Terahertz Spectroscopy for Characterization of Hydrogen Bonding and Cross-linked Structure Dynamics in Polyurethane

Abstract

Terahertz (THz) absorption spectra of cross-linked polyurethane films were observed at 30–180 °C. The obtained spectra displayed characteristic absorption bands. A band observed at 2.6 THz was assigned to the C=O···N-H hydrogen bond vibration using previously reported data. DFT calculation results confirmed that a band at 7.5 THz arises owing to the torsional vibration of cross-linked molecules containing urethane bonds. The slight changes in the temperature-dependent spectra were analyzed by the first derivative of absorption intensity with temperature. The thermal behavior of absorption intensities indicates the dynamics of hydrogen bonds and cross-linked structures in polyurethane films.