(168e) Synergy between the Ether and the Sulfonic Group of Sulfonated Block Copolymer Membranes for Direct Methanol Fuel Cell Applications

Maritza Pérez-Pérez, Eduardo Ruiz-Colón and David Suleiman

Chemical Engineering Department

University of Puerto Rico

Mayagüez, PR 00681-9000

The effect of increasing the number of ether groups in proton conducting polymer membranes was studied as a function of block composition. Two homopolymers, six block copolymers and six random polymers were synthesized using atom transfer radical polymerization (ATRP). The homopolymer poly(2-ethoxyethyl methacrylate) (PEEM) (C) and 2-(2-methoxyethoxy) ethyl methacrylate (PMEEM) (D) were used as a bifunctional macroinitiator for the block copolymers. Styrene was used for the block copolymer and the random polymer as the active site for the sulfonation. Three different sulfonation levels were synthesized for each PS (B) composition (i.e. 8%, 18% and 30%). The resulting membranes produced different water absorption, ion exchange capacity (IEC) and methanol permeability values. The thermal stability of the polymers was studied using thermogravimetric analysis (TGA) and the nanostructure of the casted membranes evaluated using small angle x-ray scattering (SAXS). The results reveal that the membranes are stable above 250°C and the nanostructure exhibited a disordered phase-segregated morphology. The results also show that increasing the number of ether groups increases the water absorption and the water content. Proton conductivity values range between 0.01 and 0.06 S/cm. Finally, all the methanol permeability values are lower than Nafion®, suggesting than the addition of ether and ester domains can create unique chemical and morphological membranes with improved selectivity for direct methanol fuel cell (DMFC) applications.