Temperature and pH-Dependent Response of Poly(Acrylic Acid) and Poly(Acrylic Acid-co-Methyl Acrylate) in Highly Concentrated Potassium Chloride Aqueous Solutions

In this study, the phase transition phenomena of linear poly(acrylic acid) (PAA) and linear or star-shaped poly(acrylic acid-co-methyl acrylate) (P(AA-co-MA)) in highly concentrated KCl solutions were investigated. The effects of polymer molecular weight, topology, and composition on their phase transition behavior in solution were investigated. The cloud point temperature (T-CP) of polymers drastically increased as the KCl concentration (C-KCl) and solution pH increased. C-KCl strongly influenced the temperature range at which the phase transition of PAA occurred: C-KCl of 1.0-2.2 M allowed the phase transition to occur between 30 and 75 degrees C. Unfortunately, at C-KCl above 2.6 M, the T-CP of PAA was too high to theoretically trigger the crystallization of KCl. The addition of hydrophobic methyl acrylate moieties decreased the T-CP into a temperature region where KCl crystallization could occur. Additionally, the hydrodynamic diameters (D-h) and zeta potentials of commercial PAA samples were examined at room temperature and at their T-CP using dynamic light scattering. The salt concentration (from 1 to 3 M) did not impact the hydrodynamic diameter of the molecules. D-h values were 1500 and 15 nm at room temperature and at T-CP, respectively.