Aqueous Solutions of Associating Poly(acrylamide-co-styrene): A Path to Improve Drag Reduction?

Hydrophobically modified associating polymers could be effective drag-reducing agents containing weak "links" which after degradation can reform, protecting the polymer backbone from fast scission. Previous studies using hydrophobically modified polymers in drag reduction applications used polymers with M ≥ 1000 kg/mol. Homopolymers of this high M already show significant drag reduction (DR), and the contribution of macromolecular associations on DR remained unclear. We synthesized associating poly(acrylamide-co-styrene) copolymers with M ≤ 1000 kg/mol and various hydrophobic moiety content. Their DR effectiveness in turbulent flow was studied using a pilot-scale pipe flow facility and a rotating "disc" apparatus. We show that hydrophobically modified copolymers with M ≈ 1000 kg/mol increase DR in pipe flow by a factor of ∼2 compared to the unmodified polyacrylamide of similar M albeit at low DR level. Moreover, we discuss challenges encountered when using hydrophobically modified polymers synthesized via micellar polymerization.