Liquid Crystalline Copolyester Research Articles

Thermotropic copolyesters prepared by solution polycondensation with TsCl/DMF/pyridine condensing agent

When mixtures of terephthalic acid (TPA) and 1,6-naphthalenedicarboxylic acid (NDC) or 4,4'-dicarboxydiphenylether (DCDPE), TPA, and isophthalic acid (IPA) were reacted in pyridine (Py) with Tosyl chloride (TsCl)/DMF/Py to activate the diacids, the reaction mixture was soluble in Py, despite each of the separately activated diacids being insoluble. The solubility of the activated diacids was examined at a variety of acid compositions and temperatures. It was expected that a competitive reaction among the diacids with an aromatic diol in solution might be different from those in the melt, resulting in a different distribution of the acids in the copolymers. The TPA/NDC-phenylhydroquinone and DCDPE/TPA/IPA-chlorohydroquinone copolymers were prepared in solution using TsCl/DMF/Py as the condensing agent and the transition temperatures of these liquid crystalline copolyesters were compared to those obtained by melt copolycondensation. A practical depression of the transition temperature by the solution polycondensation was observed.

Thermotropic copolyesters prepared by solution polycondensation with TsCl/DMF/pyridine condensing agent

When mixtures of terephthalic acid (TPA) and 1,6-naphthalenedicarboxylic acid (NDC) or 4,4′-dicarboxydiphenylether (DCDPE), TPA, and isophthalic acid (IPA) were reacted in pyridine (Py) with Tosyl chloride (TsCl)/DMF/Py to activate the diacids, the reaction mixture was soluble in Py, despite each of the separately activated diacids being insoluble. The solubility of the activated diacids was examined at a variety of acid compositions and temperatures. It was expected that a competitive reaction among the diacids with an aromatic diol in solution might be different from those in the melt, resulting in a different distribution of the acids in the copolymers. The TPA/NDC-phenylhydroquinone and DCDPE/TPA/IPA-chlorohydroquinone copolymers were prepared in solution using TsCl/DMF/Py as the condensing agent and the transition temperatures of these liquid crystalline copolyesters were compared to those obtained by melt copolycondensation. A practical depression of the transition temperature by the solution polycondensation was observed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3710–3714, 1999

Structure of liquid crystalline copolyesters from two acetoxybenzoic acids and polyethylene terephthalate

The molecular and supermolecular structures of thermotropic liquid crystalline copolyesters from p-acetoxybenzoic acid (B), polyethylene terephthalate (E), and m-acetoxybenzoic acid (M) were studied by Fourier transform infrared spectrometer, 200-MHz 1H-nuclear magnetic resonance (NMR), and wide-angle X-ray diffraction methods. The assignments of resonance peaks in NMR spectra are given and the effect of B/E/M molar ratio on the NMR spectra and number-average degree of polymerization of the copolyesters are discussed. The equatorial, meridional, and azimuthal scans, and their dependency on monomer mole ratio for the copolymers, are elaborated. The persistence length and orientation of the copolymer ribbons were found to increase with an increase in p-oxybenzoate unit content from 60 to 75 mol % at a fixed m-oxybenzoate unit content of 5 mol %. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2921–2925, 1999

Synthesis and properties of liquid crystalline aromatic copolyesters with lactide moieties

High molecular weight liquid crystalline copolyesters were obtained by copolycondensation of aromatic diols and diacyl chlorides with oligolactides. The molecular structure of these copolyesters was verified by NMR studies. The copolyesters form nematic melts, which can be frozen in into a nematic glass. Unexpectedly, a fibrillar structure was observed exclusively on the surface of solution cast films. In spite of a significant content of lactide moieties of the copolyesters their films and fibers are characterized by exceptional mechanical properties. Initial experiments indicated excellent biocompatibility based on cell seeding experiments and microscopic evidence.

