Liquid Crystalline Copolyester Research Articles

On the structure and thermo-mechanical properties of a thermotropic liquid crystalline copolyester amide

The microstructure at Å- and nm-scale of a thermotropic liquid crystal copolyester amide has been studied by wide-angle and small-angle X-ray scattering (WAXS and SAXS, respectively). The copolyester amide is based on random monomers of 60 mol% 2,6-hydroxynaphthoic acid, 20 mol% terephthalic acid and 20 mol% amino phenol (designated N-T-AP). In the solid state the copolyester amide is unusually crystalline and the WAXS fiber pattern exhibited equatorial and off equatorial reflections indicative of lateral packing and relative three-dimensional order. Moreover, the pattern also exhibited meridional scattering maxima and the position was aperiodic, a property also reported for the thermotropic random copolyester of 1,4-hydroxy benzoic acid and 2,6-hydroxynaphthoic acid. The meridional scattering was well-modeled by a totally random arrangement of monomers in a straight conformation, where a polymer chain was modeled by an array of points separated by the corresponding monomer length. Hence, the data is consistent with a structure formed by highly aligned macromolecules of totally random monomer sequence. Furthermore, the meridional maxima indicate monomer sequence segregation which would lead to the formation of crystallites, and the sequence segregation is reminiscent of a non-periodic layer crystal (npl).

Composition-dependent emission colors for biomass-based main-chain luminescent liquid crystalline copolyesters with excellent tensile properties

Liquid crystalline polymers with multicolor emission have attracted great attention in view of their great potential applications such as light-emitting diodes and information storage devices. However, luminescent liquid crystalline polymers...

Processability‐enhanced aromatic thermotropic liquid crystalline copolyesters via the introduction of the unsymmetrical units

AbstractA series of ternary thermotropic liquid crystalline copolyesters was synthesized through a simple one‐pot melt condensation based on 4‐hydroxybenzoic acid (HBA), 6‐hydroxy‐2‐naphthoic acid (HNA) and 4‐hydroxy‐2‐naphthoic acid (4‐HNA). The structures were modified via the introduction of the asymmetric 4‐HNA unit. High glass transition temperature values (>80°C) and relatively low melting temperature values (<265°C) were achieved with 4‐HNA molar fraction of over 0.5%, and the copolymer exhibited 5% degradation temperatures of 442–453°C and the char yields of 35.80%–36.74% at 800°C. This indicated that the introduction of asymmetric 4‐HNA blocks into the backbone provides a “torsion axis” to regulate the dense stacking between different main‐chains, which was crucial for the mobility of polyester during thermal processes. Moreover, crystallinity decreased with the increase of 4‐HNA content. The incorporation of 4‐HNA also endowed the obtained copolyester fiber with a skin‐core structure and microfiber morphology. Due to the excellent temperature resistance and fibrous morphology of P‐HBA/HNA/4‐HNA. This work provided a novel strategy to synthesize aromatic thermotropic liquid crystalline copolyesters, which can be promising candidates for processing additives or reinforcing materials with improved processing properties, and potential application in processing, personal protection, and other extreme temperature environments.

Configuration-Dependent Liquid Crystal and Gel Behaviors of Tetraphenylethene-Containing Main-Chain Copolyesters.

The construction of aggregation-induced emission-active (AIE-active) gelators with liquid crystal properties remains a challenge. Moreover, the effects of AIE configuration on liquid crystal, gel and AIE behaviors in one system are unclear. Herein, two main-chain liquid crystalline copolyester gelators with a single configuration of AIEgen TPE, mesogen biphenyl, and pendent amide groups are synthesized through melt polycondensation. Both copolyesters display smectic phase, while E-P20 possesses a wider temperature range of liquid crystal and a narrower layer distance owing to the more serious nonlinear "defect" of Z-TPE than E-TPE units. In addition, E-P20 and Z-P20 can form AIE-active gels with the minimum gelation concentration (MGC) values of 10 and 4 wt% in ethyl acetate mainly via hydrogen bonds between the pendent amide groups, respectively. These AIE-active gels show potential applications in temperature sensor, information storage, and so on.

Influence of hydroquinone content on thermotropic liquid crystalline copolymers and nanocomposites: thermo-mechanical properties and morphology.

Thermotropic liquid crystalline copolyesters (Co-TLCPs) were synthesized by varying the hydroquinone (HQ) molar ratio from 1–5 with respect to the 2,5-diethoxyterephthalic acid (ETA) monomer. The thermal properties and liquid crystalline mesophases of the synthesized Co-TLCP were investigated. All of the Co-TLCPs synthesized using a HQ molar ratio of 1–5 showed a nematic liquid crystalline phase. Among the Co-TLCPs obtained using HQ in various molar ratios, the most stable physical properties and a clear liquid crystalline phase were obtained when HQ was 4 mol. Among the various Co-TLCPs synthesized, hybrids were prepared using Co-TLCP synthesized with a 1 : 4 = ETA : HQ ratio and organoclay. A 1–10% loading of the organoclay Cloisite 93A was employed per weight of TLCP, and the clay was dispersed using the melt intercalation method. Among the Co-TLCP hybrids, the morphology and thermal properties of the hybrids were investigated according to the changes in the Cloisite 93A in the 1–10 wt% range. In general, the thermal properties were superior when the organoclay loading was 3 wt% and were inferior when the organoclay amount was 5 wt% or more. This result was confirmed by the dispersibility of the clay through transmission electron microscopy.

