Aromatic Liquid Crystalline Copolyesters Research Articles

In-depth analysis on thermal phase transition mechanism of main-chain phosphorus-containing thermotropic liquid crystal copolyester

ABSTRACTIn order to surmount drawbacks of the infrared spectroscopy (IR) itself during investigating the mesophase-transition behaviours and mechanism of the thermotropic liquid crystalline polymers (TLCPs), the elemental phosphorus as an internal marker was introduced into the main-chain TLCPs. The detail mechanism of the glass transition and mesophase phase transition of the phosphorus-containing aromatic liquid crystalline copolyester (poly(-hydroxybenzate-co-DOPO-benzenediol dihydrodiphenyl ether terephthalate) [PHDDT]) was revealed through tracing the internal marker with the perturbation correlation moving window 2-dimensional correlation and 2-dimensional correlation analysis (2DCOS) correlation IR spectra. The results showed that the phosphorus-containing unit did not participate in the glass transition of the PHDDT. The results of the 2DCOS showed that the PHDDT mesophase phase transition took place through adjustment of the phosphorus-containing units. Simultaneously, the adjustment of the phosphorus-containing unit also can induce the motion of the other groups, and the sequential orders of the spectral changes were Ar–O–Ar → ester C–O → C=O. However, the sequential orders of the spectral changes were converse during the PHDDT glass transition.

Erratum: Aromatic liquid crystalline copolyesters with low Tm and high Tg: Synthesis, characterization, and properties

Erratum: Aromatic liquid crystalline copolyesters with low T<i>_m</i> and high T<i>_g</i>: Synthesis, characterization, and properties

Effect of phase morphology on water diffusion in phosphorus-containing thermotropic liquid crystal copolyester film

In this paper, effect of phase morphology on water diffusion in phosphorus-containing aromatic liquid crystalline copolyester (P-TLCP) named as poly(-hydroxybenzate-co-DOPO-benzenediol dihydrodiphenyl ether terephthalate) (PHDDT) was investigated by two-dimensional correlation infrared (2DIR) spectroscopy, in order to understand well the relationship between structure and properties of P-TLCP. The phase morphologies of the PHDDT films were observed by polarized light microscope. The experimental results showed that the clear nematic texture, which was observed for PHDDT film treated at 250 °C for 3 min under a nitrogen atmosphere. However, lots of bright spots were observed for untreated PHDDT film due to weak crystallization of PHDDT molecules. Moreover, the density of the untreated PHDDT film (1.1631 ± 0.0257 g/cm−3) was lower than that of the treated one (1.2969 ± 0.0134 g/cm−3), indicating that the arrangement of the molecules in treated PHDDT film was compact in comparison with that in untreated one. Therefore, the average diffusion coefficient of water in treated PHDDT film was lower than that in untreated one. The mechanisms of water diffusion into PHDDT films with different phase morphologies can be obtained through 2DIR analysis in OH stretching and bending bands. It was found that water diffused into the treated PHDDT film by forming moderate hydrogen bonds prior to forming strong and weak hydrogen bonds, while diffused into the untreated one by forming strong and weak hydrogen bonds prior to forming moderate hydrogen bonds. It was also found that the spectral intensity of PO varied prior to that of CO during water diffusion into untreated PHDDT film, which was reversed for treated PHDDT film.

Surface Microcracks Decoration and Disclination Defects of Wholly Aromatic Liquid Crystalline Copolyesters

An intensive study has been conducted to map the director fields of disclination of nematic liquid crystalline copolyesters. In this study, films of two wholly aromatic main-chain polyesters containing para- (ABA/MH/TFTA) and meta-linkages (ABA/MH/TFIA) (ABA, p-acetoxybenzoic acid; MH, maleic hydrazine; TFTA, tetrafluoroterephthalic acid; TFIA, tetrafluoroisophthalic acid) were synthesized to investigate the effects of kinks on liquid crystallinity, disclination strength (S), and surface microcracks decoration. These two copolyesters were prepared by in-situ thin film polymerization and characterized by polarizing light microscope, wide-angle X-ray diffraction, as well as "rotational isomeric states" (RIS) Metropolis Monte Carlo (RMMC) simulation. An optical microscope shows that the surface microcracks forms in the nematic-mosaic texture during a rapid quenching. The ABA/MH/TFTA film exhibits disclination strength with S = +1 and S = -(1)/(2); however, disclination strengths with S = +/-1 have been observed in the ABA/MH/TFIA system. To our best knowledge, this is the first paper reporting the effects and evidence of kink (meta and para moieties) on topological defect of disclination. In addition, the RMMC analysis supports the liquid crystal formation in both polyester films with a persistence ratio greater than 6.42.

