Influence of molecular structure modifications and annealing conditions on the physical properties of thermotropic LC polyesteramides with a pheylhydroquinone derivative

Abstract

The new thermotropic liquid crystalline (LC) polyesteramides with a phenylhydroquinone derivative were synthesized by a solution polymerization. and had the following chemical structures: ## The thermotropic LC polyesteramides turned out to have a low melting temperature, a wide nematic range from the melting temperature to $350\,^circ\!C$, and thermally stable until reaching $400\,^\circ\!C$. As the number of rigid units in a main chain increased, the nematic phase appeared more apparently, and the glass transition temperature become higher. The melting temperature slightly decreased due to the destruction of the chain regularity when the LC polymer was a copolymer. The kinetics of the isothermal crystallization of the polyesteramides was studied by differential scanning (DSC), polarized optical microscopy (POM), wide-angle X-ray diffractometer (WAXD), and solid nuclear magnetic resonance (NMR) spectrometer. The quenched sample showed a well developed three-dimensional order and indicated a frozen-in liquid crystalline structure rather than a true crystal due to strong steric hindrance of side benzene groups, which was evidenced by DSC and POM. Even though the formation of a three-dimension order was hindered, it could be achieved by a long time annealing. That is, the results showed that the crystallization process of the polyesteramides occurred very slowly. The crystallization process could be described by a modified Avrami equation, and the transformation from imperfect molecular packing to ordered packing was detected successfully by spin-spin relaxation time (T$_2$) measurement. The Avrami parameters (n) of the polyesteramides had very low values because of the slow crystallization. The homopolyesteramide showed a slightly faster crystallization than the copolyesteramides. The rheological properties of the polyesteramides were dependent largly on the molecular structure and annealing conditions. The stress relaxation data showed that the copolyesteramide...