A series of polymerizable ionic liquids, dimethylaminoethyl methacrylate butyl bromide ([DMC4]Br), dimethylaminoethyl methacrylate decyl bromide ([DMC10]Br), dimethylaminoethyl dimethylacrylate butyl bromide ([DM-C4-DM]Br2) and dimethylaminoethyl dimethylacrylate decyl bromide ([DM-C10-DM]Br2) were synthesized from dimethylaminoethyl methacrylate and different brominated alkanes. Their structures were determined by 1HNMR and FTIR. Their corresponding critical micelle concentrations were 16.20, 11.20, 25.61 and 16.13 mmol/L, respectively, by conductivity method. Styrene acrylonitrile copolymers (SAN) were prepared using [DMC10]Br, [DM-C10-DM]Br2 and sodium dodecyl sulfonate (SDS) as emulsifiers, respectively. When the amount of [DM-C10-DM]Br2 (based on total mass of monomers, the same below) was 4%, the conversion rate of monomers was 90.2%, and the particle size of SAN emulsion was 320.3 nm. The initial temperature of thermal decomposition of prepared SAN was 353 ℃, and the chemical oxygen demand (COD) of wastewater was 937 mg/L. The thermal decomposition temperature of SAN prepared by this emulsifier was 22℃ higher than that of SAN prepared by the same amount of SDS, and the wastewater COD was 1512 mg/L lower.