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Partially hydrolyzed polyacrylamide (HPAM) is widely used as thickener in enhanced oil recovery (EOR), but the high temperature and salinity of oil reservoirs can reduce the viscosity and lead to polymer precipitation. To improve the performance of HPAM in high‐salinity and high‐temperature environments, the responsive amino‐terminated poly(ethylene oxide‐co‐propylene oxide) (PEOPPO) (EO/PO = 19/03) was grafted onto a HPAM backbone. The copolymers were prepared in water using 1‐ethyl‐3‐[3‐(dimethylamino)‐propyl]carbodiimide hydrochloride/N‐hydroxysuccinimide (EDC/NHS) as activators. Structural characterization was performed by 1H NMR and Fourier transform infrared (FTIR) and the responsive behavior was investigated by UV–Vis and rheology. Spectroscopic analyses confirmed that copolymers were successfully synthesized. UV–Vis showed that copolymers have combined salt and thermoresponsive character. Rheology in saline medium (ionic strength = 3.75 mol.L−1) revealed that, contrary to unmodified HPAM, HPAM‐g‐PEOPPO have thermothickening behavior and also higher viscosity than HPAM at 70 °C, suggesting the utilization of these copolymers as rheological modifiers under harsh conditions of temperature and salinity, such as the ones found in EOR applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47453.

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Amino-terminated poly(N-isopropylacrylamide) (PNIPAM-NH 2 ) was synthesized by free-radical polymerization in water by using the redox pair potassium persulfate/2-aminoethanethiol hydrochloride (KPS/AET.HCl) in a glove box under N 2(g) atmosphere. PNIPAM-NH 2 was then used to produce graft copolymers with carboxymethylcellulose (CMC) in water by applying a water-soluble carbodiimide and N-hydroxysuccinimide as activators. The samples were characterized by infrared spectroscopy and the thermal behaviour on solid state was investigated by thermogravimetry. Also, the rheological behaviour of the copolymers at 25 and 60 C was evaluated in water at 3 and 7 g/L. Contrary to CMC and PNIPAM-NH 2 , which had only one DTG peak, the thermal decomposition of the graft copolymers occurred at two steps, being the first DTG peak higher and second one lower than the corresponding precursors. Thermoassociative behaviour in water for CMC-g-PNIPAM graft copolymers depend on the amount of chain transfer agent used for the PNIPAM-NH 2 synthesis. Thermothickening effect occurred for the copolymer that had PNIPAM-NH 2 prepared with lower AET.HCl content, at a polymer concentration of 7 g/L, which is much lower than the concentrations previously reported in literature for graft copolymers with poly(N-isopropylacrylamide).

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