The phase behavior of liquid cyrstalline polymers and oligomer model compounds with alkylated tripheylenes (see figure) as the mesogenic core is studied using a combination of optical microscopy, DSC and 2H NMR. The information provided by NMR provides unique insights into the behavior of liquid crystalline phases.magnified image

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2H NMR measurements on discotic compounds based on heptyloxy-substituted triphenylenes are reported. Monomers, model dimers, polycondensates, and a cross-linked polycondensate were studied. Macroscopic alignment in a 7-T magnetic field proves that all of them exhibit discotic liquid crystalline mesophases. Their phase behavior is characterized by an analysis of the spectroscopic data as a function of temperature. While for the monomer the phase transition from the mesophase to the isotropic phase is well defined, for the dimer and the polymer biphasic behavior over a broad temperature interval is observed. 2H NMR measurements on aligned samples allow the separation of side-group motions and motions of the rigid core. In the monomers full axial rotation of the core around the column axis occurs in the mesophase, while this rotation is quenched in the dimer and the polymer. Combination of magnetic and mechanical forces allow the generation of monodomains, where the columns are aligned parallel to each other. The kinetics of this alignment process is monitored by 2H NMR spectroscopy.

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