Dielectric measurements on liquid-crystalline polymethacrylates with 4'-trifluoromethoxy-azobenzene mesogenic side groups and alkylene spacers of varying length (2-6) are reported. Several relaxation regions have been identified. The β-process (rotational fluctuation of the mesogenic unit around its long axis) and the δ-relaxation (rotational fluctuations of the mesogen around the short axis) show a behavior which is similar to that of the corresponding systems with phenylbenzoate as the mesogenic unit. The relaxation behavior of the intermediate α-process is quite unusually and has not been understood fully at present.For several reasons there is still considerable interest in the synthesis and in the properties of comb-like polymers which have calamitic mesogens in the side group. From the pointof view of basic research these systems combine properties of anisotropic liquid-crystalline materials with those of polymeric systems (/). From a more practical point of view such compounds can be used as active materials for optical data storage, holographic applications, and electro-optical devices. This is especially true for systems having azobenzene-chromophores in the mesogenic unit because the properties (shape and dipole moment) can be changed by irradiation via a trans-cis isomerization process. Moreover, in recent years increasing attention is paid to fluorine-containing liquid crystals because enhancement of properties such as favorable mesophase behavior, low viscosity, high thermal stability, and high polarity is expected (2-6).For an understanding of the phase behavior of liquid-crystalline systems in general knowledge of the dynamics is necessary. Moreover, in these materials molecular, dynamics is contemporary and important for their application in memory devices because the storage of information is directly connected with a reorientation of molecules or parts of it. Dielectric relaxation spectroscopy has proven to be a very suitable tool to study the molecular motion in these compounds for several reasons. Firstly, mesogens are usually polar. If different molecular reorientations involve 280
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