New polymer syntheses. LXVI. Copolyester of 4-hydroxybenzoic acid and 3-(4'-hydroxyphenoxy)benzoic acid or 4-(3'-hydroxyphenoxy)benzoic acid

Copolyesters of 4-hydroxybenzoic acid (HBA) and 3-(4'-hydroxyphenoxy)benzoic acid were prepared by two different procedures. Either the acetyl derivatives were polycondensed in bulk at temperatures up to 300°C or they were polycondensed in an inert reactions medium (Marlotherm-S) at 340°C. Two analogous series of copolyesters were synthesized from 4-acetoxybenzoic acid (4-HBA) and 4-(3'-acetoxyphenoxy)benzoic acid. The copolyesters were characterized by elemental analyses, inherent viscosities, ¹H- and ¹³C-NMR spectroscopy, WAXS and DSC measurements, and by optical microscopy. All copolyesters synthesized in solution were highly crystalline materials which were neither meltable nor soluble. Part of the copolyesters prepared by polycondensation in bulk were semi-crystalline, meltable, and soluble. The copolyester derived from 3-(4'-hydroxyphenoxy)benzoic acid proved to be thermotropic forming a nematic melt, whereas the isomeric copolyesters of 4-(3'-hydroxyphenoxy)benzoic acid only formed isotropic melts. © 1993 John Wiley & Sons, Inc.     

Calorimetric studies of poly (2-phenoxyethylacrylate)/5CB mixtures

The thermophysical properties of mixtures of poly (2-phenoxyethylacrylate) and 4-cyano-4′-pentyl-biphenyl, 5CB, are investigated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The polymer has a molar mass M _w = 181 000 g mol ^-1 the low molecular mass liquid crystal exhibits a nematic to isotropic transition at 35.3°C and crystallizes below 23°C. The phase diagram exhibits miscibility gaps in certain regions of temperature and composition where coexisting nematic and isotropic phases are found. From a practical point of view when considering the electro-optical applications of these systems, it proves to be useful to know precisely the amount of small liquid crystal molecules dissolved in the polymer matrix and the concentration of polymer in the nematic phase. The former quantity has a mechanical impact due to a plasticizing effect, an optical impact since it changes the polymer refractive index, while the polymer in the nematic phase shifts the transition temperatures influencing the electro-optical response of the liquid crystal. The present work addresses these important aspects using POM and DSC.     

Twist bend nematic liquid crystals prepared by one-step condensation of 4-(4-Pentylcyclohexyl) benzoic acid and alkyl diol

Twist bend nematic (N_TB)-forming 9OCCHP5 and 11OCCHP5 dimers were synthesised by one-step condensation of 4-(4-pentylcyclohexyl) benzoic acid and alkyl diol with yields as high as 80%. Although each dimer formed the N_TB phase only during the cooling process in a narrow temperature width as large as 4°C, their equiweight mixture formed an N_TB phase during both the heating and cooling processes, displaying elliptical polygonal domains and rope-like optical texture. The N_TB temperature range became wider by 29–38°C and reduced the orientational order parameter significantly from 0.39 to 0.29 with decreasing temperature.     

Synthesis of a New Liquid Crystalline Polymer as a Highly Active β-Nucleator and Its Effect on Melting and Crystallization Behaviors of Isotactic Polypropylene

A new nematic liquid crystalline polymer as a highly active β-nucleator (LCP-N) of isotactic polypropylene (iPP) was synthesized and characterized. The effect of LCP-N on thermal behavior of the iPP was investigated with differential scanning calorimetry. LCP-N showed a melting transition at 85.0°C and a nematic to isotropic phase transition at 278.0°C. The incorporation of LCP-N could lead to substantial changes in the thermal behavior of the iPP. The nucleating activity of LCP-N mainly depended on its content, mesogenic molecular structure, and thermal history of processing. A high content of β-form could be obtained by the combined effect of the optimum LCP-N concentration and crystallization temperature and time. The Φ_β reached 77% when the LCP-N content, crystallization temperature, and crystallization time were 0.4 wt.%, 125°C, and 1 h, respectively.     

