Synthesis and Characterization of Water Soluble Chitosan Derivatives.

Chitin, one of the most ubiquitous natural polymers, remains underutilized. The integral part chitin plays in natural biocomposites suggests that synthetic composites incorporating chitin should exhibit interesting properties, both with respect to strength and biodegradability. Due to a very strong hydrogen bonding, chitin is a very intractable material, but its derivative, chitosan, is very amenable to chemical modifications. Controlled deacetylation of chitin produces water soluble chitosan that is very efficient in complexing metals and natural biomolecules; major applications in water purification are reviewed. In an effort to produce more water soluble derivatives of chitosan, with potential applications in the cosmetics and flocculation industries, we have evaluated the reaction of alkyl oxiranes with chitosan. We have prepared under basic and heterogeneous conditions hydroxyethyl chitosan, hydroxypropyl chitosan, and 2-hydroxypropyl trimethylammonium chitosan chloride, which are water soluble. More lipophilic derivatives such as hydroxybutyl chitosan and hydroxy(2-phenyl)-ethyl chitosan could be produced under acidic catalysis; however these derivatives are only soluble in acidic media. Synthesis of cyanoethyl chitosan and its subsequent derivatization to aminopropyl, carboxyamidoethyl and carboxyethyl chitosan was achieved but their solubilities in water and polar organic solvents are more limited than the oxirane derivatives. A method to promote decrystallization of chitosan, which increases its reactivity, prior to its derivatization is also presented