DISSOCIATION BEHAVIOR OF POLY(ITACONIC ACID) BY POTENTIOMETRIC TITRATION AND INTRINSIC-VISCOSITY

The potentiometric titration and intrinsic viscosity were measured under various conditions to study the dissociation behavior of poly(itaconic acid) (PIA), a polyelectrolyte with the same average charge density as poly(fumaric acid) (PFA) and poly(maleic acid) (PMA) but with a different arrangement of the carboxyl groups. The titration curves showed that PIA exhibits an apparent two-step dissociation similar to PFA and PMA. The analysis revealed that the intrinsic dissociation constant of PIA is smaller than that of PFA and PMA and that the electrostatic free energy of PIA at degree of dissociation α < 0.5 is larger than that of PFA and PMA, but at α > 0.5, the value of PIA lies between those of PFA and PMA. The intrinsic viscosity increased with increasing a, attained a maximum near α = 0.5, and then decreased steeply. The dissociation behavior of PIA was discussed in terms of the discrete charge model including effects of the short-range electrostatic interaction and the difference in the dissociation behavior between α- and β-COOH. The calculated titration curve was in quantitative agreement with the observed one. It was concluded that the difference in the local distribution of charges, rather than overall charge density on a polymer chain, plays a dominant role in the dissociation behavior of polyacids with high charge density. © 1990, American Chemical Society. All rights reserved.