Structure and properties of fully aromatic thermotropic liquid‐crystalline copolyesters containing m‐hydroxybenzoic acid units

Abstract

AbstractA series of fully aromatic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a modified melt‐polycondensation reaction. The copolyesters were prepared in two series in which series I is based on a two monomer system (p‐ABA/m‐ABA) and series II is based on a three monomer system (HQDA/TPA/m‐ABA). The effect of different linear structures and kink moiety on the properties of the copolyesters were investigated systematically. The copolyesters were characterized by differential scanning calorimetry, thermogravimetric analysis, 1H‐NMR, polarized optical microscopy, X‐ray diffraction, and intrinsic viscosity measurements. It was found that the copolyesters exhibited nematic liquid‐crystalline phases when the content of linear (p‐ABA or HQDA/TPA) units was over 67 mol %. The melting or flow‐transition temperatures were decreased with an increase of the content of kink m‐ABA units. The copolyesters that contained p‐ABA as linear units had a significantly higher degree of crystallinity compared to the copolyesters that contain HQDA/TPA as the linear units, implying a higher blockiness in the polymer chains as a result of the higher reactivity of the p‐ABA units in the p‐ABA/m‐ABA system. All the copolyesters had poor solubility except the copolyesters containing at least 40 mol % of m‐ABA, which were soluble in a dichloromethane/trifloroacetic acid (70:30 v/v) mixture. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3260–3269, 2003