Molecular Motion and Relaxation Studies of Aliphatic Polyureas by Thermal Windowing Thermally Stimulated Depolarization Current Technique

摘要

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 #alpha#, #beta#, and #gamma# relaxation modes at 78.5, -44, and -136deg C for polyurea 7 and at 80, -50, and -134deg C for polyurea 9, respectively. The #alpha# 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 #beta# relaxation is caused by the local thermal motion of long-chain segments. The #gamma# 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 prequency range from 10~(-6) to 10~4 Hz and temperature range from -150 to 250deg C, using the relaxation parameters obtained from the TW-TSDC method.