Polymer-dispersed liquid-crystal polymers (PDLCPs). Morphology of the LCP droplets

“Synthetic blends” of a flexible polymer forming the matrix and a liquid-crystalline polymer (LCP) forming the dispersed phase have been prepared by transesterification of PET with a mixture of sebacic acid (S), 4,4′-diacetoxybiphenyl (B) and 4-acetoxybenzoic acid (H) in the mole ratio 1:1:2. A change of the synthesis conditions causes marked variations of the chemical composition and the morphology of the phases. The SEM investigation of the inner morphology of the LCP droplets of blends consisting of two phases with fairly different aromatic content has shown that the LCP macromolecules are aligned tangentially at the matrix surface boundary, and that the nematic director configuration is toroidal. When the two phases have closer chemical composition, and are therefore supposed to possess improved mutual compatibility, a perpendicular anchoring of the LCP fibrils to the matrix cavity surface, and an axial configuration of the nematic director, are observed. The expected effect of the nematic configuration of the LCP droplets on their ability to deform into fibrils under appropriate flow conditions is preliminarily discussed.     

Rheology of low nematic transition temperature thermotropic liquid crystalline copolyester HBA/HQ/SA

The rheology of a liquid crystalline copolyester of hydroxybenzoic acid, hydroquinone, and sebacic acid (HBA/HQ/SA copolyester) was studied on both a rotational and a capillary rheometer. DSC studies show that the copolyester has a crystalmesophasic and a broad mesophasic-isotropic transition at 170°C and 220°C. Optical texture observations show the mesophase is characterized by line defect textures, which are characteristic of a nematic structure. At 220°C, both isotropic and nematic phases coexist with the latter being the major. As temperature reaches 250°C, a clear dominance of isotropic phase is observed. At this temperature, the nematic phase of irregular shapes randomly disperses within the isotropic matrix. Subsequent rheological studies were thus conducted in crystal/nematic biphase, single nematic phase, nematic/isotropic biphase, and the near single isotropic phase. Dynamic strain sweep measurements show that a linear viscoelastic region exists at all temperatures tested. The maximum strain amplitude for the linear viscoelastic region is found to be highly structure dependent; it is > 100% in the nematic phase, ∼20% in the biphases, and only about 5% in the isotropic phase. The concurrence of curves obtained at different temperatures in a Cole-Cole plot of G′ vs. G″ indicates similar structures in the nematic phase and biphases. Measurements of steady shear viscosity using a rotational rheometer and a roundhole capillary rheometer show that in the nematic phase the copolyester behaves as a shear thinning fluid for a wide shear rate range of 1 ∼ 10,000 s⁻¹, in which the power law index is about 0.6 ∼ 0.8, and the viscosity is < 10 Pa.s at shear rates >1 s⁻¹.     

Processing of thermotropic liquid crystalline polymers and their blends—analysis of an in-situ LCP composite system

Thermotropic LCP/LCP fiber blends were prepared by a combination of meltblending and hot-drawing, using a wholly aromatic copolyester KU-9211 (also called K161 from Bayer A.G.) and an aliphatic containing LCP (liquid crystalline polymer) PET/PHB60 (from Kodak Tennessee Eastman). Morphological evidence, including scanning electron (SEM) and transmission electron microscopy (TEM), showed that the dispersed phase consisted primarily of highly oriented, 0.5 to 2 μm diameter rigid-rods of aromatic fibers imbedded in a matrix of predominantly aliphatic LCP fibrils with diameters in the range of 20 to 50 nm. An interphase of approximately 50 nm strongly bonded the two phases together. The fiber blends were characterized using dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), gas chromotography/mass spectroscopy (GC/MS), and rheological measurements. It appears that the processing conditions employed for melt blending had caused PET/PHB60 to undergo chain scission, thereby creating chemical interactions between the two LCP components during the melt blending process. Differential scanning calorimetry (DSC) thermograms as well as nuclear magnetic resonance (NMR) spectra of the extracted fraction from the mixture of 30 wt% K161/70 wt% PET(PHB60) confirmed the chemical interaction between the two thermotropic liquid crystalline polymers.     

