Novel pentaerythritol-based carbosilane dendrimers centered at carbon have been synthesised. Starting from tetraallyl ether based upon pentaerythritol as the core molecule, a succession of alternate Pt-catalyzed hydrosilyla-tion of allyl groups with HSiCl3 and allylations of SiCl groups thus introduced with CH2=CHCH2MgBr in THF provided a divergent synthesis of three generations of carbosilane dendrimers in which the Si atoms are linked by CH2CH2CH2 groups. The reaction conditions for hydrosilylation must be well controlled. After purification by chromatography on silica gel pure products for each generation were obtained. The IR, 1H and 13C NMR spectra and elemental analysis data are consistent with the proposed structures. The molecular weights of the resulting car-bosilne dendrimers have been determined by vapor pressure osmometry.
A novel liquid crystalline dendrimer with peripheral mesogenic units was successfully prepared. Azo-reaction and Williamson synthesis were employed in the preparation of the mesogenic unit 4-[4-(6-hydroxyhexyloxy)-phenylazo]nitrobenzene (M-NO2). A terminal Si—Cl functional carbosilane dendrimer based on pentaerythritol was used as dendritic scaffold and subsequently functionalized with the aforementioned groups. Investigation of the liq-uid crystalline properties of the mesogen-functionalized dendrimer PCSi-1G-NO2 by polarizing optical microscopy, DSC, and X-ray diffraction showed that it exhibits smectic E (SE) phase, different from the corresponding mesog-enic unit, which shows nematic phase. Furthermore, the temperatures of both the melting point and the clearing point of the mesogen-functionalized dendrimer decrease, and the temperature region of the SE phase is wider than that of the nematic phase.
The observation of disclination cores of high strength S=-2, -3, -4, -5, -6, -7, -8 in a smectic C phase of Schiff-base type liquid crystal (LC) is reported. The results of polarizing optical microscope (POM), dif-ferential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) prove that the sample exhibits smectic C phase. It is suggested that the formation of the high strength disclination is mainly ascribed to the stronger anchoring of LC molecules on the substrate due to the formation of hydrogen bonds between the pendent hydroxyl of the LC molecule and the substrate.