Synthesis and properties of liquid crystalline aromatic copolyesters with lactide moieties

Synthesis and properties of liquid crystalline aromatic copolyesters with lactide moieties

Thermal decomposition of liquid crystalline random copoly( p-oxybenzoate-ethylene/phenylene terephthalate) by high-resolution thermogravimetry

Thermotropic liquid crystalline copolyesters consisting of three units of p-oxybenzoate ( B ), ethylene terephthalate ( E ), and phenylene terephthalate ( P ), were studied by a high-resolution thermogravimetry from ambient temperature to 800°C to ascertain their thermostability and kinetics parameters of thermal decomposition in both nitrogen and air. Overall activation energy data of the major decomposition had been evaluated through three calculating techniques. The thermal degradation takes place in three steps in nitrogen and air. The degradation temperatures are higher than 450°C in nitrogen and 444°C in air and increase with increasing B-unit content at a fixed P-unit content of 5 mol%. The temperatures at the first (and second) maximum weight-loss rate are higher than 456°C (and 524°C) in nitrogen and 451°C (and 520°C) in air and also increase with an increase in B-unit content. The first and second maximum weight-loss rates range from 10.9 to 12.3 %/min in nitrogen and from 4.2 to 5.5 %/min in air, and also increase slightly with increasing B-unit content. The char yields at 500°C in both nitrogen and air range from 42.1 to 51.1 wt% and increase with increasing B-unit content. But the char yields at 800°C in nitrogen are ranging from 16.0 to 22.4 wt% that is much higher than those in air. The activation energy and Ln (pre-exponential factor) for the major decomposition are usually larger in nitrogen than in air and decrease in nitrogen but increase slightly in air with an increase in B-unit content at a given P-unit content 5 mol%. The activation energy, decomposition order, and Ln (pre-exponential factor) of the thermal degradation for the terpolyesters, are situated in the ranges of 206–258 kJ mol −1, 1.7–2.6, 32–40 min −1, respectively. These results have also been compared with the results obtained by traditional thermogravimetry at a constant heating rate.

Multi-oriented and fibrous liquid crystalline networks based on linear mesogenic polymers

Crosslinkable liquid crystalline co-polyesters based on substituted terephthalic acid moiety have been synthesised and their phase behaviour characterised. The network formation by thermally activated radical reaction has been examined on polymers with different amounts of monomer units bearing reactive acryloyloxy substituents at the terephthalic group. The relatively low melting temperatures allow fibre extrusion to be performed from a polymer matrix containing the crosslink reaction activator. Successive thermal curing produces a stabilisation of the macroscopic orientation of the liquid crystalline network.

Structural, rheological, and mechanical properties of ternary blends of PEN, PET, and liquid crystalline polymer

AbstractStructural, rheological, and mechanical properties of ternary blends of a liquid crystalline copolyester (LCP) composed of p‐hydroxybenzoic acid and 2,6‐hydroxynaphthoic acid, poly(ehtylene naphthalate)(PEN), and poly(ethylene terephtalate) (PET) were investigated using capillary rheometry, tensile testing, scanning electron microscopy, and X‐ray diffraction. Viscosity‐shear rate behavior of the ternary blends is very similar to that of pure polymers and their binary blends. The activation energy of flows of the ternary blends was smaller than those of PEN and PET. Tensile modulus and strength of extruded strands of the blends increased with increasing LCP content. The extruded strands of the blends consist of a crystalline and oriented LCP phase and an amorphous and unoriented PEN/PET blended phase. Tensile mechanical properties and structures of the ternary blends were discussed.

Thermomechanical properties of radiation‐modified blends of polyethylene with liquid crystalline copolyester

AbstractThe results of investigation of gamma irradiated blends of high‐density polyethylene (PE) with thermotropic polymer liquid crystal (PLC) are presented. The PLC used was a copolyester of 40% poly(ethylene terephthalate) with 60% p‐(hydroxy‐benzoic acid). The PLC content in the blends was 0, 5, and 10 wt%. The constituents were blended with the use of a single screw extruder. The specimens were prepared by compression molding. The irradiation of the samples was performed by a Co60 γ‐radiation source in inert atmosphere (argon) up to absorbed relatively low doses (up to 200 kGy; 1 Mrad = 10 kGy). The morphological, thermal, and mechanical properties were investigated for irradiated and unirradiated samples. The influence of gamma irradiation and addition of PLC on the temperature dependence of the elastic modulus as well as the effect of a “form memory” of the materials examined are discussed. It was found that an addition of the PLC affects substantially the stress‐strain relationship in tension at temperatures above the melting point of PE for the irradiated samples. The features of thermomechanical behavior of the PE + PLC blends, previously irradiated and oriented, at isometrical heating and cooling were also established. The results obtained testify that the addition of PLC to PE makes it possible to improve considerably the thermosetting properties of the heat‐shrinkable polymeric products.

