Thermotropic Polyesters Research Articles

In Situ Preparation of Thermotropic Liquid Crystalline Polyester and Nylon 10T

Poly-decamethylene terephthalamide (PA10T) is one of high temperature special engineering plastics, which is widely used in aviation automobile, and electronic industries. However, its bad processability, poor crystallinity, and toughness may affect its further applications. In this work, the melting polycondensation synthesis of thermotropic liquid crystalline polyester (TLCP) prepolymer was explored. This synthesized TLCP was then added into PA10T via in-situ compounding, to obtain the polydecamethylene terephthalamide / thermotropic liquid crystalline polyester composites (TLCP/PA10T). The TLCP was found easy to be oriented, which can reduce the entanglement of PA10T and improve the processing properties of PA10T. Moreover, the anisotropy under tensile conditions after the TLCP orientation can form microfibers and improve the mechanical properties of the composites. The relationship between crystallization properties, tensile strength and TLCP content of TLCP/PA10T composites was also studied. Such TLCP/PA10T composites can serve as a high temperature special engineering plastic in industrial manufacturing.

Reactive Processing Route to Thermotropic Polyesters with a Low Processing Temperature and Enhanced Relaxation Time

The processing temperature of thermotropic liquid crystalline polymers (LCPs) can be reduced by increasing the flexibility of the backbone, simultaneously decreasing the relaxation time and resulti...

Synthesis and Properties of Thermotropic Poly(oxybenzoate-co-oxynaphthoate) Copolyester Modified by a Third AB Type Monomer

The synthesis and modification of high performance thermotropic liquid crystal polyesters (TLCP) are still being investigated due to their excellent properties. In this study modification of poly(oxybenzoate-co-oxynaphthoate) (P-HBA/HNA), a random copolymer of 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), by 5 mol% of one of three AB type monomers (AB type monomers are those who have hydroxy and carboxylic end groups), vanillic acid (VA), 4-hydroxyphenylacetic acid (HPA) and 4-hydroxycinnamic acid (HCA), was conducted. The influence of the AB type third monomer on the liquid crystal properties, melting behavior, thermal stability, microstructure and fiber morphology of the resulting modified terpolyesters was comparatively studied relative to the parent copolymer. When 5 mol% of the HBA units were replaced, the resulting terpolyesters had much lower melting temperatures and could be easily melt processed, while the modified terpolyesters exhibited higher melting and glass transition temperatures when 5 mol% of the HNA units were replaced. Weaker melting peaks and larger melting ranges were observed for the modified terpolyesters, attributed to the existence of nonperiodic layer crystallites caused by the modifiers. The obtained terpolyesters showed good thermal stability and could be melt processed in a broad nematic phase temperature region. The molecular chain packing of the modified terpolyesters was almost destroyed by the third AB type reactants. Fibers prepared from the resulting terpolyesters exhibited well developed fibrillar structure and higher orientation factors, indicating that modification of the P-HBA/HNA by using the AB type monomers to improve its properties would be useful.

Controlling Processing, Morphology, and Mechanical Performance in Blends of Polylactide and Thermotropic Polyesters.

Thermoplastic composites based on thermotropic liquid crystalline polymer (LCP) materials are interesting candidates for reinforced composite application due to their promising mechanical performance and potential for recyclability. In combination with a societal push toward the more sustainable use of materials, these properties warrant new interest in this class of composites. Though numerous studies have been performed in the past, a coherent set of design rules for LCP design for the generation of injection-molded reinforced thermoplastic composites is not yet available, likely due to the complex interplay between LCP and matrix components. In this study, we report on the processing of poly(l-lactide) with two different LCPs, at relatively low processing temperatures. The study focuses on critical parameters for the morphological development and mechanical performance of LCP-reinforced composites. The influence of blend composition and the processing conditions, on the mechanical response of the composites, is investigated using rheology, wide-angle X-ray diffraction, mechanical analysis, and microscopy techniques. The study conclusively demonstrates that both the matrix viscosity and viscosity ratio between the dispersed and matrix phase, determine the deformation and breakup of the dispersed LCP droplets during extrusion. In addition, the thermal dependence of the viscosity ratio appears to be a critical parameter for the composite performance after injection molding. For example, during injection molding, stretching and molecular orientation of the LCP phase into highly oriented fibrils are prevented when the viscosity ratio increases rapidly upon cooling. In contrast, melt drawing proves to be a more effective processing route as the extensional flow field stabilizes elongated droplets, independent of the viscosity ratio. Overall, these findings provide valuable insights in the morphological development of LCP-reinforced blends, highlighting the importance of the development of viscoelastic properties as a function of temperature, and provide guidelines for the design of new LCP polymers and their thermoplastic composites.