Calorimetric studies of poly (2-phenoxyethylacrylate)/5CB mixtures

The thermophysical properties of mixtures of poly (2-phenoxyethylacrylate) and 4-cyano-4'-pentyl-biphenyl, 5CB, are investigated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The polymer has a molar mass M w = 181 000 g mol -1 ; the low molecular mass liquid crystal exhibits a nematic to isotropic transition at 35.3°C and crystallizes below 23°C. The phase diagram exhibits miscibility gaps in certain regions of temperature and composition where coexisting nematic and isotropic phases are found. From a practical point of view when considering the electro-optical applications of these systems, it proves to be useful to know precisely the amount of small liquid crystal molecules dissolved in the polymer matrix and the concentration of polymer in the nematic phase. The former quantity has a mechanical impact due to a plasticizing effect, an optical impact since it changes the polymer refractive index, while the polymer in the nematic phase shifts the transition temperatures influencing the electro-optical response of the liquid crystal. The present work addresses these important aspects using POM and DSC.     

Influence of the order parameter and of the director orientation on the surface tension of free nematic films

Abstract

A radial hydrodynamic flow in the nematic phase of free, suspended cylindrical films of 4-n-heptyl- and decyloxybenzoic acid and in 4,4′-di-n-heptyl-oxyazoxybenzene has been observed. The flow starts about 7°C before the phase transition into the smectic C phase. Under the same experimental conditions such a hydrodynamic flow is not established in free nematic films of 4-n-heptyl-and octyloxy-4′-cyanobiphenyl, 4,4′-dimethoxyazoxybenzene and N-(4-ethoxybenzylidene)-4′-n-butylaniline after the completion of the transition from the isotropic liquid to the nematic phase. The observed hydrodynamic flow is explained by a non-linear temperature dependence of the surface tension.     

The influence of annealing on thermal transitions in a nematic copolyester

Thermal transitions of a glassy, main chain, liquid crystalline, random copolyester, HIQ‐40, have been characterized. HIQ‐40 is made from 40 mol percent p‐hydroxybenzoic acid (HBA) and 30 mol % each of p‐hydroquinone (HQ) and isophthalic acid (IA). This polymer is soluble in organic solvents, permitting the preparation of thin, solution‐cast films that are in a glassy, metastable, optically isotropic state. On first heating of an isotropic HIQ‐40 film in a calorimeter, one glass transition is observed at low temperature (approximately 42°C), and is ascribed to the glass/rubber transition of the isotropic polymer. A cold crystallization exotherm centered near 150°C is observed. This is associated with the development of low levels of crystalline order. A broad melting endotherm is centered at about 310°C; this endotherm marks the melting of crystallites and the transformation to a nematic fluid. A nematic to isotropic transition was not observed by calorimetry. After quenching from the nematic melt, a T_g is observed in the range of 110–115°C and is associated with the glass/rubber transition of the nematically ordered polymer. Annealing optically isotropic films at temperatures above the isotropic glass transition results in the systematic development of axial order. In these annealed samples, T_g increases rapidly until it is near the annealing temperature, then T_g increases more slowly at longer annealing times. In as‐cast films annealed at 120–135°C, the light intensity transmitted through a sample held between crossed polarizers in an optical microscope (a qualitative measure of birefringence and, in turn, axial order) initially increases rapidly and uniformly throughout the sample and, at longer annealing times, approaches asymptotic values that are higher at higher annealing temperatures. The increase in transmitted intensity is ascribed to the development of axial order. The uniform increase in transmitted intensity suggests that ordering occurs by a rather global process and not via a nucleation and growth mechanism. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 505–522, 1999     

Orientation and anchoring effects in stretched polymer dispersed nematic liquid crystals

The induction of liquid crystal orientation through mechanical stretching was investigated for polymer dispersed liquid crystals (PDLCs) by means of infrared dichroism. Using a nematic liquid crystal BL006 and polyacrylic acid as the polymer matrix, it was possible to stretch the PDLC films with BL006 in either the isotropic or the nematic phase. After cooling the films under strain to room temperature, the molecular orientation of BL006 was found to be much higher for films that contained isotropic liquid droplets of BL006 at the time of stretching than for films that had nematic droplets. Stretching PDLC films with isotropic droplets results in no molecular orientation, but the orientation is induced during the subsequent cooling when BL006 goes through the isotropic-to-nematic phase transition. Interestingly for PAA/BL006, the nematic director orients along the long axes of the elongated droplets despite liquid crystal anchoring perpendicular to the polymer interface.     

