10.34 - Alternative Hydrocarbon Membranes by Step Growth

Recent research on the hydrocarbon aromatic ionomer membranes by step growth polymerization are reviewed in this chapter. Several kinds of aromatic polymers such as sulfonated poly(arylene ether sulfone)s, poly(arylene ether ketone)s, polyimides, poly(p-phenylene)s, and poly(benzimidazole)s are discussed from an historical viewpoint up to the most recent progress. The discussion includes synthetic methods and chemical, physical, and electrochemical properties for fuel cell applications. In particular, the authors focus on how to balance the conflicting properties: proton conductivity under high-temperature and low-humidity conditions and chemical and physical stability. The effective and promising approaches are membranes with very high ion exchange capacity, sequenced copolymer structure (hydrophilic/hydrophobic block copolymers), and highly dense sulfonic acid groups. Fuel cell performance with some of the membranes is also discussed. The chapter concludes with future prospects for the development of advanced membrane materials.