ABSTRACT:A new kind of hydrophobically associating water-soluble terpolymer P(AM-NVP-DMDA) was synthesized by free radical terpolymerization. Compared with micellar terpolymerization, this terpolymerization can be conducted in aqueous solution in absence of external surfactant, because the hydrophobic monomer is surface active. Synthesis, structure, and solution properties of P(AM-NVP-DMDA) terpolymer were studied, including its electrolyte effect, rheological behavior, temperature dependence of viscosity, dilute solution property, and the polymer-alkali, polymer-surfactant interaction. The terpolymer shows strong hydrophobic effect, and the terpolymer aqueous brine solution exhibits high viscosity at low polymer concentration. Incorporation of N-vinyl-pyrrolidone into the terpolymer causes an improvement in thermal stability of the terpolymer. The transmission electron photomicrograph analysis of the terpolymer indicates that the presence of the microphase separation of the terpolymer in aqueous solution plays an important role in the viscosification efficiency of the terpolymer.