Periodate Oxidation of Methylcellulose: Characterization and Properties of Oxidized Derivatives

Marguerite Rinaudo

doi:10.3390/polym2040505

Abstract

In this paper, the behavior of oxidized methylcelluloses is compared with that of the initial methylcellulose, an amphiphilic cellulose derivative. Methylcelluloses are important for many applications in the cosmetic and food industries. The mechanism of thermo-gelation of methylcellulose is briefly explained as well as the method of oxidation of polysaccharides. Then, our experiments involve the preparation of oxidized methylcelluloses: three degrees of oxidation are prepared and the new polymers are characterized by NMR, IR, SEC and rheology. Oxidation with periodate theoretically allows introduction of two aldehydic groups on C2–C3 glycol positions of anhydroglucose units. This reaction not only enhances the flexibility of the cellulosic backbone, but also causes a decrease in the molecular weight. In particular, the rheological behavior of methylcellulose and oxidized methylcellulose as a function of temperature is examined. The oxidized methylcelluloses prepared, being rich in aldehyde functions, become interesting intermediaries to prepare new cellulose derivatives. In this paper, three examples of reductive amination based on the reaction of modified methylcelluloses and −NH2 groups of different molecules are described: β-alanine produces a polyelectrolyte; chitosan and hyaluronan-ADH (derivative obtained with adipic dihydrazide allowing introduction of −NH2 functions on HA backbone) are crosslinked and give new biocompatible hydrogels.

Highlights

Methylcelluloses are important cellulose ether derivatives which become water soluble in an intermediate range of substitution degree DS with an amphiphilic character and associative properties
Other polysaccharides have been oxidized with metaperiodate, from which: (i) methylcellulose and hydroxyethyl cellulose [22,23,24,25] were produced for their hemostatic properties; (ii) guar and hydroxypropyl guar were oxidized to access the degree of substitution at secondary hydroxyls of hydroxypropyl guar [26]; (iii) alginates were oxidized at different rates and it was shown that the flexibility of the polysaccharide decreases in direct relationship of the opening of uronic acid [15,27,28]; (iv) dextran and scleroglucan were oxidized with periodate [29,30,31]
New oxidized methylcelluloses were prepared and characterized; all the experiments were performed on a low molecular weight initial methylcellulose (Mw~31,500) with the objective to reduce the viscosity of polymer mixtures when needed especially for crosslinking experiments

Summary

Introduction

Methylcelluloses are important cellulose ether derivatives which become water soluble in an intermediate range of substitution degree DS (with 1.4 < DS < 2.5) with an amphiphilic character and associative properties. In spite of their important applications, their mechanism of gelation was discussed for a long time in the literature [3,4] and our group participated in this debate [1,2,5,6,7] For this purpose, methylcelluloses were prepared under homogeneous conditions (in dimethylacetamide DMAc/6% LiCl as solvent) with different degrees of methylation (with iodomethane) and compared to commercial samples having nearly the same average degree of methylation (DS) [1,8]. Methylcelluloses were prepared under homogeneous conditions (in dimethylacetamide DMAc/6% LiCl as solvent) with different degrees of methylation (with iodomethane) and compared to commercial samples having nearly the same average degree of methylation (DS) [1,8] Their behavior is completely different when temperature varies, indicating the strong influence of methyl group distribution along the cellulosic backbone.

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Conclusion