EFFECTS OF INORGANIC SALTS ON THE PROPERTIES OF AQUEOUS POLY(VINYLPYRROLIDONE) SOLUTIONS

Cloud point curves and theta temperatures have been determined for aqueous solutions of poly(vinylpyrrolidone) at several concentrations for a variety of inorganic salts (phosphates, monohydrogen phosphates, sulfates, carbonates, dihydrogen phosphates and fluorides). The resulting dependency of the critical temperatures theta (mostly between 289 and 350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing the theta temperatures is PO43- > HPO42- > SO42- almost-equal-to CO32- > H2PO4- > F-. The order for cation is Na+ > K+. The changes brought about in theta temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.