The rheological properties of aqueous solutions of a hydrophobically modified poly(acrylic acid) were studied by diffusing-wave spectroscopy microrheology at various concentrations and temperatures and the formation of the transient network by hydrophobic association of the polymer chains was characterized. The Winter-Chambon power-law regime was found in a high frequency range accessible by microrheology, the physical gel point was successfully determined from the uniqueness of loss tangent, confirmed by the time-cure superposition of the mean-square displacement of the probe particles whose shift factors showed the critical power-law behaviors as a function of the relative distance from the gel point. The zero-shear viscosity as a function of the polymer concentration showed a plateau near the microrheologically determined gel point, indicating the presence of clusters which break before relaxing thus are rheologically undetectable. The largest relaxed cluster size was estimated to be 40 - 60 nm depending of the temperature. (C) 2017 Elsevier Ltd. All rights reserved.