Liquid Crystalline Polyesters Research Articles

Formation of nanoparticles during melt mixing a thermotropic liquid crystalline polyester and sulfonated polystyrene ionomers: Morphology and origin of formation

The formation of nanoparticles and the mechanism of their formation in a blend of a thermotropic liquid crystalline polyester (LCP) and the zinc salt of a lightly sulfonated polystyrene ionomer (Zn-SPS) were investigated using Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and gas chromatography–mass spectroscopy (GC–MS). Transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) were used to study the morphology of the blends and structure of nanoparticles. The origin of nanoparticle formation appeared to be related to the development of phenyl acetate chain ends on the LCP that arose due to a chemical reaction between the LCP and residual catalytic amounts of zinc acetate and/or acetic acid that were present from the neutralization step in the preparation of the ionomer. Two-dimensional X-ray diffraction patterns for the blends revealed that chain-packing within nanoparticles was different than that of the LCP or the homopolymers prepared from the LCP co-monomers. The crystals formed in the nanoparticles were also stable to much higher temperature (>350 °C) than the parent LCP crystallites that melted at ∼280 °C.

Curing and Morphology Studies of Thermosets from Blends of a Main Chain Liquid Crystalline Polyester and Diepoxide/Diamine

AbstractSummary: Blends of the commercial liquid‐crystalline polyester Rodrun LC‐3000 (60–90 wt.‐%) with a bisphenol A‐diglycidyl ether based diepoxide (DOW D.E.R.330) and an aromatic diamine (MCDEA) prepared in a twin‐screw extruder have been compression‐moulded and cured either isothermally at 260 °C or in a temperature ramp between 160 and 230 °C. The blends were investigated with SEM and thermal analysis (DSC, DMTA). Blends with 80% Rodrun and less cured at 260 °C and the blend containing 60% Rodrun cured in a temperature ramp showed macro‐phase separation followed by reaction‐induced micro‐phase separation (RIPS) both in the Rodrun‐rich and in the epoxy‐rich macro‐separated phases. Blends containing 90, 80 and 70% Rodrun moulded at 160 °C and cured in the temperature ramp showed only RIPS and a morphology rather similar to that of the uncured blends that was most likely co‐continuous; the blend with 90% Rodrun cured at 260 °C showed RIPS and a dispersed epoxy phase in a Rodrun matrix. Phase composition has been determined by extraction of the soluble fraction and chemical analysis.SEM showing the reaction induced micro‐phase separation for sample REA90/10i.magnified imageSEM showing the reaction induced micro‐phase separation for sample REA90/10i.

Structures and Phase Transformations of Asymmetric Bent Main-Chain Liquid Crystalline Polyesters

A series of new asymmetric bent main-chain liquid crystalline (LC) polyesters (BPE-Cn) were synthesized through the condensation polymerization of A−B type asymmetric α,ω-carboxylic acid−hydroxyl-terminated monomers containing different even numbers of methylene spacers (BPCA-Cn-PmOH, where n = 6, 8, and 10). Differential scanning calorimetry results showed three phase transition processes in this series of BPE-Cn samples. The phase change with the lowest transition temperature is cooling rate dependent, while the two higher temperature transitions are cooling rate independent. One-dimensional (1D) powder wide-angle X-ray diffraction (WAXD) results at different temperatures revealed that during cooling this series of polymers exhibits a low-ordered LC phase and a highly ordered smectic crystal phase before developing a crystalline phase at lower temperatures. The phase structures and symmetry were identified by 2D WAXD and selected area electron diffraction (SAED). On the basis of 2D fiber WAXD patterns, the low ordered LC phase was identified to be an anticlinically tilted SmC (SmCA) phase, which was constructed by an alternating synclinic SmC phase in each chemical repeating unit layer along the fiber drawn direction. The highly ordered smectic phase was an anticlinically tilted SmH (SmHA) phase, which was again constructed by an alternating synclinic SmH phase in neighboring layers. On the basis of the crystallographic point of view, this smectic crystal phase had an orthorhombic unit cell. The crystalline structure was determined to be an orthorhombic unit cell (KO) with Pna21 symmetry in these three polyesters. The crystalline structures and symmetry were also confirmed by SAED experiments. As the number of methylene units increased, the dimensions of the crystal structures also increased, yet they retained a zigzag conformation. A two-chain packing model of the KO phase with four chemical repeating units was proposed on the basis of the experimental diffraction patterns and qualitatively supported by simulated structural diffractions. Additionally, the phase identifications were also supported by the observation of texture changes in polarized light microscopy. Even though the zigzag molecular arrangement remains in the low ordered SmCA and the highly ordered SmHA phases which mimics the bent-core small molecules, chiral characteristics such as helical supramolecular structures are not observed due to the covalent bonding connections in this series of BPE-Cn polymers.

