Liquid Crystal Copolyester Research Articles

Preparation and properties of phosphorus-containing thermotropic liquid crystal copolyester fibers with excellent flame retardance and mechanical property

In order to acquire polymeric fibers have both excellent flame retardance and mechanical properties, high molecular weight phosphorus-containing liquid crystal copolyesters derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-dihydroxypheny)-10-hydro-9-oxa-10-phospha phenanthrene-10-oxide (DOPO-HQ) were synthesized via “one-pot” melt polymerization, and then the fibers were obtained by melt spinning method. The structure and property of the copolyesters were studied elaborately by experimental characterization technique and molecular simulation method. Shear shinning behavior was observed from rheology measurement, indicating that the copolyesters had excellent melt fluidity and spinnability. The rigidity of molecular chain was efficiently improved by the phosphorus-containing monomer DOPO-HQ and naphthalene HNA units which could be reflected by the molecular simulation results as well as high Tg values. The flame retardant mechanism of the phosphorus-containing flame retardant copolyester was systematically studied via limiting oxygen index (LOI), vertical burning (UL-94) test, cone calorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the copolyesters exhibit synergistic flame retardant mechanism of gas phase and condensed phase. Meanwhile, mechanical property of the as-spun fibers could be significantly improved by increasing the spinneret draw ratio (SDR) attributed to high molecular chain orientation. The maximum tensile strength of the as-spun fiber was 0.77 GPa observed for P-HNA60P20 at a relatively low SDR of 29. It was shown the unique combination of good thermal stability, spinnability as well as mechanical and flame retardant properties of the copolyesters would make them could be used as high-performance flame retardant materials.

Synthesis and properties of high‐performance biobased liquid crystal copolyesters modified by small amount of 2,5‐furandicarboxylic acid

AbstractHigh‐performance bio‐based liquid crystal copolyesters derived from 6‐hydroxy‐2‐naphthalenoic acid (HNA), 4,4′‐dihydroxybiphenyl (BP), bio‐based 2,5‐furandicarboxylic acid (FDCA) and suberic acid (Sa) were successfully designed and prepared by “one‐pot” melt polycondensation method. The influence of small amount (1–5 mol%) of FDCA on structure and properties of the copolyesters were fully investigated. Aromatic heterocyclic FDCA units had unique effect on molecular structure and properties of the copolyesters ascribed to its high stiffness and nonlinearity. The glass transition temperature, melting temperature and initial decomposition temperature of the copolyester was improved. In addition, a small amount of FDCA addition was conducive to crystallization, which can be attributed to FDCA addition increasing the molecular chain interaction. The copolyesters exhibited a broad liquid crystal phase temperature range and viscous behavior, which provided great convenience for its melt processing. The tensile strength and modulus of injected splines were in range of 82.38 ~ 121.30 MPa and 2.68 ~ 3.95 GPa, respectively, which were much higher than those of PET, PLA and other biobased polyesters. The obtained copolyester has good thermal stability, melt processing ability, mechanical properties and hydrophilicity, which indicates that they have great potential for medical and packaging applications.

Structure and properties of aromatic naphthalene thermotropic liquid crystal copolyester/MWCNT composites

Aromatic naphthalene thermotropic liquid crystal copolyesters (N-TLCP) have strong intermolecular forces and possess excellent comprehensive properties. In this study, the N-TLCP/MWCNT nanocomposites derived from 6-hydroxy-2-naphthoic acid (HNA), 2,6-naphthalene dicarboxylic acid (NDA), terephthalic acid (TA), 4,4′-dihydroxy biphenyl (BP) and carboxyl MWCNT were prepared via in situ “one-pot” melt polymerization method. The structure and properties of N-TLCP/MWCNT composites were fully analyzed. The interaction between MWCNT and TLCP matrix was confirmed by FTIR, XPS, Raman spectrum and rheometric measurements; and the strong interaction was observed for addition of a small amount of MWCNT (<0.5 wt%), which was attributed to the fact that the functional group COOH on the surface of MWCNTs enhances the dispersion state of the CNTs and molecular interaction through hydrogen bond/chemical covalent bonds. As a result, the glass transition temperature, melting temperature, thermal stability and mechanical properties of the N-TLCP/MWCNT composite was improved. However, more addition of MWCNT would tend to aggregate and impact the molecular weight and structure of the N-TLCP by the chemical reaction between its COOH group and OH group of the N-TLCP, which is not favor for improving the mechanical properties.