Optical Properties of a Liquid-Crystalline Random Copolyester

We have investigated the optical properties of Vectra A910, a commercially produced liquid-crystalline copolyester consisting of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid subunits. The polymer is highly fluorescent in the near UV with an emission maximum at 428 nm (2.90 eV) and an excitation maximum at 376 nm (2.66 eV). The time-resolved fluorescent decays at room temperature were found to fit stretched exponential decays. Furthermore, the fluorescence kinetics were found to be highly dependent upon the emission wavelength. These results are consistent with the disorder from the random nature of the copolymer.

Thermal and mechanical properties of amorphous copolyester (PETG)/LCP blends

Blends of amorphous copolyester (PETG) having an aliphatic cyclic segment and liquid crystalline copolyester (LCP) were prepared in solution blending technique. Specimens for mechanical testing were prepared by a miniature injection molding machine. For PETG/LCP blends, the difference between the two T gs was too small to define the resolution of two T gs by DSC. Also, DSC study revealed that the crystallization of PETG was occurred by the addition of LCP in the matrix. The tensile and modulus mechanical behaviors of the PETG/LCP blends were improved with increasing LCP content, whereas the elongation-at-break showed reverse results for it. This result could be explained by that the interface adhesion of PETG and LCP was poor but LCP acted as a reinforcing agent in the blends. The fracture of the blends represents the incompatibility of the PETG/LCP blend.

Modification of Randomness by Transesterification of Thermotropic Liquid Crystalline Copolyesters

Several different liquid crystalline copolyesters were thermally posttreated above their melt transition temperatures to increase their degree of randomness. Both poly(ethoxyphenylene terephthalate-co-ethylene terephthalate)s (poly(EPT-co-ET)) and poly(phenylphenylene terephthalate-co-ethylene terephthalate)s (poly(PPT-co-ET)) were prepared in 70:30 mole ratios of EPT:ET and PPT:ET and thermally randomized. The randomization reactions were controlled by variations in the duration and temperature of the reaction. The compositions of the copolymers remained constant in these reactions while the comonomer sequence distribution was changed. The inherent viscosities of the copolymers increased as a result of the reaction presumably because of increases in molecular weight. Increased randomness resulted in decreased crystallinities of the copolyesters, as observed by reduced enthalpies of fusion and crystallization, lower melt transitions, and lower crystallization temperatures.

Small molecule penetrant diffusion in aromatic polyesters: a molecular dynamics simulation study

Molecular dynamics (MD) simulations have been used to study diffusion of methane in three highly impermeable aromatic polyesters that are good barrier materials. These are amorphous poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalene dicarboxylate) (PEN), and the nematic mesophase of the thermotropic liquid crystalline copolyester (LCP) of p-hydroxy benzoic acid (HBA) and 2,6 hydroxy naphthoic acid (HNA). Diffusion coefficients were determined in the temperature ranges of 450–625 K for PET, 500–625 for PEN, 425–530 K for the LCP, where values are large enough to be accessible to MD in practical computation times. Extrapolation, via Arrhenius plots, of the coefficients to near room temperature gave good agreement with experimental data in that region. This was found even though the glass transition temperatures ( T g) of PET (350 K) and PEN (390 K) lie in the intervening temperature range. This finding confirms previous observations that a low temperature hopping regime for small penetrants sets in on cooling well before the T g of the host. Analysis of diffusant trajectories in terms of diffusive jump size distribution also shows that the low temperature hopping regime remains in place over the temperature range studied in these low diffusion coefficient polymers. Correlation of diffusion coefficients with free volume was examined. The LCP, even though diffusion there is highly anisotropic, is found to lie on a correlation found previously for five other polymers studied via MD. However, PET and PEN fail badly and are found to diffuse much more slowly than inferred from free volume vs diffusion coefficient behavior in the other polymers.

