Due to the negative impact of environmental pollution and increasingly intense global climate changes, in recent decades many researches have been focused on the development of coatings for the preservation of cultural heritage made of bronze. Polyurethane coatings have a number of specific properties that make them suitable for use in the protection of bronze cultural heritage. In addition, durability is expected from the coating used as a protective layer in different environmental conditions, which can consequently cause changes in the structure of the coating and eventually cause its deterioration. Therefore, it is of great importance to study coupling agents that play the role of adhesion promoters, that is, that improve the adhesion of the coating to the metal surface. For this purpose, in this work, bronze surfaces were modified with self-organizing monolayers with three types of phosphonic acids, after which a one-component polyurethane coating was applied. In order to examine the influence of phosphonic acids on adhesion and the effectiveness of corrosion protection of polyurethane coating, corrosion studies were conducted during the three weeks of continuous immersion of bronze samples in a solution of simulated acid rain by measuring polarization resistance and electrochemical impedance spectroscopy. Tests of the adhesion of the polyurethane coating to the bronze surface were performed using the pull-off method. The surface of the samples before and after exposure to the corrosive environment was characterized by Fourier transform infrared spectroscopy.