[en] Novel thermosensitive copolymers were obtained by γ-initiated copolymerization of 2-hydroxyethylacrylate with relatively hydrophobic monomers - methylacrylate (MA) and butylacrylate (BuA). The compositions of copolymers and their molecular-weight characteristics were determined using NMR(1^H)- and (13^C)-spectroscopy (Bruker ARX 300) and gel-penetrating chromatography (a chromatograph with Aligent 1100 series RI detector) methods. It was shown that aqueous solutions of copolymers have lower critical solution temperature (LCST), the value of which may be regulated by varying the content of the hydrophobic component in copolymer. It was determined that interaction of copolymers with polyacrylic acid (PAA) in aqueous solutions is followed by the formation of interpolymer complexes (IPC) stabilized by a cooperative system of hydrogen bonds. The critical pH value of complexation (pH_crit.) was used as a quantitative criterion of the ability of macromolecules to form interpolymer complexes (IPC). The effect of various factors on IPC stability was studied. It was shown that the increase of polymer concentration, molecular weight of polyacid, ionic strength of solution, as well as the content of MA and BuA hydrophobic units in copolymer results in increase of the ability of the given system to form complexes. It was determined that substantial contribution of hydrophobic interactions to an additional stabilization of IPC is made by buthylacrylate units, this being indicated by corresponding pH_crit. values. The influence of interaction of HEA-MA and HEA-BuA copolymers with PAA on the phase separation temperature (T_ph.s.) of aqueous solutions was studied. It was determined that depending on the acidity of medium the presence of PAA may contribute to the increase of T_ph.s. and to its decrease as well. The effect being observed was shown to be caused by the formation of hydrophobic IPC at low pH values, as well as by the possibility of formation of hydrophilic associates with the participation of HEA-BuA and PAA macromolecules at pH values which are slightly higher than critical pH values of complexation. Film material on the basis of HEA-MA-PAA and HEA-BuA-PAA polycomplexes were obtained by the γ-radiation cross-linking method, it was shown that their physico-chemical behavior may be regulated by varying the irradiation dose and the ratio of polymer components