Thermotropic Copolyesters Research Articles

Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containing m‐hydroxybenzoic acid units

AbstractFibers of fully aromatic thermotropic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a high‐temperature melt‐spinning technique. Two types of the copolyesters were prepared by a high‐temperature melt polycondensation reaction using 33 mol % of kink (m‐ABA) and 67 mol % linear monomer units (p‐ABA, TPA, HQDA), and characterized by differential scanning calorimetry (DSC), polarized optical microscopy, wide‐angle X‐ray diffraction (WAXD), and intrinsic viscosity measurements. The mechanical properties and the morphology of the fibers were also determined by tensile tester, WAXD, and scanning electron microscopy (SEM). The copolyesters exhibited phase‐separated nematic liquid crystalline morphology within a broad temperature range in an isotropic matrix. DSC analysis of the copolyesters revealed broad endotherms associated with the nematic phases. The melting and spinning temperatures were in a processable region. Fibers exhibit well‐developed fibrillar structure parallel to the fiber axis. The highly oriented morphology of the fibrils is slightly dependent on the type of the linear monomer. The strength and modulus values determined for the fibers that contain equal molar composition of the linear p‐ABA, HQDA/TPA units are comparable to other reported rigid systems containing fully aromatic species. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2580–2587, 2002

Single‐point determination of intrinsic viscosity of wholly aromatic thermotropic copolyesters in 1,1,1,3,3,3‐hexafluoro‐2‐propanol

AbstractA series of wholly aromatic thermotropic copolyesters based on 4‐hydroxybenzoic acid, hydroquinone, and 2,6‐naphthalene dicarboxylic acid were synthesized by direct melt polymerization with or without different added transesterification catalysts. Nine procedures for calculation of the intrinsic viscosities from a single viscosity measurement for polymer solutions, including a proposed one, were applied for the thermotropic copolyesters in 1,1,1,3,3,3‐hexafluoro‐2‐propanol at 30°C. Various forms of the Huggins and Kraemer equations, singly or combined, yielded intrinsic viscosities that were in good agreement with extrapolated values obtained in the usual manner from multipoint viscosity measurements over a wide range of concentrations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3396–3401, 2001

Single-Point Determination of Intrinsic Viscosity of Semirigid Thermotropic Copolyesters in Phenol/1,1,2,2-Tetrachloroethane

A series of semirigid thermotropic copolyesters with different compositions were prepared from p-hydroxybenzoic acid (HBA), hydroquinone (HQ), terephthalic acid (TPA) and poly(ethylene terephthalate) (PET) by acidolysis reaction and following polycondensation. Fourteen procedures of calculation of the intrinsic viscosities from a single viscosity measurement for polymer solutions, including three proposed ones, have been applied for the copolyesters in phenol/1,1,2,2-tetrachloroethane (60/40, v/v) at 30°C. It is found that various forms of the Huggins and Kraemer equations, used singly or in a combined form, yield intrinsic viscosities in good agreement with those extrapolated values obtained in the usual manner from multipoint viscosity measurements over a wide range of concentrations.

Blends of a thermotropic copolyester and a thermotropic copoly(ester–amide): structure and mechanical properties

Rodrun 5000/Vectra B950 blends were obtained by direct injection moulding at two injections rates. The blends were partially miscible and unreacted under the processing conditions used. Higher orientations and properties were obtained at the lower injection rate due to the higher overall orientation obtained. The produced orientation and the negative volume of mixing of the blends led to a range of LCP materials with intermediate modulus and tensile strength and slightly higher ductility.