The preparation and properties of segmented‐chain liquid crystalline polyesters based on 4,4′‐dihydroxybiphenyl by interfacial polycondensation

AbstractThermotropic homopolyesters were prepared through interfacial polycondensation of 4,4′‐dihydroxybiphenyl with sebacoyl chloride. The optimal conditions of the process, in terms of the best yield, were studied through investigating the type of organic phase, amount of phase transfer agent, time and temperature of reaction, and volume ratio of aqueous to organic phase. The structure of the sample that had the best yield (53.235% ± 5%) was determined by means of elemental analysis, infrared spectra, and X‐ray. The effect of the molar ratio of the monomers on the yield and inherent viscosity was investigated. The inherent viscosity of the samples varied between 0.095 and 0.25 dL/g. The mesophase formed at elevated temperatures was studied by differential scanning calorimetry, polarized light microscopy, and depolarizing transmittance measurements. Our observations revealed that poly(4, 4′‐diphenyl sebacate), in contrast to previous reports that suggest this polymer is smectgenic, could produce nematic phase. It could be concluded that the chemical structure ordering of the poly(4, 4′‐diphenyl sebacate) plays a significant role in its liquid crystalline behavior. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1594–1606, 2005

Development of co-continuous structure in liquid crystalline polyester

We investigated liquid crystallization of liquid crystalline polyester BB-5 during isothermal annealing by digital high-fidelity microscope and light scattering. A liquid crystalline spherical domain having a radius of micrometers appeared by annealing at around 180°C. The domain grew dendritically in all directions. Neighboring liquid crystalline regions coalesced and then interconnected. The interconnected structure changed to a co-continuous two-phase structure with increasing ordering of the liquid crystalline phase, and the interface between the liquid crystalline phase and the isotropic phase became smoother over time. Liquid crystallization stopped before volume filling the whole space, and the liquid crystalline phase and isotropic phase coexisted. The liquid crystalline region became narrower with an increase in the temperature of the liquid crystallization. Such structural development is different from the liquid–liquid phase separation via spinodal decomposition, and it may be attributed to the segregation of non-liquid crystallizable low molecular weight molecules from the growth front by fractionation of the molecular weight distribution during the liquid crystallization in terms of the instability of the diffusion-controlled interface.

Rheological Properties and Associated Structural Characteristics of Some Aromatic Polycondensates Including Liquid-Crystalline Polyesters and Cellulose Derivatives (IUPAC Technical Report)

Article Rheological Properties and Associated Structural Characteristics of Some Aromatic Polycondensates Including Liquid-Crystalline Polyesters and Cellulose Derivatives (IUPAC Technical Report) was published on March 1, 2005 in the journal Chemistry International (volume 27, issue 2).

