pH DEPENDENT RHEOLOGY OF HYDROPHOBICALLY MODIFIED ALKALI SOLUBLE EMULSION (HASE) POLYMERS

Two sets of Hydrophobically modified Alkali Soluble Emulsion (HASE) polymers were investigated using steady shear viscosity and dynamic frequency measurements. One set of HASE polymers contained a fixed ratio of ethyl acrylate (EA) to methacrylic acid (MAA) and a hydrophobe (C₁₂, C₁₈, or C₂₂) containing monomer (macromonomer). The second set of HASE polymers contained a fixed amount of MAA but the amount of C₁₈ macromonomer was varied (1%, 5%, or 10% by mass). Aqueous solutions of the polymers (1% by mass) were tested at pH = 3, 5, 7 and 10. The neutralization process is known to impact the solution viscosity, therefore, samples “back-titrated” from pH = 10 to pH = 7 were also tested. The samples at pH = 3 and 5 had the lowest viscosities. Samples directly adjusted to pH 7 had a much higher viscosity and a yield stress, which increased with increasing hydrophobe size. The samples at pH = 10 had the highest viscosity and yield stress values. Samples back-titrated to pH = 7, were lower in viscosity than the samples directly adjusted to pH = 7. The dynamic frequency results at pH = 10 show additional characteristic timescales which shift as a function of the hydrophobe size.