X-ray scattering experiments on oriented polysiloxanes with paired mesogens and different distances between these swallow-tailed side groups show a remarkable dependence of the smectic monolayer thickness on the degree of dilution, whereas the interplanar distances of the side groups remain nearly constant. Due to the dominating interaction of the mesogenic moieties, the flexible main chain is forced to take part in the layer formation. A packing model is proposed to explain the results of the X-ray studies. For polymers with five or more dimethylsiloxane copolymer segments, a diffuse scattering appears in the smectic as well as in the isotropic phase. This scattering is independent of the orientation of the samples. It is probably caused by the main chain and has also been observed for the unsubstituted poly(hydrogenmethylsiloxane).

ABSTRACT:A comprehensive and chronological account of dendrimers based on [1,3,5]-triazines is provided. Synthetic strategies to install the triazine through cycloaddition, cyclotrimerization, and nucleophilic aromatic substitution of cyanuric chloride are discussed.Motivations and applications of these architectures are surveyed, including the preparation of supramolecular assemblies in the solution and solid states and their use in medicines, advanced materials, and separations when anchored to solid supports. V

Structural investigations on six combined liquid-crystalline polymers using the X-ray technique are described. The measurements have allowed a characterization of the liquid-crystalline phases and have led to our first ideas about the phase structures. All mesogenic groups are arranged parallel to each other, the shortest segment in the main-chain or in the side-chain determines the smectic layer spacing. A modified designation for liquid-crystalline phases of high polymers is proposed.

A large number of new synthesized as well as known chiral dopants with respect to their helical twisting power (HTP), the phase stability of cholesteric solution prepared by doping nematic LC mixtures, the host dependence of the chiral induction, and the photostability has been examined. The evaluation led to the result that only few compounds fulfill the stringent application requirements of LCD manufacturing, especially with reference to bistable cholesteric devices

Liquid-crystalline polymalonates with a definite distance between the contact points of two neighbouring side groups were synthesized. The mesogenic group is azobenzene with a terminal nitro-substituent acting as an indicator for dielectric measurements. The influence of the number of methylene groups in the main chain on the polymorphism and the dielectric behaviour has been investigated. Generally, the thermal stability of the mesophases decreases when the main chain spacer becomes longer. The relaxation frequency for the reorientation of the mesogenic side group around the short axis increases with increasing number of methylene groups in the main chain in both, the isotropic and liquid-crystalline phases.CCC 0025-1 16)3/93/$05.00