PURPOSE: To obtain the titled excellent emulsifier especially useful for the emulsion polymerization of an ethylenic unsaturated nomoer by using a compd. obtained by sulfonating the ester compd. which is formed by esterification of the addition product of allylalkylphenol and alkylene oxide with maleic anhydride.
CONSTITUTION: Alkylphenol such as nonylphenol and allyl chloride are heated in the presence of a catalyst, and allowed to react with each other. Alkylene oxide is added to the obtained reaction product. The product is diesterified with maleic anhydride, and then sulfonated with sodium bisulfite to obtain the compd. shown by the formula. In the formula, R 1 is 4W18C alkyls, etc., R 2 is hydrogen or 4W18C alkyls, etc., A is 2W4C alkylenes, etc., (n) is 1W200 integer, and M is an alkali metal atom or NH 4 . About 0.1W20wt%, basad on the whole monomer, of the emulsifier is used to polymerize the monomer, and a water-based resin dispersion having excellent stability is obtained.