Water soluble copolymers. 55: N-isopropylacrylamide-co-acrylamide copolymers in drag reduction: Effect of molecular structure, hydration, and flow geometry on drag reduction performance

Non‐ionic, hydrophobically associating, water soluble N‐isopropylacrylamide‐co‐acrylamide (IPAM) copolymers have been synthesized and characterized specifically for the study of drag reduction. The drag reduction (DR) performance has been measured with a rotating disk rheometer and a capillary flow apparatus. The DR studies were performed in deionized water, 0.514 M NaCl and 1 M urea. DR efficiency is dependent on copolymer structure, composition, and solvation. Copolymers showing intermediate values of hydrophobic character are found to be the most effective drag reducers. For this copolymer series, IPAM‐70 (the copolymer synthesized with 70 mole% N‐isopropylacrylamide in the feed) is the most efficient drag reducer. The DR properties of the IPAM copolymers are influenced by hydrophobic associations as well as hydrogen bonding. The effects of salts from the Hofmeister series, cosolvents such as dioxane, and temperature are also examined. Drag reduction performance of the various copolymers is correlated to empirical relationships involving degree of polymerization, second virial coefficient or other solvation parameters, and concentration.