Semi-rigid Polyesters Research Articles

Thermodynamic properties of a series of semi-rigid polyesters

The thermodynamic properties of a series of poly[oxy(2,2′ dialkylpropane-1,3-diyl) carboxybisphenyl-4,4′-dicarbonyl] have been investigated by P-V-T-measurements as a function of the length of one side-chain at the 2′-position.

Liquid crystalline semirigid polyesters based on phenylstilbene analogues of 1,3,4‐thiadiazole

Semirigid polyesters composed of phenylstilbene analogues of 1,3,4‐thiadiazole, 2‐(2‐phenylethenyl)‐5‐phenyl‐1,3,4‐thiadiazole (PEPT), linking an octamethylene chain at different disubstituted (3,3′‐, 3,4′‐, 4,3′‐ and 4,4′‐) positions, were prepared from four diphenols of the PEPT and sebacoyl chloride by interfacial polycondensation. The effect of polymer structure on thermotropic liquid crystalline (LC) and optical properties is discussed. Differential scanning calorimetry (DSC) measurements, optical texture observations and powder X‐ray diffraction patterns showed that the polymer linking the octamethylene chain at the 4,4′‐position (4,4′‐PEPT) has a linear structure and forms an enantiotropic nematic LC phase. Polymers linking the octamethylene chains at the 4,3′‐ (4,3′‐PEPT), the 3,4′‐ (3,4′‐PEPT) and the 3,3′‐positions (3,3′‐PEPT) positions have a less linear structure and display monotropic smectic phase or no LC phase. Solution and solid‐state UV‐visible and emission spectra indicated that the polyesters exhibit absorption maxima due to the PEPT moieties and fluoresce blue light, but low or no quantum efficiencies were recognized. The polyesters emitted weak polarized fluorescent light at room temperature.

チアジアゾールのジスチリルベンゼン類似物とオリゴエチレンオキシド鎖から成る蛍光性液晶ポリエステル

Semi-rigid polyesters composed of distyrylbenzene analogues of 1, 3, 4-thiadiazole (TD) and oligoethylene oxide chains (m=3, 5, 6) were synthesized and their liquid crystalline (LC) and optical properties were evaluated. The resulting polyesters not only formed stable thermotropic LC smectic phase, but also fluoresced blue light in chloroform solutions and showed bluish-green fluorescent emission in solid states based on the TD analogue.

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

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

Thermotropic liquid-crystalline polymers containing five-membered heterocyclic groups. X. Relationships between structures of semirigid polyesters based on three disubstituted 2,5-diphenyl-1,3,4-thiadiazoles and thermotropic liquid-crystalline and optical properties

Thermotropic liquid-crystalline (LC) semirigid polyesters based on three terphenyl analogues of 1,3,4-thiadiazole (2,5-diphenyl-1,3,4-thiadiazole)s (DPTD) linking undecamethyleneoxy chain at different substituted positions were synthesized from three disubstituted (4,4′-, 3,4′-, and 3,3′-) dioxydiundecanols of DPTD and four diesters, and the relationships between polymer structures and LC and optical properties were investigated. DSC measurements, texture observations, and wide-angle X-ray analyses revealed that the polymers composed of DPTD moiety having a more linear molecular structure and 1,4-phenylene unit or short aliphatic chain tend to exhibit LC smectic C and/or A phases. The following observations were made: (1) the emergence of smectic C and/or A phases in all the polymers on the basis of 4,4′-disubstituted DPTD, (2) formation of enantiotropic smectic C and/or A phases in the polymers containing a 1,4-phenylene unit in the main chain, (3) formation of a more stable smectic C phase in the polymers having a short aliphatic [(CH2)4] chain, and (4) a decrease of the mesomorphic property of the polyesters in the order of 4,4′-DPTD > 3,4′-DPTD > 3,3′-DPTD. Solution and solid-state ultraviolet–visible and photoluminescent spectra indicated that all the polyesters display maximum absorbances and blue emissions arising from the DPTD moiety, whose peak maxima were shifted to lower wavelengths in the order of 4,4′-DPTD > 3,4′-DPTD > 3,3′-DPTD as well as the aforementioned LC property. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2676–2687, 2003

Elastic constant anisotropy and disclination interaction in nematic polymers I. Apparent variation in anisotropy

This work presents the effect of elastic anisotropy and disclination interaction on wedge disclinations in the nematic phase of thermotropic polymers, by combining experimental measurements, (this paper part I), with numerical simulation (part II [1]). In part I, the decoration provided by spontaneous banded texture gives much information about the defect structure of polymeric nematics. Working with a semi-rigid polyester, the optical images of +1/2 disclinations revealed by banding enable the distortion to be determined as a function of polar coordinates from the cores. Continuum theory allows the apparent elastic anisotropy, ϵ , of bend and splay constants of the copolyester to be determined from the distortion measurement. The values of ϵ , are seen to vary greatly in the range −1 to +1 between different +1/2 disclinations in the same sample. The statistics of the measurement indicate that the distribution of the values of ϵ is random. The implication of these observations is that the curvature of wedge disclinations is affected not only by the elastic anisotropy of the material, but also by other factors. The possible reasons are discussed: the interaction of neighbouring disclinations has been numerically analysed to be the predominant factor in [1]. This work also implies that values of the intrinsic elastic anisotropy obtained by measuring the distortion of individual wedge disclinations must be viewed with some circumspection.

