Tailored Media for Homogeneous Cellulose Chemistry: Ionic Liquid/Co-Solvent Mixtures a Martin Gericke, Tim Liebert, Omar A. El Seoud, Thomas Heinze* Introduction Controlled chemical modification of cellulose, the most abundant bio-polymer worldwide, grants access to a large variety of compounds for applications ranging from multi-kiloton products for food and construction material industry to highly engineered materials for medical and biotechnological applications. [1] In this context, homoge- neous cellulose derivatization is advantageous because it results in better control of the heat and mass transfer within the reaction mixture, of the average degree of substitution (DS), and the distribution pattern along the polymer chain. [2] Nevertheless, up to now all commercial cellulose derivatives are prepared via heterogeneous processes. In scientific research, the well known cellulose solvents, LiCl/ N,N-dimethylacetamide (DMA) and tetrabutylammonium fluoride  3H 2 O/dimethyl sulfoxide (DMSO), are commonly used for chemical derivatization but their high costs, plus the energy required for recycling have precluded their commercial application. [2] These drawbacks can be atte- nuated by exploiting ionic liquids (ILs). [3] Their negligible vapor pressure, high polarity, and chemical as well as thermal stability make ILs suitable candidates for deriva- tization of cellulose under homogeneous conditions. [4] In addition to the improved safety factor, IL recycling is feasible, e.g., by phase separation and removal of volatile components by evaporation. [5] Equally important, is the Full Paper M. Gericke, T. Liebert, T. Heinze Institute of Organic Chemistry and Macromolecular Chemistry, Friedrich Schiller University of Jena, Centre of Excellence for Polysaccharide Research, Humboldtstraße 10, D-07743 Jena, Germany Fax: þ49 3641 94 8272; E-mail: thomas.heinze@uni-jena.de O. A. El Seoud Institute of Chemistry, University of Sa ˜o Paulo, P. O. Box 26077,05513-970, S. P., Sa ˜o Paulo, Brazil a Supporting Information is available from the Wiley Online Library or from the author. Co-solvents can minimize two of the major problems associated with the use of ionic liquids (ILs) as solvents for homogeneous derivatization of cellulose: high viscosity and limited miscibility with non-polar reagents or reaction products. Thus, the effects of 18 solvents and 3 binary solvent mixtures on cellulose solutions in three ILs were systematically studied with respect to the solution phase behavior. The applicable limits of these mixtures were evalu- ated and general guidelines for the use of co- solvents in cellulose chemistry could be advanced: Appropriate co-solvents should have E N T values (normalized empirical polarity) > 0.3, very low ‘‘acidity’’ (a < 0.5), and relatively high ‘‘basicity’’ (b  0.4). Moreover, novel promising co- solvents and binary co-solvent mixtures were identified. Macromol. Mater. Eng. 2011, 296, 483–493 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/mame.201000330 483