A series of chitosans have been grafted with quaternary ammonium cationic monomers, as well as acrylamide using Ce(IV) to induce macroradical formation on the polysaccharide backbone. The materials, which have long chain branches per molecule between 0.3 and 5.5, are shown to provide very high specific flocculation efficiency, at the very least equal to the entirely synthetic materials which have been previously documented in the literature. A charge ratio, determined from the polymer concentration at which flocculation takes place, the charge density of the polymer, and the surface charge of the suspended matter are proposed as metrics to evaluate the occurrence of charge neutralization and bridging or charge patch flocculation mechanism. Furthermore, a window of application (WA) for flocculants, which characterizes the region of concentration wherein the polyelectrolyte can remove 99% of the supernatant turbidity, has been defined. It was shown to depend on the square root of the ionic strength and varies inversely with the Debye length, providing a fundamental basis for the concept of the WA. A mathematical expression is presented which links the WA with the salt concentration and the number of branches of the grafted polymer. Grafted chitosans have been shown to be more robust than polyacrylamides in testing against model kaolin suspensions. (c) 2006 Wiley Periodicals, Inc.