<p>A graft copolymer with thermoresponsive poly-2-isopropyl-2-oxazoline side chains and an aromatic polyester backbone containing aliphatic spacer –(CH₂)₄– was synthesized and studied using NMR, GPC, static and dynamic light scattering, and turbidimetry. The molar mass of the main and side chains, their length, as well as the number of side chains and the density of their grafting were determined. The conformation in aqueous solution was assessed. The behavior in water when heated over a wide range of concentrations and temperatures was studied. The phase separation temperatures and their dependence on concentration were obtained, and LCST = 50&#xa0;°C was determined. Kinetic characteristics of equilibrium establishment in solution and the formation of supramolecular structures were analyzed. The influence of the spacer length and side chain length on the thermoresponsiveness and self-organization of copolymer macromolecules was discussed. It was shown that, due to the long side chains and short distance between grafting points, phase separation upon heating is preceded by intramolecular aggregation.</p>