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Polysulfone ionomers functionalized with benzoyl(difluoromethylenephosphonic acid) side chains for proton-conducting fuel-cell membranes



Polysulfones carrying benzoyl(difluoromethylenephosphonic acid) side chains were prepared and investigated for use as proton-conducting fuel-cell membranes. In the first step, polysulfones were lithiated and reacted with methyl iodobenzoates to prepare p- and o-iodobenzoyl polysulfones. Next, the phosphonated polysulfones were prepared via CuBr-mediated cross-coupling reactions between the iodinated polymer and [(diethoxyphosphinyl)difluoromethyl]zinc bromide. Finally, dealkylation with bromotrimethylsilane afforded highly acidic [BOND]CF2[BOND]PO3H2 derivatives. The replacement of the iodine atoms by [BOND]CF2[BOND]PO3Et2 units was almost quantitative in the case of o-iodobenzoyl polysulfone. Membranes based on ionomers having 0.90 mmol of phosphonic acid units/g of dry polymer took up 6 wt % water when immersed at room temperature, and conductivities up to 5 mS cm−1 at 100 °C were recorded. This level of conductivity was comparable to that reached by a membrane based on a sulfonated polysulfone having 0.86 mmol of sulfonic acid/g of dry polymer. Thermogravimetry revealed that the aryl[BOND]CF2[BOND]PO3H2 arrangement decomposed at approximately 230 °C via cleavage of the C[BOND]P bond. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 269–283, 2007.

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