Synthesis and properties of high performance biobased liquid crystal polyester based on furandicarboxylic acid and sebacic acid

In this study, a series of high-performance biobased liquid crystal copolyesters derived from 6-hydroxy-2-naphthoic acid (HNA), 4, 4ʹ-Dihydroxybiphenyl (BP), biobased 2,5-furandicarboxylic acid (FDCA) and sebacic acid (SeA) were successfully designed and prepared via “one-pot” melt polycondensation method. The addition of nonlinear and rigid FDCA units broke the regularity of the molecular chain but increased the chain rigidity, thus, endowing the unique thermal behavior, which the melting temperature decreased from 163.0 to 125.3 ℃, while the glass transition temperature decreased first and then increased slightly to 75.7 ℃ as increased the FDCA units to 7.5 mol%. Furthermore, DSC and XRD results showed that a small amount (1 mol%) of FDCA units did not impair crystallization ability of the copolyesters, whereas excess of FDCA hindered the molecular chain packing. The DMA results also demonstrated that the addition of FDCA restricts the chain motion and improves the rigidity of the copolyester as reflected by the higher storage modulus. The incorporation of nonlinear FDCA units lowered the initial degradation temperature slightly, but still exhibited enough thermal stability to be melt processed as compared with its relative low melting temperatures. The copolyesters exhibited a broad temperature range of nematic liquid crystal phase as well as shear thinning and viscous melt flow behavior, which were beneficial for its melt processing. The tensile strength and modulus of the injection molded splines were in range of 82.51–103.27 MPa and 2.05–2.72 GPa, respectively, which were much higher than the common biobased copolyesters such as PLA, PCL and other FDCA-containing polyesters. The increased modulus and decreased fracture strain of the copolyesters containing FDCA units further verified the high rigidity of the molecular chain. Moreover, the in-vitro cytotoxicity and water contact angle results proved that the copolyesters have good biocompatibility. The resulted copolyesters combined with excellent melt processing ability, mechanical property and good biocompatibility have great promising applications as biomedical and biodegradable materials.

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

A series of thermotropic liquid crystal copolyesters (Co-TLCPs) was prepared by melt polymerization using 2,5-diethoxyterephthalic acid (DTA), 2,7-dihydroxynaphthalene (DHN), and p-hydroxybenzoic acid (HBA) monomers, where the HBA content was varied (0–5 mol). At 3 mol HBA, the Co-TLCPs formed nematic mesophases, while below this concentration, the liquid crystalline phase did not appear. The Co-TLCP sample with 3 mol HBA was subjected to melt spinning and heat-treated under various conditions (temperature and time) to investigate their effect on the thermo–mechanical properties and degree of crystallinity. The objective was to determine the critical heat treatment condition that can maximize the properties of the spun Co-TLCP fibers. The microstructure of the heat-treated fiber was investigated using scanning electron microscopy, and the optimal annealing conditions were confirmed based on the morphology of the fiber, which exhibited a skin–core structure owing to the varying heat and pressure conditions applied during spinning.

Design and synthesis of liquid crystal copolyesters with high-frequency low dielectric loss and inherent flame retardancy

Ultra-low dielectric loss (Df) and low dielectric constant (Dk) materials are urgently required in high-speed and large-capacity transmission, in which the wholly aromatic liquid crystal polymer (LCP) has gained attention due to its excellent dielectric properties. However, the relationship between molecular structure and dielectric properties is still not clear. In this study, two copolyesters containing phenyl or naphthyl structures are synthesized, as well as the effects of benzene and naphthalene mesogens on dielectric properties are investigated. The synthesized copolyesters containing naphthalene structure have good comprehensive properties with high thermal stability (T5% = 479 °C and Tg = 195–216 °C), inherent flame retardance (LOI = 33.0–35.0 and UL-94 V-0 level at 0.8 mm), low Dk (2.9–3.0@10 GHz) and low Df (0.0027–0.0047@10 GHz). Naphthalene mesogen can reduce the dielectric loss more significantly than benzene at high frequency by reducing the density and mobility of polarizable groups, which leads to the effectively limited dipole polarization in copolyesters. Consequently, we proposed a new strategy for designing low Dk and low Df materials.