Tailoring the glassy mesophase range of thermotropic polyesters through copolymerization of 4,4’-bibenzoate and kinked isomer

The substitution of a linear biphenyl monomer with its meta isomer in liquid crystalline polyesters affords (co)polyesters with tunable liquid crystalline (LC) and thermomechanical properties. Melt transesterification afforded two (co)polyester series based on the semi-aromatic homopolymers poly(diethylene glycol 4,4′ bibenzoate) and poly(butylene 4,4′ bibenzoate) at high molecular weights. In each series, the linear dimethyl-4,4′ bibenzoate (4,4’BB) was systematically exchanged with its kinked isomer, dimethyl-3,4′ bibenzoate (3,4’BB). The incorporation of the meta isomer resulted in tunable crystalline and LC properties. Differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), X-ray diffraction (XRD), and polarized optical microscopy (POM) elucidated that the kinked structure of 3,4’BB disrupted crystallization at low incorporations, significantly lowering the melting transition temperature (>50 °C) in each series. The LC properties were less impacted due to the biphenyl structure resulting in LC glasses with wide mesogenic windows. Dynamic mechanical analysis (DMA) further demonstrated the tunable nature of the thermomechanical properties resulting from the (co)polymerization of these isomers.

Жидкокристаллические термотропные полиэфиры с мезогенными фрагментами на основе п-окcибензоила

Жидкокристаллические термотропные полиэфиры с мезогенными фрагментами на основе п-окcибензоила

Dielectric relaxation of thermotropic liquid crystalline polyesters based on α,ω-alkylene-di-4-hydroxybenzoates and 4,4′-alkylenedioxy-dibenzoic acid

Two structurally isomeric homologous series of semiflexible thermotropic liquid crystalline polyesters were analysed by dielectric spectroscopy in temperature intervals varying from 253 to 403 K. Each series is characterised by a well-distinct behaviour of the dielectric loss versus temperature with a minor diffuse and a more confined relaxation occurring at lower and higher temperatures, respectively. Extrapolations from semilog plots of frequency (f) versus reciprocal absolute temperature (1/T) indicated that the principal relaxation is related to the glass transition temperature as defined by DSC. The analysis of data according to WLF equation indicated that the size and the kind of the polymethylene groups influence the apparent activation energy. A parity effect, connected to the length of polymethylene segments within each series, was finally detected on the relative position of the maximum relaxation, the odd numbers showing in any case higher temperature values.

Annealing studies on a thermotropic liquid crystalline polyester meltblown fabric

Meltblown fabrics composed of a thermotropic liquid crystalline polyester were subjected to heat conditioning at various temperatures. Physical effect of the treatment was investigated by tensile testing of the fabrics and the individual fibers. The fabrics exhibited increased tensile strength by more than 100% after the heat conditioning due to inter-fiber bonding in the fabric structure and morphological reorganization of the thermotropic polymer. The calorimetric behavior of the polymer was further investigated to obtain information about the internal structure. Structural change during the annealing was also visually observed under a polarized light microscope.

Processing and performance of aromatic-aliphatic thermotropic polyesters based on vanillic acid

In this work we report on the processing, melt-drawing, and performance of new vanillic acid based aliphatic-aromatic thermotropic polyesters. It is demonstrated that these materials are easily processed from their nematic melts yielding highly oriented products. Furthermore, we demonstrate that a molecular weight (Mw) of roughly 30 kg/mol is required in order to successfully perform spinning on these polymers. The application of a polymer with lower Mw results in poor mechanical performance and fiber breakage during the winding process. Wide-angle X-ray diffraction analysis has been performed on the fibers and it is demonstrated that the orientation parameter increases with increasing draw-ratio of the fiber. Although these polymers are readily processed from their thermotropic melts, the obtained fibers only retain their orientation up to temperatures in the range of 120–130 °C, after which they start to melt. In general, these fibers exhibit tensile moduli in the range of ∼10 GPa and a tensile strength around ∼150–200 MPa. FTIR and solid-state NMR experiments indicate that only the aromatic components are molecularly oriented during the spinning process. In contrast, the aliphatic moieties exhibit a high mobility, normally corresponding to a local isotropic motion. It is expected that the poor molecular orientation of the aliphatic moieties in these aliphatic-aromatic thermotropic polyesters contribute to the relatively low tensile modulus of the fibers, obtained after the extrusion and melt-drawing process.

