Synthesis And Characterization Of Dendritic Liquid Crystalline Macromolecule

Dendritic crystalline copolymer is expected to solve the characteristic problem of bad unoriented-directional mechanical strength of the main-chain liquid crystalline copolymers. As a result of the forming of liquid crystal phase, dendritic crystalline copolymer synthesized by introducing crystal unit has a prominent change in its property, and it shows great potential application prospects in functional materials, such as, reversible optical information storage materials, nonlinear optical materials, ferroelectric liquid crystal materials and electro optical displaying materials and so on.Firstly, in this paper, using methanol as solvent and ethylenediamine as the initiated core , a series of dendritic Polyamidoamine(PAMAM, 0.5G-2.0G) were successfully synthesized via a divergent method, namely an exhaustive Michael addition of amino groups with methylacrylate(MA), followed by amidation of the resulting esters with ethylenediamine(EDA). In the synthesis of half-generation product, we chose the reaction conditions as follows: the molar ratio of EDA: MA was 1:8, reacted at 35℃for 15h; and integer-generation product: the molar ratio of EDA: half-generation product was 1:8, at 25℃for 24h. Both the yield of half and integer generation product can reach 98%. The detection results of FT-IR, ¹H-NMR and ¹³C-NMR comfirmed the existence of various kinds of characteristic functional and terminal groups of the as-prepared PAMAM, and the results coincided with its theoretical structure.Secondly, we synthesized two kinds of liquid crystal units with azobenzene structure and schiff base structure, and then dendritic crystalline macromolecules were successfully synthesized by grafting the liquid crystal units to the terminal of the PAMAM molecule. The structure of liquid crystal units and dendritic crystalline macromolecule has been characterized by FT-IR and ¹H-NMR, and the results coincided with its theoretical structure.Lastly, the DSC(Differential Scanning Calorimetry) curves showed the clearing point and the transition temperature of different liquid phase of the target liquid crystalline macromolecule, which possessed a wide range of phase transition temperature. POM(Polarizing Optical Microscopy) photographs comfirmed its typical texture of nematic liquid crystal. In fact, dendritic azobenzene liquid crystalline macromolecule belonged to bidirectional liquid crystal. While, liquid crystal phase of schiff-base liquid crystalline macromolecule maintained a wide range from its glass transition temperature(Tg) to thermal decomposition temperature(Td). Then, TGA curve showed that the sample had a good thermal stability, its Td was at around 270℃. Furthermore, XRD pattern showed a broad peak in the range of 2θ=18-22°, implying the typical nematic characteristic structure of the as-prepared schiff-base liquid crystalline macromolecule. At the present, the reports about this kind of dendritic liquid crystalline macromolecule are rare, and the study of the product we synthesized in this paper has not been found in and abroad.