Influence of alkali-soluble associative emulsion polymer architecture on rheology

We examined the influence of the following synthesis parameters on the aqueous-solution rheology of alkali-soluble associative emulsion polymers in steady simple shear, oscillatory shear, and extensional shear: macromonomer structure (hydrophobe size and structure, double-bond structure, and moles of ethoxylation between hydrophobe and double bond), carboxylic acid monomer concentration, polymer glass transition temperature, and water solubility of the monomers in the polymer backbone. Polymers made with large-molar-volume hydrophobes of complex structure show enhanced thickening power, low shear viscosity, shear-thinning viscosity, and viscoelasticity (i.e., properties are less dependent on shear strain) compared to polymers made with smaller hydrophobes. Optimal values exist for concentrations of carboxybic acid and macromonomer as well as for water solubility and glass transition temperature of the polymer. Consistent with rheological data, static light-scattering data show that polymers containing complex hydrophobes aggregate, even in a mixed solvent chosen to enhance molecular dispersion, and have a much larger apparent molecular weight in solution than do polymers that do not contain associative macromonomer.