Abstract: A polymer formed from a monomer mixture comprising, (a) from 77 to 88 mol % of acrylamide or methacrylamide; (b) from 11.9 to 18 mol % of 2-acrylamido-2-methylpropane sulphonic acid, or salts thereof; and (c) from 0.1 to 5 mol % of a quarternary ammonium salt of dimethylaminoethyl acrylate or dimethylaminoethyl methacrylate, in which the quaternary ammonium salt of the monomer component (c) is the methyl chloride salt or dimethyl sulphate salt, preferably the methyl chloride or dimethyl sulphate quaternary ammonium salt of dimethylaminoethyl acrylate, more preferably the methyl chloride quaternary ammonium salt of dimethylaminoethyl acrylate, and in which the polymer has a reduced specific viscosity of at least 5 dL/g. The invention also provides a process for preparing this polymer and also a process for treating an aqueous slurry comprising particulate material employing said polymer.