Behaviour of the poly(maleic anhydride-co-vinyl acetate) copolymer in aqueous solutions

The alternate copolymer obtained from maleic anhydride and vinyl acetate, poly(maleic anhydride-co-vinyl acetate) (PMAVA), was studied by viscosimetric and potentiometric methods. In aqueous solutions this copolymer is hydrolyzed to two neighbouring carboxyl groups in a structural unit and behaves as a dibasic polyacid. The viscosimetric behaviour of PMAVA was studied in function of copolymer concentration, neutralization degree, concentration of the NaCl added and three samples of different molecular weights were synthesized. The rather low viscosity of the copolymer aqueous solution increases with decreasing PMAVA concentration which makes evident the polyelectrolyte character of this copolymer. By potentiometric titration the PMAVA solutions were studied both in the absence and in the presence of NaCl. The estimated values of pK01 and pK02 correspond to the first and to the second ionization stage, respectively. The electrostatic free energy of the polyion, Ge, was calculated with reference to the number of the structural units in a macromolecule, in function of the neutralization degree.