UV-A and UV-B banning highly soluble photocrosslinkable thermotropic liquid crystalline copolyesters with ether linkage in the backbone

Four random copolyesters were synthesized by the polycondensation of a chalcone diol 3-(4-hydroxy-3methoxyphenyl)-1-(4-hydroxyphenyl)prop-2-en-1-one (HMPP) with the common diacid, namely, 4,4′-oxybis(benzoic acid) with two varying diacids (terephthalic acid and isophthalic acid) and two varying diols (1,4-dihydroxyanthraquinone and 1,5-dihydroxyanthraquinone). The chalcone diol was synthesized by acid-catalyzed Claisen-Schmidt reaction. These four random copolyesters were synthesized by solution polycondensation technique and were characterized by qualitative solubility tests and viscosity measurements. The monomeric moieties incorporated in the copolyester backbone was established by FT-IR, 1H NMR and 13C NMR spectroscopic techniques. Tg, Tm and Tiso were determined by DSC thermograms and found to be in the range of 59–97 °C, 123–143 °C and 160–252 °C, respectively. The copolyesters displayed nematic phase without involving methylene-flexible spacers in the polymeric backbone. The phase transition was found to be reproducible on heating and cooling above Tm. The photocrosslinking ability was ascertained by recording UV spectra at different time intervals of irradiation of UV light from 150-watts, 365-nm mercury lamp at room temperature in DMF. Herein, for the first time, we report the synthesis and characterization of a series of novel photosensitive liquid crystalline chalcone polymers without spacer chains. In addition to these, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been performed to ascertain the cross-linking nature of the synthesized polymer from computed absorption spectra. All these polyesters exhibit a good photocrosslinking property by absorbing UV-A light. They continue to absorb UV-B light (which is more dangerous to human skin and eyes) after the crosslinking. As these polymers filter UV-A and UV-B rays one after another, a switching system can be evolved from these materials. These polymers exhibit high thermal stability and UV filtering ability at both UV-A and UV-B regions and have good solubility ensuring their application-oriented nature.

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.

High-Performance Liquid Crystalline Polyesters: Influence of the Synthetic Pathway on the Thermal Properties

Liquid crystalline (LC) copolyesters derived from 4-hydroxybenzoic acid, terephthalic acid, and bisphenol A were synthesized under a variety of reaction conditions. Carboxylic groups in the raw materials were involved in either direct polycondensation or transesterification reactions. Protecting the carboxylic groups via methyl ester or phenyl ester formation was found to increase the yield and the molecular weight of the samples. It turned out that the maximal value of the degree of polymerization and, consequently, the highest heat resistance was observed for the samples prepared using phenyl esters of carboxylic acids.

Synthesis and Characterization of a novel liquid crystalline Copolyester using 4, 4’-Biphenol

Synthesis and Characterization of a novel liquid crystalline Copolyester using 4, 4’-Biphenol

Preparation of liquid crystalline polymer networks containing a cinnamyl group in the main chain with tunable thermal actuation behavior

ABSTRACTA series of liquid crystalline copolyesters (LCPs) with different concentrations of a photocrosslinking moiety have been synthesized by random polycondensation with 4,4′‐bis(6‐hydroxyhexyloxy)biphenyl, 2‐phenylsuccinic acid, and 4‐(6‐hydroxyhexyloxy)cinnamic acid (6HCA). Multifunctional monodomain liquid crystal networks (LCNs) with considerable and tunable actuation behavior are obtained by postphotocrosslinking. The influence of the photocrosslinking moiety on the phase transition behavior of the LCP and actuation behavior of the LCN has been investigated. The results suggest that incorporating 6HCA suppresses the smectic phase of the LCP and decreases the nematic‐isotropic phase transition temperature. Moreover, the starting actuation temperature of the LCN decreases from 55 to 40 °C as the 6HCA reached 50%. In addition, the actuation force and storage modulus of the LCN actuators are enhanced by incorporating a high concentration of 6HCA. A 1.64 MPa contractile force can be achieved, and it can lift burdens 1300 times heavier than its weight when 50% 6HCA is incorporated into the LCP. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 904–911

Remarkable mechanical enhancement achieved by interfacial strengthening of organic/inorganic/fiber composites

In this study, a series of organic/inorganic composites were fabricated by melt-mixing ultra-high molecular weight polyethylene (UHMWPE) powder with a mixture of magnesia, potassium di-hydrogen phosphate and water. The microstructure and chemical composition of the composites were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Three point bending tests showed that the flexural strength and toughness of the composites were improved with the increase of polymer content. The flexural strength of the composite with 25.0wt% UHMWPE was 7.7MPa, and can be dramatically enhanced to 21.1MPa by incorporating only 0.1vol% of oriented thermotropic liquid crystalline copolyester (TLCP) fibers. The improvement is due to the enhanced interfacial bonding between the polymer and fibers, which was much stronger than that between the inorganic phase and fibers, making the fibers adequately contribute to the mechanical strength of the three-component composite. Our results demonstrated that the interfacial strengthening between fiber and inorganic matrix achieved by interpenetrated organic phase helps to establish a strong composite system.