Synthesis and properties of high performance biobased liquid crystal copolyesters toward load-bearing bone repair application

In order to acquire satisfactory load-bearing bone substitute, a series of high performance biobased liquid crystal copolyesters derived from 4-hydroxybenzoic acid (HBA), phloretic acid (HPPA), vanillic acid (VA) and lactic acid (LA) were designed and prepared via “one-pot” melt polymerization method in this work. The structure and properties of the copolyesters were fully investigated by experimental measurements and molecular simulation. The copolyesters showed relative low melting temperatures (176–229 °C) and controllable crystallinity (15.3–36.5%), due to the increased molecular chain mobility caused by LA units and the multi-component copolymerization effect. Broad temperature range of nematic liquid crystal phase, good thermal stability as well as shear shinning and viscous melt flow behavior were observed for the copolyesters, indicating they had excellent melt processing ability. As compared with polyetheretherketone (PEEK) materials, the copolyesters exhibited better mechanical properties and hydrophilicity, which of the tensile strength and water contact angle were in range of 95 to 175 MPa and 72.5 to 84.8°, respectively, ascribing to the combination effect of its liquid crystal nature and chemical structure. In addition, the cytotoxicity test showed the copolyesters have good biocompatibility. It is shown that the unique combination of potential biodegradability, excellent mechanical properties, hydrophilicity and biocompatibility of the copolyesters make them prospective and suitable for application in load-bearing bone repair area.

Thermal degradation and pyrolysis behavior of wholly aromatic phosphorus-containing thermotropic liquid crystal copolyesters

In this study, the thermal degradation and pyrolysis behavior of three wholly aromatic phosphorus-containing thermotropic liquid crystal copolyesters (TLCP) were investigated. The non-isothermal degradation kinetic parameters were determined using the Kissinger and Friedman method. The copolyesters exhibited two degradation stages in air but only one in N2, and better thermal stability was observed for those containing more 10-(2,5-Dihydroxypheny)-10 h-9-oxa-10-phospha-phe-nanthrene-10-oxide (DOPO-HQ) units, which could be reflected by the thermogravimetric analyzer (TGA) data and E values. The TGA coupled with Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatograph-mass spectrometer (Py-GC-MS) results showed that DOPO-HQ decomposed first in the early stage of degradation, generating gaseous pyrolysis products and forming phosphorus-containing char residue in the later stages of degradation. However, the copolyesters produced more CO2 and less organic volatiles during thermal oxidative degradation. The morphology and FTIR spectra of the char residue obtained after TGA experiments showed a continuous and dense structure due to the presence of phosphorus moieties. The microscale combustion calorimeter (MCC) and limiting oxygen index (LOI) results showed that the copolyesters have excellent flame retardant properties, and the LOI value increases monotonically with increasing of DOPO-HQ content, having a maximum value up to 73.8%, due to its excellent gas-phase and condensed-phase fire inhibition mechanisms. Overall, the resulted phosphorus-containing thermotropic liquid crystal copolyesters exhibited excellent thermal stability and flame retardancy, the thermal degradation and pyrolysis research would be a good guidance for its processing and application.

Synthesis and properties of high performance aromatic thermotropic liquid crystal copolyesters based on naphthalene ring structure

In order to obtain thermotropic liquid crystal polymers (TLCP) with excellent comprehensive performance, naphthalene monomers (amount exceeding 50 mol%) of 6-hydroxy-2-naphthoic acid (HNA) and 2,6-naphthalene dicarboxylic acid (NDA) were used to prepare wholly aromatic TLCP with strong molecular interaction via “one-pot” melt polymerization method in this work. The structure and properties of the copolyesters were fully investigated by experimental measurements and molecular simulation. The simulation results indicated that the naphthalene TLCPs had less chain mobility and stronger molecular interactions, and resulted in a linear rigid chain conformation, endowing the copolyesters with superior properties. As compared with the control copolyester M without naphthalene units, the resulted copolyesters had higher glass transition and melting temperature, higher melt tension, better thermal stability and fiber mechanical property. Overall, the rigidity, molecular interaction and properties of the obtained copolyesters could be efficiently improved after incorporation of the naphthalene units, which is beneficial for its processing and application.

