Dissolution Behavior of HASE Polymers in the Presence of Salt: Potentiometric Titration, Isothermal Titration Calorimetry, and Light Scattering Studies

Potentiometric titration, static and dynamic light scattering, and isothermal titration calorimetry were used to study the salt effects on the dissolution behavior of Hydrophobically Modified Alkali-Soluble Emulsion (HASE) polymer emulsions in aqueous medium.The negative logarithm dissociation constant (p K a ) curves reveal that HASE polymer exhibits a conformational transition from a compact hard sphere to a random coil during the process of neutralization. Addition of a neutral salt reduces the energy necessary to extract protons from carboxylic acid groups, which favors the neutralization process. The latex particles expand with extent of neutralization (α) in the early stage of titration, thereafter the swollen particles dissociate into smaller clusters. The addition of salt screens the electrostatic repulsion between the polymer chains, and consequently reduces the hydrodynamic radius ( R h ) of the polymer clusters. The results also show that the polymer chains tend to form intramolecular association rather than intermolecular association in the presence of salt, which promotes the dissociation of polymer particles. The thermodynamic quantification of the dissolution behavior of model HASE polymer was achieved using the isothermal titration calorimetric technique. The results reveal that neutralization is an exothermic process dominated by enthalpy. The comparison of the titration data in different salt conditions show that the Δ G for the neutralization process is more negative at high salt content, suggesting that the dissolution is enhanced by the presence of a neutral salt.