Dynamics of side-chain liquid-crystalline polymers: A dielectric spectroscopy investigation - art. no. 031703

We have studied the dynamics in two side-chain liquid-crystalline derivativ es of poly(norbornene diethylester) with dielectric spectroscopy within the temperature range 190-433 K and the pressure range 1-3000 bars. Optical mi croscopy, x-ray scattering, and differential scanning calorimetry (DSC) rev ealed the formation of a nematic- and a smectic-A phase, respectively, in t he polymers with the shorter and longer spacers. Multiple relaxation proces ses exist originating from the backbone and mesogenic dipoles. In the smect ic-A phase two relaxation processes exist above the DSC glass temperature ( alpha and alpha') which merge with decreasing temperature or with increasin g pressure. thus suggesting a common molecular mechanism. The faster proces s is the segmental (alpha) relaxation associated with the dynamic glass tra nsition. whereas the slower process reflects mainly the side-chain dynamics within the smectic layers. Pressure was found to increase the glass temper ature in the nematic and smectic phases and the dT(q)/dP was 18.7 and 16.9 K/kbar. respectively. However, the effect of pressure in inducing the isotr opic-to-smectic transition is more drastic as dT(S1)/dP = 26.4 K/kbar.