Orientation and anchoring effects in stretched polymer dispersed nematic liquid crystals

The induction of liquid crystal orientation through mechanical stretching was investigated for polymer dispersed liquid crystals (PDLCs) by means of infrared dichroism. Using a nematic liquid crystal BL006 and polyacrylic acid as the polymer matrix, it was possible to stretch the PDLC films with BL006 in either the isotropic or the nematic phase. After cooling the films under strain to room temperature, the molecular orientation of BL006 was found to be much higher for films that contained isotropic liquid droplets of BL006 at the time of stretching than for films that had nematic droplets. Stretching PDLC films with isotropic droplets results in no molecular orientation, but the orientation is induced during the subsequent cooling when BL006 goes through the isotropic-to-nematic phase transition. Interestingly for PAA/BL006, the nematic director orients along the long axes of the elongated droplets despite liquid crystal anchoring perpendicular to the polymer interface.     

Thermodynamics of nematic phases formed from semiflexible chain polymers

In co[poly(ethylene terephthalate)-p-oxybenzoate] containing 30 mole % oxybenzoate units, the ethylene terephthate units crystallize. The copolymer melts in the temperature range 180–210°C to form a nematic phase which, at a higher temperature, transforms to an isotropic liquid. The latent heat of the first transition is 5 cal/g, and the thermodynamic melting temperature, 247°C, is essentially that expected for a random copolymer of this composition. The nematic → isotropic transition occurs at 244°C, with an enthalpy change of 3.2 cal/g (10% of the heat of fusion of poly(ethylene terephthalate)). We conclude that semiflexible polymers form a nematic phase which is rather highly disordered. The model of the nematic phase treated by Flory is modified to increase its entropy through incorporation of chain bends (which must be correlated in position and direction with those in neighboring molecules). This increases the chain extension, as measured by the fraction (1–f) of collinear chain bonds, required to form the nematic phase. For binary polymer-solvent systems, an appropriate scaling of f values leaves the phase diagram as predicted by Flory's treatment essentially unchanged.     

Thermotropic homopolyesters—VI. A study of polymers based on 4′-hydroxyphenyl-4-hydroxybenzoate

Polyesters were synthesized from 4′-acetoxyphenyl-4-acetoxybenzoate and dibasic acids having 6–12 methylene units using the transesterification procedure described by van Luyen and Strzelecki. These polymers are designated S_n, where n is the number of methylene units in the diacid. The transition temperatures of our polymers stand in reasonable agreement with those reported by Strzelecki and Liébert. The nematic phase extends over a broad temperature range (70–100°), and the biphasic region spans an additional 50°. The texture of the nematic phase is normal for S7-1 having η_inh = 0.30 dl/g, but the other polymers show bright nematic droplets on a darker background. The density of droplets decreases with increasing η_inh in the S7 series, and as η is increased for the other polymer homologues. Only S7-1 exhibits Williams domains on application of an electric field. Quite different properties are found for the polyester having η_inh = 0.80 dl/g prepared from 4′-hydroxyphenyl-4-hydroxybenzoate and the diacid chloride. It melted sharply 24° higher, and its nematic phase showed a normal texture. Moreover, its nematic-isotropic transition appears in the DSC as a sharp peak, and the biphasic region spans only 9°. We believe the transesterification reaction occasionally involves the internal ester linkage in the monomer unit, producing a polymer with no definite repeating unit structure and a distribution of hard segment lengths.     

