Modified β-cyclodextrin and N-phenethyl-methacrylamide were utilized to react with acrylamide and acrylic acid to synthesize hydrophobically associating polyacrylamide (HMPAM) via photoinitiated free-radical micellar copolymerization. HMPAM was characterized using Fourier transform infrared (FT-IR) spectroscopy, ¹H nuclear magnetic resonance (¹H NMR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and viscometry. Compared with partially hydrolyzed polyacrylamide (HPAM), HMPAM demonstrated superior properties on aspects of thickening ability, salt tolerance, temperature resistance and oil displacement efficiency. It was found that the apparent viscosity reached a maximum at 45 °C and the viscosity retention ratio reached 87.56% at 95 °C; at a certain range of salinity, HMPAM exhibited an evident salt-thickening phenomenon; the simulative enhanced oil recovery tests illustrated that HMPAM could remarkably enhance oil recovery by 16.4% while HPAM could enhance oil recovery by 10.8%. Moreover, the viscoelasticity and surfactant compatibility of HMPAM were investigated. The results indicated that HMPAM has potential application for enhanced oil recovery.

Hydrophobically modified polyacrylamide with hyperbranched structure (HDPAM) was synthesized by water free-radical copolymerization based on functional hyperbranched polyamide-modified ultrafine silica as functional monomer and methacryloxyethyl-dimethyl cetyl ammonium bromide as hydrophobic monomer. The chemical and spatial network structure of HDPAM were investigated by means of FTIR, ¹H NMR, TGA and SEM, respectively. The rheological measurements indicated that the HDPAM solution was viscoelastic fluid. With the increase of HDPAM concentration, both intermolecular association efficiency of hydrophobic groups and apparent viscosity of HDPAM solution increased. HDPAM solution had good thixotropy and temperature tolerance property. Moreover, compared with HPAM, HDPAM demonstrated superior properties on the aspects of viscosification property, temperature resistance and salt tolerance.