The relationship between the structures of semi-rigid homo- and copolyesters based on 5,5'-diphenyl-2,2'-bis(1,3,4-thiadiazole)s and their liquid crystalline and optical properties

New semi-rigid homo- and copolyesters composed of the quaterphenyl analogue of 2,2'-bis(1,3,4-thiadiazole) (BTD), 5,5'-diphenyl-2,2'-bis(1,3,4-thiadiazole) (DBTD), were prepared by high temprature solution polycondensation of monomers, 3,3'- and 4,4'-dioxydiundecanol derivatives of DBTD with four dimethyl esters, and their liquid crystalline (LC) and optical properties were investigated. DSC measurements, texture observations using a polarizing microscope equipped with a hot stage, and powder X-ray diffraction showed that the homopolymers containing the 4,4'-DBTD unit form more stable LC phases than those having the 3,3'-DBTD unit. The 4,4'-DBTD-containing polymers and the 3,3'-DBTD unit-poor copolymers, except for the 3,3'-DBTD unit-rich copolymers and the 3,3'-DBTD-containing homopolymers (which formed highly ordered smectic or crystal mesophases), displayed a thermotropic LC smectic C phase. Solution and solid state UV-vis and photoluminescent (PL) spectra showed that the polyesters display miximum absorbances and bluish-green or blue emission based on the DBTD unit, where the Stokes shifts were observed. The peak positions in the UV-vis and the PL spectra of homopolymers composed of the 4,4'-DBTD unit were at higher wavelengths than those in the corresponding 3,3'-DBTD-containing homopolymers, due to its more conjugated structure. In the copolymers the peak maxima were shifted to shorter wavelengths with the increase of 3,3'-DBTD content.     

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     

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.     

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.     

Thermotropic liquid‐crystalline polymers having five‐membered heterocycles as mesogens, 3. New semi‐rigid thermotropic liquid‐crystalline polyesters based on a twin biphenyl analogue of 1,3,4‐thiadiazole

New semi‐rigid thermotropic liquid crystalline (LC) polyesters containing a twin biphenyl analogue of 1,3,4‐thiadiazole in the main chain were prepared by melt polycondensation of the bismethyl ester derivative of twin 2‐phenyl‐1,3,4‐thiadiazole having a decamethylene segment in the central part with three aliphatic diols. The polymer with an octamethylene segment forms a monotropic nematic phase and those with decamethylene and dodecamethylene segments form enantiotropic smectic phases, although their LC states are unstable. The melting and isotropization temperatures decrease with increasing length of alkylene spacers.     

Synthesis and optical and electrochemical properties of thermotropic,liquid‐crystalline,semirigid copolyesters based on 2,5‐diphenyl‐1,3,4‐thiadiazole units

Novel thermotropic liquid‐crystalline (LC) copolyesters were prepared with three disubstituted (4,4′‐, 3,4′‐, and 3,3′‐) dioxydiundecanol derivatives of terphenyl analogues of 1,3,4‐thiadiazole [2,5‐diphenyl‐1,3,4‐thiadiazole (DPTD)], and their optical and electrochemical properties were examined. Their structures were characterized with Fourier transform infrared, ¹H NMR spectroscopy, and elemental analyses. The thermal and mesomorphic properties of the copolyesters were investigated with differential scanning calorimetry measurements, polarized microscopy observations, and X‐ray analyses; the data suggested that these copolymers formed LC smectic or nematic phases. The mesomorphic tendency decreased in the following order: 4,4′‐DPTD and 3,4′‐DPTD copolyesters > 4,4′‐DPTD and 3,3′‐DPTD copolyesters > 3,4′‐DPTD and 3,3′‐DPTD copolyesters. Solution and solid‐state ultraviolet–visible (UV–vis) and photoluminescence spectra indicated that the copolyesters displayed maximum absorbances and blue emissions according to the DPTD unit; the peak maxima of absorption and emission spectra of the copolyesters shifted to lower wavelengths in the aforementioned order for the LC properties. Cyclic voltammetry measurements indicated that the electrochemical band gaps of the polyesters estimated from the onset of reduction and oxidation processes were almost the same as the optical band gaps determined from the solid‐state UV–vis spectral data. The DPTD unit enhanced the hole‐injection barrier and improved the charge‐injection balance in these polyesters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1511–1525, 2005     

