The relative effectiveness of anions and cations in altering macromolecular conformation was reported to be independent of the nature of the macromolecule. However, in terms of the degree of changes, macromolecule-dependent ion action cannot be underestimated. The designed poly(organophosphazenes) have been selected for this study due to its versatility of the substitution with a fixed backbone. To set up the systematic explanation on the ion action related with molecular interactions, ions and polymers are arranged based on the water binding ability. As a characteristic factor specific in the thermothickening system, the temperature at which the viscosity of the polymer solution reaches the maximum (T-max) has been compared. Anions with strong water binding ability more effectively lower the T-max of the hydrophobic poly(organophosphazenes). Meanwhile, the Tmax of the cation-complexed poly(organophosphazenes) are lowered by the sequence of water binding ability of the complexed cations. In both the anion and cation interactions, poly(organophosphazenes) substituted by longer PEG and more hydrophilic amino acid ester, show differentiated result due to different interaction with water when compared with other polymer systems in this study. Ion interaction with poly(organophosphazenes) mediated by water supports interfacial interactions expressed by interaction parameters, which strongly depends on the polymer structure and ion type. (C) 2008 Wiley Periodicals, Inc.