High fire-safety phosphorus-containing polyethylene terephthalate with well-balanced comprehensive performances by reactive blending with liquid crystalline copolyester

With increased public awareness of fire-safety, flame retardant materials have been widely used and developed. Among them, a polyester called CPET, synthesized by the copolymerization of polyethylene terephthalate and 2-carboxyethyl (phenyl) phosphinic acid, has a good fire-safety and has been employed in the manufacture of synthetic fibers. However, the fabricated fiber made of CPET simultaneously possessing good flame retardancy and mechanical properties is a dilemma. Herein, we resolve this problem through the reactive blending of CPET with a type of thermotropic liquid crystal copolyester (PPDT) and subsequently solid-state polymerization (SSP). Thus, the fire-safety of the CPET/PPDTSSP blend improves greatly. The peak heat release rate, total heat release, and total smoke release decrease by 31.2%, 16.3%, and 11.0%, respectively, compared with those of CPET. Meanwhile, the CPET/PPDTSSP shows better crystallization and mechanical properties than CPET. The strength at yield and Young’s modulus of CPET/PPDTSSP increase by 20.0% and 15.8%, respectively. This blend shows great potential in the fabrication of fire-safety fibers with high strength.

Thermotropic liquid crystalline copolyester fibers according to various heat treatment conditions

Thermotropic liquid crystal copolyester (TLCP) was synthesized using a melt polymerization method, with a molar ratio composition of 2,5-diethoxy terephthalic acid (ETA), hydroquinone (HQ), and p-hydroxybenzoic acid (HBA) of 1:1:3. TLCP exhibited nematic liquid crystalline mesophase and maintained nematic textures under all heat treatment conditions applied. The synthesized TLCP was processed into fibers using a capillary rheometer. The liquid crystalline mesophase, thermo-mechanical properties, and morphology of TLCP fibers obtained under various heat treatment conditions were investigated. The thermo-mechanical properties of the heat-treated fibers were improved compared to those of the as-spun fibers. The best results were obtained for TLCP fibers annealed at 230 °C for 9 h. The heat-treated fibers showed a well-developed microfiber morphology compared to the as-spun fibers. In the spun fibers, a skin–core morphology was observed regardless of the heat treatment conditions, and a well-developed fiber morphology better than the core area was observed in the skin area. The diameter of the fiber heat-treated at 230 °C for 9 h was approximately 60–110 nm.

Synthesis and Properties of Thermotropic Copolyesters Based on Poly(ethylene terephthalate) and 4'-Acetoxy-4-biphenyl-carboxylic Acid.

A series of novel copolyesters based on polyethylene terephthalate (PET) and 4′-hydroxy-biphenyl-4-carboxylic acid (HBCA) was obtained by melt polycondensation of bis(2-hydroxyethyl) terephthalate and 4′-acetoxybiphenyl-4-carboxylic acid (ABCA) as co-monomers with Sb2O3 as a catalyst. Using this synthetic procedure, a set of copolymers containing 20–80 mol% of HBCA units was prepared. According to NMR spectroscopy, the copolymers were of random composition. Copolyesters comprising 60–80 mol% of HBCA possessed increased heat resistance and formed nematic melts at 270 °C and higher. The liquid crystal (LC) phase formation was accompanied by transition to non-Newtonian characteristics of the melt flow, as well as an equalization of storage and loss moduli values. According to XRD and polarizing microscopy, the LC glassy phase of the copolyesters coexists with crystalline regions of poly-(4′-hydroxy-4-biphenylcarboxylate), non-melting up to 400 °C and above. The mechanical characteristics of these LC copolyesters showed similar or better values than those of well-known LC polymers. These novel copolyesters can be useful in obtaining heat-resistant materials with an ordered structure and, as a consequence, improved performance.

