Structural Features and Mechanical Properties of Hydrogels Based on PVP Copolymers, Obtained in the Presence of a Solvent

The paper analyses the effect of the solvent amount and nature on the structure and mechanical properties of hydrogels based on copolymers of 2-hydroxyethylmethacrylate (HEMA) with polyvinylpyrrolidone (PVP). The synthesis of pHEMA-gr-PVP copolymers was carried out by the copolymerization method in the presence of metal ions of variable oxidation states in solvents with various nature: water, dimethyl sulfoxide (DMSO), diethylene glycol (DEG), and cyclohexanol (HOCy). The structure of the copolymers was evaluated by the PVP grafting efficiency, its actual content in the copolymer, and the molecular weight between crosslinks (M_C). Taking the example of water, an increase in the solvent content up to 50 mass parts causes an increase in the efficiency of PVP grafting, which occurs due to enhanced macromolecule mobility through the dilution of the starting composition, hence the decrease in its viscosity. It was established that the nature of the solvent significantly affects the crosslinking density of the polymer network in the series H₂O, DEG, DMSO, HOCy, an increase in the M_C is observed causing a decrease in the hardness and elasticity of hydrogels and an increase in their water-retention capacity and swelling coefficient. The obtained results prove the possibility of targeted regulation within wide limits of the structure and properties of hydrogels based on pHEMA-gr-PVP copolymers through control of polymerization conditions (selection of the type and concentration of solvent).