Effect of microstructural arrangement of MDI‐based polyurethanes on their photoproperties

Abstract

ABSTRACTAmong the vast variety of polyurethane applications, several applications use the fluorescing nature of some of the polyurethanes. Even though 4,4′‐methylenebis(phenylisocyanate) (MDI)‐based polyurethanes fluoresce, their applications are rare because of the lack of knowledge about the fluorescence behavior of these polymers. In this study, the fluorophores responsible for the emission spectra of MDI‐based polyurethanes were identified, and their emission behavior was investigated. When excited, these polymers produce two prominent emission peaks located at 356 nm and 423 nm, which are assigned to the radiative relaxation of excited isolated hard segments and excited crystalline hard segment bundles of the MDI‐based polyurethanes, respectively. It was found that both chromophores can be excited by 293 nm UV radiation. The observed intensity variations of the two peaks with exposure time were attributed to the localized UV melting‐assisted migration of isolated hard segments. This migration facilitates the formation of crystalline hard segments. As the two chromophore populations are inversely propositional to each other, the relative intensity of the two emission peaks varies with UV exposure in a similar manner. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47431.