Study on mechanism of a simple method to regulate salt tolerance of hydrophobically associating water-soluble polymers

Salt tolerance is one of the important properties of hydrophobically associating water-soluble polymers (HAWSPs). In this work, HAWSPs with different hydrophobic monomer (M12) contents (0.3 mol% and 0.5 mol%) were synthesized. The viscosity of two polymers was measured. Molecular simulation (MS) were carried out to elucidate the salt tolerance mechanism. Results show that the polymer with a higher M12 content exhibits better salt tolerance. With increasing salt content, the radius of gyration of the polymers continuously decreases when M12 content is low, while it tends to increase and then decrease under high M12 contents. Combined with the spatial conformation, it can be found that only sufficient hydrophobic monomers can enhance the association effect of the polymers, forming more hydrophobic microregions and improving the viscosity. The radial distribution function results demonstrate the little effect of salt on hydrogen bonds. This work illustrates that simply adjusting the content of hydrophobic monomers is an effective strategy to regulate the salt tolerance of the polymers, which can significantly reduce the cost of salt-tolerant polymers.