Water-Soluble Core–Shell Hyperbranched Polymers for Enhanced Oil Recovery

Novel water-soluble core–shell hyperbranched polymers (HBPAMs), consisting of nano-SiO2 as the core, hyperbranched polyamidoamide (PAMAM) as the subshell, and linear hydrophilic chains as the outermost layer, were synthesized through an in situ free-radical polymerization strategy. The PAMAM hybrid nano-SiO2, which is preferentially modified by 3-aminopropyltriethoxysilane, was prepared by successively repeating the Michael addition of methyl acrylate and amidation reaction of ethylenediamine. By varying the numbers of functionalized branch-cell units, the numbers of outmost linear hydrophilic chains can be tuned with the mean diameter being 462 nm for HBPAM-1 and 573 nm for HBPAM-2. Rheological measurements demonstrated that HBPAMs were classical power law fluids, and the critical shear rate shifts toward the higher region as the number of linear hydrophilic chains of the outermost shell increase. The intersection modulus and relaxation time were elaborately calculated. Static experiments convincingly proved that the three-dimensional (3D) morphology endowed HBPAMs with excellent shear degradation resistance, desirable salt resistance, and temperature tolerance. Core flooding experiments further confirmed that this unique type of core–shell polymer may have robust applications for enhanced oil recovery (EOR).