The influence of the methacrylic acid (MAA) content (0-10 mol %) on the incorporation of polyoxyethylene nonylphenyl ether (Emulgen 911, HLB 13.7) nonionic emulsifier inside polymer particles during emulsion copolymerization of styrene (S) and MAA was investigated. The amount of incorporated emulsifier after centrifugal washing with 2-propanol to remove adsorbed emulsifier from the surfaces was directly measured by gel permeation chromatography (GPC) and H-1 NMR. The level of incorporation increased with increasing MAA content and reached 74% of the total amount of emulsifier at 10 mol % MAA. At lower MAA contents (0-3 mol %), the particle size distribution was bimodal because of formation of new particles by secondary nucleation. However, only limited secondary nucleation occurred at higher MAA contents (6-10 mol %), and monodisperse particles were thus obtained.