Based On The Liquid Crystalline Copolyester Expansion Polymer Materials Design And Synthesis

Through molecular design, 4 series and 13 kinds of polyesters composed of rod-flexible spacer alternating units with laterally attached rods in the main chain were synthesized, with aiming to prepare auxetic polymeric materials having negative poisson ratio. The chemical structure of all intermediates and monomers was confirmed by measurements of melting point, -NMR, IR, and Elemental Analysis. The chemical structure and property of polymers were characterized by using NMR, IR, GPC, DSC, TG, X-ray diffraction, and a polarized microscope equipped with a thermalstage. The influences of the content of laterally attached rods and the volume of end substituted group to the polymer properties were studied systematically. The relationship between structure and property was discussed in detail. All of the polymers entered into liquid crystalline states when heated to above their melting point Tm, clear threaded texture could be observed, illustrating the polymers having a nematic liquid crystal character. Three endothermal peaks on the first heating scan of DSC measurements were usually observed, the former two peaks could be attributed to the melting of crystals with different perfection, the final one could be assigned to the transition from liquid crystal state to isotropic fluid state. The liquid crystalline state could be readily retained at room temperature. Due to the low Tg and the excellent stability of nematic state at room temperature with very wide liquid crystal temperature range, the polymers could be easily molded in the high order nematic state, which provides a promising method to prepare auxetic polymeric materials by the advantage of nematic field. It can be found that the molecular weight of polymers was in a range from 4,000 to 10,000, this may result from the difficulty in the strict control for the equimolar charging of the three monomers with different functional group. The introduction of laterally attached rods has dual influence on the structure and property of polymers. The steric hindrance of bulky laterally attached rods would decrease the regularity of the polymer chain folding, leading to the decrease in crystallization ability. On the other hand, with the increase of laterally attached rod content, the content of benzene ring in the main chain was also increased, which resulted in the increase of main chain rigidity, resulting in higher melting point Tm and clearing point T1, while, a narrower temperature range of nematic liquid crystal state. Also, the content of ester groups increased, resulted in the low decomposition point Td and the low final weight loss. With the volume increase of end group, the temperature range of nematic liquid crystal state became wider, which could be attributed to the different polarizing ability of the end group. The Td of all polymers is about 200 0C higher than their Tm an I T1, which assured enough thermal stability for the thermalplastic molding of the polymeric materials.