The Evaluation of Cross-Linker Content Impact on the Swelling Capacity of Poly(1-Vinyl-2-Pyrrolidone) Hydrogels

Poly(1-vinyl-2-pyrrolidone), p(VP), is a polar, hydrophilic, amphoteric polymer, derived from a monomer of 1-vinyl-2-pyrrolidone. It is used in many branches of industry (in the production of glues, paper and detergent). Due to its solubility in water and low cytotoxicity is one of the most used polymers in medicine. The aim of this study was to examine swelling behavior of synthesized poly(1-vinyl-2-pyrrolidone) hydrogels. By free radical polymerization of 1-vinyl-2-pyrrolidone, samples of poly(1-vinyl-2-pyrrolidone) hydrogels with 1.0, 2.0 and 3.0 mol% of ethylene glycol dimethacrylate (EGDM) as cross-linker were synthesized. The polymerization reaction was initiated by the addition of 2,2'-azobis(2-methylpropionitrile) (AZDN) initiator, and the reactants were dissolved in an adequate amount of methanol. Data obtained by scanning electron microscopy (SEM) were used to determine the structure and pore size of the freeze-dried hydrogels, swelled to equilibrium state. Synthesized p(VP) hydrogels were used to test swelling behavior and their sensitivity to changes in pH values (3.0, 6.0 and 9.0) and temperature (25-80°C). The swelling process was monitored gravimetrically. Swelling of hydrogels p(VP) is most intense at room temperature (25°C). The most intensely swelling is in a alkaline fluid, pH=9.0 (αe=141.98 for the sample with 1 mol% EGDM). In a fluid of pH 6.0 they achieved equilibrium degree of swelling αe=67.46. At 25°C the smallest degree of swelling of p(VP) is in the strong acidic fluid, pH=3.0 (αe=34.13). The thermo-sensitivity testing showed that degree of swelling decreases along with temperature increasing. The phase transition is in the temperature interval from 40°C to 45°C. The lowest degree of swelling of p(VP) was achieved in the highest tested temperature at 80°C (α=12.13). Porous structure of p(VP) hydrogels were confirmed by SEM micrographs. It can be concluded that with a decrease in the amount of cross-linker increases the pore size and degree of swelling of synthesized cross-linked p(VP) hydrogels.