Liquid Crystalline Copolyester Research Articles

Anomalous Temperature Dependence of Viscosity of Thermotropic Polyesters

A rheological study of a series of thermotropic liquid crystalline copolyesters containing varying proportions of hydroxybenzoic acid, isophthalic acid, and hydroquinone has shown unexpected behavior. Certain compositions were observed to exhibit a POSITIVE temperature coefficient of viscosity (viscosity increasing with shear rate) over the entire shear rate range. Other compositions showed flow curves which intersected at critical shear rates. This behavior is explained by a variation in chain stiffness with composition (high hydroxybenzoic acid content resulting in stiffer chains) which results in a biphasic melt. The unusual rheological behavior is a manifestation of the competition between isotropic and anisotropic phases, which is influenced by composition, temperature, and shear.

Primary normal-stress difference for two liquid crystalline copolyesters

The primary normal-stress difference,N 1, was determined in both steady and transient shear flow experiments for thermotropic copolyesters of 60 and 80 mole% p-hydroxybenzoic acid (PHB) and polyethylene terephthalate (PET).N 1 was observed to be negative for the 80 mole% system at low shear rates and temperatures below 332 °C (a tensile stress, e.g. σ11 is taken here to be positive). At higher shear rates and for temperatures above 332 °C,N 1 was found to be positive. Values ofN 1 for the 60 mole% pHBA/PET system were always positive over the same range of shear rates. Although it is not certain as to the origin of the negative values, a probable cause is small density changes upon the inception of flow as well as the existence of a solid phase or some texture development in the melt. However, it is shown that it is thermodynamically admissible for liquid crystalline fluids to exhibit negative values ofN 1.

Stiff chain persistence lengths in liquid crystalline copolyesters

AbstractThis paper describes a continuation of our X‐ray diffraction work on the structure of the mesomorphic copolyesters prepared from p‐hydroxybenzoic acid (HBA) and 2‐hydroxy‐6‐naphthoic acid (HNA). The X‐ray patterns of meltspun fibers of these copolymers show a series of aperiodic meridional maxima, and these are predicted by a model consisting of stiff extended chains of completely random copolymer sequence. The calculated intensity data are independent of the chain length for the model, except that the width of the peak at d≃2.1Å decreases with increasing chain length. For 58/42 copoly(HBA/HNA) the best agreement obtained is for a chain length of 11 monomers, and this corresponds to a correlation or persistence length for the stiff chain conformation in the solid state. This effect has been modeled for an infinite chain by deriving experimental monomer length distribution functions, from a survey of the conformations of models of typical random chain sequences. The distribution function is then incorporated into the intensity calculations and leads to prediction of peak widths that are comparable to those observed.

X-ray studies of the structure of liquid-crystalline copolyesters: treatment of an atomic model as a one-dimensional paracrystal

Diagramme de fibre RX de copolyesters prepares a partir d'acide p-hydroxybenzoique (I) et acide hydroxy-2 naphtoique ou a partir de (I), dihydroxy-2,6 naphtalene et acide terephtalique

Rheological Properties of Liquid Crystalline Copolyester Melts. II. Comparison of Capillary and Rotary Rheometer Results

In an earlier paper capillary rheometer results were presented for two liquid crystalline copolyesters consisting of 60 mole % and 80 mole % p‐hydroxybenzoic acid (pHBA) and polyethyleneterephthalate (PET). In this paper obtained by means of cone‐and‐plate (CP) and parallel plate (PP) attachments of a Rheometrics Mechanical Spectrometer are compared with the capillary data. In particular, it is observed that over the range of conditions studied, viscosity data obtained in the CP and PP agree with those obtained by means of the capillary rheometer. Furthermore, there is no dependence of the viscosity on geometric or dimensional factors as is observed for low molecular weight liquid crystals under some conditions. Although the viscosity is still shear rate dependent for shear rates as low as 5×10−2 sec−1, it is shown by stress relaxation experiments following the cessation of steady shear flow that no significant yield stresses exist. The primary normal stress difference (N1) for the 60 mole % pHBA/PET copolyester is always positive under steady shear conditions but N1 for the 80 mole % pHBA/PET system can be negative for certain temperatures and shear rates. Calculated values of the die swell using Tanner's theory and cone‐and‐plate data for the 60 mole % pHBA/PET system were considerably higher than the measured values while the agreement between the theory and measured values was quite good in the case of the 80 mole % system.

