**5. Conclusions**

The charge-transfer complex between polyvinylpyrrolidone and 2-hydroxyethyl methacrylate has been determined to affect the polymerizability of PVP/HEMA formulations and the structure of the resulting copolymers. Increasing Кst for the PVP/HEMA complexes has been shown to increase the cross-linking degree of the formed polymer network. It has been revealed that loosely cross-linked PVP/HEMA copolymers and hydrogels based on them can be developed without any radical initiator or in the presence of iron(II) and iron(III) ions. The synthesized hydrogels have increased water content, and their mechanical properties can be easily tuned in a wide range. Moreover, the hydrogels possess high permeability for low-molecular water-soluble substances. Hydrogels also are able for selective sorption of drugs, including a blood anticoagulant heparin. The developed hydrogel materials have been widely tested in industry and recommended for manufacturing various products of medical applications.
