The anionic dispersion block copolymerization of styrene and 1,3-butadiene has proved a sui: table technique to synthesize block copolymers of tailor-made blocklength under technically relevant conditions. For this purpose, however, an efficient analytical on-line technique is required to control the Concentrations of individual reactants and product. The present communication shortly outlines the potential of non-invasive light-fiber Fourier-transform Raman spectroscopy in combination with a self-modeling curve-resolution analysis to monitor the polymerization progress and to derive concentration profiles of the two monomers and polybutadiene without prior calibration of the investigated system.