Conjugates of hindered phenols (HP) with oligomeric polyethylene glycols (molecular weight M 3400-22000) in aqueous solutions have high antioxidant activity and thermosensitivity, which is characterized by the lowest critical mixing temperature (LCMT), upon which the polymeric antioxidant is released from the solution. This process is observed visually or by the method of photon correlation spectroscopy. The value of the LCMT depends on the M of polymer and the hydrophobicity of the HP, determined by the nature of the substitution. Changing LCMT can serve as an indicator of the chemical and structural changes that occur in the system, also the presence and concentration of electrolyte in it.