The detailed characterization of poly(styrene)-b-poly(tetrahydrofuran) (pS-b-pTHF) multiblock copolymers (17800 g mol(-1) <= M-n <= 46800 g mol(-1)) generated via urethane linkages is presented. The synthesis of the block copolymers is enabled via a mechanistic switch of the thiocarbonyl thio end group of a poly(styrene) to dihydroxyl terminated polymers that subsequently react with a diisocyanate terminated polytetrahydrofuran based prepolymer to form multiblock copolymer structures. The characterization of the multiblock copolymers and their substructures includes size exclusion chromatography (SEC), liquid chromatography at critical conditions (LCCC), nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy as well as matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. To obtain even further details of the polymer size and its composition, SEC with triple detection as well as newly developed SEC coupled online to IR spectroscopy was carried out. The quantification of the average block fractions via online SEC-IR (41-61 mol % pTHF) is in very good agreement with the results obtained via NMR spectroscopy (39-66 mol % pTHF).