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

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, alpha. Th e conductometric titration curves of 0.1 wt.% HASE emulsion latex reveal th ree equivalence points. However, only two equivalence points are evident fr om 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 a t the surface of the latex particles. This is followed by the neutralizatio n of the methacrylic acid groups, which then causes the latex to swell. The final stage of the neutralization involves the reaction of the remaining c arboxylic acid groups. The negative-logarithm-dissociation-constant (pK(app )) curves obtained from the titration data reveal that the HASE polymer exh ibits a conformational transition from a compact hard sphere to a random co il during the process of neutralization. The hydrodynamic radius (R-h) of 0 .02 wt.% HASE polymer system determined from dynamic light scattering indic ates that the latex particle swells with increasing alpha until alpha reach es 0.4, thereafter the particles dissociate into several smaller clusters.