ABSTRACTA novel activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) initiation system composing of an initiator sodium chloroacetate, a catalyst ferric chloride, and a reducing agent ascorbic acid was developed to improve the gelation time of thein situcrosslinked polymer system. The kinetics of polymerization of acrylamide showed features of a living/controlled process in which the concentrations of the growing radicals [P·] are kept constant throughout the polymerization process. Compared with conventional potassium persulfate initiators, the gelation time of thein situcrosslinked polymer system can be improved to 40 h or even longer using the ARGET ATRP initiation system at 80 °C due to the low radical concentration and slow polymerization reaction. Core flooding test showed that the ARGET ATRP initiating system developed could initiate the polymerization reaction of thein situcrosslinked polymer system in the core. However, the gelation time was extended in comparison to that of the result obtained in the bottle, resulting from the dilution and adsorption of ARGET ATRP components during the injection process. The research expands the application field of the ARGET ATRP principle and has a promising prospect on controlling the gelation time of thein situcrosslinked polymer system. © 2020 Wiley Periodicals, Inc. J. Polym. Sci.2020,58, 519–527