Natalia N. Makarova

A new structural type of liquid crystal Crystal structures and thermotropic mesophases of dihydroxytetraalkyldisiloxanes: Columnar phases with hydrogen bonded assemblies

Abstract Previous structural investigations of mesogenic organosilicon compounds (1, 3-dihydroxytetraalkyldisiloxanes, [R2(OH)Si]2O, R = C n H2n+1) which form thermotropic phases are outlined. The crystal and molecular structure determination of a non-mesogenic member of this series [Me2(OH)Si]2O is described. It is inferred that the mesophases formed by this family of compounds belong to a new structural type with columnar stacks of the molecules laced together with hydrogen bonds.

Structure Investigations of Thermotropic Liquid Crystalline Monomer and Polymer Organosilicon Compounds

Structures of monomolecular siloxane derivatives forming mesophase due to the presence of the one-dimensional system of hydrogen bonds are described on the basis of X-ray investigations of LC and TC phases. X-ray investigations of related polymer compounds was used as a ground for polymer structure modeling on an atomic level.

Molecular Properties of Mesomorphic Poly (decamethyl-cyclohexasiloxane) in Solution

Abstract The molecular properties of a non-classical mesogenic polymer - poly (decamethyl-cyclohexasiloxane), and low molecular analogs of its monomer unit have been studied by electrooptical Kerr effect in solution. It was shown that every polar hexasiloxane cycle in the polymer chain acts independently under influence of external electric field. Based on the results of the study of dipole moments and electrooptical properties of low- molecular-mass cyclohexasiloxanes with different polar side-groups (CH3, -C6H5, -OH, -OC2H5) it was established that hexasiloxane cycle is able to preserve its conformation (i.e. its form and size) because of its polar properties depend weakly on the type of side-substituents. An observed stability of polar hexasiloxane cycle under the external action may be considered as responsible for the ability of poly(cyclohexasiloxanes) to form highly organized mesomorphic phases.

Conformational flexibility of the twelve-membered siloxane ring

ConclusionsThe conformational analysis of the molecules of twelve-membered cis- and trans-2,8-dihydroxycyclohexasiloxanes showed that intramolecular dehydration with the formation of a bicyclic system is possible for the cis isomer with the approach of the OH groups on account of the large conformational flexibility of the ring. For the trans isomer this approach is only possible with cleavage of the bonds in the ring at the intermediate stages.