Double-hydrophilic block copolymers of ethylene oxide and acrylic acid or methacrylic acid have been synthesized via radical polymerization using two different methods. Depending on the synthesis method used, branched or linear structures have been obtained, Solution properties of two different kinds of block copolymers have been investigated by dynamic light scattering and viscosimetry. The effects of the solution pH, ionic strength, and temperature on the complexation of the polymers have been studied. Branching affects strongly the flow properties of the polymer solutions. Rheologically the solutions of branched polymers are Newtonian. Fast diffusion of the polymer substructures could be detected by light scattering. Linear block copolymers show shear thinning behavior, as expected. The conformations of the polymer chains have been shown to depend on the solution pH, ionic strength and temperature. Also, the structure of polyelectrolyte complexes changes with temperature at low pH.