The effect of structure and composition of poly(methyl methacrylate) (PMMA) main chain and poly(propylene oxide-b-ethylene oxide) (PPO-b-PEO) graft chain on solution behavior was evaluated. Separated samples of homopolymers were also analysed to provide comparisons, The solutions were prepared by dissolving the sample in selective mixtures of tetrahydrofuran (THF) and hexane. The polymer solutions were submitted to viscometric measurements as function of the solvent composition. The ratio of ethylene oxide/propylene oxide (EO/PO) units determines the modification in molecular conformation of the (PPO-b-PEO) block copolymers as function of the solvent composition. The macromolecular structure is the most important factor on the graft copolymers behavior. The structure in which ethylene oxide is linked to the main chain provides higher interaction between graft copolymers and solvent (THF/hexane).