Our investigation of free-standing vertical films of hydrophobically modified poly(acrylic acid) sodium salt by the X-ray reflectivity technique shows that the organization of these films strongly depends on the molecular weight and hydrophilic-hydrophobic monomer unit ratio of the copolymers. Long polymer chains with a low amount of hydrophobes form films composed of two layers of coils facing each other. In contrast, short polymer chains with a higher degree of hydrophobic modification form films with a well-defined semiordered structure whose properties are closely linked to the properties of the corresponding solution. We show that this structure is of electrostatic origin. Finally, the comparison of films made of the copolymers in their charged and neutral forms shows that the dominant force within the two types of film is respectively the counterion osmotic pressure and the energy of adsorption of the hydrophobic monomers.