Study on in situ reinforced composites of thermoplastic resins

Typical crystalline thermoplastic resin polypropylene (PP) and amorphous thermoplastic copolymer acrylonitrile–butadiene–styrene (ABS) were respectively blended with self-made novel low-melting point thermotropic liquid crystalline polyester (TLCP) that contained phosphorus and nitrogen elements (PN-TLCP). Then, the PP/PN-TLCP and ABS/PN-TLCP in situ-reinforced composites were prepared. The effects of PN-TLCP on mechanical property, microstructure, processability, and thermal stability of these two composites were investigated. The results showed that the strength and rigidity of matrix were improved, indicating that PN-TLCP played a role of enhancement. Meanwhile, PN-TLCP could form microfibrillar structure in PP and ABS matrix, which was the main reason of the formation of in situ composites. In the forming process, PN-TLCP could induce PP resin to form β-crystal, which was why the toughness of PP was improved. In addition, PP and ABS exhibited better processing flowability and their melt flow rates were respectively increased 18% and 56% after blending with PN-TLCP. Besides, PN-TLCP was highly beneficial to improving the thermal stabilities of matrix. Various tests showed that this kind of TLCP was suitable for crystalline thermoplastic resin PP and its composites would have more outstanding comprehensive properties.

Thermotropic Polyesters from 2,5-Furandicarboxylic Acid and Vanillic Acid: Synthesis, Thermal Properties, Melt Behavior, and Mechanical Performance

In this work, we address the synthesis of novel aromatic–aliphatic biobased polyesters showing thermotropic behavior in the melt. Successful incorporation of different biobased monomers such as 2,5-furandicarboxylic acid (2,5-FDCA), suberic acid (SuA), and vanillic acid (VA) in thermotropic liquid crystalline polymers (TLCPs) is made possible by performing synthesis at low temperatures. The chemical structures, molecular weights, phase transitions, thermal behavior, and mechanical performance of the synthesized polymers are studied using polarization optical microscopy, WAXD, DSC, TGA, DMTA, solid-state NMR spectroscopy, rheology, and tensile tests. It is shown that the incorporation of the rigid, aromatic 2,5-FDCA moiety enhances the formation of blocky copolymers, whereas the VA moiety tends to decrease the block formation. However, when combined, nonblocky TLCPs containing 2,5-FDCA and VA with high aromatic content can be obtained. These materials show a low temperature transition from the crystalline ...

Aromatic thermotropic polyesters based on 2,5-furandicarboxylic acid and vanillic acid

This paper addresses a route to synthesize bio-based polymers with an aromatic backbone having a liquid crystalline (LC) phase in the molten state. The LC phase is employed to achieve uniaxial orientation during processing required in e.g. fiber spinning. For this purpose 2,5-furandicarboxylic acid (2,5-FDCA) and O-acetylvanillic acid (AVA), obtained from natural resources, are used as monomers. Similar to the 2,6-hydroxynapthoic acid used to perturb the crystalline packing of poly(oxybenzoate) in the Vectran® series, these bio-based monomers are used to lower the crystal to liquid crystal transition temperature. Considering that the poly(oxybenzoate) can also be obtained from natural resources, the adopted route provides the unique possibility to synthesize bio-based polymers that can be used for high performance applications. To obtain the desired polymers, a synthetic route is developed to overcome the thermal instability of the 2,5-FDCA monomer. Experimental techniques, such as optical microscopy, FTIR spectroscopy, DSC, and TGA are employed to follow the polymerization, phase transitions and evaluate thermal stability of the synthesized polymers.

Synthesis and characterization of liquid crystalline copolymers containing poly (ether sulfone) segments

A new block copolymers (BCP) containing poly (ether sulfone) (PES) with different chain lengths and thermotropic liquid crystalline polyester (TLCP) segments were synthesized by high temperature solution polymerization of the constituent monomers of TLCP and PES oligomers terminated with a hydroxyl group. The chemical structure and inherent viscosity of BCP were characterized by Fourier transform infrared spectroscopy, Ubbelohde viscometer and solubility test, respectively. The thermal behavior, liquid crystallinity, texure and thermal stability of liquid crystalline block copolymer were investigated by a variety of experimental techniques including differential scanning calorimetry, polarizing light microscopy and thermogravimetric analysis. BCP showed a single glass transition temperature and melting point but blends of corresponding homopolymers were biphasic. It showed the typical nematic texture above its Tm depending on the composition and good thermal stability. Such block copolymers can be used as compatibilizer or melt viscosity modifying agent for the blends due to their chemical structure similar to the blend partners, respectively.

