Block copolymers are a class of polymeric materials made by the covalent bonding of at least two macromolecular chains each with a different chemical nature. The performance of these materials is highly dependent on the physical and chemical properties of the constituting blocks, especially with regard to their chemical composition and molecular weight distribution. Usually, the block copolymer molecular weight is determined using Size-Exclusion Chromatography (SEC). In addition to traditional techniques, Diffusion Order SpectroscopY (DOSY) was introduced in the early 90s to obtain polymer composition and molecular weight information. In the present work, we have successfully used DOSY as a method to monitor block co-polymer polymerization as well as to account for the SEC results of a typical analysis.