Preparation method of vinyl pyrrolidone-dimethylamino ethyl methacrylate copolymer

The invention provides a preparation method of a vinyl pyrrolidone-dimethylamino ethyl methacrylate copolymer. The preparation method comprises the following steps: step one, adding dimethylaminoethylmethacrylate and diethyl sulfate into an ethyl alcohol solvent to obtain a quaternarization system, and reacting to obtain a pre-polymer quaternary ammonium salt; step two, adding the pre-polymer quaternary ammonium salt, N-vinyl pyrrolidone and an initiator into water for reacting to obtain a polymerization reaction system; and step three, adding the initiator into the polymerization reaction system for eliminating residual monomers so as to obtain the product. The preparation method has the beneficial effects that the product with the viscosity range of 5000 mPa.s to 150000 mPa.s can be produced, the yield can be 99.5%, the residual rate of monomers is below 0.02%, the product is colorless, transparent and free of peculiar smell, ethyl alcohol and water are taken as solvents, the initiator can preferably participate in the reaction, the cost is lower, few side reaction products are generated, and compared with acetone and methylene dichloride commonly used in the field, the productis low in toxicity and more environmentally-friendly.