## 1 Introduction  
Municipal and industrial wastewaters, such as from printing and dyeing, food processing, or chemical production industries, contain large amounts of organic pollutants, are of poor quality, and pose a severe threat to underground and surface water resources. Flocculation technology is of vital importance, with a wide range of applications in water and wastewater treatment plants. The performance of flocculation is largely affected by the presence of flocculants that enhance the aggregation of particles to form large, rapid-setting flocs either through charge neutralization or chain-bridging mechanisms [1]. Chloride is a mainstream flocculating agent in the water and wastewater treatment industry. It has characteristics such as a low required dosage, a high electrical-neutralization capability, fast floc growth, and decreased sludge production [2, 3]. But its flocculation stability is poor, especially for colloid adsorption that bridges weaker-than-organic polymer flocculants. Poly-diallyldimethylammonium chloride is a stable, organic polymer flocculant. It has an excellent flocculation effect but with a high cost [4, 5, 6]. Through the study of organic-inorganic composite flocculants, we found that the synergistic effect of polydimethyl diallyl ammonium chloride and polyaluminum chloride can significantly improve the flocculation effect [7, 8]. However, due to the weak hydrogen bond between the inorganic and organic phase, the anti-shear ability of the floc is poor. Therefore, the preparation of a new organic-inorganic hybrid flocculant by the hybrid method has been proposed. The formation of a strong bond between polydimethyl diallyl ammonium chloride and polyaluminum chloride polymer can not only electrically neutralize inorganic particles but also bridge the polymerization of organic polymers. Moreover, P(aluminum chloride-co-diallyldimethylammonium chloride) is cheaper than other cationic polymers. Therefore,P(aluminum chloride-co-diallyldimethylammonium chloride) is expected to be used in water treatment, printing and dyeing wastewater, sewage treatment, etc. To produce P(aluminum chloride-co-diallyldimethylammonium chloride) hybrid flocculant, the high charge density of an inorganic flocculant and the high bridging ability of an organic polymer flocculant were combined [7; 8]. This improved the surface morphology structure, the charge distribution of the inorganic particles, and its adsorption bridging and charge neutralization capabilities. The organic and inorganic particles can be linked by hydrogen or covalent bonding to keep their performance stable. A hybrid flocculant can maximize the synergies between inorganic and organic components, with a better flocculating efficiency than single-component flocculants or composite flocculants. Usually, there are three ways to form covalent bonds in an organic-inorganic phase. First, the active groups on the polymer chain, such as a carboxyl group, a halogen, or a sulfonic acid group, or other chemical reactions with an inorganic particle's active surface groups form covalent bonds [9; 10; 11]. Second, the hydrolysis and condensation process of certain groups on the polymer chain forms covalent bonds, such as -Si(OR) [12; 13]. Last, there is the grafting method on an inorganic particle's surface [14; 15; 16]. Template copolymerization is the combination of a preformed macromolecule through hydrogen or ionic bonds and another monomer that is not, and the monomers adsorb on the template to form a block structure. In this study, the basic idea of synthesizing covalently bound hybrid flocculants by template copolymerization was as follows: Firstly, a \"molecular bridge\" was established between inorganic hydroxyl polyaluminum and organic dimethylally ammonium chloride by using a silane coupling agent, which has groups that react with both inorganic substances and organic substances. Dimethyldially ammonium chloride polymerization was initiated by using ammonium persulfate, and a covalent PAC-PDMDAAC hybrid flocculant was obtained.