Dissociation behaviors of carboxyl and amine groups on carboxymethyl‐chitosan in aqueous system

Abstract

Several carboxymethyl‐chitosan (CMCS) samples with different deacetylation degree and/or substituted degree were prepared from the carboxymethylation reaction of chitosan under soft conditions. The products were dissolved in standard HCl aqueous solution to carry out potentiometric titration by using NaOH as titrating solution at different ionic strengths. Then the dissociation behaviors of protonated carboxyl and amine groups were investigated under their degree of dissociation (α) and protonation constant (pKα) had been calculated. Moreover, influences of the intrinsic and extrinsic parameters on the dissociation behavior of CMCS were also considered in this article. As a result, dissociations of carboxyl and amine on CMCS exhibited unusual behaviors in comparison with carboxyl of carboxymethyl‐cellulose and amine groups of chitosan, respectively. The pKα values of carboxyl declined slightly at early dissociation stage but subsequently maintained constant. In contrast, the pKα of ammonium increased with its dissociation degree despite that there was an inflexed change on its dissociation curve. The potentiometric behavior of carboxyl was hardly affected by variation of deacetylation degree or substituted degree. However, these intrinsic parameters played more important role on dissociations of ammonium on CMCS. The ionic strength of media could bring screening effect on dissociaciation of both sorts of ionizable groups of CMCS. By increasing the ionic strength of media, screening effect on dissociations increased significantly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1419–1429, 2008

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“…[25,29,41,48,[107][108][109] Moreover, the correlations between the DS and the reaction conditions are presented in Figure 9. [25,29,41,48,[107][108][109] Moreover, the correlations between the DS and the reaction conditions are presented in Figure 9.…”

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“…[41][42][43][44][45] Moreover,c arboxymethylationw as used on Cassia angustifolia seed gum and chitosant oi mprove their rheological properties for biomedical applications. [46][47][48] In addition to aw ide range of studies on the carboxymethylation of biomass, others tudies have been performed to analyze other carboxyalkylation reactions. Carboxyalkylation is aw ell-known derivatization process that induces products with primary and/or secondary alcoholgroupsifaliphatic or aromaticu nits of polymers are etherified by ad irect alkylation methodw ith monohalocarboxylic acids.…”

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