Twin liquid crystals and segmented thermotropic polyesters containing azobenzene—effect of spacer length on LC properties

AbstractWe report systematic studies on a homologous series of twin liquid crystalline (LC) molecules based on phenyl and naphthyl azobenzene (PnP and NpnNp) as well as segmented copolyesters based on them. The twin series had the structure azobenzene–oligooxyethylene–azobenzene, where the ethyleneoxy length was varied from 2 to 6 units. The LC properties of the twin series depended on the chemical structure of the azochromophore and also the length of the central oligooxyethylene segment. The PnP series exhibited smectic LC properties for n > three oligooxyethylene units. Conversely, NpnNp series exhibited spherulitic phases only for the shortest member –Np2Np. One non‐LC short spacer twin (P2P) and one LC long spacer twin (P6P) were incorporated as part of a main chain polyester composed of fully aliphatic segments of sebacate and di or tetraethylene glycol (DEG/TEG) units by melt polycondensation. Non‐LC P2P formed LC polymers even at low (5 mol %) incorporation in DEG‐based copolymers, whereas the LC‐P6P could do so only at 30 mol % incorporation. The LC properties of the twin molecules as well as copolymers were studied using differential scanning calorimetry, polarized light microscopy (PLM) along with variable temperature wide angle X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis and Characterization of Liquid Crystalline Polyester/Graphene and a Study of Their Properties

A new rod-like thermotropic liquid crystalline polyester (TLCP) material and its nanocomposites based on different concentrations of graphene were synthesized by in-situ high-temperature solution polymerization. The resulting nanocomposites were characterized using XRD, microscopic analysis (POM, SEM, and TEM), spectroscopic analysis (FT-IR, UV-Vis, and fluorescence), and thermal analysis (TGA and DSC). The XRD and POM methods showed that the composite materials exhibited only the nematic phase. The TEM images revealed that the graphene were distributed in the polymer with sizes ranging from 100 to 200 nm. The absorption spectroscopy data showed that the electronic properties of graphene were mostly retained without damaging their two-dimensional electronic properties, together with the analysis of the maximum absorption spectrum and concentration of the composites in terms of the Lambert-Beer law. The fluorescence from the TLCP moiety was almost completely quenched and red shifted by graphene, indicating that the linkage mode facilitated effective energy and electron transfer between the rod-like TLCP and the extended pi-system of graphene. Therefore, this novel nanocomposite material exhibits excellent thermal properties based on the thermogravimetric analysis.

Erratum: A novel thermotropic liquid crystalline copolyester containing phosphorus and aromatic ether moity toward high flame retardancy and low mesophase temperature

A series of thermotropic liquid crystalline polyesters containing phosphorus and aromatic ether groups (TLCP-AEs) were synthesized from p-acetoxybenzoic acid (p-ABA), terephthalic acid (TPA), 4,4′-oxybis(benzoic acid) (OBBA), and acetylated 2-(6-oxid-6H-dibenz(c,e) (1,2) oxaphosphorin 6-yl) 1,4-benzenediol (DOPO-AHQ). The chemical structure and the properties of TLCP-AEs were characterized by Fourier-transform spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetry analysis (TGA), scanning electronic microscopy (SEM), polarizing optical microscopy (POM), limiting oxygen index, and UL-94 tests, respectively. The results showed that TLCP-AEs had low and broad mesophase temperatures (230–400 °C). TLCP-AEs also showed excellent thermal stability; their 5%-weight-loss temperatures were above 440 °C and the char yields at 700 °C were higher than 45 wt %. All TLCP-AE polyesters exhibited high flame retardancy with a LOI value of higher than 70 and UL-94 V-0 rating. The SEM observation revealed that TLCP-AEs had good fibrillation ability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1182–1189, 2010

Properties of Thermotropic Liquid Crystalline Polyester Nanocomposites Derived from Multi-Walled Carbon Nanotubes

A series of nanocomposites containing multi-walled carbon nanotubes (MWNTs) and terephthaloyl-di-p-oxybenzoyl chloride-triethylene glycol copolyester (T-T) were prepared by in-situ high-temperature solution polycondensation. The liquid crystalline properties and thermal stability of the resulted MWNTs/T-T nanocomposites were investigated by wide-angle X-ray diffraction (WAXD), polarized optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA), respectively. The results showed that MWNT doping at a low concentration improved the thermal stability of T-T matrix and expanded the nematic temperature range without largely changing its conformation, making it more suitable for processing. The dispersion of MWNTs and interfacial interactions between the thermotropic liquid crystalline polymer (TLCP) molecules and the carbon nanotubes (CNTs) were investigated by scanning electron microscopy (SEM) and optical spectroscopies. The UV-vis spectroscopy and fluorescence spectra supported a strong pi-pi* interaction between the polymer and the nanotube.

