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Polyacrylamide and its derivatives are widely used in oilfields due to their efficient viscosity building and drag-reducing properties. At present, the commonly used products of polyacrylamide include two types: polymer powder and polymer emulsions. However, the low dissolution rate of powdered products and the instability of polymer emulsions limit their application. Here, we constructed a pH-sensitive inverse polymer emulsion of poly(acrylamide-co-acrylic acid-co-2-acrylamide-2-methylpropyl sulfonic acid), showing a phase separation and phase inversion from W/O to O/W at pH o 6 and pH 4 8 due to a pHswitchable surfactant N,N-dimethylcyclohexylamine/Oleic acid complex (DM-OA). The demulsification or phase inversion of the W/O polymer emulsion can release the polymer that was originally in the aqueous phase, and the released polymer can quickly dissolve in water to perform its function of viscosity building and friction reduction. Therefore, this pH-sensitive modified-polyacrylamide polymer emulsion shows a fast dissolution rate with a dissolution time of about 1 min and a long storage stability. The utilization of stimuli-responsive surfactants to construct pH-responsive water-soluble polymer W/O emulsions provides a new approach to the preparation of water-soluble polymer emulsion additives that can be quickly dissolved and stored for long periods of time in water-treatment, papermaking and oil recovery fields. [ABSTRACT FROM AUTHOR]