Self-Soluble Hydrophobically Associating Polyacrylamide Inverse Emulsions with Extraordinary Thickening Properties

Polyacrylamide-based inverse emulsions are one class of fascinating products possessing excellent aqueous thickening ability, rapid solubility, and tailorable properties in many industrial fields, but further improvement of their performances and simplification of their applicational operations are still challenging. Traditionally, post-addition of an inverting agent into the produced inverse emulsion is necessary to enable the product to become soluble in water. In this study, cetylmethyldiallylammonium chloride (CMDAAC) and stearyl methacrylate (SMA) were used as functional monomers to copolymerize with traditional monomers acrylamide, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid, achieving inverting agent-free self-soluble hydrophobically associating polyacrylamide (HAPAM)-based inverse emulsions with high monomer conversion (>97%) and high molecular weights (>10 million Da). With an increasing SMA dosage in recipes, the micelle sizes of the obtained emulsions become smaller, and thickening ability, shearing property, temperature and salinity tolerances, as well as synergism with sodium dodecyl sulfate of the obtained polymers in aqueous solutions were increasingly enhanced due to the improved hydrophobic interactions. For SMA-containing polymers, 0.5–1.5 mol % SMA dosages make the obtained polymers desensitized to temperature, and even a slight thermo-thickening effect is observed for 2.0 mol % SMA dosage samples. Meanwhile, the introduction of CMDAAC and/or SMA imparts polymers with remarkable salt-thickening behavior at an NaCl concentration above a certain value, and the inflection points shift to lower NaCl concentrations with increasing SMA contents. This work presents a species of inverting agent-free self-soluble high-performance HAPAM inverse emulsions with great applicational potentials in harsh conditions for oil and gas development.