The viscoelastic properties of a 4-branched poly(ethylene oxide)-poly(propylene oxide)poly(ethylene oxide) copolymer in aqueous solutions have been studied in all parts of its phase diagram. In the unimer zone, the solution behaves like a Maxwellian fluid. The formation of micelles induces the presence of a secondary relaxation process on the dynamic mechanical response of the system. When the micelles condense into a crystalline body centered structure, the solution exhibits theological properties similar to the behavior of an entangled polymer. The crystal's terminal relaxation time tau is strongly dependent on the value of the stress used in the dynamic mechanical test. Stress-time relationships can also be observed with yield stress measurements. First of all, the structural origin of these phenomena has been explored. The relevance of several already proposed mechanisms has been analyzed and discrepancies between rheological results and SANS experiments discussed. We have been able to demonstrate that the evolution of the crystalline phase's terminal relaxation time with stress can be described with an approach derived from Eyring's theory. Moreover, this theological relaxation time has been interpreted as being characteristic of a micelle's diffusion in a crystalline structure. Finally, the values of the diffusion length and the intermicellar energy have been calculated and compared to already existing theories. (C) 2004 The Society of Rheology.