Smectic–like order in the log–rolling flow of thermotropic random copolymers. A time–resolved wide–angle X–ray scattering study

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Romo-Uribe Angel 2001Smectic–like order in the log–rolling flow of thermotropic random copolymers. A time–resolved wide–angle X–ray scattering studyProc. R. Soc. Lond. A.4571327–1342http://doi.org/10.1098/rspa.2000.0720SectionRestricted accessResearch articleSmectic–like order in the log–rolling flow of thermotropic random copolymers. A time–resolved wide–angle X–ray scattering study Angel Romo-Uribe Angel Romo-Uribe Ticona, Celanese AG, 86 Morris Avenue, Summit, NJ 07901, USA () Google Scholar Find this author on PubMed Search for more papers by this author Angel Romo-Uribe Angel Romo-Uribe Ticona, Celanese AG, 86 Morris Avenue, Summit, NJ 07901, USA () Google Scholar Find this author on PubMed Search for more papers by this author Published:08 June 2001https://doi.org/10.1098/rspa.2000.0720AbstractUnder a suitable combination of molecular weight, temperature and shear rate thermotropic random copolymers display macromolecular orientation orthogonal to the flow direction and along the vorticity axis; Romo–Uribe & Windle have called this a ‘log–rolling’ flow. Time–resolved wide–angle X–ray scattering has enabled the detection of a 002 meridional reflection as the orthogonal orientation develops from the non–oriented molten phase. Therefore, similar sequences of the random copolymer self–assemble during the log–rolling flow, giving rise to a smectic–like phase. After cessation of shear, neither the molecular sequence assemblage is lost nor is macromolecular orientation relaxation observed. Furthermore, applying shear to macromolecules that are already orthogonal to the velocity axis disrupts the chain register due to the macromolecular disorientation prior to the transition to the flow–aligning regime. Strikingly, after cessation of shear, the macromolecules recoil towards the orthogonal orientation and the molecular sequence assembly is re–established. The smectic–like order is therefore the mechanism that stabilizes the log–rolling flow. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Romo-Uribe A (2022) Wide-angle X-ray diffraction and small-angle X-ray scattering studies of elastomer blends and composites Elastomer Blends and Composites, 10.1016/B978-0-323-85832-8.00010-9, (209-242), . Parisi D, Seo J, Schaake R, Rhoades A and Colby R (2021) Shear-induced nematic phase in entangled rod-like PEEK melts, Progress in Polymer Science, 10.1016/j.progpolymsci.2020.101323, 112, (101323), Online publication date: 1-Jan-2021. Romo-Uribe A (2021) Sequence segregation in the melt and viscoelasticity of thermotropic liquid crystalline polymer. A rheo-X-ray scattering study, Polymer, 10.1016/j.polymer.2020.123315, 213, (123315), Online publication date: 1-Jan-2021. Romo-Uribe A (2020) Scattering and Other Miscellanies Techniques for the Characterization of Shape Memory Polymers Shape Memory Polymers, Blends and Composites, 10.1007/978-981-13-8574-2_12, (269-309), . Reyes-Mayer A, Alvarado-Tenorio B, Romo-Uribe A, Benavente R, Jaffe M and Molina-Ocampo A (2015) Nanostructure reorganization in a thermotropic copolyester. A simultaneous WAXS and SAXS study, Polymers for Advanced Technologies, 10.1002/pat.3708, 27:6, (748-758), Online publication date: 1-Jun-2016. Romo-Uribe A (2007) Molecular orientation in sheared molten thermotropic random copolyester, Rheologica Acta, 10.1007/s00397-007-0192-9, 46:9, (1139-1152), Online publication date: 1-Dec-2007. Rendon S, Burghardt W and Bubeck R (2007) Orientation dynamics in commercial thermotropic liquid crystalline polymers in transient shear flows, Rheologica Acta, 10.1007/s00397-007-0177-8, 46:7, (945-956), Online publication date: 1-Aug-2007. This Issue08 June 2001Volume 457Issue 2010 Article InformationDOI:https://doi.org/10.1098/rspa.2000.0720Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Published online08/06/2001Published in print08/06/2001 License: Citations and impact Keywordstime–resolved X–ray scatteringthermotropic random copolymersnematic and smectic polymersmolecular sequence self–assemblymacromolecular orientation and relaxationlog–rolling and flow–aligning flow

