Self assembly in aqueous solutions of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) has been studied. The onsets of aggregation and the relative viscosity increase coincide. Below the gelation temperature both relative and zero-shear viscosities grow as the square root of total polymer concentration, defining polymer solutions as semidilute and unentangled. Significant differences between complex and stead,v-shear viscosities in the low-shear, low-frequency regions are observed, in contrast to the Cox-Merz rule. Gelation is characterized by the appearance of well-defined, slow relaxation modes above frequencies corresponding to the liquidlike flow. The gel elasticity can be related to the functionality of aggregates that increases with the polymer concentration.