Effect of thermal history on the morphology of thermotropic liquid crystalline copolyesters based on PET and PHB

Morphological studies were carried out on thermotropic liquid crystalline copolyesters based on poly(ethylene terephthalate) (PET) and para-hydroxybenzoic acid (PHB), where PHB content varied from 30 mole percent up to 80 mole percent. The technique of chemical etching, using n-propylamine as the etchant, coupled with scanning electron microscopy was utilized to obtain structural information. Scanning electron microscopy results on chemically etched, compression moulded films show that selective chemical etching of the PET rich regions occur. This indicates that the morphology of the copolymers is hetergeneous in nature. Further support regarding a hetergeneous morphology was obtained by transmission electron microscopy. A morphological model has been proposed based on these results. The observance of non-equilibrium behaviour associated with amorphous PET regions (as seen from d.s.c. measurements) also strongly indicates the presence of a phase rich in PET and thus supports the non-homogeneous morphological model. Thermal analysis of these copolyesters suggests that the chain structure is non-random and this is an agreement with results published by Wunderlich et al. The glass transition temperature typically associated with PET is present and remains constant in all copolymers compositions where PET is the continuous phase. Further, the melting temperatures obtained experimentally are higher than the values predicted by theory for random copolymers and the melting endotherms are relatively narrow. These observations also indicate a non-random chain structure. Structural studies conducted on films compression molded at different temperatures show that morphological rearrangement occurs at higher temperatures with the formation of domains of the order of 10 microns.

Effect of flow history on the morphology of thermotropic liquid crystalline copolyesters

AbstractMorphological studies have been carried out on a thermotropic liquid crystalline copolyester based on poly(ethylene terephthalate) (PET) and para hydroxybenzoate (PHB) that has been subjected to different types of flow histories. Wide angle X‐ray scattering investigations and chemical etching (n‐propylamine is the etchant) in conjunction with electron microscopy studies conducted on end gated injection molded plaques of the 60 percent PHB and 80 percent PHB copolyesters indicate that a highly oriented skin region and a less oriented core region is present. Chemical etching studies performed on microtomed layers of end gated and center gated plaques show that the etching is less pronounced in the skin region and is more pronounced in the core. The microtomed layers of the end gated injection molded plaques when analyzed by ESCA indicate the presence of a “PHB rich” skin region and a “PET” rich core region. Biaxial orientation, as denoted by WAXS measurements, is observed when the 60 percent PHB copolyester is squeezed between lubricated parallel plates.

The structure of liquid crystalline copolyesters prepared from 4-hydroxybenzoic acid, 2,6-dihydroxy naphthalene, and terephthalic acid: 2. Atomic models for the copolymer chains

The X-ray fibre patterns from copolyesters of 4-hydroxybenzoic acid, 2,6-dihydroxynaphthalene, and terephthalic acid show meridional maxima that are aperiodic. The positions of these peaks can be reproduced by calculation of the scattering characteristics of copolymer chains of random sequence modelled as linear arrays of points, where each point represents a monomer separated from adjacent points by the appropriate monomer lengths. By introducing atomic models for the monomers, good agreement is also obtained between the observed and calculated intensities. It is shown that the intensity agreement is improved by refinement of the orientation of the monomers with respect to the fibre axis.

X-ray studies of the structure of thermotropic copolyesters

Abstract This paper describes x-ray analysis of the structure of a group of wholly aromatic thermotropic liquid crystalline copolyesters, focusing on two systems: condensation copolymers of 4-hydroxy-benzoic acid (HBA) and 2-hydroxy–6-naphthoic acid; and of HBA, 2,6-dihydroxy-naphthalene, and terephthalic acid. The fiber diagrams of these copolymers contain a series of aperiodic meridional maxima that shift in position with the monomer ratio. We have shown that these characteristics are predicted by a structure consisting of an array of chains of completely random monomer sequence. The positions of the maxima are predicted by a simple model in which the monomers are represented by points, separated from their neighbors by the appropriate monomer lengths. Use of atomic models for the monomers leads to prediction of both the positions and the intensities of the maxima. Calculations for nonrandom sequence distribution show that all but minimal blockiness can be ruled out. From the breath of the meridional ma...

