Preparation and Characterization of Pullulan/Poly(N-vinylimidazole) Gels

Pullulan/Poly(N-vinylimidazole) (PNVI) hybrid materials have been prepared and characterized according to their physicochemical properties. Graft copolymerization and cryopolymerization/cryogelation approaches were applied in the preparation of pullulan/poly(N-vinylimidazole) samples. Graft copolymerization of PNVI onto pullulan backbone was studied in aqueous solution by using ammonium persulphate initiation. A maximum grafting yield of 513% was obtained using 8.00 g/L pullulan, 0.66 M NVI and 0.18 M ammonium persulphate at 40°C for 3 h reaction duration conditions. Water soluble pullulan-graftPNVI samples were obtained that exhibited antibacterial and antifungal activities. These samples precipitate out of solution via complex formation with polyanions such as tripolyphosphate and citrate ions. Epichlorohydrin (ECH) crosslinked pullulan gel was used as substrate for grafting of PNVI to obtain pullulan/PNVI hybrid gels. The maximum grafting yield obtained for pullulan-ECH-graft-PNVI samples was 189% when 8.0 g/L pullulan gel, 0.57 M NVI and 0.18 M ammonium persulphate were used at 40°C for 3 h reaction duration conditions. Lower grafting yields were obtained due to the heterogeneous nature of the reaction medium when compared to the grafting yields in solution. Pullulan-ECHgraft-PNVI exhibit superabsorbency within 700-1300% and 6000-8500% ranges equilibrium water retention capacity in distilled water and in aqueous acidic medium respectively. Cryogels of pullulan in the presence of ECH, PNVI cryogels in the presence and in the absence of ECH and pullulan/PNVI cryogels in the presence of ECH were prepared. Product yields and gel fraction yields were determined and correlated with cryogel preparation conditions. Similar to pullulan-ECH-graft-PNVI samples, the cryogels acted as hydrogels with maximum equilibrium swelling capacities of 425%, 240%, 270% and 620%, for pullulan-ECH, PNVI, PNVI-ECH, and pullulan-ECH-PNVI cryogel samples, respectively