Layered structure and Xe sorption and diffusion properties of low-density liquid-crystalline polyesters with n-alkyl side chains

Four low-density liquid-crystalline polyesters with n-alkyl side chains, B–C n ( n is a carbon number of n-alkyl group), were synthesized from the 1,4-di-( n-alkyl ester) of 1,2,4,5-benzenetetracarboxylic acid and 4,4′-biphenol, to clarify the effect of side chain length on higher ordered structure in the solid state and gas sorption and diffusion properties of these polyesters. All the B–C n ( n=6, 10, 14, 18) samples behaved as a thermotropic liquid crystal and formed a layered structure composed of alternating rigid aromatic main chain layers and flexible n-alkyl side chain layers. In the crystal phase, the distance between the rigid aromatic main chain layers, namely the layer spacing, linearly increased with n, indicating that the conformational feature of n-alkyl side chains was trans-rich. This finding was supported from the 13C NMR chemical shift values of methylene carbons in B–C14 and B–C18. Xe sorption of B–C n was restricted to the side chain layer, which is almost a liquid-like environment, and these sorption isotherms obeyed Henry's law. The density of side chain layers was estimated from experimental values of layer spacing and density, under some speculate assumptions, but that determined individually by 129Xe NMR spectroscopy was coincidence. The estimated density of side chain layers became higher with increasing n, as well as n-alkane liquid, and closed to that of the polyethylene in rubbery state. Xe solubility coefficient corrected with the estimated side chain layer's density decreased with increasing n. On the other hand, the diffusion coefficient of Xe in B–C n increased with n, and this was supported from the NMR spectral width of the 129Xe in B–C n. These results also indicate that the main chain layers of B–C n were very dense and could not sorb Xe.

Structure and mechanical properties of new hybrid composites based on polyamide 6,6 reinforced with both glass fibers and a semiaromatic liquid crystalline polyester

AbstractPolyamide 6,6 (PA66) composites with 30% glass fiber (GF) were blended with a semiaromatic liquid crystalline copolyester (Rodrun 5000 (R5)) up to 40% R5 by injection molding. The composites showed two amorphous phases. Interchange reactions took place between the two polymers, leading to good interfacial adhesion. The addition of 20% R5 was enough to counteract the viscosity increase provided by the GF. The synergistic increases in the modulus of elasticity were attributed to the increase in the skin thickness at increasing R5 content. The tensile strength of the composites remained constant on LCP addition, despite the lower tensile strength of R5 compared with that of PA66/GF. The notched impact strength increased notably at increasing R5 content. Polym. Compos. 25:601–608, 2004. © 2004 Society of Plastics Engineers.

Nano-composites derived from melt mixing a thermotropic liquid crystalline polyester and zinc sulfonated polystyrene ionomers

A nano-composite was produced by simply melt mixing a blend of a thermotropic liquid crystalline polyester (LCP) and the zinc salt of a lightly sulfonated polystyrene ionomer at 300°C. The nano-particles, which were in the form of relatively uniform rectangular prisms of ca. 30nm×30nm×200nm, formed from the LCP phase due to an ester-interchange reaction between the LCP and residual catalytic amounts of zinc acetate that were present from the neutralization step in the preparation of the ionomer. The nano-particles possessed a different crystal pattern and higher melting point than the parent LCP, and they were easily oriented when the blend melt was uniaxially stretched. The nano-particles provided reinforcement of the ionomer comparable to what would be expected of short fibers with a modulus of at least 25GPa.

Influence of UV irradiation on the blue and red light photoinduced processes in azobenzene polyesters

Birefringence induced in a series of liquid crystalline side-chain azobenzene polyesters with different substituent groups was investigated under irradiation with 488 and 633 nm linearly polarized lights. Two different initial conditions have been used: the effect of a previous irradiation with UV light that yields the films into the isotropic state at room temperature (RT) was compared with the quenching from temperatures above the isotropic transition temperature T i. UV–visible spectra of the thermally quenched films show the presence of aggregates when measured at RT. We have found that UV light irradiation creates a high concentration of cis isomers and breaks the aggregates, but they are formed again after a few days in dark at RT. Orientation of the chromophores perpendicular to the polarization of the 488 nm light and parallel to the polarization of the 633 nm light was confirmed by dichroism measurements.

