Synthesis and physical properties of thermotropic liquid crystalline poly(ester-imide)s

Abstract

A series of thermotropic liquid crystalline poly(ester-imide)s were synthesized by melt polymerization of 2,6- or 2,7-diacetoxynaphthalene acid and n-(ω-carboxyalkylene) trimellitic imides and p-acetoxybezoic acid. We investigated the influence of molecular structure on the phase transitions, the crystallization and the hysteresis of the viscoelastic properties in part I. All n-2,6 PEIM with 2,6 substituent positions on naphthalene ring exhibited liquid crystalline phases, whereas all n-2,7 PEIM with 2,7 substituent positions do not. This result may suggest that the kink structure of n-2,7 PEIMs prevents the production of liquid crystalline polymer and hinders even the crystal formation. All CP54 and CP104B copoly(ester-imide)s synthesized with n-2,6 PEIMs exhibit the thread-like textures which is a typical texture of the nematic phase. They have low melting temperatures and slow crystallization because of the structural irregularity, which originated from the large differences in the length of aliphatic units in the main chain. These copoly(ester-imide)s was solidified in the nematic glassy state. When the homopolymers n-2,6 PEIMs have the relatively regular monomeric sequence and they show the strong dependence of a viscoelastic property on the crystallization, while copoly(ester-imide)s with irregular monomeric sequence show almost no thermal history because of a very slow crystallization. It is recognized that structural regularity of polymer chains affects strongly the viscoelastic properties of copolymers. The slow crystallization of copoly(ester-imide)s gives rise to a higher molecular orientation of a fiber even when melt spinning is carried out near the melting temperature because of the absence of crystallites during the spinning. In part II, the isothermal crystallization kinetics of thermotropic liquid crystalline 4-2,6 PEIM was studied by using DSC in temperature range of 190~240℃. The polymers show the heat and entropy of fusion. It indicates tha...