Abstract: Undecylenic acid/maleic anhydride-dodecanol (UMA-DA) polymer was prepared by esterification reaction using dodecanol(DA) and undecylenic acid(UA)/maleic anhydride(MAH) as copolymer.The polymer is used as an emulsifier in the emulsion polymerization of UA and methyl methacrylate(MMA). FT-IR analysis showed that the self-made undecylenic acid/maleic anhydride(UMA) copolymer acted with DA by esterification of an acid anhydride with a hydroxyl group.The proton signal at δ 3.2-3.4 of —O—CH₂—in ¹H NMR show that UMA-DA copolymer was prepared successfully.The critical micelle concentration(CMC) value of UMA saponification was determined by surface tension method. The CMC value of UMA-DA was 9.6 g/L, and the surface tension γ_CMC was 23.04 mN/m. The γ_CMC value of UMA-DA is much lower than that of pure water(71.97 mN/m). The particle size and particle size distribution index(PDI) increased, butthe gel rate gradually decreasedwith the increase of UMA-DA dosage in emulsion polymerization. The emulsion is relatively stable, and the total monomer conversion rate reaches 98.1% when the amount of the self-made emulsifier UMA-DA is 10% of the total monomer and the ratio of UA to MMA is 10 : 90.