Chitosan Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 73

hosting molecules. The adsorption experiments were conducted under different condi-
tions with a view to establishing appropriate conditions for dye adsorption.
CDs have received much attention because of their unique ability to form host-guest
complexes with various organic compounds. Grafting CD molecules into chitosan leads to
a molecular carrier exhibiting promising properties because of the cumulative effects of
size specificity and the transport properties of CDs. Due to the CD moiety present in the
chitosan backbone, it was found that β-CD-grafted chitosan has some selectivity for the
adsorption of TNS, bisphenol A, p -nonylphenol, and cholesterol and has stronger inclusion
and slow release ability with iodine. This CD-grafted polymer has also confirmed the
host-guest complex with p -nitrophenol, p -nitrophenolate, tert-butylbenzoic acid, 6-thiopu-
rine, p -dihydroxybenzene, and copper ions. Due to the inclusion properties, the CD-grafted
chitosan was found to be useful in drug delivery, cosmetics, decontamination of water
containing textile dyes and metal ions, and analytical chemistry.

2.11 Graft Copolymers of Chitosan
Graft copolymerization is the main method used to modify chitosan chemically. In recent
years, a number of initiator systems such as ammonium persulfate (APS), potassium per-
sulfate (PPS), CAN, thiocarbonationpotassium bromate (TCPB), potassium diperiodato-
cuprate(III) (PDC), 2,2-azobisisobutyronitrile (AIBN), and ferrous ammonium sulfate
(FAS) have been developed to initiate grafting copolymerization [227-230]. Graft copoly-
merization can also be initiated by irradiation and enzymes. Grafting parameters such
as grafting percentage and grafting efficiency are greatly influenced by several parameters
such as the type and concentration of initiator, monomer concentration, reaction tempera-
ture, and time. The properties of the resulting graft copolymers are widely controlled by
the characteristics of the side chains, including molecular structure, length, and number.
To date, many researchers have studied the effects of these variables on the grafting param-
eters and the properties of the resultant grafted chitosan (Table 2.3).

TAble 2.3
Different Graft Copolymers of Chitosan and Ways of Grafting
Initiator Monomers Grafted

Copolymerization via
radical-induced
radical generation

CAN (NH 4 ) 2 Ce(NO 3 ) 6 Acrylonitrile [231,232]

N -isopropyl acrylamide [233]
Acrylic, methylacrylic acid [234]
Methyl methacrylate,
2-hydroxyethylmethacrylate [235-237]
Vinyl acetate [235]
Vinyl pyridine [229]
N , N 0-dimethyl- N -methacryloxyethyl- N -
(3-sulfopropyl)ammonium [238]
Dimethylamino ethyl methacrylate [239]
Acrylamide [240]
Triethylene glycol dimethacrylate [241]
N -vinylimidazole [242]