Synthesis and characterization of aromatic polyesters with dicyanovinyl substituents

The synthesis, characterization, and structure—property relations of aromatic polyesters with dicyanovinyl substituents is presented. Two comparable series of polyesters based on 3,4-dihydroxybenzylidenemalononitrile and 3,4-dihydroxy-5-methoxybenzylidenemalononitrile were prepared. As aromatic diacid components, terephthalic acid, phenylterephthalic acid, isophthalic acid, and 2-phenylisophthalic acid were used. The polyesters were prepared by solution polycondensation. GPC investigations revealed the existence of substantial amounts of defined cyclic products. These cycles could be isolated by preparative GPC. The polyesters are soluble in common low boiling organic solvents, particularly the phenyl-substituted ones. The polyesters are amorphous and have glass transition temperatures between 140 and 170°C. The absorption maxima are in the 306–322 nm range. The cut-off wavelength is between 400 and 428 nm. The polyesters with methoxy substitutent have generally the absorptions at longer wavelength. The refractive index of thin films of these polyesters were between 1.61 and 1.63 at 632.8 nm. © 1993 John Wiley & Sons, Inc.     

Synthesis and mesophase characterization of liquid crystalline polyesters with bulky,rigid, lateral substituents

The synthesis and characterization of aromatic polyesters containing various symmetrically di-substituted hydroquinone monomers is described. The homopolyesters made from these monomers and terephthalic acid (TA) did not melt. Copolyesters of TA with mono- and di-substituted hydroquinone formed liquid crystalline melts. Optical microscopy showed schlieren, marbled, and droplet textures characteristic of the nematic phase. DSC experiments were also in accord with mesophase formation as multiple transitions characteristic of first-order phase changes were found. In general, the crystal-nematic transition was about 300°C, whereas the nematic-isotropic change was over 400°C. All the polyesters were prone to decomposition near or above the isotropization temperature. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of block copolymers having liquid crystalline behaviour

A series of four block copolymers based on aromatic acetoxy-polysulphone (Ac-PSF), terephthalic acid (TPA), m-phthalic acid (MPA), acetoxy-benzoic acid (Ac-HBA), and a di(acetoxy)bisphenol monomer were synthesized. Their structures were determined by IR, thermal mechanical analyses and solubility tests. They all exhibit liquid crystalline behaviour.     

Synthesis and characterization of new aromatic polyesters containing cardo decahydronaphthalene groups

Three cardo bisphenols containing decahydronaphthalene group viz., 4,4′-(octahydro-2(1H)-naphthylidene)bisphenol, 4,4′-(octahydro-2(1H)-naphthylidene)bis-3-methylphenol and 4,4′-(octahydro-2(1H)-naphthylidene)bis-3,5-dimethylphenol were synthesized starting from commercially available 2-naphthol and were utilized for synthesis of new aromatic polyesters by phase transfer-catalyzed interfacial polycondensation with isophthaloyl chloride, terephthaloyl chloride and a mixture of isophthaloyl chloride and terephthaloyl chloride (50:50 mol %). Inherent viscosities and number average molecular weights (M_n) of polyesters were in the range 0.35-0.84 dL/g and 13,300-48,500 (Gel Permeation Chromatography, polystyrene standard), respectively. Polyesters were readily soluble in organic solvents such as dichloromethane, chloroform, tetrahydrofuran, meta-cresol, pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, and 1-methyl-2-pyrrolidinone at room temperature and could be cast into tough, transparent and flexible films from their chloroform solutions. Wide-angle X-ray diffraction measurements revealed the amorphous nature of polyesters. The glass transition temperature of polyesters was in the range 207-287 °C. The temperature at 10% weight loss (T₁₀), determined from thermogravimetric analysis of polyesters, was in the range 425-460 °C indicating their good thermal stability.     

Synthesis of reactive aromatic polyesters having pendant chlorohydrin moieties

A monomer containing a chlorohydrin moiety, propyl chlorohydrin diphenolate (PCHDP), was synthesized. Reactive polyesters having these pendant chlorohydrin moieties were prepared by the interfacial polycondensation of isophthaloyl chloride with PCHDP or with PCHDP and diphenolic acid using phase transfer catalyst. The molar ratio of reactants and the phase ratio of water to organic solvent strongly affect the molecular weight of resulting polymers and polymers with high molecular weight are obtained at the molar ratio of 1.0–1.15 and the phase ratio of 2.0–3.5. Swelling of the growing polymers is dependent on the molar ratio of the reactants and the phase ratio because of the hydrophilic and hydrophobic nature of the pendant chlorhydrin moiety. The resulting polymers are not soluble in any solvent except water in which hydrolysis occurs. Thus so, the structure of polymers was confirmed by ¹³C CP/MAS NMR. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of liquid–crystalline polyesters with chiral and achiral twin spacers

