Analyses of structure and thermal properties of synthesized crosslinked poly(1-vinyl-2-pyrrolidone-co-vinyl acetate) hydrogels

This paper describes the process for the synthesis of chemically crosslinked copolymer hydrogels based on monomer 1-vinyl-2-pyrrolidone and comonomer vinyl acetate, using the varied content of ethylene glycol dimethacrylate as a crosslinker, by the free radical polymerization method with thermal initiation. The content of unreacted reactants after poly(1-vinyl-2-pyrrolidone-co-vinyl-acetate), p(VP-VA), hydrogels synthesis was examined using high-pressure liquid chromatography (HPLC) method. Structure characterization of the obtained p(VP-VA) hydrogels was performed using the Fourier transform infrared spectroscopy (FTIR). In this study, the influences of crosslinker content and temperature on the swelling behaviour of p(VP-VA) were studied. Quantities of unreacted comonomers and crosslinker, calculated in relation to the initial amount present in the reaction mixture, confirmed their successful conversion into p(VP-VA) hydrogels. These unreacted values of 1-vinyl-2-pyrrolidone (in range of 0.605-1.609%), vinyl acetate (in range of 2.486-4.798%), and ethylene glycol dimethacrylate (in range of 0.889-3.240%) were within acceptable limits, and they were removed from the final products. FTIR spectra were verified that the copolymerization process was performed, and chemically crosslinking of polymer chains occurred by breaking double bonds from the reactants. Obtained crosslinked copolymers could be classified in the class of negative-thermosensitive hydrogels because they can swell and pass through a phase transition when heated from the swollen state at 25ºC to contracted state at 80ºC.