<Original>Dielectric Properties of (Cellulose Oligo-Oxymethylene Ether) Acylates

Abstract

The dielectric properties of (cellulose oligo-oxymethylene ether) acylates were measured over a wide frequency and temperature range. The resulting complex dielectric constants (ε^*) were found to be closely related to complex dynamic modulus (E^*) in the region of the mechanical β and γ processes through the following expression: (ε^*-ε_U)l(ε_R-ε_U)=1-(E^*-E_R)l(E_U-E_R) where ε_R and ε_U are the relaxed and unrelaxed dielectric constant, while E_R and E_U are the relaxed and unrelaxed dynamic modulus. From this, we used the dielectric relaxation data for discussing the ft and y processes so far detected by mechanical experiment. In the dielectric measurement at constant temperatures, the γ absorption for the acetate exhibited a marked peak, while the ft absorption appeared as a low frequency shoulder to the γ peak. The normalized absorption curves for the f process in the acetate at temperatures between -70℃ and 0℃ reduced to a single curve (master curve). However, the absorption curves below -80℃ deviated from the master curve, but instead, they were on the master curve for the pivalate. In accord with this, the plots of (ε_R-ε_U) vs. temperature in the γ region for the acetate changed sharply at about -80℃. From these findings, the molecular relaxation mechanism for the f process in the acetate was considered to be different below and above ca. -80℃. The similar results were drawn for other COAs with linear side chain. It was also shown that the β process gave unexpectedly large values of the activation entropy (100eu or more), and the process was confirmed to be due to the micro-Brownian motion of the side chain.