Synthesis and characterization of new polyhydrazides based on 2,5-bis(mercapto-acetichydrazide)-1,3,4-thiadiazole moiety

New interesting class of novel polyhydrazides containing 1,3,4-thiadiazole moieties in the main chain was synthesized. A solution polycondensation technique was used in the synthesis of these polymers. The new monomer namely: 2,5-bis(mercapto-acetichydrazide)-1,3,4-thiadiazole III was synthesized from the nucleophilic replacement of 2,5-dimercapto-1,3,5-thiadiazole I with ethylchloroacetate, followed by hydrazinolysis. The model compound VII was synthesized from the monomer 2,5-bis(mercapto-acetichydrazide)-1,3,4-thiadiazole III with benzoyl chloride and characterized by ¹H- NMR, IR, and elemental analyses. The polyhydrazides were synthesized from the polymerization of monomer III with 4,4^′-biphenic, 3,3^′-azodibenzoyl, 4,4^′-azodibenzoyl dichlorides. These polymers were characterized by elemental and spectral analyses, viscometry and solubility. The thermal properties of these polymers were determined by thermal gravimetric analyses, and differential thermal analysis, and correlated with their structure. The crystallinity of some polymers was tested by X-ray analyses.     

Preparation and properties of new wholly aromatic polyesters containing a terphenyl analogue of 1,3,4-thiadiazole in the main chain

Novel wholly aromatic polyesters 8 containing a terphenyl analogue of 1,3,4-thiadiazole (2,5-diphenyl-1,3,4-thiadiazole) in the main chain were synthesized by high-temperature solution polycondensation of a diacyl chloride derivative of 2,5-diphenyl-1,3,4-thiadiazole 6 with four hydroquinones 7 in 1-chloronaphthalene. These polymers 8 are insoluble in most organic solvents and decompose very rapidly above 400°C in air without showing thermotropic liquid crystalline melts.     

Fully aromatic thermotropic liquid crystalline polyesters of 3,4′-dihydroxybenzophenone

A series of fully aromatic, thermotropic polyesters, derived from 3,4′-dihydroxybenzophenone and various aromatic dicarboxylic acids, was prepared by the high-temperature solution polycondensation method and examined for thermotropic behavior by a variety of experimental techniques. The aromatic dicarboxylic acids used in this study were 2,6-naphthalenedicarboxylic acid, 4,4′-bibenzoic acid, and terephthalic acid. The two homopolymers of 3,4′-DHB with either 2,6-NDA or 4,4′-BBA formed nematic LC phases at 285°C and 255°C and also exhibited isotropization transitions (T_i) at 317°C and 339°C, respectively. The copolymer of 3,4′-DHB with 50% TA and 50% 2,6-NDA also formed a nematic LC phase and had a broader range of LC phase than that of its respective homopolymers. Two other copolymers of 3,4′-DHB, both containing 50% 4,4′-BBA, also formed nematic LC phases at low T_f values. All of the thermotropic polyesters had high thermal stabilities. © 1994 John Wiley & Sons, Inc.     

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 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.     

Thermal stability and degradation behavior of novel wholly aromatic azopolyamide-hydrazides

