The grafting of butyl acrylate onto poly(styrene-block-butadiene) is investigated by two-dimensional (2D) liquid chromatography. Separating the graft backbone and the graft product by liquid chromatography at the critical point of adsorption in the first dimension and size exclusion chromatography in the second dimension, detailed information in the coordinates chemical composition and molar mass are obtained. It is shown that the grafting reaction results in the formation of a complex product due to the fact that in addition to grafting the graft backbone undergoes partial degradation. Combining 2D chromatography and FTIR spectroscopy in a quasi on-line setup, all components of the graft product can be identified. Via selective detection, the chemical composition drift of the different fractions can be determined.