Segregation processes in segmented polyurethaneurea solutions observed by fluorescence depolarization

The onset of a segregation process in segmented polyurethaneurea (SPUU) solutions was studied by fluorescence spectroscopy using free fluorescein as a probe. For SPUUs with a given molecular weight and a constant ratio of the hard to soft segments, the time-resolved fluorescence measurements reveal the environmental inhomogeneity on the excited lifetime of fluorescein. It is shown in this work that the critical concentration for the segregation process detected by fluorescence spectroscopy through the transition of the anisotropy ratio of the fluorescein occurs at a concentration lower than that observed by small angle X-ray scattering (SAXS). These experimental results indicate that fluorescence depolarization can be used as an alternative method to investigate the structural transition in SPUU solutions.