Cellulose dissolved in anhydrous dimethylacetamide (DMAc)/LiCl solution and treated with dialkylaminosulfur trifluoride (DAST) became highly branched and actually gained in molecular weight. The branching was thought to arise from the action of HF which is generated from the consumption of DAST. Subsequent experiments involving the direct addition of HF to anhydrous cellulose/DMAc/LiCl produced highly branched materials with greater polydispersity and greater molecular weight than the starting cellulose. This branching was likely due to the well known reactivity of glycosyl fluoride endgroups. Although the mechanism is not new, the combination of homogeneous cellulose dissolution and low levels of HF under anhydrous conditions represents a novel method for synthesizing a new class of cellulose derivatives. The potential utility of this method for producing branched cellulose derivatives and blocky cellulosic copolymers is discussed.