Chapter 4 focuses on polyacrylamide polymers. First, the theory and application of flocculation will be discussed, covering the necessity of flocculation, its main mechanisms, factors influencing flocculation, and the application of flocculants. Next, the application fields and selection of polyacrylamide will be introduced, covering issues such as application fields, reasonable selection, molecular weight, as well as quality and salinity. Then elaborate on the polymerization method of acrylamide; Further explain the synthesis methods of cationic acrylamide polymers, including the synthesis of various copolymers; Finally, the diallyldimethyl ammonium chloride polymer is described, covering raw material requirements, an introduction to the synthesis method, and the polymer production process.