Self-assembled polymeric micelles can be used as efficient particulate emulsifiers. To explore the relationship between the structure and the oil–water interfacial behavior of the micelle emulsifiers, a new type of amphiphilic random copolymer, poly{(styrene-alt-maleic acid)-co-[styrene-alt-(N-3,4-dihydroxyphenylethyl-maleamic acid)]} (SMA–Dopa), was synthesized, self-assembled into micelles, and used as emulsifiers. SMA–Dopa was synthesized via an aminolysis reaction between dopamine and commercial alternating copolymer poly(styrene-alt-maleic anhydride) (SMA). Dopamine moiety facilitated the self-assembly of the SMA–Dopa in selective-solvent into stable micelles, and increased the adsorption of the SMA–Dopa at the oil–water interface. Additionally, the structural transition of the self-assembled SMA–Dopa52 micelles in response to pH and salinity changes were confirmed by means of TEM, AFM, DLS, aqueous electrophoresis techniques, potentiometric titration, and pyrene fluorescence probe methods. Micelles shrunk with increasing salinity, and flocculation of the shrunken primary micelles occurred at salt concentration exceeding 0.1 M. The micelles swelled with increasing pH, and the disassociation of the SMA–Dopa52 micelles occurred at pH above approximately 6.5. The structure of the micelles plays a crucial role in the oil–water interfacial performance. Micelles with various structures were used as emulsifiers to adsorb at the styrene–water and toluene–water interfaces. The emulsifying characteristics demonstrated that self-assembled SMA–Dopa52 micelles with moderately swollen structure (at 2 < pH < 6) combine the advantages of the solid particulate emulsifiers and polymeric surfactants, possessing excellent emulsifying efficiency and good emulsion stability. Moreover, the emulsifying performance of the SMA–Dopa52 micelles could be enhanced by the addition of salt.