Phase transitions in laterally substituted semi-rigid polyesters

The thermal transitions of a series of polyesters of the type poly[oxy(2,2′-dialkyl-propane-1,3-diyl)carboxybisphenyl-4,4′-dicarbonyl] have been investigated using Differential Scanning Calorimetry. Crystallization as well as the glass-transition were studied with emphasis on the crystallization of the dimethylpropane derivative. The general tendency to show stable mesophases decreases with increasing length of the lateral alkyl substituents attached to the spacer. The glass transition is definitely not second order and more order parameters are required to describe the glassy state.

Thermotropic liquid crystalline polymers containing five-membered heterocyclic groups VIII. Synthesis, and liquid crystalline and photoluminescent properties of semi-rigid polyesters based on a distyrylbenzene analogue of 1,3,4-thiadiazole

New semi-rigid polyesters composed of the distyrylbenzene analogue of 1,3,4-thiadiazole, 2,5-bis(2-phenylethenyl)-1,3,4-thiadiazole and aliphatic (dodeca-, deca- and octamethylene) chains were prepared by high temperature solution polycondensation; their liquid crystalline (LC) and photoluminescent properties were investigated. Differential scanning calorimetry, polarizing microscopy and powder X-ray diffraction show that the polyesters having both dodeca- and decamethylene chains form a thermotropic smectic C phase and a lyotropic LC phase in trifluoroacetic acid, but the polyester containing octamethylene chains only exhibits a thermotropic smectic C phase. Solution and solid state absorption and fluorescent spectra indicate that all the polyesters in this work display absorption maxima based on the 2,5-bis(2-phenylethenyl)-1,3,4-thiadiazole moiety, emitting blue light in HFIP solutions and bluish-green light in solids; the Stokes shifts are 80.1-80.7 nm in solution and 74.2-87.2 nm in the solid state.

Thermodynamic properties of a series of semi-rigid polyesters

The thermodynamic properties of a series of poly[oxy(2,2′ dialkylpropane-1,3-diyl) carboxybisphenyl- 4,4′-dicarbonyl] have been investigated by P-V-T-measurements as a function of the length of one side-chain at the 2′-position.The pressure-and temperature dependence of the specific volume was recorded from room temperature to 300 °C and from ambient pressure to 200 MPa. Depending on the chemical constitution glass-transitions, enantiotropic and monotropic mesophase transitions were identified. A pressure-induced transition in the glass was observed in one case and unusual behaviour of the volume for a first order mesophase transition in another case.

Synthesis and Properties of Liquid-Crystalline Semi-Rigid Polyesters Based on Isophthalates of Nitro- or Methoxyazobenzene and Dioxydiundecanols of Biphenyl or 2,5-Diphenyl-1,3,4-Thiadiazole

Semi-rigid polyesters having nitro- or methoxyazobenzene unit in the side chain and calamitic mesogen (biphenyl or 2,5-diphenyl-1,3,4-thiadiazole unit) in the main chain were prepared by melt polycondensation of diethyl isophthalates composed of the azobenzene units with three dioxydiundecanol derivatives of the mesogenic units and their thermotropic liquid crystalline (LC) and optical properties were evaluated. The assigned structures of polymers were characterized by FTIR and 13 C NLR spectroscopy and elemental analyses. Differential scanning calorimetry (DSC) measurements, optical texture observation, powder X-ray analyses and miscibility tests indicated that most of the polyesters form thermotropic LC (smectic B, C, and E) phases and the polymer having the nitroazobenzene in the side chain forms the most stable LC phase. Absorption spectra of the polyesters in solutions and in films showed absorption maxima based on the azobenzene or the 2,5-diphenyl-1,3,4-thiadiazole unit, whereas their emission spectra were not observable.

Semi-rigid polyesters analysed using the“strong-fragile” concept

Semi-rigid polyesters from diphenyl dicarbonic acid and some branched propyl and butyl spacers have been investigated using Differential Scanning Calorimetry. From Δc p at Tg and the determination of the fragility index m, we studied the strong-fragile behaviour of these materials. All the samples appear thermodynamically strong and kinetically fragile. A comparison of these results with those obtained from glass-forming liquids leading to linear polymers -such as PET, PCT, PEN or poly-methyl (a-n-alkyl) acrylates- shows that a modification of the polymer rigidity leads to change the fragility index m and the Acp at the glass transition.

