Chitosan graft copolymerization

D. Mechanism of Graft Copolymerization of Chitosan Model Compounds... 

Recently, Li et al. [30], Yu et al. [31] reinvestigated the mechanism of graft copolymerization of vinyl monomers onto carbohydrates such as starch and cellulose initiated by the Ce(IV) ion with some new results as mentioned in Section II. Furthermore, they investigated the mechanism of model graft copolymerization of vinyl monomers onto chitosan [51]. They chose the compounds containing adjacent hydroxyl-amine structures, such as D-glucosamine, /mn5-2-amino-cyclohexanol, 2-... 

Recent progress of basic and application studies in chitin chemistry was reviewed by Kurita (2001) with emphasis on the controlled modification reactions for the preparation of chitin derivatives. The reactions discussed include hydrolysis of main chain, deacetylation, acylation, M-phthaloylation, tosylation, alkylation, Schiff base formation, reductive alkylation, 0-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Among soluble precursors, N-phthaloyl chitosan is particularly useful and made possible a series of regioselective and quantitative substitutions that was otherwise difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone [89]. 

The possibility of grafting synthetic polymer to chitosan has attracted much attention in the last years as a new way to modify the polysaccharide and develop practically useful derivatives. Graft copolymerization reactions introduce side chains and lead to the formation of novel types of tailored hybrid materials composed of natural and synthetic polymers. Grafting chitosan is a common way to improve chitosan properties such as formation of inclusion complexes [99], bacteriostatic effect [100], or to enhance adsorption properties [101, 102]. Although the grafting of chitosan modifies its properties, it is possible to retain some interesting characteristics such as mucoadhesivity [103], biocompatibility [104,105] and biodegradability [106]. 

Zohuriaan-Mehr MJ (2005) Advances In chitin and chitosan modification through graft copolymerization a comprehensive review. Iran Polym J 14 235-265... 

Liu L, Chen LX et al (2006) Self-catalysis of phthaloylchitosan for graft copolymerization of epsilon-caprolactone with chitosan. Macromol Rapid Commun 27 1988-1994... 

The physical and mechanical properties of chitosan can be amefiorated by using graft copolymerization and crosslinking. Chitosan forms aldimines and ketimines with aldehydes and ketones, respectively. Upon hydrogenation with simple aldehydes, chitosan produces A-alkyl chitosan [60]. The physicochemical and biological properties [61] as well as conformational structures [62] of chitosan are very effective for biomedical applications. 

Singh, D.K. and Ray, A.R. 1994. Graft copolymerization of-2 hydroxyethyhnethacrylate onto chitosan films and their blood compatibility. J Appl Polym Sci. 53 1115-1121. 

PROPERTIES OF SPECIAL INTEREST Natural resources basic polysaccharides nontoxic biodegradability bioactivity biosynthesis interesting derivatives (chitosan) toughness graft copolymerization chelating ability for transition metal cations immobilizes enzymes by chemical linking or adsorption chiral polymer. 

Chitosan can be chemically modified by etherification and esterification of its hydroxyl groups, by the N-substitution of its nucleophilic amino group (C-2), or by graft copolymerization to get a broad range of chitosan derivatives that can easily dissolve in the entire range of pH [93]. 

D.W. Jenkins, S.M. Hudson, Review of vinyl graft copolymerization featuring recent advances toward controlled radical-based reactions and illustrated with chitin/chitosan trunk polymers, Chem Rev. 101 (11) (2001) 3245-3274. 

L. Liu, L. Chen, Y.E. Fang, Self-catalysis of phthaloylchito-san for graft copolymerization of e-caprolactone with chitosan. Macromol. Rapid Commun. 27 (2006) 1988-1994, doi 10.1002/ marc.200600508. 

Apart from polyplexes that are a spontaneous outcome of polynucleotide condensation by cationic polymers, nanoparticles can be obtained by directly using cationic polymers such as chitosan, or by coating nanoparticles that are not cationic by grafting/copolymerization, or by simple electrostatic interactions with cationic polymers, lipids or surfactants. 

In order to improve the properties of these unique polysaccharides and to develop new advanced materials, much attention has been paid to their chemical modification. These polymers have two reactive groups suitable for this purpose, namely, primary (C6) and secondary (C3) hydroxyl groups in the case of chitin whereas chitosan has additionally the amino (C2) group on each deacetylated unit. All these functions are susceptible to a variety of classical reactions which can be applied here in a controlled fashion to obtain a vast array of novel materials based on the two polysaccharides which can also be modified by either crosslinking or graft copolymerization. This topic has been extensively studied and thoroughly documented [5-7]. 

Jayakumar, R., Prabaharan, M., Reis, R.L., and J.F. Mano. 2005. Graft copolymerized chitosan—Present status and applications. Carbohydrate Polymers 62 142-215. 

Xie et al. (2001) have reported that the water-soluble chitosan derivatives prepared by graft copolymerization of maleic acid sodium onto hydroxypropyl chitosan and carboxymethyl chitosan sodium, exhibit scavenging activities against hydroxyl radicals. 

A. Carreira, E. Gonsalves, P. Mendon( a, M. Gil, and J. Coelho, Temperature and pH responsive polymers based on chitosan applications and new graft copolymerization strategies based on living radical polymerization. Carbohydrate Polymers, 80 (3), 618-630, 2010. 

G. Huacai, P. Wan, and L. Dengke, Graft copolymerization of chitosan with acryhc acid under microwave irradiation and its water absorbency, Carbohydr. Polym., 66 (3), 372-378, 2006. 

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