SOLUBILITIES OF NAPHTHALENE AND BIPHENYL IN AQUEOUS POLYMER SOLUTIONS

The solubilities of naphthalene and biphenyl in aqueous solutions of neutral polymers and polyelectrolytes are measured and discussed. The polymers used were polyacrylamide (PAAm), polyvinyl alcohol (PVA), soluble starch (SS), polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), polyacrylates (PAA), polyethylene-sulfonates (PES), polyphosphates (PP), salts of polyethylenimine (PEI), and its low molecular weight analogs having various gegenions. The solubilities of naphthalene and biphenyl increase, as does the polymer hydrophobicity, in the order PAAm < PVA < SS ≈ PEG < PEI < PAA < PVP. For low molecular weight analogs of PEI·HCl, the solubility increases with increasing degree of polymerization. Alkali metal salts of PAA decrease the solubility of naphthalene or biphenyl, whereas tetraalkylammonium salts increase it. The salting-in effect by the tetraalkylammonium salts is enhanced with increasing number of carbon atoms in the alkyl groups. From the Setchénow constants of alkali metal salts of polyelectrolytes for naphthalene, the individual ionic Setchénow constant of macroions (k32,2p) was calculated to be 0.22, 0.20, 0.15, and -0.03 1. monomol-1 for PES, PP, PAA, and PEI ions, respectively. The k32,2p for weak polyelectrolytes is further discussed in terms of the hydrophobic structural effect and the electrostrictional hydration. A correlation between the Setchénow constant and the osmotic coefficient is noted.