Mixtures of poly(ethylene oxide) (PEO) end-capped on one or both ends with hexadecyl, but with the same hydrophilic-lypophilic balance, were studied using static and dynamic light scattering and dynamic mechanical measurements. In aqueous solution the mixtures form polymeric micelles with aggregation numbers that are independent of the fraction of difunctionalized PEO. Difunctionalized PEO bridges between two micelles, which leads to reversible association of the micelles. The phase behavior and the association of the micelles can be described by modeling the micelles as adhesive spheres with an adhesion parameter that depends on the fraction of difunctionalized PEO and the temperature. Above a given concentration the micelles percolate, leading to a strong increase of the viscosity and the high-frequency shear modulus. The viscosity has an Arrhenius temperature dependence with an activation energy close to that of the relaxation time that characterizes the decay of the shear modulus. At even higher concentrations an abrupt transition is observed that is characterized by the appearance of a second relaxation process with a very long relaxation time. The transition can be induced by small increases of the temperature or the concentration. The slow relaxation is attributed to restructuring of a solution of close packed micelles (e.g., hopping of micelles) while the fast relaxation, which is still visible at high concentrations, is attributed to the breakup of elastic bridges by the escape of end groups from the micelles.