Thermal stability and degradation behavior of a series of novel wholly aromatic polyamide-hydrazides containing azo groups in their main chains have been investigated in nitrogen and in air atmospheres using differential scanning calorimetry (DSC), thermogravimetry (TG), infrared spectroscopy (IR) and elemental analysis. The influences of controlled structural variations and molecular weight on the thermal stability and degradation behavior of this series of polymers have also been studied. The structural differences were achieved by varying the content of para- and meta-substituted phenylene rings incorporated within this series. Azopolyamide-hydrazides having different molecular weights of all para-substituted phenylene type units were also examined. The polymers were prepared by a low temperature solution polycondensation reaction of p-aminosalicylic acid hydrazide [PASH] and an equimolar amount of 4,4′-azodibenzoyl chloride [4,4′ADBC] or 3,3′-azodibenzoyl chloride [3,3′ADBC] or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide [DMAc] containing lithium chloride as a solvent at −10 °C. All the polymers have the same structural formula except the mode of linking phenylene units in the polymer chain. The results clearly reveal that these polymers are characterized by high thermal stability. Their weight loss occurred in three distinctive steps. The first was small and assigned to the evaporation of absorbed moisture. The second was appreciable and was attributed to the cyclodehydration reaction of the hydrazide groups into 1,3,4-oxadiazole rings by losing water, combined with elimination of azo groups by losing molecular nitrogen. This is not a true degradation but rather a thermo-chemical transformation reaction of the azopolyamide-hydrazides into the corresponding polyamide-1,3,4-oxadiazoles. The third was relatively severe and sharp, particularly in air, and corresponded to the decomposition of the resulting polyamide-1,3,4-oxadizoles. In both degradation atmospheres, the improved resistance to high temperatures was always associated with increased content of para-phenylene moieties of the investigated polymer. The better thermal stability of the wholly para-oriented type of polymer relative to the other polymers is attributed to its greater chain symmetry which is responsible for its greater close packing, rod-like structure and consequently stronger intermolecular bonds which would be more difficult to break and therefore more resistance to high temperatures. Further, with exception of 160-200 °C temperature range, where the lower molecular weight samples showed considerable weight losses which were most probably due to hydrogen bonded DMAc, all the wholly para-oriented phenylene type of polymer samples behaved similarly regardless of their respective molecular weight. This seems to indicate that the structural building units responsible for high thermal stability of the polymers are their characteristic groups, such as aromatic moieties, amide and hydrazide linkages in case of azopolyamide-hydrazides, and 1,3,4-oxadiazole rings, aromatic nuclei and amide linking bonds in case of polyamide-1,3,4-oxadiazoles, rather than the longer chain segments.     

Liquid crystalline homopolyesters having main chain calamitic mesogens and one or two side chain azobenzene moieties in the repeat units

Combined semi-rigid homopolyesters, containing both main chain calamitic mesogens and one or two side chain azobenzene units separated by aliphatic (hexamethylene, octamethylene and decamethylene) chains in the polymer repeat units, were prepared and their liquid crystalline properties characterized. Polyesters having two side chain azobenzene units and a main chain biphenyl moiety showed a higher ordered smectic B or smectic F phase, whereas the other polymers containing a main chain 2,5-diphenyl-1,3,4-thiadiazole unit and one or two side chain methoxyazobenzene units formed a smectic C phase despite the presence of different mesogens in the main and side chains. This is probably due to the compact molecular chain-packing and intra- and intermolecular interactions between the polymer backbones and the two azobenzene units.     

含硫杂环桥联的高折射率聚酰亚胺的合成与性能

合成了两种含硫杂环桥联的芳香族二胺单体,2,5-双(4-氨基苯硫基)噻吩(APST)以及2,5-双(4-氨基苯硫基)-1,3,4-噻二唑(BATT).分别采用这两种二胺单体与含硫二酐单体4,4′-双(3,4-二羧基苯硫基)二苯硫醚二酐(3SDEA)通过两步聚合法制备了两种聚酰亚胺(PI),PI-1(3SDEA-APST)与PI-2(3SDEA-BATT).系统研究了含硫杂环对PI耐热性能以及光学性能的影响.研究结果表明,与苯环相比,含硫杂环的引入在一定程度上降低了PI薄膜在可见光区(400～700nm)的光学透明性以及耐热稳定性.PI-1与PI-2薄膜的起始热分解温度(T5%)分别为418℃与466℃.PI薄膜在450nm处的透光率低于50%.但是含硫杂环的引入可以显著提高PI薄膜的折射率.PI-1与PI-2的折射率分别为1.7527和1.7490.两种材料的双折射均小于0.01.     

