Aromatic liquid crystalline copolyesters with low T_m and high T_g: Synthesis, characterization, and properties

Abstract

In this study, a series of aromatic copolyesters P‐BPAx with lower melting temperature and higher glass transition temperature derived from hydroxybenzoic acid (HBA), 6‐hydroxy‐2‐naphthoic acid (HNA), bisphenol A (BPA) and terephthalic acid (TA) were synthesized via melt polymerization. The copolyesters were characterized by FTIR, solid state 13C NMR, DSC, TGA, polarized optical microscopy, X‐ray diffraction, and rheometry measurements. With addition of BPA, the resulting copolyester's melting temperature decreased from 260 to 221°C and its glass transition temperature increased from 70 to 135°C, compared with the parent copolyester P‐HBA70 (HBA/HNA copolymer). With exception of copolyester P‐BPA5.0 (225–280°C), the copolyesters could maintain liquid crystalline behavior in a broad temperature range from 230°C to higher than 410°C. The ability to form nematic liquid crystalline phase disappeared when BPA concentration became higher than 15 mol %. X‐ray diffraction analysis showed crystallinity decreased as the BPA content increased. A slightly distorted O" and a substantially distorted O′ orthorhombic phase was observed for P‐BPA2.5. Upon annealing at 220°C, the O" phase disappeared and the O′ phase became stronger gradually. Rheology study data showed the ability to process the copolyesters improved in those compositions containing <2.5 mol % BPA. Continuing to increase concentrations of BPA, they became intractable. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40487.

Annealing effect of thermotropic liquid crystalline copolyester fibers on thermo- mechanical properties and morphology

“…This increase in T m caused by the HBA monomer of the rigid rod-type can be attributed to the ease of molecular packing. [21][22][23][24] The isotropic temperature (T i ) showed the same trend as the T m (Table 3). A liquid crystalline phase was not observed for TLCPs with 0-2 mol HBA because of the bent structure of DHN and the exible alkoxy side group of DTA, as was observed for the T m .…”

Dependence of the Physical Properties and Molecular Dynamics of Thermotropic Liquid Crystalline Copolyesters on p-Hydroxybenzoic Acid Content

“…Liquid crystallinity, which occurs between T m and T i , can be observed using an optical polarizing microscope [34,35]. Figure 5 shows the liquid crystallinity observed for polymers in the TLCP-I and TLCP-II series at various temperatures.…”

Reprocessable Triple-Shape-Memory Liquid Crystalline Polyester Amide with Ultrahigh Thermal Resistance

“…According to the Bragg equation, the interplanar space corresponding to each peak can be obtained. Among them, the average intermolecular space (2θ = 20.0°) reflecting the rodlike liquid crystalline mesogens is 4.4 Å, and the interplanar spaces of 2θ = 27.9° and 2θ = 43.1° belong to the (211) crystallographic plane of the HBA homopolymer (pHBA). , Its average intermolecular spaces are 3.2 and 2.1 Å, respectively, implying the presence of highly thermally stable pHBA (nano)­crystallites . Through observing photomicrographs, it is found that cured RLCP still manifests the typical nematic liquid crystalline texture (Figure B); hence, the curing process does not influence its liquid crystallinity because of the outstanding thermal stability of the all-aromatic liquid crystalline main chain and steady liquid crystallinity of RLCP over a broad temperature range (Figure ).…”