Direct observation of director fields of disclinations in the nematic mesophase of a main chain thermotropic aromatic polyester by surface microcrack decoration

For a main chain thermotropic aromatic polyester with a flexible spacer, Cr 194 N 245 I (°C), the director fields around disclinations in the nematic mesophase can be decorated by both the solidification-induced band texture and surface microcracks. Director fields of various types of disclinations, including inversion walls, in the nematic mesophase of this semi-rigid polyester have been observed directly by polarizing optical microscopy. It was found that when the polymer was pre-sheared in the nematic state and then quenched to room temperature, a shear-induced band texture was observed, which relaxed slowly during annealing at 200°C, and then on quenching the solidification-induced band texture and surface microcracks appeared, displaying the pattern of the disclination fields. Pre-shearing is a necessary condition for the appearance of microcracks. On annealing, disclinations of various types were generated, quite often connected by inversion walls in the direction of pre-shearing. In some areas of the specimen where the shear-induced bands had not been completely relaxed during annealing, the shear-induced band texture was shown by the birefringence and surface microcracks to have a supermolecular structure of sinusoidal chain fibrils.

Thermotropic liquid-crystalline polymers having five-membered heterocycles as mesogens, 6. Synthesis, thermotropic liquid-crystalline and photoluminescent properties of novel semi-rigid polyesters based on a terphenyl analogue of 1,3,4-thiadiazole

Novel semi-rigid thermotropic liquid-crystalline (LC) polyesters containing terphenyl analogue of 1,3,4-thiadiazole in the main chain were synthesized by melt polycondensation of a dioxydiundecanol derivative of 2,5-diphenyl-1,3,4-thiadiazole with four aromatic diesters, and their structures were confirmed from FTIR, 13C NMR spectra and elemental analyses. Differential scanning calorimetry (DSC) measurements and polarizing microscope observations of textures showed that all the polymers form enantiotropic LC (smectic) phases. UV-vis and photoluminescence (PL) spectra indicated that polyesters without nitro groups display maximum absorbances arising from 1,3,4-thiadiazole moiety and blue-emission maxima, the Stokes shifts being 69.5–79 nm in solution and 54–97 nm in the solid state.

Thermotropic liquid-crystalline polymers having five-membered heterocycles as mesogens, 6. Synthesis, thermotropic liquid-crystalline and photoluminescent properties of novel semi-rigid polyesters based on a terphenyl analogue of 1,3,4-thiadiazole

Novel semi-rigid thermotropic liquid-crystalline (LC) polyesters containing terphenyl analogue of 1,3,4-thiadiazole in the main chain were synthesized by melt polycondensation of a dioxydiundecanol derivative of 2,5-diphenyl-1,3,4-thiadiazole with four aromatic diesters, and their structures were confirmed from FTIR, 13C NMR spectra and elemental analyses. Differential scanning calorimetry (DSC) measurements and polarizing microscope observations of textures showed that all the polymers form enantiotropic LC (smectic) phases. UV-vis and photoluminescence (PL) spectra indicated that polyesters without nitro groups display maximum absorbances arising from 1,3,4-thiadiazole moiety and blue-emission maxima, the Stokes shifts being 69.5–79 nm in solution and 54–97 nm in the solid state.

Thermotropic Liquid-Crystalline Polymers Having Five-Membered Heterocycles as Mesogens V. Relationship between Polymer Structure and Thermotropic Liquid-Crystallinity in Semi-Rigid Polyesters Composed of Twin 2-Phenyl-1,3,4-thiadiazoles Having Central Aliphatic Chains

Semi-rigid polyesters based on twin biphenyl analogues of 1,3,4-thiadiazole (2-phenyl-1,3,4-thiadiazoles) with hepta- and octamethylene chains in the central part were synthesized by melt polycondensation of bismethyl ester derivatives of twin 2-phenyl-1,3,4-thiadiazole with α, ω-alkylenediols and dioxydialcohol derivatives of biphenyl. The relationship between polymer structure and thermotropic liquid-crystallinity (LC) was investigated by differential scanning calorimetry (DSC), polarizing microscope observations, miscibility tests and temperature-dependent X-ray analysis. All the polymers derived from α, ω-alkylenediols appeared to form enantiotropic or monotropic nematic phase independent of the lengths of aliphatic chains. Among the polyesters containing the biphenyl unit, most polymers with octamethylene segment between the twin 2-phenyl-1,3,4-thiadiazoles showed the nematic phase, but polymers composed of the twin biphenyl analogue having the central heptamethylene chain had no LC melts.

Novel Thermotropic Liquid Crystalline Polymers: Rigid and Semi-Rigid Polymers with Flexible Side Chains

Abstract Two series of rigid and semi-rigid polyesters and polyamids with flexible side chains were prepared by solution and melt as well as interfacial polycondensation of 2,5-dialkoxyterephthaloyl chloride with various diols and diamines. Thermal behaviors of the polymers were studied by DSC, TGA and polarizing microscopy. The results indicated that only rigid polymer systems form nematic mesophase. However, none of the semi-rigid polymers formed nematic melts. The structures of both polyesters and polyamides were also examined by the wide angle X-ray scattering. Analysis of sharp reflection, appeared at the lower angle of X-ray diffractograms of rigid polymers, suggested that rigid polymers crystallized to form a layered structure in the solid state.