含甲氧基偶氮苯基元的苯甲酸衍生物的合成与液晶性研究

合成和表征了新型的含有甲氧基偶氮苯液晶基元的3,4,5-三取代苯甲酸衍生物Dn, 研究了结构对其相行为的影响. 结果表明, 在Dn中, 羰基(C=O)和羟基(OH)之间的氢键相互作用存在于结晶态、液晶态和各向同性状态, 在各向同性态时氢键较弱. 通过对其分子结构的调控, 有效地抑制了微相分离和强的分子间的相互作用, 得到了具有单向向列型液晶行为的3,4,5-三取代的苯甲酸衍生物.     

Shift of the nematic–isotropic phase transition temperature in a thin layer of a metallomesogenic complex

The effect of boundaries on the nematic–isotropic phase transition temperature in a melt of a metallomesogenic complex was studied for the first time. This was done by comparison of the electro-optical constant of the isotropic phase with the dielectric and optical anisotropy of the nematic phase on the basis of the Landau–de Gennes theory. In a real experiment, the two liquid phases (nematic and isotropic ones) coexist in a range of several degrees around the transition. According to polarization microscopy data, the phase transition temperature decreases by more than 10°C as the metallomesogen layer thickness is reduced from 200 to 5 μm.     

Influence of the order parameter and of the director orientation on the surface tension of free nematic films

A radial hydrodynamic flow in the nematic phase of free, suspended cylindrical films of 4-n-heptyl- and decyloxybenzoic acid and in 4,4'-di-n-heptyl-oxyazoxybenzene has been observed. The flow starts about 7°C before the phase transition into the smectic C phase. Under the same experimental conditions such a hydrodynamic flow is not established in free nematic films of 4-n-heptyl-and octyloxy-4'-cyanobiphenyl, 4,4'-dimethoxyazoxybenzene and N-(4-ethoxybenzylidene)-4'-n-butylaniline after the completion of the transition from the isotropic liquid to the nematic phase. The observed hydrodynamic flow is explained by a non-linear temperature dependence of the surface tension.     

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

A series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.     

一种液晶共聚酯/粘土纳米复合材料的制备及其相转变温度

一些无机微粒被广泛用做聚合物的增强材料,其中特别引起人们注意的是一种粘土,即蒙脱土（ｍｏｎｔｍｏｒｉｌｌｏｎｉｔｅ）．蒙脱土具有层状结构,其特点一是微粒尺寸小,二是可以和多种单体发生插层聚合反应,给出聚合物／蒙脱土纳米复合材料［１～３］．纳米复合材料指的是其基质中分散相的尺寸至少有一维小于１００ｎｍ数量级的复合材料．由于其纳米尺度效应、大的比表面积以及强的界面相互作用,纳米复合材料的物理力学性能优于相同组分常规复合材料．因此,无论从基本理论研究角度还是从应用角度上看,对聚合物纳米复合材料的研究都…     

Thermotropic homopolyesters. III. Preparation and properties of polymers based on 4′-hydroxyphenyl-4-hydroxycinnamate

Low-molecular-weight 4′-acetoxyphenyl-4-acetoxyoinnamate, as well as several polyesters synthesized from this monomer and aliphatic dibasic acids, exhibit thermotropic nematic phases. DSC heating curves for all of the polymers exhibit multiple transitions. The amount of crystallinity of these polymers at room temperature is small and the degree of order along the chain axis in the crystalline phase is poor. For the lower homologues the nematic phase exists over a broad temperature range of approximately 100°C. The polyester from chiral (+)-3-methyl adipate forms a thermotropic cholesteric phase. Both the diacetoxy monomer and azelate polymers of low molecular weight adopt the homeotropic texture on glass slides, but with increasing molecular weight the planar texture becomes preferred. Investigation of the effects of electric fields in the conduction regime upon the nematic phase of the diacetoxy monomer revealed that Williams domains are formed only with difficulty. In most cases, a stationary pattern appeared instead. At higher voltage the dynamic scattering mode (DSM) was obtained, and above this a field-induced transition to the isotropic phase. The azelate polyesters exhibited Williams domains and the DSM in the conduction regime. The formation time for Williams domains was fairly short for polymers having η_inh < 0.44 dL/g, but increased to 80 min when η_inh = 0.68 dL/g. The DSM was only observed for polymers having η_inh < 0.61 dL/g. For these polymers the critical frequency separating the conduction and dielectric regimes exhibits a stronger temperature dependence than that of low-molecular-weight nematogens. A new instability pattern is reported for the azelate polyesters in the dielectric regime.     