Ionic conductivities of the LiCF3SO3 complexes with liquid crystalline aromatic polyesters having oligo(oxyethylene) pendants

We have synthesized new aromatic polyesters (DiPEG-HQ and DiPEG-BP) by condensation polymerization of a terephthalic acid derivative bearing a pendant oligo(oxyethylene) (195-1,195-2), which has a methoxy terminal group, and two different aromatic diols, hydroquinone and 4,4′-biphenol. The synthesized polymers were characterized by differential scanning calorimetry (DSC), polarizing microscopy, and X-ray diffractometry for their liquid crystallinity (LC), thermal transitions, and structural morphologies in mesophases. The morphology of the LC phases depends strongly on the length of the rigid backbone repeating unit. The DiPEG-BP polymer having a longer repeating unit exhibits both layered and nematic structures before isotropization, whereas the DiPEG-HQ polymer having a shorter repeating unit shows only the layered structure in the mesophase. We found that the layer spacing for DiPEG-HQ is larger than that for DiPEG-BP. Both polymers easily form complexes with LiCF3SO3; we studied this complex formation by FT-IR spectroscopy. The layer spacing of the polymer-electrolyte composites increases upon increasing the amount of the lithium salt. The polymer/salt electrolyte mixtures we investigated at molar ratios of EO: salt in the range of 5–20 exhibit electrical conductivity values at 40 °C of 2.4 × 10−5 and 1.1 × 10−5 S/cm for DiPEG-HQ/LiCF3SO3 andDiPEG-BP/LiCF3SO3, respectively. At 80 °C, these values are higher: 4.6 × 10−4 and 2.5 × 10−4 S/cm, respectively. The activation energy of conductivity depends strongly on the salt concentration.

Two types of aggregation structure formed in a thermotropic aromatic polyester

The aggregation structures of the enantiotropic liquid crystalline polyester, K145N213 (°C), were investigated using polarizing optical microscope (POM), wide-angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). Depending on annealing temperature, two types of aggregation structure (AS), I and II, were formed. AS I was grown directly from nematic melt, while AS II was formed from supercooled liquid crystalline state. By comparing AS I and AS II it was found that there was much difference between them, such as the morphology, the melting behaviour and the pattern of WAXD. The experimental results showed that the aggregation behaviour of AS II was more like that of the conventional crystalline polymers, while AS I made conspicuous difference. A sketch map of the formation mechanism of AS I was suggested, which showed that the particular AS I was composed of nematic domains.

Viscosity‐reducing effects of two semiflexible liquid‐crystalline polyesters with different chain rigidities in a matrix of polycarbonate

AbstractTwo liquid‐crystalline polyesters (LCPs) with different chain rigidities were synthesized and melt‐blended with polycarbonate (PC) at an LCP concentration of 2 wt %. The first LCP (LCP1) was based on hydroxybenzoic acid (HBA), hydroquinone (HQ), sebacic acid (SEA), and suberic acid (SUA) and contained a relatively high concentration of flexible units (SEA and SUA). The other one (LCP2) was based on HBA, hydroxynaphthoic acid, HQ, and SEA and contained a lower concentration of flexible units. LCP2 had a much lower melting point, a higher clearing temperature, and a lower shear viscosity than LCP1. The blending was carried out at 265, 280, and 300°C for both systems. The extent of the viscosity reduction induced by the addition of LCP1 depended on the compounding temperature, and the lowest viscosity was achieved with blending at 280°C. This was attributed to the large interfacial area and interactions between the flexible segments of LCP1 and PC chains at the interface. For PC/LCP2, the viscosity reduction was not significantly dependent on the compounding temperature, and when it was compounded at 280°C, its viscosity was significantly higher than that of PC/LCP1 at high shear rates, even though LCP2 had lower viscosity. A scanning electron microscopy study revealed that, with compounding at 265 and 280°C, LCP2 was poorly dispersed in the PC matrix in comparison with LCP1, and the glass‐transition‐temperature depression caused by the addition of LCP2 was relatively small. This indicated that interfacial interactions in PC/LCP2 were weaker, thereby explaining their different rheological behavior in comparison with PC/LCP1. With compounding at 300°C, the compatibility of both systems improved because of transesterification reactions, but this did not lead to a lower viscosity because of the lack of physical interfacial interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 960–969, 2004

