Phase behavior and structure identification of novel dendritic side-chain liquid crystalline polymers

Dendritic polymers are macromolecular compounds that contain a branching point in each structural repeating unit.5 Recently, liquid crystalline dendritic polymers have proven to be an interesting new family of mesogenic compounds with dimensions and molecular weights between small molecular mass mesogens and high molecular weight main-chain or side-chain liquid crystalline polymers. These liquid crystalline dendrimers can exhibit nematic (N) and smectic A (SA) or smectic C (SC) thermotropic liquid crystalline phases.;A series of side-chain dendritic polynorbomenes (DPNB) has been synthesized by living ring-opening metathesis polymerization. The side groups are a second generation G2(OH) monodendron based on the AB 2 mesogenic monomer, 13-hydroxy-1-(4-hydroxyphenyl)-2-(4-hydroxy-4 ''-p-terphenylyl) tridecane building block. Both monomer (G2NB) and polymers (DPNB) exhibit multiple phase transitions during cooling and heating in DSC experiments. During cooling, the monomer exhibits a supramolecular layered structure that is formed by the dendritic skeleton before a hexagonal molecular packing structure that is formed by mesogenic groups at the molecular level within the layer. The supramolecular layered structure can be tilted away from the fiber direction. However, the mesogenic groups within the layer are always packed perpendicular to the Lyer structure. An N phase can be identified under Polarized Light Microscopy in the high temperature region.;Four different phases were identified in addition to the isotropic melt by Wide Angle X-ray Diffraction and Small Angle X-ray Scattering synchrotron experiments and Polarized Light Microscopy in a series of DPNBs. Molecular weight has no effects on the phase behaviors above a critical molecular weight. Polymers exhibit a supramolecular ShB phase that has a layered structure at the supramolecular level as well as hexagonal packing at the molecular level within each layer in the low temperature region. Two SA phases are identified in the intermediate temperature region. One of the SA phases is overlapped with ShB phase at relatively low temperature. This phase can be separated in DSC experiments by annealing the samples at certain temperatures for different times. An N phase can also be identified just below the isotropic temperature.