Study Of The Synthesis And Mesomorphism Of Liquid Crystalline Dimers And Liquid Crystalline Dendrimer

Liquid crystal materials have been widely applied in display and other special area for their outstanding thermoelectric properties. Great progress has been achieved in the research on the synthesis, performance and application of liquid crystal compounds. However, more excellent liquid crystal materials are required due to the further development of technology and the increasing civil demand. In this thesis, five novel liquid crystal compounds were synthesized. The relationship between molecular structure and liquid crystalline properties, especially the effect of aspect ratio and rigidity of the mesogen were carefully investigated.Firstly, using10-Undecen-l-ol as the initial reactant, a novel liquid crystal monomer was synthesized. And a novel Schiff-base type liquid crystalline dimer with two mesogens was obtained by reaction of the monomers and1,4-butanediamine. The structures of these compounds were characterized by FT-IR,1H NMR,13C NMR and ESI-MS. The liquid crystalline behavior of the compounds was characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD). The typical nematic phase texture can be observed in monomer and dimer, and smectic C phase was also found in the dimer. Moreover, the dimeric compound exhibited wider mesophase temperature ranges and higher thermal stability.Secondly, in order to study the influence of aspect ratio and rigidity on the liquid crystal properties of liquid crystal monomer and dimer, a novel biphenyl-containing liquid crystal monomer and the corresponding Schiff-base type liquid crystalline dimer were prepared. Both of them showed typical nematic phase texture, wide mesophase temperature ranges and high thermal stability. In contrast to the formerly synthesized liquid crystal compounds, it is concluded that the rigidity of biphenyl structure does enlarge the mesomorphic ranges and enhance the thermal stability. However, motility and orientation of molecules are meanwhile confined.Finally, a novel liquid crystalline dendrimer was successfully synthesized by grafting the liquid crystal monomers to the terminals of the polypropylene imine (PPI) molecule. Typical layer structure of smectic A phase was observed by POM and XRD characterization. Microphase separation of different molecular parts of the liquid crystal dendrimer is responsible for the formation of more regular arrangement of liquid crystal molecules. More complicate mesophases may be obtained by tuning the structure of the dendritic core, dendrimer generation and terminally attached mesogenic units.