In situ composites: effect of elongational flow velocity on thermotropic liquid crystalline co-polyester fibrillation in thermoplastic/TLCP systems

This study focuses on the TLCP fibrillation process in a thermoplastic (PP) matrix during melt blending. The process of blending includes a single extrusion process in a twin-screw extruder with compatiblization and injection moulding of the extrudates. The TLCP, VA950 in situ fibrillation, compatiblization with PP and retainment of fibrils in the injection-moulded samples has already been achieved in our earlier study. However, the fibrillation process remains a complex issue. There are many factors like viscosity ratio, capillary number, composition, and flow speed which will affect the fibrillation. The elongational flow seems to be a more important factor affecting the TLCP fibrillation. The present study aims to identify the important factors which influence the TLCP fibrillation at their near-critical conditions. The morphological features and mechanical properties show that the compatiblization and elongational flow speed are very important for effective fibrillation.

Structure and temperature behavior of thermotropic liquid-crystalline Ultrax copolyesters

Phase and relaxational transitions in the commercial thermotropic liquid-crystalline copolyesters Ultrax 4002 and Ultrax 4003 were studied by X-ray diffraction, differential scanning calorimetry, and mechanical analysis. In spite of only a slight difference in the compositions of the copolyesters, considerable differences in their structure and temperature behavior were observed. In particular, it was shown that the degree of crystallinity differs by more than a factor of 2 for the as-spun fibers upon annealing above the glass-transition temperature. The type of crystalline structure as well as the ability to crystallize are also different. The glass-transition temperature of both copolyesters is determined as the temperature of the appearance of mobility of the most rigid comonomer units and does not depend on the composition of the materials. Annealed copolyesters are semicrystalline materials with a two-phase structure, where the crystalline phase coexists with a liquid-crystalline one. The structure of the latter is characterized by aperiodic positions of smecticlike layers in space. On heating the materials the crystalline phase is transformed into a pseudohexagonal mesophase indicating features of a second-order phase transition.

Ionic Naphthalene Thermotropic Copolyesters: Enhanced Compressive Properties of Fibers

Compressive properties of fibers made from ionic naphthalene theromotropic polymers (NTPs) were investigated. These (main-chain) thermotropic liquid crystalline polymers (LCPs) are wholly aromatic copolyesters, which contain 1 mol % ionic groups with either monovalent Na ion or divalent Ca ion. The SEM observations of kink band formation on both a single knotted fiber and a deformed fiber under axial compression in a composite suggest enhanced compressive properties for the ionic NTP fibers as compared with nonionic NTP fibers. It is believed that the enhancement of the compressive properties is due to the presence of strong lateral ionic bonds in the ionic NTP fibers, which provide interlinks both between molecules and between supermolecular domains. Tensile strength values of the ionic NTP fibers are slightly higher than those of the nonionic NTP fibers, even though the take-up speed, and thus the molecular orientation, is lower for the ionic NTP than for the nonionic NTP. This reflects the beneficial effect of ionic bonds in enhancing tensile properties.

On the molecular orientation and viscoelastic behaviour of liquid crystalline polymers: the influence of macromolecular architecture

