A terpolymer (PAAP) of acrylamide, sodium 2-acrylamido-2-methylpropane sulfonate, and vinyl biphenyl as a hydrophobic monomer was synthesized to obtain a polymeric oil-flooding agent with low molecular weight and application in oil reservoirs with medium to low permeability. The intermolecular self-assembling mechanisms in the PAAP solutions were investigated with a pyrene fluorescence probe as functions of the polymer concentration, surfactant, and temperature. The hydrophobically associating morphologies of PAAP in an unsalted solution were observed with scanning electron microscopy. The results show that the high Solution viscosity of PAAP was due to the strong intermolecular hydrophobic associations of the biphenyl groups, and the critical association concentration was 0.05 g/dL for the unsalted and brine PAAP solutions. The nonpolarity and association degree in the hydrophobic microdomains were greatly influenced by the polymer concentration. With the addition of the optimum sodium dodecyl benzene sulfonate concentration, the interpolymer hydrophobic associations were strengthened remarkably via the connection of the surfactant with biphenyl groups from different polymer chains. The number and sizes of the aggregates increased in the range of 20-50 degrees C. These results demonstrate that the thickening effect of the PAAP polymer in the aqueous solution was due to intermolecular associations of the biphenyl groups. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 404-412, 2010