Novel self-dyed wholly aromatic polyamide–hydrazides covalently bonded with azo groups in their main chains

Thermal characteristics of several novel self-dyed wholly aromatic polyamide–hydrazides covalently bonded with azo groups in their main chains and containing o-hydroxy group as a substituent group in the aryl ring of the aminohydrazide part of the polymers have been investigated in nitrogen and in air atmospheres using differential scanning calorimetry, thermogravimetric analyses, infrared spectroscopy, and elemental analyses. The effect of introducing different predetermined proportions of para- and meta-phenylene moieties into the backbone chain of the polymers on their thermal characteristics has been evaluated. Azopolymers having different molecular masses of all para-oriented phenylene type units were also thermally characterized. These polymers were prepared by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or mixtures of various molar ratios of 4,4′ADBC and 3,3′ADBC in anhydrous N,N-dimethyl acetamide containing 3 % m v^?1 LiCl as a solvent at ?10 °C. All the polymers have the same structural formula except the mode of linking phenylene units in the polymer chain. The content of para- and meta-phenylene moieties was varied within these polymers so that the changes in the latter were 10 mol% from polymer to polymer, starting from an overall content of 0–100 mol%. The results reveal that these polymers are characterized by high thermal stability and could be cyclodehydrated into linear aromatic polymers with alternating 1,3,4-oxadiazole and benzoxazole structural units within the same polymer approximately in the region of 200–480 °C, either in nitrogen or in air atmospheres by losing water from the hydrazide and o-hydroxybenzamide groups, respectively. Along with the cyclodehydration, the polymer may lose molecular nitrogen from the azo groups. This is not a true degradation, but rather a thermo-chemical transformation reaction of the evaluated polymers into the corresponding poly(1,3,4-oxadiazolyl-benzoxazoles). The resulting poly(1,3,4-oxadiazolyl-benzoxazoles) start to decompose in the temperature range above 330–560 °C, either in nitrogen or in air atmospheres without mass loss at a lower temperature. The thermal and thermo-oxidative stabilities of the polymers are affected by the nature and amount of arylene groups incorporated into their chains, being higher for polymers with greater content of para-oriented phenylene rings, which permits more interchain hydrogen bonds as a result of greater chain symmetry, packing efficiency, and rod-like structure. Increasing the content of para-oriented phenylene rings leads to a strong improvement in both the initial decomposition temperature as well as in the residual mass at a particular temperature. The stability of the polymers was found to be independent of their molecular masses. This confirms that high thermal stability is not a polymer property which would depends upon the length of its macromolecular chains, but rather upon its chemical structure in which all and every atomic group contributes by its own thermal stability to the macroscopic properties of the whole polymer.     

Substituent Effects on Reduction Potentials of Meta-substituted and Para-substituted Benzylideneanilines

Effects of meta-substituent of 3,4'/4,3'/3,3'-substituted benzylideneanilines (XBAYs) on the electrochemical reduction potentials (E_(Red)) were investigated, in which 49 samples of target compounds were synthesized, and their reduction potentials were measured by cyclic voltammetry. The substituent effects on the E_(Red) of target compounds were analyzed and an optimality equation with four parameters (Hammett constant σ of X, Hammett constant σ of Y, excited-state substituent constant σ_CC^ex of X, and the substituent specific cross-interaction effect Δσ_CC^ex2 between X and Y) was obtained. The results show that the factors affecting the E_(Red) of 3,4'/4,3'/3,3'-substituted XBAYs are different from those of 4,4'-substituted XBAYs. For 3,4'/4,3'/3,3'-substituted XBAYs, σ(X) and σ(Y) must be employed, and the contribution of Δσ_CC^ex2 is important and not negligible. Compared with 4,4'-substituted XBAYs, X group contributes less to 3,4'/4,3'/3,3'-substituted XBAYs, while Y group contributes more to them. Additionally, it was observed that either para-substituted XBAYs or meta-substituted XBAYs, the substituent effects of X are larger than those of Y on the E_(Red) of substituted XBAYs.     

