Intramolecular association of poly(maleic acid/octyl vinyl ether) in aqueous solution

The properties of aqueous solutions of poly(maleic acid/octyl vinyl ether), PMAOVE, were studied by pyrene solubilization and fluorescence, solution viscosity, and phase separation induced by inorganic salts. The results indicate the existence of hydrophobic intramolecular microdomains formed by the octyl side groups. Pyrene solubilization and intramolecular alkyl chain association diminish sharply as the polymer is neutralized and unfolds with increasing ionization. The saturation solubilization of pyrene by PMAOVE corresponds to a ratio of 35 octyl side chains per pyrene at higher polymer concentrations for the unneutralized polymer, and 42 at constant pH 4.0. Some hydrophobic solubilization averaging one pyrene per polymer molecule persists up to complete neutralization. Besides pH, the polymer conformation is also sensitive to solution ionic strength. A compact conformation is induced by the addition of 0.01 M NaCl, as indicated by the low reduced viscosity at low pH. Further increase to about 0.1 M leads to the precipitation of PMAOVE at concentrations of 500 ppm and above. Precipitation or phase separation of PMAOVE solutions at pH 4 by bivalent cations occurs at much lower salt concentrations than with single-valent cations. With barium in particular, the phase separation is not a simple precipitation. A very weak gel phase separates from the solution. Only minor differences are detected with a range of anions of sodium salts in precipitating PMAOVE at pH 11. In contrast to PMAOVE, the less hydrophobic lower homologue poly(maleic acid/methyl vinyl ether), PMAMVE, shows no hydrophobic solubilization of pyrene and is not precipitated by addition of NaCl up to saturation of the salt.