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 (–CxN)
at 2244 cm21 for chitosan-graft-polyacrylonitrile (C-g-PAN) and carbonyl (–CyO) at 1730 cm21 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 8C for 2 h under nitrogen atmosphere for
1% chitosan solution and for C-g-PMMA 140 mM methylmethacrylate at 75 8C 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 8C and a melting peak for C-g-PMMA at around 400 8C. C-g-PMMA
could be thermopressed into films. Residual monomers were not found by HPLC in graft copolymers stored even for longer periods.