Dynamics of Defect Annihilations in Polymerization of Aromatic Liquid Crystalline Polyesters

We have studied the annihilation process of disclinations during in situ thin film polymerization of a series of aromatic liquid crystalline polyesters by using a polarizing light microscope (PLM). The decreases both in isotropic molten area during liquid crystal (LC) phase formation and in distance between LC disclination pairs during annihilation are found to follow a power law relation. However, abnormal annihilation phenomena, which have not been previously reported, are observed. A faster annihilation rate in the late stage of the annihilation process and an increase in the distance of a disclination pair can occur if the LC system is a reacting system or if the surroundings have other ongoing annihilations.

Rheological properties and associated structural characteristics of some aromatic polycondensates including liquid-crystalline polyesters and cellulose derivatives (IUPAC Technical Report)

Abstract A comparative experimental study of shear-flow rheological properties of thermotropic polymer liquid crystals by eight different laboratories is described. The materials involved four different liquid-crystalline polyesters (LCPs), a glass- fiber-filled liquid-crystalline polyester,hydroxypropyl cellulose (HPC), and two non-liquid-crystalline high-temperature polymers, a poly(etheretherketone) (PEEK), and a polyarylate (PAR). Studies were made in both steady shear-flow and dynamic oscillatory experiments. The data from the various laboratories involved were compared. The level of agreement in the data was much less for most liquid-crystalline polymers than for similar isotropic melts. The Cox –Merz rule is valid for PEEK and PAR, but not for the LCPs and HPC. The occurrence of low levels of extrudate swell and high levels of uniaxial orientation in extrudates of the LCPs and HPC is described.

Effect of the Thermal History on the Thermal and Rheological Behavior of a Thermotropic Polyester

The biphasic behavior and phase transitions of a thermotropic main-chain liquid crystalline polyester, the poly(oxytrimetilen-etilen glycol p,p′-bibenzoate), was studied by X-ray diffractometry, differential scanning calorimetry (DSC), and rotational rheometry. The liquid crystalline mesophase structure of the polymer evolves from Smectic C to Smectic A at around 100°C and changes to the isotropic state at about 200°C. The annealing of polymer samples at different temperatures within the smectic–isotropic transition gives rise to double endotherm and exotherm peaks on the heating and cooling DSC traces. These peaks are attributed to the preferential segregation of the lower molecular weight molecules from the liquid crystalline to the isotropic phase in the biphasic zone. The rheological studies are consistent with this result. The dynamic moduli measured at constant frequency in temperature ramps using polymer samples with different thermal histories reveal that the type of annealing processes applied in the biphasic zone generates different evolution of the rheological data.

Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

In contrast to the conventional photoorientation process with blue light, an orientation of 4-cyano-4‘-alkoxyazobenzene side groups parallel to the electric field vector of the incident light is generated upon irradiating films of a liquid-crystalline side-chain polymer with linearly polarized red light. The polyester is characterized by smectic and nematic phases g24SX26SA34N46i and a strong tendency to form J-aggregates. The process requires a photochemical pretreatment by irradiation with UV light or an exposure to visible light of high power density to produce a certain concentration of the Z-isomer, which destroys any initial orientational order and J-aggregates. The orientation process is cooperative, whereas the light-induced orientation of the photochromic moiety causes an ordering of the alkylene spacers and even of the main-chain segments into the same direction. The most probable mechanism of this two-step process is the angular-selective transformation of the bulky Z-isomers to the rodlike E-isomeric formed by the red light. The aligned E-azobenzene side groups become strongly J-aggregated. Very high values of dichroism of about 0.8 and birefringence of about 0.3 were generated as a result of this combination of the photoinduced orientation process and the thermotropic self-organization, which take place simultaneously under the irradiation conditions. The process results in a uniaxial prolate order of the film, whereas conventional photoorientation leads to a biaxial oblate order. These two different three-dimensional orders have been characterized by FTIR polarization spectroscopy and exhibit also varying intermediate thermal stabilities.

