Fluorescence Studies of an Alkaline Swellable Associative Polymer in Aqueous Solution

Rheology measurements and fluorescent probe experiments were used to study the association process in aqueous solutions of an alkali swellable copolymer of methacrylic acid, ethyl acrylate, and an ethoxylated hydrophobic monomer. The pyrene-probe experiments monitor hydrophobic cluster formation in the polymer solution and indicate a rearrangement of the system as a function of pH. The polymer, present as a latex at pH < 4, dissolves at pH 5.7. In this solution, many small hydrophobic domains are present. As the pH is raised and the polymer further neutralized, the viscosity of the solution increases, accompanied by formation of a smaller number of larger hydrocarbon domains, detected as a large increase in the extent of pyrene excimer emission.