Abstract <p>The influence of coordination crosslinking with zirconium acetylacetonate Zr(AcAc)₄ and sulfonation on the properties of polyphenylquinoxaline (PPQ) is comprehensively investigated using surface energy models (OWRK and vOCG), Hansen solubility parameters (HSPs), measurements of swelling in H₃PO₄, IR spectroscopy, and quantum-chemical calculations performed in terms of the density functional theory (DFT). Sulfonation of PPQ leads to a significant increase in the polar and acid–base components of the surface energy, which is in good agreement with the calculations of the electrostatic potential (ESP) and dipole moment. A pronounced correlation is found between the surface HSPs (calculated on the basis of contact angles) and the degree of swelling in H₃PO₄. Coordination crosslinking with the use of Zr(AcAc)₄ (0.5 wt %) provides the polymer with stability in phosphoric acid. The calculations of the binding energy and bond order confirm the formation of strong coordination bonds between Zr⁴⁺ ions and nitrogen atoms. The modification of PPQ makes it possible to regulate the key characteristics, such as swelling and suitability for operation in aggressive environments, of proton-conducting membranes.</p>