Preparation of Main-Chain Thermotropic Polyesters With Two Types of Mesogens Connected Alternatively by Aliphatic Spacers

A homologous series of main-chain thermotropic polyesters (PBTn, n = 2, 4, 6) containing biphenyl and triad aromatic ester mesogenic units interconnected by n-methylene spacers in the main chain were prepared from terephthaloyl bis(4-oxybenzoyl chloride) (TOBC) and 4,4′-bis(ω-hydroxyalkyloxy)biphenyls (n-BP, n = 2, 4, 6) by solution polycondensation. The chemical structures of the monomers and PBTn were characterized by spectroscopic techniques and elemental analysis. The solubility, supermolecular structures, thermal and liquid crystalline properties of PBTn were investigated by differential scanning calorimetry (DSC), polarizing microscopy (PLM), small-angle X-ray scattering (SAXS), thermogravimetric analyses (TGA), and wide-angle X-ray diffraction (WAXD), and they were found to be closely dependent on the length of the methylene spacers. The increasing methylene units led to improved solubility, broader liquid crystalline range, reduced mesophase-isotropic transition point, higher thermal stability, and decreasing crystallinity. The decomposition temperatures (5% mass loss) of the polymers were above 380°C in nitrogen atmosphere and only PBT4 and PBT6 exhibited smectic mesophases as well as high viscosity in the mesophase.

Synthesis and Properties of Thermotropic Liquid Crystalline Polyesters with Flexible Polymethylene Spacer

Polymethylene bis(p-hydroxybenzoates) were prepared from methyl p-hydroxybenzoate and different diols by melted transesterification reaction. Three liquid crystalline polyesters were synthesized from terephthaloyl dichloride and polymethylene bis(p-hydroxybenzoates). Its structure, morphology and properties were characterized by Ubbelohde viscometer, Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), polarized optical microscopy (POM) with a hot stage, and wide-angle X-ray diffraction (WAXD). Results indicated that the intrinsic viscosities were between 0.088 and 0.210 dL/g. Optical microscopy showed that the TLCP has a highly threaded liquid crystalline texture and a high birefringent schlieren texture character of nematic phase and has wider mesophase temperature ranges for all polyesters. DSC analysis were found that the melting point (Tm), isotropic temperature (Ti) of TLCPs decreased and the temperature range of the liquid crystalline phase became wider with increased number of methylene spacers in the polyester. The WAXD results showed that TLCPs owned two strong diffraction peaks at 2θ near 19° and 23°.

Two New Thermotropic Liquid Crystalline Polyesters and their Composites: Synthesis and Characterization

Two new series of liquid crystalline polyesters were synthesized using melt polycondensation reaction.Glass fiber,as a reinforcement,was meltpolymerized with 4-acetoxybenzoic(ABA),4,4＇-diacetoxybiphenyl, isophthalic acid(IA) and terephthalic acid(TA) to make TLCP/GF composites with a good mechanical properties.All the obtained compounds were characterized by conventional spectroscopic methods. The structure of the target compounds and intermediates was conformed by the IR, 1H NMR and SEM. The thermal behavior of the polymers has been characterized using polarized optical microscopy and differential scanning calorimetry. The effect of monomer structure and mechanical properties has been investigated on the prepared polyesters. These compounds show a high birefringent Schlierene texture characteristic of the nematic phase on heating and cooling experiments. This was further confirmed using differential scanning calorimetric investigations.The melting points of polymers having a central 4,4’-biphenyldicarboxylate residue have broad endotherms. The glass transition temperature values of polyesters are not effect by the glass fiber.According to the SEM result showed that the composite had strong fiber-matrix adhesion.The effect of copolymerization with added glass fiber in synthesis process is compared with that of the anlogous homopolyesters by other processing mode.Our finding shows that the copolymers exhibit reduced technical process and maintained mechanical properties.