Characterization of poly(oxyethylene) complex formation with alkali-metal cations in a cation-exchange resin phase

Abstract

The thermodynamics of poly(oxyethylene)(POE) complex formation with alkali-metal cations in a cation-exchange resin phase have been investigated. The present study elucidates the thermodynamic origin of POE complexation selectivity between alkali cations or between terminal groups in the ligand, and permits speculation of stable structures of the ligand. POE, having a long lipophilic terminal group, tends to adopt the extended form both in solution and in the resin phase, whereas that having a small terminal group favours more compact forms. From evaluations of the contributions of each process to the overall ΔH, the selectivity between terminal groups in the ligand is found to emerge from the ΔH required for the conformational change of the ligand. In contrast, selectivity of POE complex formation between alkali cations is explained by a difference in ΔS, principally by that released by the desolvation of the metal cation.