Synthesis and gelation properties of HPMC-g-poly(AM/AA/APEG2400) quaternary copolymer

To improve the stability of the polymers applied to profile control in high-temperature and high-salinity reservoirs, a water-soluble graft-copolymer HPMC-g-poly(AM/AA/APEG2400) was synthesized from hydroxypropylmethylcellulose (HPMC), acrylamide (AM), acrylic acid (AA), and allyl polyoxyethylene ether (APEG2400) via free-radical copolymerization using potassium persulfate (KPS) as the initiator. The molecular weight (Mw) of HPMC-g-poly(AM/AA/APEG2400) was controlled by the addition of the chain-transfer agent, sodium formate (SF), to the polymerization medium and was measured by capillary viscometry. Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), proton nuclear magnetic resonance (1H NMR), and scanning electron microscopy (SEM) were performed to characterize the graft-copolymer. The rheological properties of the graft-copolymer were investigated at different salinities and temperatures. The graft-copolymer solution showed better salt resistance, temperature tolerance, and long-term thermal stability than partially hydrolyzed polyacrylamide (HPAM). In addition, hydrogels were prepared using the graft-copolymer with varying Mw (346 × 104–1319 × 104), a crosslinker (hexamethylenetetramine–resorcinol, (HMTA–RC)), and additives (citric acid, (CA), and ammonium phosphate monobasic, (MAP)), and the hydrogels exhibited adequate strength and tunable gelation time. The hydrogels prepared using the graft-copolymer with high Mw possessed excellent long-term stabilities with negligible syneresis at 45 °C after 130 d, for the same conditions, the syneresis of conventional hydrogels prepared by HPAM reached approximately 90%.