In Situ Infrared Spectroscopic Study on Liquid Crystalline Phase Formation of a Random Copolyester Consisting of 60 mol% p-Hydroxybenzoic Acid/40 mol% Ethylene Terephthalate

Conformation change occurring during the formation of the liquid crystalline phase was investigated by using the in situ Fourier transform infrared spectroscopy. An isotropic glass of a random liquid crystalline copolyester consisting of 60 mol% p-hydroxybenzoic acid/40 mol% ethylene terephthalate was prepared with the cast from a solution and was heated from the room temperature up to 300°C. The onset of the transformation from the gauche conformers to the trans conformers of the ethylene glycol group was observed at ca. 60°C. The change in packing was indicated by the change in the intensity of the bands assignable to the aromatic rings around 150°C. Liquid crystalline phase formation observed with the optical method started to occur at ca. 200°C in association with the loss of the packing.

Molecular mobility in liquid-crystalline phase of oriented wholly aromatic copolyester as revealed by proton magnetic resonance

Broad line proton magnetic resonance (PMR) has been used for the study of molecular motion in wholly aromatic thermotropic liquid-crystalline (LC) copolyester at high temperatures up to 340°C. Specimens were thin highly oriented fibers produced from a copolymer of hydroxybenzoic acid and hydroxynaphthoic acid (HBA/HNA). In the vicinity of the thermotropic transition temperature a fine structure of PMR spectra was revealed for as-spun fibers. Annealing leads to smoothing of this structure. Theoretical spectra were calculated and compared with the experimental ones. This made it possible to obtain information on large-scale segmental motion of macromolecules in the LC phase. Heat treatment leads to retardation of the chain cooperative mobility. Dynamic inhomogeneity of the fibers at high temperatures is discussed.

Reactive blending of poly(ethylene terephthalate) with a liquid crystalline copolyester and polyhydroxyether

Poly(ethylene terephthalate) modified with a dianhydride (PET–anhydride) was melt-blended with a liquid crystalline copolyester (Vectra A) in the presence of a small amount of a liquid crystalline polyhydroxyether. The mechanical properties of a blend consisting of PET–anhydride/Vectra A/polyhydroxyether were drastically improved compared to blends without polyhydroxyether or without anhydride. Melt-spun fibers of PET–anhydride/Vectra A/polyhydroxyether in a 80/20/0.75 weight ratio displayed a much higher tensile modulus (17 GPa) and tensile strength (214 MPa) than did a 80/20 PET–anhydride/Vectra A blend (4 GPa and 60 MPa, respectively). A similar increase in modulus and strength was found for a 90/10/0.75 relative to a 90/10 blend. The tensile moduli of the blends can well be described by the Tsai–Halpin equation. A better fibril formation was observed, which was attributed to an improved viscosity ratio. Reactions between the various functional groups during melt processing were indicated by viscosity measurements. The polyhydroxyether may act as a reactive compatibilizer which improves the interfacial adhesion, chemically and/or physically. WAXD recordings of both blends showed a crystalline and highly oriented Vectra phase. The PET phase was unoriented and amorphous in a PET/Vectra blend and semicrystalline and weakly oriented in a PET/Vectra/polyhydroxyether blend. Postdrawing of the various blend fibers to λ = 4 increased the modulus by about 40% and the tensile strength by more than 100%, mainly through orientation of the PET phase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1107–1123, 1999

Reactive blending of poly(ethylene terephthalate) with a liquid crystalline copolyester and polyhydroxyether