热致性液晶共聚酯(PET/60PHB)粘弹性质与温度之间的关系

聚对苯二甲酸乙二酯/60聚羟基苯甲酸(PET/60PHB)共聚酯熔体是多相体系。本文用Rheometrics Mechanical Spectrometer 605流变仪分相态研究其粘弹性质。发现在液晶、微晶共存态,熔体具有各向同性熔体的流变性质。当熔体中各向异性相占优时,熔体的流变性质与一般聚合物熔体的差别很大。当各向同性相占优时,熔体的流变行为具有两重性。一方面,随着ω增大,G′远离G″;另一方面,η_(?)=η~8(当ω=γ时)。     

Co[poly(ethylene terephthalate-p-oxybenzoate)] and its blends with poly(ethylene terephthalate): Transesterification reaction and fractured surface morphology

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, viz., P28, P46, P64, and P82, were synthesized. These copolyesters were blended with poly(ethylene terephthalate) (PET) at the level of 10 wt % at 293°C for different times. The results from proton NMR analysis reveal that a significant amount of the transesterification has been detected in the cases of PET/P28, PET/P46, and PET/P64 blends. The blending time necessary before any transesterification reaction could be detected depends on the composition of copolyester, e.g., a time less than 3 min is needed for both PET/P28 and PET/P46 blends, while a longer time of 8–20 min is needed for the PET/P64 blend. It is concluded that the higher the mol ratio of the POB moiety in the copolyester is the longer the blending time needed to initiate the transesterification. The degree of transesterification is also increased as the duration of melt blending is prolonged. Two-phase morphology was observed by scanning electron microscopy (SEM) micrographs in all the blends. It was observed that the more similar the composition between the copolyester and PET in the blends is the better the miscibility or interfacial adhesion between the two phases. Moreover, the miscibility can be markedly improved by the duration of melt blending. © 1996 John Wiley & Sons, Inc.     

X-ray and neutron scattering studies of poly(ester carbonate)/poly(ethylene terephthalate) alloys

Quenched blends of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) have a single T_g and behave as single-phase amorphous alloys up to 67% PET. However, small-angle neutron scattering (SANS) data show that the PET molecules are not statistically distributed as classical Gaussian coils in the PEC matrix. In quenched amorphous PEC-rich films (a single phase), PET-rich domains of varying PET concentration appear to be randomly distributed in the PEC matrix, and the excess SANS intensity is attributable to fluctuations in PET concentrations. Wide- and small-angle X-ray scattering data and SANS results show incomplete phase separation of PET and PEC molecules upon annealing. A possible model for annealed blends (two phases) might be domains of folded-chain, crystalline PET with interlamellar amorphous regions composed of a mixture of PET and PEC molecules. These domains are dispersed in the amorphous PEC matrix.     

Viscoelastic properties of a 60 mol% para-hydroxybenzoic acid/40 mol% poly(ethylene terephthalate) liquid crystalline copolyester. I: Effect of temperature history

In this paper, the rheology of a 60 mol% para-hydroxybenzoic acid (PHB)/40 mol% poly(ethylene terephthalate) (PET) copolyester (herein referred to as PHB60/PET40) produced by Unitika Co., Japan, was investigated using viscoelastic property temperature sweeps. In addition to the large-scale hysteresis (super-cooling) of viscoelastic properties that has also been seen with other PHB-based materials, in which it is possible for several PHB linkages to occur side by side along the polymer backbone (most notably the PHB60/PET40 polymer produced by Tennessee Eastman), smaller-scale viscoelastic transitions, one present in heating, and believed to be associated with the partial isotropization of liquid crystalline material, and the other apparent on cooling, occurring at a lower temperature than the first and thought to be associated with the opposite process, were observed. When overall mol% PHB composition along individual chains is considered, the well-defined appearance of the additional smaller-scale rheological transitions seen here is believed to be due to a unimodal composition distribution, rather than a bimodal distribution of which there is increasing evidence in the Tennessee Eastman materials. This difference is believed to be caused by differences in the preparation technique used for the Unitika version of the polymer.     

