1 Investigations of the radiolysis of aqueous solutions of polymers have attracted considerable interest, which is mainly due to the development of the radiation-chemical synthesis of hydrogels. This method of synthesis implies irradiation of aqueous solutions of crosslinkable polymers, such as poly(vinyl alcohol), polyvinylpyrrolidone, poly(ethylene glycol), and poly(ethylene oxide). The process of macrochain crosslinking resulting in the formation of hydrogels upon γ -irradiation of aqueous solutions of polymers is initiated by water radiolysis transient products, first of all, hydroxyl radicals. The interaction of OH radicals with a macromolecule leads to hydrogen atom abstraction followed by recombination of macroradicals. As a result, the polymeric chains are crosslinked to form a three-dimensional polymeric network, that is, a hydrogel.Poly(ethylene oxide) (PEO) is one of the polymers that are commonly used for the synthesis of hydrogels. The PEO-based hydrogels possess a set of properties that make these materials suitable for biological (separation and purification of proteins), medical (drug delivery systems of prolonged action and wound dressing), chemical (separation of metal cations), and other applications (the examples may be found elsewhere [1][2][3][4][5]). Recently, we have demonstrated the feasibility of synthesis of a PEO hydrogel with a physically immobilized crown ether, which can selectively bind metal cations due to specific complex formation [6]. Although the radiation-chemical synthesis of PEO hydrogels was investigated in numerous works, to our knowledge, there are a few publications on the radiolysis of PEO and its aqueous solutions. Zainuddin et al. [7] have 1 E-mail: olzak@mail.ru shown that both crosslinking and scission of polymer chains occur simultaneously upon γ -irradiation of solid poly(ethylene oxide) in the absorbed dose range up to 20 kGy. In this case, the prevalence of crosslinking or scission depends on both absorbed dose and molecular weight of the polymer. On the other hand, the radiolysis of dilute aqueous PEO solutions was studied by pulse radiolysis [8,9], which made it possible to determine the rate constants for the reactions of OH radicals, H atoms, and hydrated electrons in this system. These studies have demonstrated that hydroxyl radicals are the main precursors of macroradicals from PEO. However, data on the nature and radiation-chemical yields of intermediates resulting from the radiolysis of PEO and its aqueous solutions are very scarce.Detailed information on the composition and yields of radical products of radiolysis and their reaction kinetics can be obtained in low-temperature ESR spectroscopic studies. In this case, it is possible not only to identify the radicals trapped after irradiation of a frozen solution, but also to follow the character of their postirradiation transformations occurring upon gradual freezing-out of molecular mobility. Note that the frozen solutions of water-soluble polymers are complex microheterogeneous systems and, thus, the r...
