Solution Properties and Microstructure of Branched Acrylamide-Based Copolymers

Novel branched acrylamide-based copolymers (PAE) were synthesized by an aqueous free radical copolymerization technique using acrylamide (AM), sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS) and p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VE, polymerization number: 18) to improve the poor salt resistance of the oil-flooding polymer at high salt concentrations. The PAE polymer was characterized with Fourier transform infrared (FT-IR) spectroscopy and proton nuclear magnetic resonance (H-1-NMR). The PAE brine solutions exhibited salt-thickening twice and heat-thickening twice over the ranges of NaCl concentration and temperature. For 2.0 g . L-1 PAE containing 0.93% (molar fraction) VE, the apparent viscosities of 5.0 and 90.0 g . L-1 NaCl solutions were 1167.0 and 338.0 mPa.s at 30 degrees C, respectively. This showed the excellent thickening property and salt resistance of the polymer. The apparent viscosity of the 5.0 g.L-1 NaCl solution was still up to 685 mPa.s at 85 degrees C, which exhibited good heat resistance of the polymer. Moreover, the polymer showed good surfactant and interfacial activities. The scanning electron microscope (SEM) morphologies showed that unique associated structures were formed for PAE in water and continuous network structures were still formed in the brine solution of PAE. Results indicated that the extense polymer chains in water were still able to expand comparatively in the brine solution.