DECREASED SOLUBILITY OF ALKALI-METAL SALTS BY HEATING IN POLY(ETHYLENE OXIDE) OLIGOMERS

Several inorganic salts, homogeneously dissolved in poly(ethylene oxide) (PEO) oligomers, were crystallized by heating. The solubility of these salts (classified here as type 1) decreased considerably with increased temperature. However, an other group of inorganic salts (type 2) did not crystallize upon heating. The effect of terminal hydroxyl group fraction of PEO on the solubility of salt in the PEO was analyzed. It was concluded that the type 1 salts were solubilized mainly by the terminal hydroxyl groups of the PEOs. In contrast, type 2 salts are solubilized by not only terminal hydroxyl groups but also ether oxygens, and these salts are known to form complexes with high molecular weight PEO. The cation of the type 1 salts was solvated by both terminal hydroxyl groups in PEO oligomers. This negative temperature dependence of solubility of type 1 salts was attributed to the destabilization of the cation solvating structure by heating.