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The hydration of carboxylic acid groups in ion exchange resins was studied by means of dielectric measurements. For three resins carrying carboxylic groups with quite different pK-values the dielectric constant and the dielectric loss were measured as a function of frequency, water content, and temperature. A comparison of their behaviour showed that the observed dielectric dispersion is due to a Maxwell-Wagner mechanism. In the course of the water adsorption the resin with very weak carboxylic acid groups exhibited a discontinuity of the dielectric constant, if one molecule of water was attached to two carboxylic groups. This can be explained by assuming that the carboxylic groups which are connected by hydrogen bonds in the dry state begin to dissociate at the above mentioned water content. As a consequence, the formation of H 5 O 2⊕ -complexes becomes possible. The corresponding increase of the proton mobility leads to the observed Maxwell-Wagner effects. Hydration structures of the carboxylic acid groups below and above this critical water content are proposed.

zeitschrift für naturforschung b

Die Hydratation von Carboxyl-Gruppen in Ionenaustauscherharzen Eine dielektrische Untersuchung / The Hydration of Carboxylic Acid Groups in Ion Exchange Resins A Dielectric Investigation