Thermotropic liquid crystalline polymers containing five-membered heterocyclic groups IX. Synthesis and optical properties of liquid crystalline semi-rigid polyesters composed of a quinquephenyl analogue containing 1,3,4-thiadiazole and aliphatic chains†

Novel semi-rigid polyesters containing a quinquephenyl analogue containing 1,3,4-thiadiazole and a central 1,3-phenylene unit in the main chain were synthesized by high temperature solution polycondensation of a dimethyl ester derivative of 1,3-bis(5-phenyl-1,3,4-thiadiazol-2-yl)benzene with an aliphatic (octa-, deca- and dodecamethylene) diol. The proposed structures were confirmed using FTIR and 1H NMR spectroscopies, and elemental analyses; their liquid crystalline and photoluminescent (PL) properties were examined by means of differential scanning calorimetry, optical texture observations using polarizing microscopy, powder X-ray diffraction, and UV-vis and PL spectra measurements. These measurements showed that the polymers not only show a monotropic solid smectic or disordered crystal phase, but also PL properties with blue emission in HFIP solutions and in the solid phase, Stokes shifts of 116.5–119 nm being observed.

Microhardness of PET-based liquid crystalline copolyesters: influence of the microstructure

The Vickers microhardness of PET-based liquid crystalline copolyesters has been investigated. The copolyesters have been synthesized by transesterification of PET with equimolar amounts of sebacic acid (S) and hydroquinone (Q) (or 4,4′-dihyroxybiphenyl (B)) and with varying amounts of 4-hydroxybenzoic acid (H). The variation of the Vickers microhardness of PET-S-Q-H and PET-S-B-H liquid crystalline polyesters with the composition have been interpreted by the microstructure of the materials. The increase in the concentration of 4-hydroxybenzoic acid (H) in both types of copolyesters leads to an increase in intermolecular distance and to enlargement of the domain size. This, on its, turn, leads to a decrease in the materials' microhardness. The effect that the mixing time of the reactive blends of equimolar amounts of PET and poly(phenylene sebacate) (PQS) PET/PQS has upon the microhardness values has been also studied. The variation of the microhardness of PET/PQS blends prepared for different mixing times follows the same tendency as that of the melting enthalpy (i.e. the degree of crystallinity). Both parameters have lower values with the longer mixing time. The decreased crystallinity during the transreaction results into materials having higher creep rate under load.

Structure and properties of amorphous polyamide/liquid crystalline polyester blends

AbstractAmorphous polyamide (AP)/liquid crystalline polyester (VA) blends were obtained by extrusion‐injection molding (EI) throughout the whole composition range. The phase behavior, chemical nature and morphology of the blends were studied, and the mechanical properties discussed and compared with those of the 10 and 30% VA blends obtained by direct injection molding (DI). The blends showed two almost pure slightly reacted amorphous phases. The apparently higher reaction level of the EI blends, although small, led to a more homogeneous, fine and fibrillated morphology, attributed to a lower interfacial tension. Significant synergisms in the modulus of elasticity (up to 25%) and in the tensile strength (up to 40%) were seen in EI blends. The similar values of both specific volume and orientation in the blends and in the pure components suggest that the contribution to the modulus of the dispersed VA rigid particles is greater than that due to the proportion of VA in the blend. The 10% VA DI blend showed a similar behavior in these two properties, indicating that the DI procedure is preferred, provided that only stress‐related properties are sought. At 30% VA content, the moduli of elasticity were similar by the two molding processes, but the clearly lower tensile strength and lower ductility of the easier DI procedure, means that the more complex, but more effective, EI procedure is the one of choice for high performance materials.