Chemical modification of biopolymers-mechanism of model graft copolymerization of chitosan
Mechanism of graft copolymerization of vinyl monomers onto chitosan initiated by Ce(IV) ion, one of the important ways of chemical modification of chitosan, has been investigated by means of kinetics measurement and polymer chain structure analysis. It is found that when Ce(IV) ions
reacts with adjacent hydroxylamine structure in chitosan, a chelate complex is first formed and then it disproportionates to radical for initiation of graft copolymerization. There exist two ways for such initiation depending upon the reaction temperature. For a reaction temperature lower
than 40°C, a -CHO group and a -C=NH group are introduced, and the aldehyde group reacts with Ce(IV) ions to form an acyl radical which initiates a graft polymer chain in this saccharide unit. For temperatures higher than 90°C, the -C=NH group hydrolyzes to form an amine and an aldehyde
group which also reacts with Ce(IV) ions. In this case there should be two aldehyde groups, i.e. two initiation sites, in one adjacent hydroxyl-amine structure. That means that the initial radical in the chitosan/Ce(IV) system is similar to that in the cellulose/Ce(IV) one, but the former
usually gives a lower grafting reactivity than the latter due to the higher stability of the chelate.
Keywords: Ce(IV) initiation; Graft copolymerization; adjacent hydroxylamine/Ce(IV); chitosan model/Ce(IV); reaction mechanism
Document Type: Research Article
Affiliations: Department of Chemistry, Peking University, Beijing 100871, China
Publication date: 01 January 1993
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