Preparation method of cationic polymer

The invention discloses a preparation method of a cationic polymer. The structural formula of the cationic polymer is disclosed as Formula I. The method comprises the following steps: (1) reacting 3-butenyl-1-ol with sodium hydroxide to obtain 3-butenyl-1-sodium alkoxide; and (2) reacting hexamethyl proguanil with the 3-butenyl-1-sodium alkoxide to obtain a cationic monomer tri(dimethylamino)methyl-3-butenylether hydrochloride disclosed as Formula II; and (3) in the presence of an emulsifier and an initiator, carrying out reversed-phase emulsion polymerization on acrylamide and the tri(dimethylamino)methyl-3-butenylether hydrochloride to obtain the cationic polymer disclosed as Formula I. The cationic polymer prepared by the method can be used as an organic flocculant, has the characteristics of favorable water solubility and the like, is convenient to use, and is especially suitable for solving the problem of low removal rate of emulsified oil and solid suspended substances in oily sewage produced by heavy oil oilfields. Besides, the flocculant has the advantages of low scum generation amount, and low water content and high oil content in scum.