Study On Synthesis And Properties Of Bisphenol-A Thermotropic Liquid Crystal Polyarylester

Bisphenol-A polyarylesters are one kind of thermotropic liquid crystal polymers, developed in the1970s after the liquid crystal polyamide. Marcromolecule chain contains rigid aromatic ring and ester bond mainly. Bisphenol-A polyarylesters display excellent tensile strength and modulus, heat-resistance, and small linear expansion coefficient, better processability than lytropic liquid crystal polymers or heterocyclic polymer. However, the melting points of wholly absolute-inflexible polyarylesters are so high that always be higher than their decomposition temperatures or be disposed before the liquid crystal phases could be formed, they are not suitable to be processed therefore. Molecular design should be adopted to decrease the melting point for actual applications.In this thesis, acetic anhydride, bisphenol-A, terephthalic acid (TA) and isophthalic acid (IPA) are used as raw materials to prepare thermotropic liquid crystal polymers by mean of melt polymerization. Firstly, bisphenol-A-diacetate is prepared and purified for melt polymerization, and bisphenol-A polyarylesters with various monomer rations are prepared. Polyarylesters with different thermal properties, crystallinity, molecular weight, melt index and other parameters are investigated employing differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD) and other methods. Solid state polymerization is performed to increase the molecular weight, solving the problems that polyarylesters are easily to be decomposed and darkening in the condition of high temperature. Crystallization, molecular weight, thermal performance, melt index, rheology, mechanical capacity and molecular structure of bisphenol-A polyarylesters effected by solid state polymerization are concerned in this paper.1) When the excessive content of bisphenol-A-diacetate is about10%, the polyarylester is of highest molecular weight; without IPA, the melting point of the product is higher than380℃and there are no characteristics of thermotropic liquid crystal at the temperature till400℃. After introducing IPA, the melting point decreases below380℃,and reaches320℃when the IPA addition is60wt%. The temperature of fastest thermal decomposition for polyarylesters is above500℃, indicating good thermal properties.2) As the increase of IPA, crystallinity decreases gradually. Nematic liquid crystals phase can be deserved when the amount of IPA is5-15wt%, and the thermotropic liquid crystal behavior-schlieren texture disappears when the amount is beyond this range; tensile strength decreases with small variation of breaking elongation.3) At constant temperature, shear thinning behavior is displayed with the increase of shear rate. In addition, apparent polymer viscosities drop drastically with the increasing of temperature.4) Temperature and time are two major parameters in solid state polymerization and their affections to the viscosity are studied. After solid state polymerization with suitable temperature and time, molecular weight, melting point, crystallinity and sample tensile strength are all increased, and banded texture of nematic phase for thermotropic liquid crystal can be observed. The molecular weight tends to fall if the solid state polymerization is carried at temperature higher than310℃for more than20hours.