COMPLEX-FORMATION OF POLYOXYETHYLENES WITH POTASSIUM-ION AT THE SOLUTION/ION-EXCHANGE RESIN INTERFACE AND THEIR CHROMATOGRAPHIC BEHAVIOR

Polyoxyethylene (POE) oligomers, which are capable of forming complexes with some hard cations, are separated on a cation-exchange resin of an alkali metal ion form in terms of the number of oxyethylene units. In this paper, the chromatographic retention behavior on a potassium ion-form cation-exchange resin is discussed on the basis of the thermodynamic characteristics of the complex formation at the solution/ion-exchange resin interface. Studies on the stoichiometry of the complexes show that POE having a long terminal group tends to adopt an extended zigzag conformation in the resin phase, whereas that having a short terminus forms a more compact complex. The chromatographic retention is obviously correlated with the length of the termini; the longer the termini the weaker the retention. This proved to be due not to the enthalpy changes of the complexation but to the number of metal ions participating in the complexes. Also, thermodynamic results indicate that differences in the complex formation constants between POE having long termini and that having short ones can be explained by an enthalpic change required for the conformational change in the complexation process. The chromatographic behavior of POE can thus be elucidated by studying the nature of the complexes formed in the resin phase.