Hydrophobic Modification of Polyacrylamides with Oligo(Lactide): A Comparative Study in Two Solvent Systems

The control and modification of polyacrylamide viscosity through the incorporation of hydrophobic monomers have gained considerable attention due to their cost-effectiveness and potential use in enhanced oil recovery. Hydrophobically modified polyacrylamide copolymers containing oligo-(lactide) macromonomers were synthesized by free radical polymerization in two solvent mixtures: methanol/water and tetrahydrofuran/water. A macromonomer with five repeating units was incorporated at 2, 5, and 10 mol %, as determined by proton nuclear magnetic resonance. Copolymers obtained in tetrahydrofuran/water showed higher incorporation efficiency but lower molar mass than those synthesized in methanol/water, according to size-exclusion chromatography. The latter presented better rheological performance, with higher dynamic viscosities in aqueous solution. Although molar mass affected the results, hydrophobic interactions proved to be the main factor in viscosity enhancement, as homopolymers displayed inferior behavior.