Enhancing the temperature resistance, salt resistance, and viscoelasticity of polyacrylamide via hydrophobic association: a rheological perspective

Using acrylamide, methyl acryloyloxyethyl trimethyl ammonium chloride, acrylamidomorpholine, and eicosyl dimethyl allyl ammonium chloride as raw materials, herein, a high-temperature- and salt-resistant hydrophobic associative polymer—ADOC—is synthesized via free-radical polymerization in an aqueous solution. The synthesis of ADOC is confirmed via Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance. The involved molecular microaggregation structure is observed through scanning electron microscopy, and associative-network molecular aggregates are formed. The rheological properties of ADOC are determined using a rheometer; the critical associative mass fraction of ADOC is found to be 0.22%. Notably, ADOC is tested in different solvents, with the final viscosities in clear water, a sodium chloride aqueous solution, and a calcium chloride solution being 58.32, 39.68, and 20.19 mPa·s, respectively. It also demonstrates satisfactory thermal stability and a high shear viscosity recovery rate (90%). Although the molecular structure is disrupted under high shear, the molecules regain a certain entanglement structure when the involved external force disappears, allowing the viscosity to rise after 1 h of shear at a rate of 170 s⁻¹ at 180 ℃. Thixotropy testing reveals a pronounced thixotropic ring. Viscoelasticity testing shows that for the involved ADOC solution, G′ > G”, indicating a robust linear plateau region and high solution viscosity owing to intermolecular associations. The viscosity of 0.6% ADOC after 1 h of shear at 170 s⁻¹ and 180 ℃ was 58.32 mPa·s. These findings demonstrate that ADOC possesses exceptional temperature and shear resistance properties, making it promising for future use in exploiting deep and ultradeep oil reservoirs.