External impacts on structure and relaxation properties of thermotropic liquid crystal copolyester

The methods of thermally stimulated depolarization (TSD) and X-ray diffraction analysis were used to study the impact of electric and temperature fields on the relaxation properties, structure, and molecular mobility of a liquid crystal (LC) copolymer based on polyethylene terephthalate (PET) and n-hydroxybenzoic acid (n – HBA). It was shown that polarization in the LC state besides the main relaxation transition leads to the formation of additional high-temperature maximum on current thermograms of thermally stimulated depolarization (TSD). The data of X-ray diffraction analysis indicate a change in the orientation of mesogenic units after polarization in an electric field. The results were explained by the combined action of electric and temperature fields on the conformational structure of the liquid crystal copolyester, namely, a change in the degree of crystallinity of the studied copolyester under the influence of external fields.

Synthesis and properties of wholly aromatic phosphorus-containing thermotropic liquid crystal copolyesters with excellent fibre formation ability

ABSTRACT In this study, wholly aromatic phosphorus-containing thermotropic liquid crystal polymers (TLCP) derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-Dihydroxypheny)-10 h-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO-HQ) are successfully synthesised via one pot melt polymerisation method. Although, the resulted copolyesters are amorphous, high glass transition temperature (182–196 °C) is observed due to the existence of kinked DOPO-HQ unit and crankshaft HNA monomer. The nematic liquid crystal behaviour is found for all of the copolyesters under POM at relatively low temperature (190–207 °C). The copolyesters show good thermal stability and high char yield under both nitrogen and air atmosphere, which of the initial degradation temperature (T5%) and char yield are above 450 °C and 50%, 439 °C and 29%, respectively. Dynamic rheology results show that viscous modulus of the obtained copolyesters are much more prominent under both frequency and temperature sweeping mode, indicating have excellent processing ability. The fibres can be easily drawn from the melt, and exhibit well oriented fibrillated structure. The convenient polymerisation method, excellent thermal stability and fibre formation ability of the phosphorus-containing TLCP endow them much potential use in the safety protection field.

Synthesis and properties of novel photocrosslinkable aromatic-aliphatic liquid crystal copolyesters based on poly(ethylene glycol) and cinnamic acid

ABSTRACTFirstly, PEGn-TA monomers with carboxyl functional groups were synthesised by terephthalic acid (TA) and poly(ethylene glycol) (PEG) with molecular weight of 200, 400 and 600. Then, photocrosslinkable thermotropic liquid crystal copolyesters derived from PEGn-TA, 4,4ʹ-biphenol, 4-hydroxy-cinnamic acid and 4-hydroxy-benzoic acid were successfully obtained by Vilsmeier adduct solution polymerisation method. Influence of PEG molecular weight on thermal behaviour, liquid crystal mesophase, hydrophilicity, structure and photoactivity were investigated by various measurements. Experimental results indicated that all copolyesters showed nematic mesophase textures, relative low melting temperatures, and two glass transitions as well as better hydrophilicity were observed for those contained higher PEG molecular weight. Photocrosslinking rate was increased first and then decreased due to effect of flexible PEG moieties. The resulted copolyesters with liquid crystal behaviour, excellent hydrophilicity and photoactivity could be potentially used as biomaterial.

Investigations of Current Generated in Construction of Polarization in Vectra A, Liquid Crystal Copolyester

&lt;div&gt;&lt;p&gt;&lt;em&gt;The Thermally Stimulated Polarization Current (TSPC) is used to study the dielectric behavior of Vectra A, liquid crystal copolyester. The TSPC spectra of samples of Vectra A for various polarizing fields (3.8 kV/cm- 19.2 kV/cm) have been investigated. A dipolar relaxation is observed in the low temperature region ~ 30 &lt;sup&gt;o&lt;/sup&gt;C due to orientation of naphthalene groups present in Vectra A which is termed as peak-P&lt;sub&gt;1&lt;/sub&gt;. In the higher temperature region above 110 &lt;sup&gt;o&lt;/sup&gt;C, the dipolar and space charge peaks are in composite form. TSPC cycle is performed to distinguish the dipolar and space charge peaks. Also, the TSPC spectra of annealed and doped samples of Vectra A are studied. The results obtained from TSPC spectra are compared with TSDC spectra of samples of Vectra A.&lt;/em&gt; &lt;/p&gt;&lt;/div&gt;

