Tailored cellulose esters: synthesis and structure determination

A broad variety of cellulose esters with complex and sensitive (against hydrolysis and light) structures was synthesized homogeneously in N,N-dimethylacetamide (DMAc)/LiCl and in the new solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride (TBAF) via in situ activation of the carboxylic acids with N,N'-carbonyldiimidazole (CDI). New esters of chiral (-)-menthyloxyacetic acid, of unsaturated 3-(2-furyl)-acrylcarboxylic- and furane-2-carboxylic acid, acids with crownether moieties (4'-carboxybenzo-18-crown-6), and with carboxymethyl-beta-cyclodextrin were accessible in a one-pot reaction. Because of the mild conditions and the efficiency of the reaction via imidazolides, very pure and highly functionalized cellulose derivatives were obtained up to a degree of substitution of 2.5 possessing a degree of polymerization in the range of the starting cellulose. Structure determination was carried out by different one- and two-dimensional NMR techniques confirming the high purity of the esters and a pronounced regioselectivity for the primary OH function. The structural features, the purity, the solubility, and the film forming properties, make these materials desired products for the preparation of membranes with tailored separation characteristics.