The invention discloses a method for synthesizing a dimethyl diallyl
ammonium chloride cationic
monomer. In the method, a change is made to the conventional
feeding mode that
dimethylamine and
allyl chloride are fed according to a ratio of 1:1, and the
feeding mode that
dimethylamine and
allyl chloride are fed according to a ratio of 1:1 in a first stage is divided into two steps on the basis of the conventional one-
step method, wherein in the first step,
dimethylamine and
allyl chloride are fed first according to a ratio of 1:0.5; and in the second step, allyl
chloride and
sodium hydroxide are fed according to a ratio of 0.5:1. After reaction for a certain time period, allyl
chloride in the same amount is dripped continuously and thus the cationic
monomer product is obtained. The cationic
monomer product is distilled under reduced pressure to remove volatile impurities,
sodium chloride is removed by suction
filtration, an alkali is added to remove involatile impurities, and thus, thehigh-purity dimethyl diallyl
ammonium chloride cationic monomer is obtained. In the invention, the dimethylamine loss caused by volatilization at normal temperature is avoided, the reaction is performed under a low pH value condition, the generation of impurities is reduced, and thus, high-purity cationic monomer is obtained.