Molecular motion and relaxation studies of aliphatic polyureas by thermal windowing thermally stimulated depolarization current technique

Abstract

Molecular motion and relaxation studies using a thermal windowing thermally stimulated depolarization current (TW-TSDC) were performed for aliphatic polyureas 7 and 9. Global thermally stimulated depolarization current gave three characteristic major peaks corresponding to the α, β, and γ relaxation modes at 78.5, −44, and −136°C for polyurea 7 and at 80, −50, and −134°C for polyurea 9, respectively. The α relaxation is related to the large-scale molecular motion due to micro-Brownian motion of long-range segments. This relaxation is significantly related to the glass-transition temperature. The β relaxation is caused by the local thermal motion of long-chain segments. The γ relaxation is caused by the limited local motion of hydrocarbon sections. Temperature dependence of relaxation times was expressed well using Vogel–Tammann–Fulcher (VTF) expression. 3-D simulation of dielectric constants of dielectric strength and loss factor were performed in the frequency range from 10−6 to 104 Hz and temperature range from −150 to 250°C, using the relaxation parameters obtained from the TW-TSDC method. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 88–94, 2000