The influence of macromolecular architecture on the flow‐induced orientation of main‐chain thermotropic liquid crystalline polymers (LCPs) is investigated using in situ wide‐angle X‐ray scattering. In order to get more insight into the interrelationship between microscopic and rheological behaviour, the viscoelastic properties of the nematic melts were also studied. The LCPs studied are wholly aromatics , composed only of mesogenic units, and semiflexibles , which consist of mesogenic units separated by alkyl spacers. Rheo‐X‐ray scattering evidenced the detrimental influence of the flexible spacers on the orientation process. The wholly aromatic LCPs readily orient along the flow direction, even under modest shear flows ( γ = 0.1 s‐1). The semiflexible LCPs, however, display lower levels of orientation than the wholly aromatics, and the quality of the orientation worsens as the length of the flexible spacer increases. The rheological characterization shows that, like conventional flexible‐chain polymers, the thermotropic LCPs exhibit a linear viscoelastic (LVE) regime. Moreover, dynamic measurements, within the LVE regime, suggest a level of elasticity in the nematic melts. As the length of the alkyl spacer increases, the rheological behaviour is more akin to that displayed by common flexible molecular chains. The poor shear orientation exhibited by the semiflexible LCPs is then associated with a molecular network formed by the less‐than‐rigid molecular chains. Furthermore, the steady shear viscosity is always smaller than the dynamic viscosity, i.e. the Cox‐Merz rule does not hold. This is due to the fact that steady shear induces molecular orientation, whereas oscillatory shear does not. The relaxation of orientation after steady shear showed that the molecular orientation relaxes after hundreds of seconds. The shear stress, however, relaxes within only a few seconds. Strikingly, the rate of molecular orientation relaxation was slower for the semiflexible than for the wholly aromatic LCPs.

Syntheses and properties of thermotropic copolyesters of p-hydroxybenzoic acid

Two series of thermotropic copolyesters of p-hydroxybenzoic acid (HBA) were synthesized by direct thermal polycondensation. One comprised aromatic copolyesters from HBA, terephthalic acid, bis(4-hydroxyphenyl) ketone (BHP) and resorcinol. The other comprised semi-aromatic copolyesters from HBA, terephthalic acid, BHP and α,ω-diols with carbon atom number of 4, 6, 8, 10. The properties of the two series were characterized by polarized light microscopy, differential scanning calorimetry and wide angle X-ray diffraction. Most of the resulting copolyesters could form a nematic phase over a wide temperature range above their melting points. The effects of variation in composition and monomer structure on the properties of copolyesters were discussed.

Influence of the preparation method on the mechanical properties of a thermotropic liquid crystalline copolyester

The dependence of the mechanical properties of injection molded tensile specimens of a liquid crystal polymer (Rodrun) on the preparation method of the specimen were studied by means of the change in each of four processing parameters over the maximum range that the machine allowed, whilst holding the other parameters constant. The parameters studied were the injection rate, the melt temperature, the screw rotation rate during plasticization and the injection pressure. The common analysis of the results of this and previous works, allows us to propose parameter ranges at which the mechanical properties are independent of the preparation method.

Copolycondensations of bisphenols with aggregates of isophthalic acid and terephthalic acid activated by tosyl chloride/dimethylformamide/pyridine in different manners

A mixture of isophthalic acid (IPA) and terephthalic acid (TPA) was activated by a tosyl chloride/dimethylformamide/pyridine (Py) condensing agent in two steps via the treatment of a mixture of the initially activated IPA/TPA with additional TPA followed by the activation of TPA with the agent. The resulting mixture showed a solubility in Py different from that obtained by the activation of them all at once; the difference might be due to different structures of the aggregates of the activated IPA and TPA at the same composition of the diacids. The structures of the aggregates were evaluated on the basis of melting points and the IR spectra of a mixture of dimethyl esters of IPA and TPA produced by the quenching of the reaction mixtures with methanol. The mixture obtained by two-step activation showed lower melting points and spectral changes due to enhanced associations of the esters with respect to the mixture prepared by the activation of them all at once. The aggregates were also examined in terms of the distributions of IPA and TPA in thermotropic copolyesters prepared from methylhydroquinone and chlorohydroquinone by their transition temperatures and 13C NMR. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3884–3892, 2001

Morphology and mechanical properties of direct injection molded polypropylene/thermotropic copolyester blends

AbstractBlends of two grades of polypropylene (PP) with thermotropic copolyester (Rodrun) contents of up to 40% were obtained by direct injection molding at different processing temperatures. In the skin of the molded specimens rather long fibers were seen in blends with low‐viscosity PP, whereas sheets were found when the high‐viscosity PP was the matrix. In the core, the viscosity of the matrix played a more relevant role than the viscosity ratio on the orientation level of the dispersed Rodrun phase. The better mechanical properties of the blends with the low viscosity PP are attributed to the morphology change of the dispersed phase from sheets to fibers when the viscosity of the matrix decreased.

