Studies on graft copolymerization of chitosan with synthetic monomers

Graft copolymerization of acrylonitrile and methylmethacrylate onto chitosan using potassium persulfate as an initiator was studied. Evidence for graft-copolymerization was obtained by infrared spectroscopy and CP-MAS 13C-NMR data. The appearance of nitrile (–CN) at 2244 cm−1 for chitosan-graft-polyacrylonitrile (C-g-PAN) and carbonyl (–CO) at 1730 cm−1 for chitosan-graft-polymethylmethacrylate (C-g-PMMA) confirmed graft-copolymerization. CP-MAS 13C-NMR showed the appearance of a signal at 33 ppm assigned to the N–CH group. With varying monomer concentration (40–180 mM), the percentage degree of substitution varied from 2 to 50. Maximum grafting efficiency was obtained with 120 mM acrylonitrile and 0.74 mM potassium persulfate at 65 °C for 2 h under nitrogen atmosphere for 1% chitosan solution and for C-g-PMMA 140 mM methylmethacrylate at 75 °C gave maximum substitution. X-ray diffraction showed changes in crystallinity pattern. Slightly different mechanisms in side chain substitution for these two copolymers were envisaged. DSC thermogram showed a decomposition peak for C-g-PAN at around 255 °C and a melting peak for C-g-PMMA at around 400 °C. C-g-PMMA could be thermopressed into films. Residual monomers were not found by HPLC in graft copolymers stored even for longer periods.