Dependence of properties of liquid crystalline aromatic copolyesters on monomer sequence-copolyesters derived from terephthalic acid, 2,7-naphthalenediol and p-hydroxybenzoic acid

Summary An aromatic copolyester with the ordered sequence of terephthalic acid (TA)-p-hydroxybenzoic acid (HB)-2,7-naphthalenediol (ND)-p-hydroxybenzoic acid (HB) was prepared and its properties were compared with those of the corresponding random copolyester having the same overall monomer composition. Thermal and crystallizing properties of the two polymers are quite different. The former exhibits significantly higher glass transition and melting temperatures than the latter. The former's degree of crystallinity also is much higher than the latter's. Both polymers are thermotropic and form nematic melts.     

Structural,rheological, and mechanical properties of ternary blends of PEN,PET, and liquid crystalline polymer

Structural, rheological, and mechanical properties of ternary blends of a liquid crystalline copolyester (LCP) composed of p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, poly(ehtylene naphthalate)(PEN), and poly(ethylene terephtalate) (PET) were investigated using capillary rheometry, tensile testing, scanning electron microscopy, and X-ray diffraction. Viscosity-shear rate behavior of the ternary blends is very similar to that of pure polymers and their binary blends. The activation energy of flows of the ternary blends was smaller than those of PEN and PET. Tensile modulus and strength of extruded strands of the blends increased with increasing LCP content. The extruded strands of the blends consist of a crystalline and oriented LCP phase and an amorphous and unoriented PEN/PET blended phase. Tensile mechanical properties and structures of the ternary blends were discussed.     

Co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester. II. X-ray diffraction analysis

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester with different compositions were prepared by the copolymerization of either poly(ethylene terephthalate) (PET) polymer or its oligomer with p-acetoxy-benzoic acid. The polymeric products were subjected to solid-state polymerization for various time intervals. Effects of composition ratio and solid-state polymerization time on X-ray diffraction behavior were investigated. It is found that the effect of transesterification induced by solid-state polymerization causes an increase in crystallinity with the copolyesters having high mol % of p-oxybenzoic acid (POB) moiety and causes a decrease in crystallinity with the copolyesters having high mol % of PET moiety. In general, the crystallinity of copolyesters is first increased and then decreased as solid-state polymerization time proceeds. However, the crystallinity of copolyester having POB/PET = 80/20 composition is increased generally at 4-h solid-state polymerization. It is also found that the crystallinity of copolyesters is decreased by quenching. The copolyester based upon either PET oligomer with 4-h solid-state polymerization or PET polymer with 8-h solid-state polymerization shows the most similar X-ray diffraction pattern with that of Eastman 10109. © 1993 John Wiley & Sons, Inc.     

Effect of polymerization conditions on the microstructure of a liquid crystalline copolyester

The melt polycondensation of mixtures of sebacic acid (S), 4,4′‐diacetoxybiphenyl (B), and 4‐acetoxybenzoic acid (H), carried out for the synthesis of semiflexible liquid–crystalline copolyesters referred to as SBH 1 : 1 : x, has been studied with the aim of clarifying the effect of the reaction conditions on the microstructure and the thermal properties of the products. It has been shown that the segregation of a liquid–crystalline phase within the polymerizing mixture, coupled with the thermodynamic tendency of the two phases to undergo compositional differentiation as polymerization proceeds, is responsible for the formation of blocky, rather than ideally random, copolyesters with poor processibility, when the mole ratio of H to the other two monomers is higher than x ≈ 1.90. The results of this study have shown that this unwanted effect can be considerably limited by carrying out the polycondensation at a relatively high temperature from the very beginning, rather than by the standard technique involving progressive heating of the reaction mixture, thus allowing the production of SBH copolyesters with a higher degree of aromaticity. The results are discussed in terms of the relative rates of the condensation reactions, which are responsible for chain growth, and of the concurrent acidolysis and esterolysis reactions leading to copolyester sequence reorganization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 141–150, 2000     

Characterizations for blends of phosphorus-containing copolyester with poly(ethylene terephthalate)

