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• RAFT-based synthesis of salt-resistant hydrophobic association polymerPDMA2 with various molecular weights. • Molecular dynamics simulation was used to investigate the salt tolerance of polymers. • The change in rock wettability can help with fracturing and oil displacement integration. The salt resistance of hydrophobically relating polymer fracturing fluid is one of the main indicators to meet the fracturing operation. Thus, a chain transfer agent was created in this study. Hydrophobically related polymer PDMA2 was synthesized in an aqueous solution through the RAFT approach. The salt resistance mechanism of the polymer was elucidated using molecular simulation software. The experimental results demonstrated that the salt resistance of the polymer can be enhanced by introducing long hydrophobic chain monomers via RAFT polymerization. Inorganic salt ions can improve the polymer skeleton and facilitate polymer chain bonding. The rotation radius of the hydrophobic polymer PDMA2 lowers as the salt concentration rises, allowing polymer molecule interaction. Combined with spatial conformation and fluorescence spectrum analysis, PDMA2 containing hydrophobic monomer was discovered to improve the association effect of polymer and produce more hydrophobic microregions. The radial distribution function results show that increasing the salt content compresses the polymer's main chain. On the polymer backbone, the radial distribution function between N-N atoms grows. This study demonstrates that the hydrophobic-association polymer can meet the service conditions of oilfield mineralized strata and lower the consumption of freshwater resources. [ABSTRACT FROM AUTHOR]

[Display omitted] • A salt-responsive hydrophobically associating polymer (HSRP) was synthesized. • This hydrophobically associating polymer shows an unusual salt-responsive self-assembling transition. • A reasonable core–shell model was proposed for the salt-responsive behavior. • HSRP is expected to find wide applications in saline reservoirs based on its excellent salt-responsive properties. A salt-responsive hydrophobically associating polymer (HSRP) with a molecular weight of 1.21 × 106 g/mol was synthesized and characterized. It has the characteristics of strong association and low molecular weight by choosing monomers and adjusting the polymerization system. HSRP exhibited a high sensitivity to salt ions owing to the peculiarities of its molecular structure. Through various experimental tests, this study further expanded and complemented the salt-thickening effect of hydrophobic association water-soluble polymers. In brine, HSRP exhibited low apparent viscosity and shear stress. In addition, HSRP demonstrated better thixotropic properties and viscoelastic behavior as the salinity increased, which was attributed to a self-assembling transition. The effect of salinity on self-assembling behavior of supermolecules and rheological properties of HSRP was examined through macroscopic properties and microscopic mechanisms. A reasonable core–shell model was proposed for the salt-responsive behavior: The hydrophilic backbones curled up, forming a shell, and the hydrophobic branched chains interassociated to form a core. In brine, HSRP displayed excellent viscoelasticity and low friction. It is expected to find wide applications in tertiary recovery and fracturing in saline reservoirs based on its excellent salt-responsive properties. [ABSTRACT FROM AUTHOR]