Poly(ethylene terephthalate) modified with a dianhydride (PET–anhydride) was melt-blended with a liquid crystalline copolyester (Vectra A) in the presence of a small amount of a liquid crystalline polyhydroxyether. The mechanical properties of a blend consisting of PET–anhydride/Vectra A/polyhydroxyether were drastically improved compared to blends without polyhydroxyether or without anhydride. Melt-spun fibers of PET–anhydride/Vectra A/polyhydroxyether in a 80/20/0.75 weight ratio displayed a much higher tensile modulus (17 GPa) and tensile strength (214 MPa) than did a 80/20 PET–anhydride/Vectra A blend (4 GPa and 60 MPa, respectively). A similar increase in modulus and strength was found for a 90/10/0.75 relative to a 90/10 blend. The tensile moduli of the blends can well be described by the Tsai–Halpin equation. A better fibril formation was observed, which was attributed to an improved viscosity ratio. Reactions between the various functional groups during melt processing were indicated by viscosity measurements. The polyhydroxyether may act as a reactive compatibilizer which improves the interfacial adhesion, chemically and/or physically. WAXD recordings of both blends showed a crystalline and highly oriented Vectra phase. The PET phase was unoriented and amorphous in a PET/Vectra blend and semicrystalline and weakly oriented in a PET/Vectra/polyhydroxyether blend. Postdrawing of the various blend fibers to λ = 4 increased the modulus by about 40% and the tensile strength by more than 100%, mainly through orientation of the PET phase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1107–1123, 1999

Crystallization and melting behavior of liquid crystalline copolyesters based on poly(ethylene terephthalate)

A series of copolyesters were prepared by the incorporation of p-hydroxybenzoic acid (HBA), hydroquinone (HQ), and terephthalic acid (TA) into poly(ethylene terephthalate) (PET). On the basis of viscosity measurements, high molar mass copolyesters were obtained in the syntheses, and 1H-NMR analyses indicated the total insertion of comonomers. They exhibit nematic phase above melting temperature, as observed by polarized light microscope (PLM). Their crystallization and melting behaviors were also studied by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). It was found that these copolyesters are more crystalline than copolyesters prepared from PET and HBA. Introduction of HQ/TA disrupts longer rigid-rod sequences formed by HBA, and thus enhances molecular motion and increases crystallization rate and crystallinity. Isothermal crystallization at solid phase polymerization conditions (up to 24 h at 200°C) resulted in increased copolymer randomness (by NMR) and higher melting point, the latter attributed to structural annealing. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 369–377, 1999

Effect of the components' molar mass and of the mixing conditions on the compatibilization of PE-LCP blends by PE-g-LCP copolymers

The rheology, morphology, and mechanical properties of blends of high-density polyethylene (HDPE) with a semiflexible liquid crystalline copolyester (SBH) were studied in order to assess the compatibilizing ability of added PE-g-SBH copolymers, and its dependence on the molar mass of the PE matrix, and on the technique used for blend preparation. The PE-g-SBH copolymers were synthesized as described in previous articles, either by the polycondensation of the SBH monomers in the presence of a functionalized PE sample containing free carboxyl groups, or by reactive blending of the latter polymer with preformed SBH. Two samples of HDPE having different molar masses, and two samples of SBH with different melt viscosity and different microstructure, were used for preparing the blends. The two components and the compatibilizer were either blended in a single batch or used to prepare binary master blends to which the third component was added at a later stage. The results indicate that the PE-g-SBH copolymers do, in fact, compatibilize the PE–SBH blends and that the effect is more pronounced with the lower molar mass PE matrix and with the SBH sample having lower viscosity. The experiments carried out on blends prepared with different techniques show that the compatibilizing ability of the graft copolymer is improved if the latter is first blended with either of the two main components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 603–613, 1999

Influence of the type of polyhydroxyether on mechanical properties of PET/TLCP/polyhydroxyether blends

In a more elaborate article, it was described that blends of poly(ethylene terephthalate) (PET), a liquid crystalline copolyester, and small amounts of a liquid crystalline polyhydroxyether showed an increase in tensile modulus and strength compared to the blends without polyhydroxyether. The results were obtained using a polyhydroxyether composed of 75 mol % biphenyl and 25 mol % phenyl units. In this article, the use of two other types of polyhydroxyether is described, one based on the α-methylstilbene unit and the other based on bisphenol A. Addition of either of these polyhydroxyethers to the PET/thermotropic liquid crystalline polymer (TLCP) blends increased the tensile modulus and strength of extruded fibers in a similar way as upon addition of the liquid crystalline polyhydroxyether. Improvement of the viscosity ratio and thereby improvement of the fibril formation, by reactions of the functional hydroxyl side groups in the polyhydroxyethers, appears to be the most important factor for the improvement of the mechanical properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1125–1131, 1999