A series of novel thermotropic main-chain chiral liquid–crystalline random copolyesters consisting of spacers of two different types—chiral and achiral—was synthesized. Polyesters (BmTa) with tartaric acid as the chiral spacer (Ta), aliphatic diols (with ‘m’ = 2–10 methylene groups) as the achiral spacers, and 4,4′-dihydroxy biphenyl (B) as the mesogen were synthesized via condensation polymerization in solution after duly protecting the 2,3-dihydroxy groups of tartaric acid by acetylation. The copolymers were characterized by Fourier transform infrared spectroscopy, ¹H and ¹³C NMR spectra, gel permeation chromatography, and thermogravimetric analysis. Transition temperatures for phase changes recorded by DSC were corroborated with the textures observed by a hot-stage optical polarizing microscope. The wide-angle X-ray diffraction (WAXD) profiles indicated a SmE phase at room temperature. The lower angle region at 2θ = 0.5–2.45 covered by WAXD indicated a layer of thickness of 161 Å, less than the molecular length for B0Ta. The [α_D] values were recorded on a digital polarimeter. The birefringence was lost at higher mesophase temperatures in lower members with m < 5, a behavior found in certain chiral systems, and the higher members with m > 5 showed a lesser number of phase transitions. On cooling, the polyesters produced a texture with the formation of transition bars. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1743–1752, 2001     

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.     

Synthesis and characterization of new cardo polyesters

New phthalide-containing bisphenols, phenolphthalein-N-(3-methylanilide) (3-PMA), and phenolphthalein-N-(4-methylanilide) (4-PMA), were synthesized from phenolphthalein and m- and p-toluidines. These bisphenols were polycondensed with terephthaloyl chloride (TPC) using an interfacial or solution polymerization technique to yield new polyesters. Copolymers were also obtained by utilizing different molar proportion of phenolphthalein (PPH) and 3-PMA or 4-PMA with TPC. The polymers prepared by solution polymerization were obtained in 93–99% yields and showed reduced viscosities in the range 0.37–0.83 dL/g. They were readily soluble in chlorinated hydrocarbons and aprotic polar solvents. The polyesters showed glass transition temperatures in the range 261–300°C as measured by DSC. Thermogravimetric analysis of the polyesters indicated no weight loss below 408°C under N₂ atmosphere. Structure–property correlations among these cardo polyesters have been discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3227–3234, 1997     

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-alpha-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2 S ,3 S )-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate ( 6 ) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P 13 and P 14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P 13 , with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P 14 , with a spacer containing four methylene units, displays a chiral nematic phase.     

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-α-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2S,3S)-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate (6) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P13 and P14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P13, with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P14, with a spacer containing four methylene units, displays a chiral nematic phase.     

Synthesis and characterization of polyesters derived from polychlorinated aromatic diacids

New, thermally stable polyesters with varying chlorine content were prepared by solution and interfacial polycondensation between chlorinated aromatic dichlorides (perchloroterephthaloyl dichloride, 2,5-dichloroterephthaloyl dichloride, and perchloro-4,4′-dichloroformyl biphenyl with different aliphatic and aromatic diols). The polymers were characterized by infrared spectroscopy, elemental analysis, differential scanning calorimetry, and thermogravimetric analysis. Their solubilities and molecular weights were also determined. The influence of chlorine content on the thermal properties of the polymers is discussed.     

Synthesis of aromatic polyesters using polymeric catalysts having quaternary ammonium salt groups

The preparation of polyester (PQ) and copolyester (PQ-DIOL) catalysts having quaternary ammonium groups was performed, and an aromatic polyester (PEA) was directly synthesized from isophthaloyl chloride and diphenolic acid by aqueous/organic interfacial polycondensation using these polymer catalysts. The yield and molecular weight of the polyester were affected by the structure of the pendant quaternary ammonium groups.     

Synthesis and properties of two new series of isomeric liquid crystalline polyesters with conjugated double bonds

Two homologous series of flexible main chain liquid crystalline polyesters with isomeric mesogenic groups containing conjugated double bonds, were synthesized and studied by differential scanning calorimetry and optical microscopy. One series (S1) has the p-phenylene-diacryloyloxydibenzoyl moiety as a mesogenic unit. The other (S2) has the terephtaloyl dioxydicinnamoyl moiety as a mesogenic unit. The reactivity of the conjugated double bonds of the p-phenylenediacryloxy unit, at the temperature of mesophase formation, impedes the stability of liquid crystalline mesophases of polymers of series (S1). Two low molecular weight analogues of polymers were also prepared and their properties compared with those of polymers of similar structure. The two model compounds form stable smectic mesophases over a wide range of temperatures, which shows the high mesomorphogenic ability of both mesogenic units.     