Thermal properties of blends of a thermotropic liquid crystalline copolyester of poly(hydroxy benzoic acid-co-ethylene terephthalate) and polyarylate

Thermal properties and transesterification reaction of blends of polyarylate (PAr) and a thermotropic liquid crystalline polymer (LCP) were investigated by differential scanning calorimetry (DSC) and Fourier Transform infrared (FT-IR) spectroscopy. In the thermogram of PAr-LCP blends, two glass transition temperatures (T g s) were observed. Phase behavior of the blends revealed that the LCP dissolved more in the PAr-rich phase than did the PAr in the LCP-rich phase, indicating partial miscibility between two polymers. The polymer-polymer interaction parameter (X 12 ) was calculated, and ranged from 0.069 to 0.076. In the calculation of the X 12 , the anisotropy of the LCP was considered. After annealing, the two T g s of the blends were shifted toward the center. In the FT-IR spectroscopy study of the annealed PAr-LCP blends, three new characteristic peaks of the ester group were detected. The DSC and FT-IR results suggested that transesterification reaction between PAr and LCP occurred under the annealed condition.

Effect of isotropization on the thermal behavior of two thermotropic copolyesters containing spirobicromane moieties

Two thermotropic copolyesters with inherent rigid spirobicromane (SPI) moieties were prepared to evaluate their registry effects of neighboring chains in the mesomorphic state. Due to this chain registry effect, copolyester I-19, synthesized from polycondensation of terephthaloyl bis(4-oxybenzoyl chloride) (TOBC), heptanediol (HD, 90mol%), and SPI (10mol%) exhibited different thermal behavior between samples cooled from the mesomorphic and the isotropic liquid states. Chain arrangements in copolyester I-19, once randomized by isotropization, can not be readily improved by a further annealing process. In contrast, crystallinity of copolyester II-19 prepared from reaction of TOBC, HD (90mol%), and bis(6-hydroxyhexanoxy)spirobicromane, 10mol%) (BHS) can be significantly enhanced by annealing even when previous thermal treatment in the isotropic liquid state was performed. Suggestively, the minor component (i.e. SPI or BHS) in the corresponding copolyesters plays a decisive role in their responses toward annealing. The rigid, bent SPI moieties in copolyester I-19 efficiently retarded the crystallization process. In contrast, the flexible 1,6-dioxyhexamethyl spacers introduced in the BHS moieties greatly reduce the detrimental effect of the bent SPI moieties on the crystallization behavior of copolyester II-19.

Compatibilization of poly(ether imide)/Rodrun blends by means of a polyarylate

A compatibilization method for improving the mechanical properties of thermoplastic/liquid-crystalline polymer (LCP) blends has been tested in blends of poly(ether imide), PEI, with a thermotropic copolyester (Rodrun). It is based on the addition to the blend of a third component, both miscible with the matrix and also able to interact with the LCP. Given the miscibility of a polyarylate (PAr) with PEI up to 20% PAr content, and its probable interactions with Rodrun, a constant 20% PAr was added to the PEI matrix to test its possible compatibilizer activity in PEI/Rodrun blends. The observed decrease in the interfacial tension between the matrix and the dispersed phase induced by the PAr gave rise to a smaller size and to fibrillation of the dispersed phase. Fibrillation also gave rise to improved modulus of elasticity and tensile strength, thus proving the compatibilization activity of PAr.

