Acylation studies on chitosan and substituted chitosans.

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Moore, G.K., 1978. Acylation studies on chitosan and substituted chitosans. PhD, Nottingham Trent University.

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Abstract

Several detailed aspects of the heterogeneous and homogeneous acylation reactions of chitosan and substituted chitosan have been studied.

Acetylation of chitosan in film or reprecipitated form, using conventional cellulose techniques, were unsuccessful. However, a facile, selective technique was developed for the N-acylation of chitosan film, using methanol/carboxylic acid anhydride mixtures. The solubility parameter values of the solvent system were found to be important in the acylation reactions, no reaction occurring in media having a solubility parameter value δ < 13 Hildebrands.

O-Acetylation studies of various N-acyl chitosan films in pyridine/acetic anhydride mixtures showed that there was a minimum spacing required between the polymer chains to enable the reaction to take place. Increased distance between the chains brought about only slight improvement in the extent of reaction, whilst the presence of bulky N-acyl groups were found to hinder the reaction. O-Acetylation was found to be incomplete, only 50% of the available hydroxyl groups being acetylated after prolonged reaction times in the majority of cases.

O-Acetylation of various linear aliphatic Schiff's base derivatives of chitosan gave a similar pattern to that of the equivalent N-acyl derivatives. The N-substituents were-susceptible to hydrolysis and N-acetylation accompanied the hydrolysis. However, the aromatic Schiff's base derivatives showed marked differences to the equivalent N-acyl chitosans. O-Acetylation was found to be virtually complete in the majority of cases whereas only approximately 50% of the hydroxyl groups had again reacted in the case of the N-acyl chitosans.

A di-O-acetyl-N-acetyl chitosan has been prepared by O-acetylation of a Schiff's base intermediate followed by hydrolysis and N-acetylation. Organosoluble carbamates of some Schiff's base derivatives of chitosan have also been prepared.

Gelation of chitosan solutions in methanol/acetic acid/carboxylic acid anhydride mixtures have been followed by monitoring the reaction viscosity changes during gelation. The viscosity versus time curve was a smooth curve but kinked, indicating that the gelation process was not simple chain aggregation. Variations in temperature, anhydride and polymer concentration and co-solvents have been studied and gelation was found to start after about 60-70% of the primary amines had been acylated. A mechanism has been proposed for the gelation process based on the experimental evidence.

Item Type:

Thesis

Creators:

Moore, G.K.

Date:

1978

ISBN:

9781369313970

Identifiers: