as non‐sulfonated diamine compounds. Mixtures of sulfonated and non‐sulfonated diamine compounds were reacted with benzophenonetetracarboxylic dianhydride (BTDA) to obtain co‐SPI membranes. Molar ratios of sulfonated to non‐sulfonated diamine were systematically varied to produce copolymers of controlled compositions. The co‐SPIs were evaluated for thermal oxidative stability, ion exchange capacity (IEC), water uptake, proton conductivity, solubility, and hydrolytic stability. Proton conductivity and hydrolytic stability of the co‐SPIs were compared with the fully aromatic polyimide, homo‐SPIs (BTDA/2,4‐DABS and BTDA/2,5‐DABS). Regarding thermogravimetric analysis (TGA) analysis, it is concluded that desulfonation temperature in the range of 200–350°C suggests high stability of sulfonic acid groups. co‐SPIs with 40 mol% of 2,4‐DABS showed similar or higher proton conductivity than Nafion® 117 in water. Proton conductivity values of the co‐SPIs were mainly a function of IEC and water uptake. Consequently, the optimum concentration of 2,4‐DABS was found to be in the range of 30–40 mol% from the viewpoint of proton conductivity, IEC, and hydrolytic stability. Copyright © 2008 John Wiley & Sons, Ltd.