The Synthesis And Crystal Structure Of 3-[5-Methyl-1-(4-Methylphenyl)-1,2,3-Triazol-4-yl]-s-Triazolo[3,4-b]-1,3,4-Thiadiazole

Likewise the 1,3,4-thiadiazole nucleus which incorporates an N-C-S linkage exhibits a large number of biological activities^[1]. The fused 1,3,4-triazolo[3,4-b]-1,3,4-thiadiazoles derivatives show various biological effects, such as antifungal^[2], antibacterial, hypotensive and CNS depressant activities^[3]. The novel 3-[5-methyl-1-(4-methylphenyl)-1,2,3-triazol-4-yl]-s-triazolo[3,4-b]-1,3,4-thiadiazole 6 have been synthesized by the condensation of 4-amino-5-mercapto-3-[5-methyl-1-(4-methylphenyl)-1,2,3-triazol-4-yl]-s-triazole 5 with formic acid in the presence of phosphorus oxychloride. The compound 5 was prepared from 4 that was prepared from 1 throng 2 and 3. Recently, we obtained the crystal structure of the novel compound 3-[5-methyl-1-(4-methylphenyl)-1,2,3-triazol-4-yl]-s-triazolo[3,4-b]-1,3,4-thiadiazole, C₁₄H₁₂Cl₃N₇S, Mr=416.72, Crystallizes in the triclinic space group with unit cell parameters a=9.049(2), b=10.486(3), c=10.843(2)Å, α=116.79(2), β=93.83(2), γ-100.64(3)°. V=889.3(4)ų, Z=1, Dx-0.778 Mgm^-3. The final R was 0.0535.     

Non-equilibrium thermal behaviour of a main chain thermotropic polymer

The effect of thermal treatment on the thermodynamic properties and structure of a nematic thermotropic main chain polymer with mesogenic groups containing 3,3'-biphenylene units and octamethylene flexible spacers (BF8) has been studied by DSC and X-ray scattering. We have found that BF8 samples do not crystallize even on very slow cooling from the isotropic state, and possessed a glassy nematic structure at room temperature. The strong influence of the cooling rate on both the enthalpy of the nematic-isotropic transition and the rise of specific heat at the glass transition for BF8 samples was observed. It was attempted to explain this result in terms of the improvement of the nematic structure during cooling.     

Thermotropic liquid‐crystalline polyesters of 4,4′‐biphenol and phenyl‐substituted 4,4′‐biphenols with 4,4′‐oxybisbenzoic acid

A series of thermotropic polyesters, derived from 4,4′‐biphenol (BP), 3‐phenyl‐4,4′‐biphenol (MPBP), and 3,3′‐bis(phenyl)‐4,4′‐biphenol (DPBP), 4,4′‐oxybisbenzoic acid (4,4′‐OBBA), and other aromatic dicarboxylic acids as comonomers, were prepared by melt polycondensation and were characterized for their thermotropic liquid‐crystalline (LC) properties with a variety of experimental techniques. The homopolymer of BP with 4,4′‐OBBA and its copolymers with either 50 mol % terephthalic acid or 2,6‐naphthalenedicarboxylic acid had relatively high values of the crystal‐to‐nematic transition (448–460 °C), above which each of them formed a nematic LC phase. In contrast, the homopolymers of MPBP and DPBP had low fusion temperatures and low isotropization temperatures and formed nematic melts above the fusion temperatures. Each of these two polymers also exhibited two glass‐transition temperatures, which were associated with vitrified noncrystalline (amorphous) regions and vitrified LC domains, as obtained directly from melt polycondensation. As expected, they had higher glass‐transition temperatures (176–211 °C) than other LC polyesters and had excellent thermal stability (516–567 °C). The fluorescence properties of the homopolymer of DPBP with 4,4′‐OBBA, which was soluble in common organic solvents such as chloroform and tetrahydrofuran, were also included in this study. For example, it had an absorption spectrum (λ_max = 259 and 292 nm), an excitation spectrum (λ_ex = 258 and 292 nm with monitoring at 350 nm), and an emission spectrum (λ_em = 378 nm with excitation at 330 nm) in chloroform. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 141–155, 2002     

Viscosity and Structure of Melts of H Complexes of Acid Diesters of Aromatic Tetracarboxylic Acids with Aromatic Diamines

The viscosity, lifetime, and structure of melts of supramolecular H-bonded complexes of acid diethyl and dimethyl esters of 3,3',4,4'-(diphenyl oxide)tetracarboxylic or 3,3',4,4'-diphenyltetracarboxylic acids with aromatic diamines (diaminodiphenylmethane or m-phenylenediamine) are studied.