Potentiometric titration and dynamic light scattering of hydrophobically modified alkali soluble emulsion (HASE) polymer solutions

Abstract

Dynamic light scattering, potentiometric and conductometric titrations were used to study the dissolution behavior of hydrophobically modified alkali soluble emulsion (HASE) polymers in aqueous medium. In the titration curves, the pH, conductivity and the negative-logarithm-dissociation-constant (pK_app) are plotted as a function of the degree of neutralization, α. The conductometric titration curves of 0.1 wt.% HASE emulsion latex reveal three equivalence points. However, only two equivalence points are evident from the potentiometric titration curves. The dissolution of the HASE polymer latex can be described by a three-stage neutralization process. The first stage corresponds to the reaction of added base and –SO₃H groups situated at the surface of the latex particles. This is followed by the neutralization of the methacrylic acid groups, which then causes the latex to swell. The final stage of the neutralization involves the reaction of the remaining carboxylic acid groups. The negative-logarithm-dissociation-constant (pK_app) curves obtained from the titration data reveal that the HASE polymer exhibits a conformational transition from a compact hard sphere to a random coil during the process of neutralization. The hydrodynamic radius (R_h) of 0.02 wt.% HASE polymer system determined from dynamic light scattering indicates that the latex particle swells with increasing α until α reaches 0.4, thereafter the particles dissociate into several smaller clusters.