New trends in cellulose chemistry – highly engineered products by homogeneous synthesis

Thomas Heinze

Kompetenzzentrum Polysaccharidforschung, Friedrich-Schiller-Universität Jena,

Humboldtstraße 10, D-07743 Jena

E-mail: thomas.heinze@uni-jena.de

Although various cellulose solvents are known –a short overview will be presented– the development of new media for dissolution and homogeneous modification of the biopolymer is still an important area of research.

A new and simple system to dissolve cellulose was found to be a mixture of dimethyl sulfoxide in combination with tetrabutylammonium fluoride. Cellulose with a DP of up to 1200 can be dissolved without any pre-treatment provided the content of water is as low as possible. Chemical modification reactions to cellulose esters proof the efficiency of the solvent. Long chain aliphatic- and furancarboxylic acid esters as well as products containing crown ether structures are accessible by a mild reaction procedure applying N,N-carbonyldiimidazole as in situ activation reagent. The new cellulose esters were extensively characterized regarding their molecular structure by applying various NMR techniques. The cellulose esters nicely form membranes as revealed by means of REM and AFM.

Ionic liquids are a new type of cellulose solvents as recently published by Swatloski et al. [J. Am. Chem. Soc. 2002, 124, 4974]. In the course of our work on cellulose solvents, ionic liquids like 1-N-butyl-3-methylimidazolium chloride, 3-methyl-N-butyl-pyridinium chloride, and benzyldimethyl(tetradecyl)ammonium chloride were characterized to be non-derivatizing solvents for cellulose that was confirmed by means of ¹³C NMR spectroscopic studies. Cellulose samples with a DP of up to 1200 can be dissolved without chain degradation. The solutions may be diluted with dimethyl sulfoxide. The ionic liquids are new reaction media for the carboxymethylation and in particular for the acylation of the biopolymer. Cellulose esters with high degree of substitution could be synthesized without any catalyst [Heinze et al., Macromol. Biosci. 2005, 5, 520].