Liquid crystalline phase transitions in hexakis(4-(4'-heptyloxy)biphenoxy)cyclotriphosphazene

Hexakis(4-(4'-heptyloxy)biphenoxy)cyclotriphosphazene (HHCP) was synthesized from hexachlorocyclotriphosphazene and 4-heptyloxy-4'-hydroxybiphenyl. The mesogenicity of HHCP was studied by DSC, FTIR spectroscopy and polarizing microscopy. Enantiotropic smectic C and nematic phases were observed between 450 and 455 K and 455 and 456 K, respectively, on heating, and between 456 and 455 K (nematic) and 455 and 440 K (smectic C) on cooling from the isotropic liquid phase. The introduction of the heptyloxybiphenoxy groups as side chains into cyclotriphosphazene has generated the liquid crystalline phase. FTIR spectroscopy showed that the P=N and P-O-(C) stretching vibrations converted to lower frequencies from 1224 to 1210 cm^-1 and from 920 to 910cm^-1, respectively, at the crystalline (C)-S_c phase transition. This result suggests that the state of the cyclotriphosphazene ring dramatically changes near the C-S_c phase transition.     

Synthesis and characterization of liquid crystalline copolyester of 4-hydroxy-2,3,5,6-tetrafluorobenzoic acid with 6-hydroxy-2-naphthoic acid

4-Hydroxy-2,3,5,6-tetrafluorobenzoic acid/6-hydroxy-2-naphthoic acid copolymers (FHBA/HNA copolymer) with different copolymer compositions were prepared and the influence of FHBA residue on the thermal properties and structures of the copolymers were investigated. Introduction of FHBA decreased the crystal/nematic phase transition temperatures(T_CNs) of the FHBA/HNA copolymers. T_CNs of the copolymers were in the temperature range between 200 and 250°C, depending on the copolymer composition. They are approximately 40°C lower than those of 4-hydroxybenzoic acid/HNA copolymers. FHBA/HNA copolymers exhibited low crystallinity, and annealing treatment hardly influenced the crystalline natures. FHBA residue possibly interferes with the recrystallization during annealing. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 413–419, 1998     

New polymer syntheses 16. LC-copolyesters of 3-(4-hydroxyphenyl) propionic acid and 4-hydroxy benzoic acids

The polycondensation of 3-(4-hydroxy phenyl)-propionic acid, 4-Hypp, by means of acetanhydride or acetylchloride was conducted either in the presence or in the absence of a liquid reaction medium. DSC measurements, polarizing microscope, and X-ray diffraction studies indicate poly(4-Hypp) possesses at about 215°C a reversible first order transition between two solid phases. Copolyesters containing various mole ratios of 4-Hypp and 4-hydroxy benzoic acid, 4-Hybe, were prepared by bulk condensation with acetanhydride at 320°C. At 4-Hypp/4-Hybe ratios less than 1.0:1.5 the reaction product was heterogeneous, containing crystals of pure poly(4-Hybe). Neither increasing the reaction time nor the variation of the transesterification catalyst resulted in an entirely homogeneous copolyester. However, for 4-Hypp/4-Hybe ratios greater than 1.0:1.5, ¹³C NMR spectra indicate perfectly random sequences. Also, terpolyesters containing 3-chloro-4-hydroxy- or 3,5-dichloro-4-hydroxy-benzoic acid were heterogeneous with less than 30 mol % 4-Hypp. DSC measurements revealed for all polyesters a glass transition in the range of 55–78°C. Temperature dependent X-ray diffraction studies confirm that the solid phase is a s.c. LC-glss. Correspondingly low heat distortion temperatures were found by thermomechanical analyses. The copolyesters display under the polarizing microscope LC-phase up to temperatures of 450–480°C, where rapid thermal degradation prevents further investigations. In the case of the 4-Hypp/4-Hybe 1:1 copolyester, the LC-phase extends over a temperature range of about 400°C. TGA measurements indicate beginning thermal degradation at temperatures between 350 and 380°C.