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Abstract
Polymer systems containing dynamic covalent bonds have great application potential in the field of enhanced oil recovery. In this paper a series of polyboric acid compounds were synthesized by using polyamine and formylbenzeneboronic acid as raw materials, and then a binary composite system containing dynamic borate ester bonds was formed by mixing guar gum with the polyboric acid compound. The effects of the polyboric acid compound structure, composite system concentration, temperature, inorganic salt concentration and pH on the apparent viscosity and rheological properties of the composite system solution were investigated. The results showed that the higher the content of boric acid groups in the polyboric acid compound, the greater the solution viscosity of the composite system. The apparent viscosity of the guar gum solution increased from 350 mPa.s to 1854 mPa.s at room temperature, the highest value obtained, when the guar gum was mixed with a polyboric acid compound formed by the reaction of polyethyleneimine (PEI) and 2-formylphenylboric acid (2-FPBA) at a molar ratio of 1:4.5. Temperature and pH had a great influence on the apparent viscosity of the composite system, whereas NaCl addition had little effect on the apparent viscosity of the composite system. In addition, the rheological test results showed that the composite system had good shear resistance and structural elasticity, which meets the basic requirements of a polymer flooding agent used for enhanced oil recovery.