Highly Aromatic Liquid Crystalline Copolyesters Synthesized by Transesterification of Poly(ethylene terephthalate) with Acetoxybenzoic Acid, Diacetoxybenzene and Terephthalic Acid

New liquid-crystalline copolyesters have been synthesized by the melt transesterification of poly(ethylene terephthalate) (p(ET)) with 4-acetoxybenzoic acid (H), and varying proportions of equimolar mixtures of diacetylated hydroquinone (Q) and terephthalic acid (T). It has been shown that the risk of solidification of the reaction mixture due to segregation of a high melting phase formed by polymer chains rich in aromatic units is appreciably lowered with respect to systems where only H is reacted with p(ET). Moreover, the addition of appropriate amounts of Q and T (5-30%, with respect to H) has been shown to improve the polymers homogeneity. Thus, p(ETHQ) copolyesters with processability characteristics comparable to those of commercial p(ETH) copolyesters can be prepared with a considerably higher content of aromatic units, with a beneficial effect on mechanical properties and temperature resistance.

Isothermal Crystallization Kinetics of Poly(ethylene terephthalate) in Blends with a Liquid Crystalline Polyester (Vectra A)

The isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) in blends with a fully aromatic liquid crystalline copolyester (Vectra A) were studied with differential scanning calorimetry. PET crystallization rates decreases with increasing Vectra fractions in the blends, and the percentage of PET that is crystalline also decreases with increasing Vectra. The equilibrium PET melting temperature for blends containing 40% or more Vectra is unambiguously below that of pure PET. Attenuated total reflectance Fourier-transform infrared spectroscopy measurements indicate that PET/Vectra transesterification does not take place. The results are consistent with a scenario based on prior NMR data in which there is some interphase mixing between the liquid crystalline and flexible polymers and an increase in the fraction of gauche conformers in the PET.

Effect of Polyetheretherketone Oligomer on the Mechanical Properties of Polyetheretherketone with Aromatic Liquid Crystalline Copolyester Blends

The mechanical properties of blends of polyetheretherketone (PEEK) with an all aromatic liquid crystalline copolyester (LCP) have been investigated. Additionally, PEEK oligomers were added as a third component to the above blends in order to improve the mechanical properties. The flexural modulus and tensile strength decreased except for the blends with low LCP. In contrast, the addition of the PEEK oligomers has little effect on modulus, but flexural and tensile strength were clearly improved and the ESCA absorption caused by carbonyl group was also reduced by addition of PEEK oligomer to PEEK/LCP blend. The improvement of the mechanical properties of the blend may be due to the formation of a crosslinked product which behaves as a good compatibilising agent for PEEK with LCP during the blending process.

Effect of Polyetheretherketone Oligomer on the Mechanical Properties of Polyetheretherketone with Aromatic Liquid Crystalline Copolyester Blends

The mechanical properties of blends of polyetheretherketone (PEEK) with an all aromatic liquid crystalline copolyester (LCP) have been investigated. Additionally, PEEK oligomers were added as a third component to the above blends in order to improve the mechanical properties. The flexural modulus and tensile strength decreased except for the blends with low LCP. In contrast, the addition of the PEEK oligomers has little effect on modulus, but flexural and tensile strength were clearly improved and the ESCA absorption caused by carbonyl group was also reduced by addition of PEEK oligomer to PEEK/LCP blend. The improvement of the mechanical properties of the blend may be due to the formation of a crosslinked product which behaves as a good compatibilising agent for PEEK with LCP during the blending process.