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

✍ Scribed by Naoto Tsutsumi; Yasuyoshi Okabe

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 229 KB
• Volume: 38
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(20000101)38:1<88::aid-polb11>3.0.co;2-0

✦ Synopsis

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 ␣, ␤, and ␥ relaxation modes at 78.5, Ϫ44, and Ϫ136°C for polyurea 7 and at 80, Ϫ50, and Ϫ134°C for polyurea 9, respectively. The ␣ 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 ␤ relaxation is caused by the local thermal motion of long-chain segments. The ␥ 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 Ϫ6 to 10 4 Hz and temperature range from Ϫ150 to 250°C, using the relaxation parameters obtained from the TW-TSDC method.