X-ray analysis of the structure of liquid-crystalline copolyesters

The X-ray analyses of the structures of a group of aromatic copolyesters that form liquid-crystalline melts is described. X-ray patterns of melt-spun fibres of wholly aromatic copolymers prepared from p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) show a high degree of axial orientation and there is also evidence for three-dimensional order. The meridional maxima are aperiodic, and it is shown that their positions and intensities are predicted by a model consisting of an assembly of parallel chains of completely random monomer sequences. Analyses of the scattering by aperiodic chains are summarized, first for point monomers and subsequently for an atomic model. From the breadth of some of the meridional maxima it is possible to estimate the persistence or correlation length for the stiff-chain conformation, which is found to be between 9 and 13 monomer units, depending on the HBA/HNA ratio. Determination of the three-dimensional structure is initiated via calculation of the cylindrically averaged transform for the random chain, followed by consideration of the interference effects caused by chain packing.

Sensitivity of x-ray data to sequence distribution for liquid crystalline copolyesters

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSensitivity of x-ray data to sequence distribution for liquid crystalline copolyestersGenaro A. Gutierrez and John BlackwellCite this: Macromolecules 1984, 17, 12, 2744–2749Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://doi.org/10.1021/ma00142a053RIGHTS & PERMISSIONSArticle Views26Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Rheology and Properties of Thermotropic Liquid Crystalline Poly (Bisphenol E Isophthalate-Co-Naphthalate)

Abstract Thermotropic liquid crystalline (LC) copolyesters of Bisphenol E isophthalate-co-naphthalate compositions, have been characterized by a range of rheological and other properties. All LC copolyesters contained the same nominal ratio of comonomers, but differed in molecular weight. Properties have been compared and contrasted to those of a non-liquid crystalline Bisphenol E isophthalate polyester. Interesting features exhibited by the LC copolyesters are a (1) minimum in viscosity as a function of temperature, (2) pronounced shear thinning, (3) the absence of a Newtonian viscosity plateau at low shear, (4) an order-of-magnitude lower viscosity for a LC copolyester compared to the conventional polyester of similar apparent molecular weight and (5) much lower (perhaps even negative) extrudate swell.

X-Ray Diffraction Studies of Liquid Crystalline Polymers

Abstract Thermotropic liquid crystalline copolyesters display an ordered fluid phase at elevated temperatures which permits the development of unusually high orientation at ambient temperatures. The transition which occurs upon cooling the high temperature nematic liquid crystalline phase very rapidly (e.g. fiber spinning) results in a polymeric glass with nematic structural order. Annealing increases structural order from the nematic glass toward ideal three dimensional crystalline order. Precision X-ray diffractometry has been used to directly observe changes in structural correlations which occur with annealing. Structural transitions range in character in these copolyesters from no change upon annealing to a transition from fully two dimensional to fully three dimensional structural order. Increased three dimensional order also results in substantially increased first order character of the high temperature phase transition. The chemical structure of co-monomers determines, in part, the final degree o...

Diffraction by aperiodic polymer chains: the structure of liquid crystalline copolyesters

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDiffraction by aperiodic polymer chains: the structure of liquid crystalline copolyestersJohn Blackwell, Genaro A. Gutierrez, and Robin A. ChiversCite this: Macromolecules 1984, 17, 6, 1219–1224Publication Date (Print):June 1, 1984Publication History Published online1 May 2002Published inissue 1 June 1984https://doi.org/10.1021/ma00136a019RIGHTS & PERMISSIONSArticle Views122Altmetric-Citations46LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (683 KB) Get e-Alerts Get e-Alerts

Sandwich injection molding of thermotropic copolyesters and filled polyester

AbstractMold filling studies have shown that thermotropic liquid crystalline copolyesters of p‐hydroxybenzoicacid (PHB) and polyethyleneterephthalate (PET) fill by an advancing front mechanism similar to flexible chain polymers. The structure and orientation developed during filling as determined on solid specimens by an etching method, X‐ray diffraction, and shrinkage study on thin microtomed samples appear to be most pronounced at the surface. Based on this information copolymers of 60 and 80 mole percent PHB/PET were co‐injection molded with filled PET under various processing conditions. Because of the low viscosity of the copolyesters, they readily coated filled PET under most processing conditions to give a sheath/core structure. The bending modulus of co‐injection molded bars with as little as 35 percent PHB/PET was as high as the sample consisting of 100 percent liquid crystalline copolyester. Electron micrographs of fracture surfaces revealed excellent adhesion between the two polymers.

