Cellulose beta-ketoesters with branched alkenyl chains were prepared using cis-9-octadecenyl ketene dimer (OKD) and LiCl/1,3-dimethyl-2-imidazolidinone (DMI) as the esterifying reagent and cellulose solvent, respectively. Relationships between degree of substitution (DS) of the cellulose/OKD beta-ketoesters and reaction conditions were studied in detail. The results showed that DS values of the products were controllable up to 2.1 by selecting the reaction conditions. Solution- and solid-state C-13-NMR analyses revealed that cellulose backbones of the cellulose/OKD beta-ketoesters with DS 2.1 behave like solid in chloroform owing to strong restriction on movement of cellulose chains by the long and branched alkenyl substituents introduced. Size-exclusion chromatographic analysis showed that little depolymerization occurred on cellulose during beta-ketoesterification at room temperature, and that molecules of the cellulose/OKD beta-ketoesters with DS 2.1 had semi rigid-rod conformation in tetrahydrofuran. Thus, cellulose beta-ketoesters with densely substituents like polymer brushes or comb-shaped polymers were prepared in this study. (c) 2005 Elsevier Ltd. All rights reserved.