Synthesis of new stereoregular 2,4,6,8-tetraphenylcyclotetrasiloxanes with mesogenic groups and the influence of spatial isomerism on the phase state of individual isomers and their mixtures

The hydrosilylation of four isomers of tetra(dimethylsiloxy)tetraphenylcyclotetrasiloxane with (4′-cyanobiphenyl-4-yl)undec-10-enoate in the presence of a platinum catalyst afforded four liquid-crystalline stereoisomers of phenylcyclotetrasiloxane with mesogenic cyanobiphenyl groups. The reaction was performed for the first time. The influence of the spatial structure of the stereoisomers of tetraphenylcyclotetrasiloxanes with mesogenic groups on the formation of the liquid-crystalline state by thermooptical, X-ray diffraction, and calorimetric methods. The temperatures and enthalpies of phase transitions were determined, and their reversibility was shown. Differences in both the textures of melts formed on cooling and the phase state and in interplanar distances were found by optical microscopy and X-ray diffraction methods. Based on these data, the spatial structure of the isomers was concluded to affect the phase composition and type of packing in the liquid-crystalline state.