The structure of liquid crystalline aromatic copolyesters prepared from 4-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid

X-ray methods have been used to investigate the structure of liquid crystalline copolyesters prepared from 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA). Fibre diagrams and meridional diffractometer scans have been obtained for melt-spun specimens of five HBA/HNA ratios: 25 75 , 30 70 , 50 50 , 58 42 and 75 25 . The data indicate a high degree of axial orientation. The lateral packing is more irregular but the observation of some equatorial and off-equatorial Bragg reflections indicates the presence of some three-dimensional order. The patterns differ in the number and position of the meridional maxima, and these can be predicted accurately by a point model for aperiodic chains of totally random sequence. The sensitivity of the data to monomer ratio is illustrated by calculations across the range of composition from 100% HBA to 100% HNA.

Structural analysis of an oriented liquid crystalline copolyester

Wide angle X-ray scattering from an aligned sample of a random copolyester is presented, together with an analysis of the derived cylindrical distribution function. High local orientational correlation of chains is observed, although the global orientation is less marked. There is some evidence of lateral biaxiality, which is compared with that predicted for theoretical studies of liquid crystalline structures.

The structure of liquid crystalline copolyester fibers prepared from p-hydroxybenzoic acid, 2,6-dihydroxy naphthalene, and terephthalic acid

X-ray methods are being used to investigate the physical structure of high strength melt-spun liquid crystalline aromatic copolyester fibres prepared from the following monomers: p-hydroxybenzoic acid (B), 2,6-dihydroxy naphthalene (N), and terephthalic acid (P). The X-ray data for fibres prepared for B/N/P ratios of 60/20/20, 50/25/25, and 40/30/30 show variations in the positions and intensities of the maxima suggestive of a truly random copolymer structure rather than extensive block copolymer character. We have predicted the intensity distribution on the meridian of the X-ray patterns by modelling random chains by a linear sequence of points separated by distances corresponding to the lengths of the B, N and P residues. The positions of the maxima in the averaged squared Fourier transforms of random monomer sequences are in good agreement with those for the three observed strong meridional intensities, and the calculations reproduce the observed shifts in the positions of these meridionals as the monomer ratio is varied.

Rheological properties of liquid crystalline copolyesters

AbstractCopolyesters were synthesized by modifying poly(ethylene terephthalate) (PET) with p‐acetoxybenzoic acid (PAB) and hydroquinone diacetate/tetrasubstituted (tetramethyl, tetrachloro, and tetabromo) terephthalic acid (HQTS). It was found that the copolyesters containing 33 mol% or higher concentrations of (PAB+HQTS) from mesomorphic liquid crystalline structures. Rheological properties of copolyesters formed of PET, modified with PAB and hydroquinone diacetate/tetramethyl terephthalic acid (HQTM), were measured using a cone‐and‐plate rheometer. It was found that the copolyesters in the mesomorphic state exhibit yield values at a low shear rate (or at a low shear stress), and negative values of first normal stress difference were observed for certain compositions of (PAB+HQTM), over the range of shear rates (or shear stresses) tested.

Thermal Analysis, Mechanical and Rheological Behaviour of Melt Manufactured Polyethylene/Liquid Crystal Polymer Blends

Modification of properties of conventional thermoplastics with thermotropic liquid crystal polymers, from one hand, allows decrease their viscosities, substantially facilitating processing conditions, and, from another hand, allows increase their exploitation properties. Orientation of the labile structure of liquid crystal polymer in extrusion or injection moulding causes specific reinforcement (so-called self-reinforcement) to occur in the blends containing liquid crystal polymer. Up to now the effect of self-reinforcement is mostly investigated in the blends, containing considerable amount of liquid crystal polymer. In this research the effect of minor amounts of liquid crystalline co-polyester modifier on the properties of polyethylene is investigated. Various compositions of laboratory synthesized hydroxybenzoic acid /polyethylene terephtalate copolymer containing polyethylene composites have been manufactured by thermoplastic blending. It has been observed that 1) modulus of elasticity, yield strength and ultimate strength increase with raising the content of liquid crystalline modifier; 2) void content in the investigated polyethylene/liquid crystal copolymer composites is not greater that 1 %; 3) addition of liquid crystalline co-polyester modifier improves arrangement of PE crystalline phase.http://dx.doi.org/10.5755/j01.ms.17.2.483