A series of terpolymers containing acrylic acid (AA), methacrylamide (MAM), and a twin-tailed hydrophobic monomer (DiC(6)AM, DiC(8)AM, or DiC(10)AM) were synthesized using micellar polymerization methods. These polymer systems were characterized using light scattering, viscometry, and fluorescence methods. Viscosity studies indicate that increasing the nonpolar character of the hydrophobic monomer (longer chain length or twin tailed vs single tailed) results in enhanced viscosity in aqueous solutions. The terpolymer with the highest hydrophobicity (MAM/AA/DiC(10)AM terpolymer) exhibited the most pronounced viscosity increase with polymer concentration and thus the best associative thickening. Fluorescence nonradiative energy transfer measurements performed on this terpolymer indicate the onset of association (c*) at a concentration of similar to0.1 g/dL. Also, changes in the energy transfer efficiency and viscosity behavior as a function of pH are consistent with a concentration-dependent transition from closed to open associations.