Self-assembly and regulation of hydrophobic associating polyacrylamide with excellent solubility prepared by aqueous two-phase polymerization

The application of hydrophobic associating polyacrylamide (HAPAM) was restricted due to the poor solubility. In order to enhance the solubility of HAPAM and avoid environmental pollution, aqueous two-phase polymerization was used to prepare HAPAM in ammonium sulfate aqueous solution and a milky dispersion was obtained. The HAPAM particles dispersed in the solution spherically and the average particle size was about 7.4 μm. The hydrophobic associating polyacrylamide prepared with aqueous two-phase polymerization exhibited superior solubility and it could dissolve completely in twenty seconds. HAPAM solution could aggregate to network through inter-molecular association, leading significant increase of viscosity. Moreover, the viscosity of HAPAM solution increased with addition of inorganic salt even in nearly-saturated solution, and the viscoelasticity of HAPAM solution also enhanced obviously in the presence of salt, exhibiting excellent salt resistance. Furthermore, anionic surfactant of sodium dodecyl sulfate (SDS) could aggregate with the cationic hydrophobic monomers on the polymer chains via electrostatic attraction to form mixed micelles, which could prompt the polymer from intra-molecular association to inter-molecular association, leading remarkable increase of viscosity and viscoelasticity of the solution. In addition, The HAPAM dispersion doesn’t contain any organic solvent and could become solution instantaneously once dilution into water, which provides a green and environmentally friendly strategy for preparation of hydrophobic associating polymers. The HAPAM dispersion was well fit for the hydraulic fracturing in shell gas due to the excellent solubility and environmentally friendly property. These features indicated that HAPAM dispersion would have a great potential application in hydraulic fracturing in shell gas.