Abstract
A poly(arylene ether sulfone) known as KM180 is investigated as a suitable material for fuel cell membranes when sulfonated. The literature relating to this class of materials, sulfonation and fuel cell applications is reviewed and sulfonation and stabilisation of the polymer selected as areas of interest. The literature relating to the chain extension and crosslinking of polymers to add stability has also been reviewed. Sulfonic acids and sulphur trioxide complexes are used to sulfonate KM180 and chlorosulfonic acid selected as the most suitable. This sulfonation is then optimised to give a repeatable result. End group reactions with acid chlorides, pyromellitic dianhydride and Cymel 350 (a trifunctional crosslinking agent) are investigated in order to strengthen the polymer. It is found that catalysis is necessary. Pyromellitic dianhydride and Cymel 350 are selected for further study. Sulfination, activation by carbonyl diimidazole and interaction with butyltin hydroxide oxide are all attempted to strengthen the polymer through interactions of sulfonic acid sidechains. The interaction with butyltin hydroxide oxide is not seen. Membranes are prepared from KM180 sulfonated using chlorosulfonic acid and modified with pyromellitic dianhydride, Cymel 350, sulfinated KM180 and carbonyl diimidazole. These are compared to membranes prepared from high molecular weight KM polymer and KM180 sulfonated using chlorosulfonic acid and sulfuric acid in terms of stability and proton conductivity. The aggregation of sulfonic acid groups is considered to be the most important factor for proton conductivity and the molecular weight was considered most important for stability. The conflict of these is discussed. Suggestions are made for further work.