Abstract: The change of the chemical shift and the spin-lattice relaxation time of Al in the reaction process of partially hydrolyzed polyacrylamide(HPAM) with a low concentration and high molecular weight and aluminum citrate(AlCit) system are investigated via ²⁷Al NMR measurement. The experimental results show that after crosslinking the chemical shift of Al which crosslinked with the carboxyl of HPAM increased, but the chemical shift of Al which didn't react with HPAM almost kept the same. There are three phases of aluminum in the HPAM/AlCit crosslinking system.These three phases of aluminum correspond to three different spin-lattice relaxation time of Al. When the concentration of HPAM is less than or equal to 200 mg/L, the spin-lattice relaxation time(τ₁₃) of Al was decreased with the increase of reaction time after crosslinking, the linked polymer solution was formed mostly by intra-molecular crosslinking reaction between HPAM and AlCit when the concentration of HPAM was more than or equal to 250 mg/L, the spin-lattice relaxation time(τ₁₃) of Al was increased with the increase of reaction time after crosslinking, the linked polymer solution was formed mostly by inter-molecular crosslinking reaction between HPAM and AlCit.

Key words: Partially hydrolyzed polyacrylamide, Aluminum citrate, Spin-lattice relaxation time, Crosslinking system, Chemical shift