Dielectric Relaxation Investigations in NCO-Terminated Liquid Crystalline Polyurethane: Thermally Stimulated Depolarization Current Technique

Abstract

The various dielectric relaxation processes in NCO-terminated liquid crystalline polyurethane (LCPU) samples have been investigated using the thermally stimulated depolarization current (TSDC) technique. The TSDC results obtained for LCPU samples polarized under different poling conditions show the presence of three peaks around 60°–80°C, 110°C, and 180°C designated as β, α, and ρ in ascending order of temperature respectively. The β-peak has been associated with the dipolar nature of carbonyl groups present in the structure of LCPU. The α -peak is due to the space charge trapping mechanism via the Maxwell-Wagner-Sillars effect arising from the liquid crystalline phase and the presence of unsaturated butadiene and carbonyl groups. The ρ-peak has been attributed to the crystal-mesophase transition in LCPU. The TSD current characteristics also show anomalous behavior, i.e., reversal of the current in the high-temperature region. This has been associated with crystalline to liquid crystal phase transition and the self-polarization of mesogenic moieties.