Nonisothermal and Isothermal Degradation Kinetics of Thermotropic Liquid Crystal Copolyesters Containing BPA and BPAF Units

The thermotropic liquid crystal copolyester P-BPA2.5 and P-BPAF2.5 with low melting temperature and high glass transition temperature were obtained by introducing 2.5mol% bisphenol A (BPA), bisphenol AF (BPAF) and terephthalic acid (TA) receptively into the molecular chain of poly (oxybenzoate-co-oxynaphthoate). The isothermal and nonisothermal degradation behavior of the two copolyesters P-BPA2.5 and P-BPAF2.5 were studied by thermo-gravimetry analysis (TGA) under nitrogen atmosphere. The degradation kinetics of the copolyesters under dynamic and isothermal heating conditions was evaluated byKissinger-Akahira-Sunose (KAS) and iso-conversional methodrespectively. Results showed that the activation energy (E) values followed the order P-BPAF2.5&gt;P-BPA2.5 under dynamic heating atmosphere. However, the P-BPA2.5 showed a better thermal stability as compared with P-BPAF2.5 under isothermal heating conditions. The differences of degradation mechanism between the two copolyesters may be a reason for this phenomenon, which was discussed in detail in the text.

Thermal Oxidative Degradation Behavior of Fluorinated Thermotropic Liquid Crystal Copolyesters

In this study, the thermal oxidative degradation behavior of thermotropic liquid crystal copolyesters P-BPAFx containing 2.5-10 mol% bisphenol AF unit were evaluated by thermogravimetric analysis (TGA) technique under air atmosphere and the degradation activation energy (E) was obtained from Kissinger and Kissinger-Akahira-Sunose (KAS) method. The degradation behavior of copolyester are strongly dependent on the molar percentage of BPAF unit. Results showed that the E values obtained by the two methods increase first and then decrease slightly with increasing the BPAF unit and follow the order P-BPAF5.0&lt; P-BPAF10&lt;P-BPAF2.5, indicating P-BPAF2.5 has good thermal stability. The reason for this phenomenon was discussed in detail in the text.

The influence of bisphenol AF unit on thermal behavior of thermotropic liquid crystal copolyesters

Abstract In this study, a series of thermotropic liquid crystal copolyesters P-BPAFx modified with 2.5–10 mol% of bisphenol AF (BPAF) and terephthalic acid (TA) were synthesized via melt polymerization. The structure and properties of P-BPAFx were characterized by various measurements. The melting temperature decreased from 260 to 220 °C and glass transition temperature increased from 70 to 118 °C after introduction of BPAF and TA units, showing P-BPAFx can easily be processed in a lower temperature and have a more broad application temperature. The thermal degradation behavior was evaluated by SEM, FTIR and thermogravimetric analysis (TG). The activation energy was obtained from Kissinger and Kissinger-Akahira-Sunose (KAS) methods, and was investigated comparatively with P-HBA70. It was found that the addition of 2.5 mol% BPAF units improve thermal stability, and much higher char yield was observed for those copolyesters containing BPAF unit.

Synthesis and characterization of a new family of photoactive liquid crystalline polyesters based on α‐methylstilbene

AbstractA liquid crystal polyester and two liquid crystal copolyesters containing α‐methylstilbene moieties and aliphatic or aromatic spacers in the backbone were synthesized in good yields, with the aim of using them for photosensitive microcapsule preparation. The synthesized polymers were fully characterized with respect to thermal stability, type of mesophase, molecular weight and E–Z photoisomerization. Combination of monomers with different structures allowed adjustment of the polymer characteristics such as degree of crystallinity and glass transition temperature, as verified using X‐ray diffraction, polarized optical microscopy and differential scanning calorimetry. Quantitative 1H NMR and UV‐visible experiments were performed in order to investigate E–Z photoisomerization after photoirradiation at 364 nm. Finally, a membrane based on one of these polymers was prepared and it was found that its wettability increased on photoirradiation. © 2013 Society of Chemical Industry