In this study, the polymerization kinetics of an uncatalyzed polyester based thermoplastic polyurethane formulation was characterized with Raman spectroscopy. Measuring the normalized scattering intensity of a band originating from the TPU diisocyanate, conversion was calculated as a function of time. Kinetic parameters obtained from these experiments correlated well with those obtained from analogous calorimetric experiments and with literature values. It was concluded that Raman spectroscopy is a powerful tool for characterizing the polymerization kinetics of polyurethanes in situ. (C) 2003 Elsevier Ltd. All rights reserved.