Dynamic mechanical and thermal properties of a certain liquid crystalline (LC) diepoxide cross-linked with three different aromatic diamines were studied. For one epoxy-amine mixture, the position of the gel point was determined with the aid of frequency-dependent rheological measurements. The value of the critical relaxation exponent was 0.5. The gel point was also determined by solubility experiments. There was a clear agreement between the two methods. The degree of conversion of the epoxy groups at the gel point (55 ± 3%) corresponded well with the value predicted by the statistical theory for network formation in isotropic stoichiometric epoxy-amine mixtures. Mechanical measurements were carried out on macroscopically ordered networks in the direction of orientation. In highly ordered networks prepared from the LC diepoxide and a rigid aromatic diamine, the value of the rubber modulus deviated from the predictions of rubber elasticity theory by a factor of 30 times higher. In networks with the same high level of macroscopic orientation prepared from the LC diepoxide and a relatively more flexible diamine, the deviation from the classical theory was much less (factor of 1.7). In the rubbery region, the value of the Young's elastic modulus decreased as a function of temperature, which seems to be connected to the decrease of the order. This is confirmed by a theory, presented by T. Odijk, concerning the polymer nematic gels under tension (see Appendix). The thermal expansion coefficient of the macroscopically ordered networks was highly anisotropic. It was indeed possible to combine the good mechanical and thermal properties of conventional epoxy polymer networks with the special features that LC polymers offer.

The molecular dynamics of amorphous and liquid-crystalline (LC) side-chain polycarbonates was studied by dielectric spectroscopy at frequencies from lo-* to lo6 Hz and at temperatures from -160 to 180°C. 'Model' compounds containing no mesogenic sidegroups showed two relaxations, which originate from the carbonate group (a, P,-relaxation). By contrast, in LC-polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature Tg up to three relaxation modes were distinguished (a-, &-, h2-process); below Tg four secondary relaxations (y-, pm-, p, -, pscrelaxation) were observed. The y-relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from pm-, two additional P-processes were identified as relaxations associated with the mesogenic unit in the glassy (p,) or in the crystalline state (P, ).

A novel liquid crystalline polyacrylate, exhibiting a nematic columnar and a nematic discotic phase, the latter not found in any polymer previously, has been synthesized using a polymer analogous reaction, substituting the discotic mesogens on a reactive polymer. The highly flexible concept of the polymer analogous reaction enables us to introduce structural variations and to create and control molecular architectures. The mesophases of polymer 1, bearing the pentakis(methylphenylethynyl)benzene mesogen via a flexible undecanoxy spacer, as well as its low molar weight homologue 2, were fully characterized by optical polarizing microscopy, differential scanning calorimetry and powder X-ray diffraction. The thermal behavior of both compounds is qualitatively similar. Both materials exhibit a nematic discotic phase (N D) at higher temperatures, which is unique for the polymer, as this phase has only been observed in low molar mass materials so far. At lower temperatures 2 crystallizes, whereas 1 undergoes a transition into the nematic columnar phase (Ncol).

We have prepared a new discotic nematogen, bearing one functional tail and five methoxy substituents. The corresponding side chain polymers, prepared via a polymer analogous esterification reaction, exhibited ND phases from 50 °C until degradation above 200 °C. Addition of equimolar amounts of various trinitrofluorenone-based acceptors to the mesogen resulted in the formation of charge transfer complexes with a variety in liquid crystalline properties. Depending on the acceptor, different columnar and nematic phases are induced, including the recently discovered nematic lateral phase. The liquid crystalline properties were investigated with differential scanning calorimetry, optical polarizing microscopy, and extensive X-ray diffraction (XRD).

Introduction.Recently, discotic liquid crystals 1 (DLCs) have gained attention due to their various possible applications, e.g., as compensation layers in LCD technology and for one-dimensional conduction. However, before DLCs can be applied, knowledge and control over the mesomorphic properties, i.e., the phase behavior and transition temperatures, of such materials are crucial.Columnar mesophases (Col X ) are obtained if the diskshaped mesogens stack into columns and the columns possess a long-range 2D order. Besides the highly ordered columnar phases, two nematic phases are distinguished. In the nematic discotic (N D ) phase, the mesogens only possess orientational order. In the nematic columnar (N Col ) phase, the molecules stack into (short) columns, and the columns order in a nematic arrangement, analogous to the nematic phase in calamitic liquid crystals. Note that in this case it is the rodshaped superstructure consisting of an array of diskshaped molecules that forms the building blocks of the nematic arrangement. 2 This is an example of a nematic liquid mesophase that combines the required absence of long-range positional order with a high local degree of organization. Other examples of this phenomenon are well-known from for example wormlike micelles, 3a chromonic liquid crystals, 3b and the reentrant isotropic and nematic phases in occurring several truxene derivatives, 3c which show nematic phases with a regular local molecular arrangement.Specific supramolecular interactions, like charge transfer (CT) interactions, 4 can be used to modify liquid crystalline properties. Applying an electron-deficient acceptor to an electron-rich donor results in CT complexes with synergistic properties. We have prepared CT complexes of donors D1 5 and D2 with acceptors A1 and the macromolecular equivalent P(A1) 6 (see Figure 1). On the basis of our previous experience on similar liquid crystalline materials, we find that it is useful to prepare polymer analogues of the mesogens, since often they give rise to a much wider temperature range of mesophase formation. This in most cases is due to the effective suppression of crystallization and allows the formation of additional mesophases. 2c Moreover, instead of obtaining a crystalline phase, the mesophase can be frozen in at low temperatures, where it is stable in time. Investigation of the liquid crystalline properties of these complexes reveals a novel nematic lateral (N L ) phase and demonstrates the pronounced effect of the polymer on the phase behavior.Results and Discussion.