Synthesis and characterization of photo-crosslinkable liquid crystalline copolyesters containing arylidene-keto and chalcone moieties

A series of six photo-crosslinkable thermotropic liquid crystalline copolyesters were prepared by polycondensation method at room temperature using tetra-n-butylammonium bromide as the phase transfer catalyst. The diacid chloride involved in this process was adipoyl chloride, the common diol (diol-1), also referred to as bischalcone diol, used was 3,3′-benzene-1,4-diylbis[1-(4-hydroxyphenyl)prop-2-en-1-one] and six different arylidene diols were involved as varying diols (diol-2), in the ratio 2:1:1. The common diol and the six arylidene diols were synthesized by the acid-catalyzed Claisen-Schmidt synthesis. The inherent viscosity ηinh of these six copolyesters was found between 0.35 and 0.45. The microstructure of the repeating unit present in the copolyester chain was confirmed by FT-IR, 1H–NMR and 13C–NMR spectroscopic techniques. Thermal transition temperatures, resolved from the DSC thermograms, were found to be well above room temperature. Optical polarizing microscopy was employed to establish the liquid crystalline property and all the polymers were found to have nematic phase. The photo-crosslinking behaviour of these copolyesters was studied in DMF solution at different time intervals. The copolyesters having methoxy group in them absorb UV-A rays (315–400 nm) for a longer duration, which promotes them to be good candidates for UV filters and sunscreens.

Novel liquid crystalline copolyester containing amphi-mesogenic units toward multiple stimuli-response behaviors

Liquid crystalline copolyesters with amphi-mesogenic units consisting of azobenzene and biphenyl groups showed shape memory, revisible photo response and self-healing behaviors.

Mechanism of cement paste reinforced by ultra-high molecular weight polyethylene powder and thermotropic liquid crystalline copolyester fiber with enhanced mechanical properties

In this study, a series of cementitious composites with high toughness and flexural strength was obtained by melt-dispersing ultra-high molecular weight polyethylene (UHMWPE) into a cement matrix followed by water immersion. The structure and chemical composition of the composites were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Three point bending tests showed that the flexural strengths of the composites were improved from 5.5 MPa to 18.2 MPa with the presence of 25 wt% UHMWPE, and could be further enhanced to 28.1 MPa with the addition of only 0.1 vol% oriented thermotropic liquid crystalline copolyester (TLCP) fibers. An adhesive test revealed that the interfacial binding force between polymer and fiber was much stronger than that between cement and fiber. Our findings provide a simple way for utilizing polymer to improve the interface between the fibers and cement matrix, consequently achieving a dramatic increase in the flexural strength and toughness.

Extended Chain Lamella Formation Characteristics of Main-Chain Smectic Liquid Crystalline Copolyesters Comprising Different Length Units

A series of liquid crystal (LC) PB-8/12 copolyesters have been synthesized from 4,4′-biphenol with sebacic acid and tetradecanedioic acid, and their LC structures and morphologies have been examined. The copolyesters formed smectic I (SmI) LCs similarly as to the corresponding PB-8 and PB-12 homopolyesters; however, dissimilarity of the comonomer lengths decreased the smectic layer order while sustaining the hexagonal order in the lateral packing of the chains. The SmI LCs consisted of 100-nm-thick lamellae stacked along the polymer chain direction. The lamella thicknesses are more than two times greater than the thicknesses of the homopolyesters and comparable to or greater than the chain contour lengths, indicating the formation of extended chain lamellae.

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.

High-Performance Segmented Liquid Crystalline Copolyesters

High-Performance Segmented Liquid Crystalline Copolyesters

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

Morphological evolution of thermotropic liquid crystalline copolyester and its effects on rheological, thermal and flame-retarding behaviors of polycarbonate

Polycarbonate (PC)/phosphorus-containing thermotropic liquid crystalline copolyester (PHDDT) composites were prepared through a novel multistage stretching extrusion. The morphology of the PHDDT phase was controlled by combining an assembly of force-assembling elements (FAEs) with an extruder. SEM observation revealed that morphological evolution of PHDDT from platelets to microfibrils occurred by applying different number of FAEs. The dynamic rheological and thermogravimetric results showed that the increased interfacial area between PHDDT and PC led to a drastic reduction of the complex viscosity and a lower temperature of the maximum loss. Accompanied with the elongation of the PHDDT along flowing direction, the storage modulus and glass transition temperature of the composite were enhanced. However, compared with the system dispersed with the platelet-like phase, the micro-fibrillation of the flame-retarding PHDDT resulted in the decrease of the temperature of the heat release rate curve starting to rise up and the value of the limiting oxygen index. The confined space formed between the platelet-like PHDDT phase was considered to effectively retard the combustion of the whole material.