Multiple melting behavior of a thermotropic copolyester containing spirobicromane moiety

A thermotropic copolyester I-19 prepared from a rigid, bent spirobicromane (SPI), 1,7-heptanediol (HD), and an aromatic ester triad, TOBC (terephthaloyl bis(4-oxybenzoyl chloride), was prepared and its thermal behavior investigated by differential scanning calorimetry. Copolyester I-19 exhibited completely different DSC thermograms between samples cooled from the isotropic liquid and the mesomorphic states, a result attributable to the registry effect of the neighboring chains in the mesophase. Non-isothermal crystallization at different cooling/heating rates, and isothermal crystallization and annealing at various temperatures had been conducted to verify the origins of the complicated four melting endotherms (as Tm1, Tm2, Tm3 and Tm4 from high- to low-temperature regions) in the sample cooled from the mesomorphic state. The highest-temperature Tm1 transition is attributed to the melting of the primary crystal formed via the liquid crystalline nuclei. Tm2 and Tm3 transitions are due to melting of the less perfect, secondary crystals close and less close to the pure crystals responsible for the Tm1 transition. By choosing suitable isothermal crystallization and annealing processes, Tm2 and Tm3 transitions can be moved to merge with Tm1 to become one high-temperature single melting endotherm. The lowest-temperature Tm4 transition, which basically remained intact after different thermal treatments, is caused by the melting of the chain segments near the SPI moieties.

Effect of catalysts on thin-film polymerization of thermotropic liquid crystalline copolyester

Effect of catalysts on thin-film polymerization of thermotropic liquid crystalline copolyester

Semi-rigid thermotropic polyester containing a rigid, bent spirobicromane moieties—primary characterizations and the thermal behavior

Thermotropic copolyester TBH with inherent spirobicromane (SPI) moieties was prepared by polycondensation reaction between mixed diols of 4,4-bis(6-hydroxyhexanoyloxy)spirobicromane (BHS, 10mol%), 1,7-heptanediol (HD, 90mol%) and terephthaloyl bis(4-oxybenzoyl chloride) (TOBC). In addition, homopolyester TH (or TB) synthesized from TOBC and HD (or BHS) diol was prepared for comparison. With the incorporated SPI moieties, polyester TB is a nematic material, in contrast to the smectic C2 mesophase observed for polyester TH and copolyester TBH. The rigid, spiro SPI moieties in polyester TB are supposed to interrupt the ordered packing of the mesogenic triads required for a smectic C2 mesophase. Under diffraction scanning calorimetry (DSC) scans, copolyester TBH exhibited multiple endothermic and exothermic peaks, which are different from the much simpler thermal behavior observed for homopolyesters TH and TB. The multiple melting and crystallization transitions for copolyester TBH was due to the facile crystallization of the inherent flexible spacers and the potential registry of neighboring chains in the mesomorphic state according to the results from isothermal, non-isothermal crystallization experiments, and the X-ray diffraction study. Suggestively, the rigid, bent SPI moieties would impose a nonlinear geometry on the connected spacers and mesogenic units and consequently, influence its chain arrangement in the mesomorphic state.

Structure and properties of injection molded blends of poly(ether imide) and a thermotropic copolyester

The phase structure and mechanical properties of blends composed of poly(ether imide) and a thermotropic liquid-crystalline copolyester, Rodrun LC-5000, processed by injection molding were studied in the PEI-rich region. The addition of Rodrun to PEI produces fully immiscible blends and strongly improves the processability of PEI. Injection molding gave rise in very poor LCP blends to fine dispersed phases; in the rest of compositions it gave rise to coarse structures. This was probably due to the very large viscosity difference between the components of the blends. An increase in the melt temperature led to a smaller viscosity difference and as a consequence dispersed phase dispersion improved. The Young's modulus clearly increased with the Rodrun content. The tensile strength was maintained up to a LCP content of 5% but decreased at higher contents because of the coarse morphologies obtained. The overall mechanical behavior was a main consequence of the lack of fibrillation and of the LCP dispersion level in the matrix.