Asahi Chemical [8] and Tokuyama Soda [19] have developed similar chemistries in which the –CF2SO2F groups are replaced by carboxylic acid groups. In these perfluoro polymers, the backbone is extremely hydrophobic whereas the charged acid groups are strongly polar. Because the polymers are not crosslinked, some phase separation into different domains takes place. The hydrophobic perfluoro-polymer domains provide a nonswelling matrix, ensuring the integrity of the membrane. The ionic hydrophilic domains absorb water and form as small clusters distributed throughout the perfluoro-polymer matrix. This configuration, illustrated in Figure 10.6, minimizes both the hydrophobic interaction of ions and water with the backbone and the electrostatic repulsion of close sulfonate groups. These perfluorocarbon membranes are completely inert to concentrated sodium hydroxide solutions and have been widely used in membrane electrochemical cells in the chlor-alkali industry.
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