Effects of external conditions, solution concentration, solvent quality, added salt, and pH on the chain conformation dimension of two kinds of polyacrylamide (PAAm) flocculants, neutral-PAAm, and cationic-P(AAm-DMC) (DMC, 2-[(methacryloyloxy)ethyl] trimethylammonium chloride), in parent solutions and their flocculation performance for Kaolin suspensions have been investigated by Ubbelohde viscometer and spectrophotometer, respectively. It was found that a negative correlation existed between the flocculation performance of PAAm flocculants and their chain sizes in parent solutions. This was attributed to the expanded chain deformation of PAAm flocculants during the flocculation process from the flocculant parent solution to the Kaolin suspension and was interpreted in term of the competitive interaction among the polymeric flocculant, solvent, and Kaolin particle in the chain deformation process. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2915-2922, 2010