Free-radical chain generation of ketene during the synthesis of liquid crystalline aromatic polyesters

At the high temperatures used for the preparation of liquid crystalline aromatic polyesters (LCPs), ketene cleavage occurred from acetoxyarenes. Ketene is known to oligomerize to colored oligomers which may be responsible for an undesirable yellow color in LCPs. Thermolysis of the model compound p-acetoxybenzoate gave ketene oligomers and methyl p-hydroxybenzoate, which oligomerized. A free-radical chain reaction mechanism for ketene formation was demonstrated by the reaction of tributyltin hydride with haloacetoxyarenes.     

Parent homopolymers of liquid crystalline polyesters

A method that combines multi-temperature powder X-ray diffraction and molecular modelling is used to determine the high temperature crystal structures for poly-(p-phenylene terephthalate) (PPT) and poly-(p-hydroxybenzoic acid) (PHBA). Both have high temperature structures characterized by a degree of rotational disorder. In the case of PHBA there is a distinct high temperature phase above a well defined transition at 350°C, whereas the rotational disorder in ‘as polymerized’ PPT increases gradually between 370 and 475°C. The interchain packing at high temperatures still maintains phenyl edge to phenyl face correlations and, to some degree, carbonyl carbon to carbonyl oxygen contacts. The findings are relevant to the molecular structure and phase behaviour of liquid-crystalline polyesters as a class.     

Synthesis and characterization of polyesters derived from aromatic 1,4-dimethoxylated diacids

Polyesters were synthesized from the dichlorides of 2,5-dimethoxyterephthalic and 2,5-dimethoxy-1,4-benzenediacetic with dialcohols. The polymers were characterized by elemental analysis and infrared (IR) spectroscopy. Their intrinsic viscosity, glass transition temperature, and thermal decomposition were determined.     

Methylene-bridged aromatic polyesters. Synthesis,characterization, and radiation-induced crosslinking

Aromatic polyesters connected by methylene groups were synthesized. Two pairs of aromatic diacid chlorides, 3,3′-methylenedibenzoyl chloride and 4,4′-methylenedibenzoyl chloride were each polymerized via interfacial polycondensation with 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 3,3′-methylenediphenol, and 4,4′-methylenediphenol. For comparison, 3,3′-carbonyldibenzoyl chloride and 4,4′-carbonyldibenzoyl chloride were similarly polymerized with bisphenol A. Substitution of meta,meta' oriented phenylene groups for para,para' oriented phenylene groups had a significant and cumulative effect in reducing the glass transition temperatures of the polymers, thereby enhancing their processability. In air the methylene groups of the polyesters undergo oxidation and crosslinking at elevated temperatures. Electron beam irradiation of thin films of the methylene-linked polyesters at room temperature resulted in some chain extension and crosslinking, as evidenced by increased solution viscosity and gel formation. Irradiation at a temperature near or above the glass transition temperatures of the polymers greatly enhanced the tendency for the polymers to crosslink.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The chloromethylation of 2-acetothienone and 2-formylthiophene with , -bischloromethyl ether in 60–100% sulfuric acid was studied. An increase in the acidity of the medium promotes the formation of 4-substituted products, which, as in nitration and bromination, is explained by protonation of the carbonyl group, leading to intensification of its electron-acceptor capacity.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1353–1357, October, 1971.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The composition of the products formed in the bromination of complexes of furfural with AlCl₃ and methyl furan-2-carboxylate with AlBr₃ in chloroform and dichloroethane was studied by PMR spectroscopy and gas-liquid chromatography. Some literature data pertaining to these reactions are refined and corrected. The pathways for the formation of chloro derivatives under the examined conditions are discussed.     

Synthesis and properties of phenyl benzoate-based and biphenyl-based liquid crystalline thiol-ene monomers

Novel phenyl benzoate-based and biphenyl-based liquid crystalline thiol-ene monomers were synthesized and their properties investigated. By varying the bridging unit and spacer length, the type of mesophase can be tuned from the low ordered nematic and smectic A phase in the case of the phenyl benzoate-based monomers, to the highly ordered crystal E phase for the biphenyl-based monomers and their corresponding bromo precursors. We investigated the degree of order of the phenyl benzoate-based materials using the Haller method. Possible premature polymerization of these monomers was examined by size exclusion chromatography. The materials exhibit low transition temperatures and a high stability at typical handling times and temperatures. Consequently, these monomers are useful for in situ polymerization with anisotropic inert solvents, which could potentially lead to new architectures and enhanced electro-optical properties of devices. The use of the biphenyl-based monomers appears to be of limited use for polymerizations in anisotropic solution. However, as a result of their intrinsic high degree of molecular order, these monomers form a particularly interesting class of reactive materials that can be bulk polymerized to give main chain polymers with highly defined mechanical and optical or electro-optical properties.