High molecular weight phosphorus-containing copolyesters, poly(ethylene terephthalate)-co-poly(ethylene DDP) (PET-co-PEDDP)s, were prepared and characterized with the objective of producing a non-halogen flame retardant system for practical applications. The phosphorus-containing copolyester with 30 wt% phosphorus (P30 copolyester) was blended with PET to evaluate their characteristics and flame retardancy. Higher phosphorus content results in lower crystallinity and higher char formation after thermal degradation. The rheological behavior remains similar to that of PET. The P30/PET blend possesses higher crystallization rate than the corresponding phosphorus-containing copolyester containing equal phosphorus content. Thermal and rheological behaviors of P30/PET blends are similar to PET or the phosphorus-containing copolyesters. The P30/PET blends are miscible or compatible base on single T_gs detected by DSC or DMA. The SEM/EDX phosphorus mapping image of the P30/PET blend shows uniform distribution of the phosphorus moieties within the P30/PET matrix, another indication of a compatible or miscible blend between the phosphorus-containing copolyester P30 and PET. Flame retardancy of the P30/PET blend is identical to that of the phosphorus-containing copolyester with identical phosphorus content. Blending of high phosphorus content copolyester with virgin PET provides a feasible method to obtain a flame resistant PET with LOI greater than 28.     

Synthesis of PET-based Liquid Crystalline Copolyesters: Influence of the Overall Degree of Aromaticity on Phase Segregation

Abstract

Novel PET-based copolyesters have been synthesised by transesterification of PET with equimolar amounts of sebacic acid (S) and 4,4′-diacetoxybiphenyl (B) and with varying amounts of 4-acetoxybenzoic acid (H). The structure, the morphology, and the thermal properties of the PET-S-B-H copolyesters have been studied by scanning electron microscopy (SEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS). It has been demonstrated that segregation of a liquid-crystalline phase, during polycondensation, provides the driving force for compositional differentiation, with the result that the final products are “synthetic polymer blends”. The characteristics of PET-S-B-H copolymers have been compared with those of PET-S-Q-H copolyesters having the same molar composition (Q-hydroquinone). It has been shown that the phase segregation is more prominent in PET-S-B-H copolyesters than in PET-S-Q-H polymers of similar molar composition. The influence of the overall degree of aromaticity of the copolyester on the segregation phenomenon has been discussed.     

含两种不同共聚组分改性聚酯的结晶速率

添加己二酸、间苯二甲酸,聚乙二醇对PET进行改性,合成样品。用DSC法研究合成共聚物的等温结晶动力学。结果表明,在所选择的温度范围内,共聚物很好的符合Avrami方程。随温度的升高,共聚物的结晶速度常数K和Avrami指数n逐渐减小,结晶速度G逐渐降低。含2种柔性组分的共聚酯随着一种柔性组分含量的增加,结晶速率G上升;含一种刚性一种柔性组分的共聚酯随刚性组分含量的增加,结晶速率G下降。     

间苯二甲酸共聚酯的流变特性

对聚对苯二甲酸乙二醇酯（ＰＥＴ）中加入间苯二甲酸的无规共聚酯（Ａ２）的流变性能进行了研究。结果表明：Ａ２熔体是切力变稀流体;共聚酯大分子中第三组分的加入,使体系粘度降低,粘流活化能比ＰＥＴ高,表明共聚酯粘度对温度的敏感性较大;同一温度下,共聚酯的非牛顿指数比常规聚酯的高,说明共聚酯的流动偏离牛顿流体的程度小;共聚酯的弹性雷诺指数有所升高,但相对于常规聚酯的变化量不大。     

舒适性改性涤纶树脂的研制

主要论述了将改性剂ＳＩＰＧ、ＰＥＧ与ＢＨＥＴ进行共缩聚制备舒适性改性涤纶。探讨了改善ＰＥＧ热稳定性的途径，以及共聚酯的制备和热性能．结果表明改性共聚酯能在常规聚酯生产装置上制备，所制得的共聚酯的Ｔｇ、Ｔｃ、Ｔｍ、Ｔｄ（起始）均略低于常规ＰＥＴ；但可纺性良好．由该切片制得的纤维有良好的吸湿性和抗静电性，是一种开发高仿真丝绸纺织产品的优良原料．     

Static and dynamic mechanical properties of flame‐retardant copolyester/nano‐ZnCO3 Composites

