Highly Sulphonated Multiblock-co-polymers for Direct Methanol Fuel Cells

Multiblock-co-polymers with different ion exchange capacities were synthesised by nucleophilic aromatic step-growth polycondensation of hydrophilic and hydrophobic oligomers. The main focus of this work was to investigate the dependence of oligomer reactivity on molecular weight and how the reaction conditions need to be changed to obtain high-molecular multiblock-co-polymers, consisting of long block segments. Multiblock-co-polymers composed of short oligomers could be synthesised under mild reaction conditions. The coupling of longer oligomers required more basic reaction conditions, because the reactive functional end-groups were shielded by the long oligomeric main chain. The membranes were investigated further in terms of their properties relevant for use as polymer electrolyte membrane in direct methanol fuel cells (DMFCs). The mechanical stability of the acidic polymers was improved through ionical crosslinking with basic polybenzimidazole. A series of membranes was tested in a self- and in an air-breathing DMFC.