Macromolecular architecture of hyperbranched polymers is receiving increasing interest as the search for new tailor-made polymeric materials with strictly specified properties. The liquid-liquid equilibrium of binary solutions of hyperbranched polyesters of second generation (Boltorn H20) in water or in propan-1-ol is investigated experimentally and theoretically. For the theoretical description of the experimental phase diagram a corrected version of the lattice-cluster theory (LCT) is applied, where water occupies one lattice site and has no special structure. In contrast, propan-1-ol is considered as a chain having three segments. The LCT allows the incorporation of the architecture of the polymer and the solvent directly in the thermodynamic quantities, like Gibbs energy of mixing. However, the LCT neglected the self- and cross-association occurring in the mixture made from a polar solvent and a hyperbranched polymer with several functional groups. In order to study the influence of this association interaction on the phase behavior a modified version of the Wertheim theory is combined with the LCT. The developed model shows a good performance for the calculation of the demixing curve in comparison with experimental data, especially in the diluted concentration range. Additionally, the interfacial properties (interfacial tension, concentration profile) between the demixed phases are predicted applying LCT and LCT in combination with the Wertheim theory in the special version of the density gradient theory. This situation allows the investigation of the influence of association forces on interfacial properties. (C) 2010 Elsevier B.V. All rights reserved.