Novel phosphorus‐containing copolyester nanocomposites were synthesized by in situ polymerization with 2‐carboxyethyl(phenylphosphinic) acid (CEPPA) and nano‐ZnCO₃. The flame retardancy and static and dynamic mechanical properties of poly(ethylene terephthalate) (PET)/nano‐ZnCO₃ composites and phosphorus‐containing copolyester/nano‐ZnCO₃ composites were evaluated with limiting oxygen index measurements, vertical burning testing (UL‐94), a universal tensile machine, and a dynamic mechanical analysis thermal analyzer. The phosphorus‐containing copolyester nanocomposites had higher limiting oxygen indices (ca. 32%) and a V0 rating according to the UL‐94 test; this indicated that nano‐ZnCO₃ and CEPPA greatly improved the flame retardancy of PET. The static mechanical test results showed that the breaking strength, modulus, and yield stress of the composites tended to increase with increasing nano‐ZnCO₃ content; when 3 wt % nano‐ZnCO₃ was added to PET and the phosphorus‐containing copolyester, the breaking strength of the composites was higher than that of pure PET. Dynamic mechanical analysis indicated that the dynamic storage modulus and loss modulus of the PET composites increased markedly in comparison with those of pure PET. However, the glass‐transition temperatures associated with the peaks of the storage modulus, mechanical loss factor, and loss modulus significantly decreased with the addition of ZnCO₃ and CEPPA. The morphologies of the composites were also investigated with scanning electron microscopy, which revealed that nano‐ZnCO₃ was dispersed homogeneously in the PET and copolyester matrix without the formation of large aggregates. In addition, the interfacial adhesion of nano‐ZnCO₃ and the matrix was perfect, and this might have significantly affected the mechanical properties of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Syntheses and properties of the PET‐co‐PEA copolyester

An aliphatic‐aromatic random‐block copolyester of poly(ethylene terephthalate) (PET), and poly(enthylene adipate) (PEA), PET‐co‐PEA, was synthesized via melt polycondensation. The chemical structure of the products were characterized by two kinds of spectroscopic techniques (Fourier transform infrared and ¹H‐NMR). The thermal properties of the copolyester were characterized by thermogravimetry analysis, differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy. It was found that the crystallization ability, melting point, glass transition temperature of the random‐block coplyester decreased apparently. Meanwhile, the tensile strength and hydrolysis performance were measured as well. The result showed that the random‐block copolyesters PET‐co‐PEA displayed excellent properties in elasticity and strength. In addition, the potential degradability was found in hydrolysis measurement. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44967.     

Morphology development and non isothermal crystallization behaviour of drawn blends and microfibrillar composites from PP and PET

Microfibrillar composites (MFC) were prepared from the blends of polypropylene (PP) and poly (ethylene terephthalate) (PET) at a fixed weight ratio of 85/15. The blending of the mixture was carried out in a single screw extruder, followed by continuous drawing at a stretch (draw) ratio 5. The stretched blends were converted into MFC by injection moulding. Scanning electron microscopy (SEM) studies showed that the extruded blends were isotropic, but both phases possessed highly oriented fibrils in the stretched blends, which were generated insitu during drawing. The PET fibrils were found to be randomly distributed in the PP matrix after injection moulding. The non isothermal crystallization behaviour of the as extruded blend, stretched blend and MFC was compared. The analysis of the crystallization temperature and time characteristics revealed that the PET fibrils in the stretched blend had a greater nucleating effect for the crystallization of PP than the spherical PET particles in the as extruded blend and short PET fibrils in the MFC.     

Study on the kinetics of transesterification reaction between poly(ethylene terephthalate) and its copolyesters

Polyethylene terephthalate (PET) was blended with two kinds of co[poly(ethylene terephthalate-p-oxybenzoate)] (POB–PET) copolyester, designated as P46 and P64, respectively. The PET and POB–PET copolyester were combined in the ratios of 85/15, 70/30, and 50/50. The blends were melt mixed in a Brabender Plasticorder at 275, 285, and 293°C for different amounts of time. The transesterification reactions during the melt mixing processes of PET with POB–PET copolyester blends were detected by proton nuclear magnetic resonance analysis. The values of the rate constants are a function of temperature and the composition of blends. The transesterification reactions that may occur during the melt mixing processes have been discussed also. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2727–2732, 1999