The batch and semi-continuous emulsion copolymerization of n-butyl acrylate and vinyl neononanoate (VeoVA 9) were monitored by remote on-line Raman spectroscopy. Monomer concentrations were calculated in real-time by a classical least squares (CLS) approach using the vinyl regions of the Raman spectra. During the batch copolymerization, conversion and copolymer composition calculated from on-line data showed good agreement with off-line gravimetry and NMR results, indicating that the CLS procedure indeed enables the calculation of individual monomer concentrations and on-line characterization of the copolymer formed. Real-time analysis of the data enabled control of the copolymer composition by suggesting how one of the comonomers should be added in a semi-continuous polymerization. NMR and gradient polymer elution chromatography corroborated the Raman results for the cc,polymer composition. Further, it was shown that only at high conversions (> 80%) monomer partitioning influences the copolylmerization behavior, since both monomers have a low solubility in water. The results demonstrate that Raman spectroscopy is very well suited Is on-line sensor in emulsion copolymerization processes.