Depending on the solvent used in the copolymerization reaction, there are generally two copolymerization methods.

(1) Solvent polymerization in benzene, toluene, xylene, trimethylbenzene, ethylbenzene, cumene, butylbenzene or a mixture thereof, white fragile solid polymer can be obtained, the relative molecular weight is about 4000. Generally, solid copolymers are neutralized with alkali into the form of their sodium salts to increase the solubility in the copolymer water. 1000 parts of maleic anhydride is dissolved in 1100 parts (mass ratio) of dried toluene and added to the polymerization reactor equipped with an electric stirrer, a reflux condenser, and a drip funnel, nitrogen is introduced to remove the air in the reactor, and the polymerization reactants are protected with nitrogen during the whole process of the copolymerization reaction. The polymerization reaction temperature is raised to the toluene reflux temperature (about 123 °C). The measured 80 parts (mass ratio) of dibenzoyl peroxide were dissolved in the measured 100 parts (mass ratio) of acrylic acid with the removal of the polymerization inhibitor, and then 700 parts (mass ratio) of dried toluene were added to the acrylic acid peroxide dibenzoyl mixture and mixed well. Under stirring, add acrylic mixture dropwise to the reactor, maintain the reflux temperature, control the drop acceleration, and make the acrylic mixture finish within 4h. Keep the temperature and continue the reaction for 30 min. The reaction copolymer is continuously precipitated from the reaction mixture, and the heating is stopped after all the copolymers are precipitated, and nitrogen gas is stopped. Filter the copolymer and dry at 125 °C for 1 h. The dried acrylic acidmaleic anhydride copolymer was saponified and neutralized with a metered 10% NaOH dilute solution to form an aqueous copolymer solution with a total solid content of 25%~30%. The aqueous solution is light yellow and the average relative molecular mass of the copolymer is about 4000.

(2) Aqueous solution polymerization If water is used as the polymerization medium, maleic anhydride must first be converted into its sodium salt form with alkali to increase its solubility in cold water. Maleic anhydride can also be added to water to heat up to 90~100 °C, so that it is dissolved in hot water, and then copolymerized, so that the co-obtained product is directly dissolved in water, and the aqueous solution is slightly yellow. The metered maleic anhydride is neutralized with isomolar sodium hydroxide to make the sodium of maleic anhydride Salt. Add an appropriate amount of deionized water to the polymerization reactor equipped with an electric stirrer, a drop funnel and a reflux condenser, dissolve the metered sodium maleic anhydride salt in the water in the reactor, and raise the reaction temperature to 95~100 °C under stirring. Take the metered ammonium persulfate and add It is put into the metered acrylic acid, and the dilute solution of acrylic acid ammonium persulfate is prepared with an appropriate amount of deionized water, and placed in the drop funnel on the reactor. When the reaction temperature in the reactor rises to the required temperature, start to add acrylic mixture dropwise, control the drop acceleration, add it within about 4h, after adding the acrylic mixture, maintain the reaction temperature to continue the reaction for 1h, stop the reaction, and obtain a light yellow to colorless copolymer aqueous solution.