Thermotropic homopolyesters: 5. Investigation of the smectic phase of polyesters based on p,p′-bibenzoic acid

We report a study of the mesophases of the homologous series of polymers prepared from p,p′-bibenzoic acid and the tetra-, hexa-, octa-, and decamethylene glycols. These polymers are designated BBn, where n is the number of methylene units in the diol. The BB4 and BB6 polymers form a thermotropic smectic phase which was independently identified as S_A by mutual miscibility studies with a known low molecular weight mesogen, TBBA, and by X-ray diffraction studies of oriented samples. The enthalpy change for the smectic-isotropic transition is only 1.4 Kcal mol^?1 a value consistent with a smectic phase of low order. The smectic layer spacing is shorter than the fully extended length of the repeating unit for both BB4 and BB6. Low molecular weight samples of BB6 exhibit three crystal modifications. The two higher temperature forms have the same c-axis spacing as the smectic layer spacing, 18.7 Å, while the polymorph stable at room temperature has a fibre repeat of 32 Å, indicating a still smaller distance per repeating unit, 16 Å. All of these values are smaller than the 20 Å length of the fully extended repeating unit. Shearing the smectic hase of BB6 polymers having η_inh < 0.45 dL/g produces a highly oriented sample in which the repeating units are perpendicular to the direction of flow. Shear of the smectic phases of polymers having higher intrinsic viscosities breaks up the smectic structure, and leads to less perfect orientation of the molecules parallel to the shear direction.     

H NMR study of thermotropic phase transitions in D2O solutions of poly(N-isopropylmethacrylamide)/poly(vinyl methyl ether) mixtures

¹H NMR spectroscopy was used to investigate thermotropic phase transitions in D₂O solutions of poly(N-isopropylmethacrylamide) (PIPMAm)/poly(vinyl methyl ether) (PVME) mixtures. In all studied solutions (polymer concentrations c=0.1-10 wt%) two phase transitions were detected at temperatures roughly corresponding to different lower critical solution temperatures of PIPMAm and PVME. While the phase transition of PVME component (located at lower temperatures) is not affected by the presence of PIPMAm in the mixture, the phase transition temperatures of PIPMAm component (located at higher temperatures) are affected by the phase separation of the PVME component. Measurements of ¹H spin-spin relaxation of residual water (HDO) molecules revealed that above the phase transition, a certain portion of water molecules is bound to polymer globular structures. A major part of bound water is present in globular structures of predominating polymer component in the mixture.     

Structure in mesogenic diol-containing polyesters

Copolyesters synthesized from two mesogenic monomers have been investigated. The monomers are 4,4′-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and the p-diester made from terephthaloyl dichloride and p-hydroxybenzoic acid. The incorporation of a very rigid, second mesogen increases the ability of BHHBP to form tilted mesophases. An untilted smectic A phase is formed initially, but the final, stable phase is a highly ordered, tilted smectic phase. Similar behavior is observed when BHHBP is combined with a mixture of the diacids of the crown ether dibenzo-18-crown-6. A copolymer of this type also forms a smectic A phase. For both types of copolymers, there is good agreement between the measured and calculated values for the layer distances.     

The synthesis and characterization of novel thermotropic liquid crystalline poly(aryl ether ketone)s

The synthesis and characterization of novel thermotropic liquid crystalline poly(aryl ether ketone)s based on the reaction of a liquid crystalline mesogen containing monomer, biphenol, and a crystal-disrupting substituted monomer, t-butyl- or phenyl-, hydroquinone with 4,4′-difluorobenzophenone are described. Two families of copolymers—a biphenol/t-butylhydroquinone series of 90,75,50, 25, and 0% biphenol, and a biphenol/phenylhydroquinone series of 75, 50, 25, and 0%—are evaluated. Thermotropic liquid crystalline behavior was observed in the copolymers containing 50 and 75% biphenol. The first order and second order transitions associated with melting, crystallization, thermotropic liquid crystalline mesophases, and glass transition temperatures (Tgs) of each copolymer are investigated. The thermal transitions are correlated with optical microscopy and X-ray and/or electron diffraction characteristics. It was observed that the Tg increases and end group concentration decreased after isothermal heat treatment indicative of further polymerization. These materials are believed to be the first known thermotropic liquid crystalline poly(aryl ether ketone)s.     

Liquid crystalline behavior of polymeric glycols terminated with aromatic diester and diacid mesogenic groups

A series of bis(benzylterephthaloyl-p-oxybenzoyl)esters (mesogen I) and bis(p-carboxybenzoyl-p-oxybenzoyl)esters (mesogen II) of several different polymeric glycols was prepared, and their thermotropic liquid crystalline behavior was studied by differential scanning calorimetry and by visual observation on the hot stage of a polarizing microscope. The polymeric glycols used were poly(ethylene oxide) (A), poly(tetramethylene oxide) (B), polybutadiene (C), and the hydrogenated polybutadiene (D) glycols, with molecular weights between 650 and 6000. With one exception, the benzyl ester derivations were not thermotropic, but the corresponding carboxylic acid derivatives were, and the related model compound, the bis(p-carboxybenzoyl-p-oxybenzoyl)ester of 1,12-dodecanediol, was also found to be liquid crystalline. The nature of the mesophases formed by the diacids derived from the macroglycol derivatives could not be clearly identified by their optical textures. Several of the diacid derivatives formed elastomeric films, even though they were still of low molecular weight, presumably because of chain extension by dimerization and association of the terminal mesogenic groups.     

Thermotropic and lyotropic mesophase formation of poly(ethylene oxide) substituted rod-coil oligomer

Summary The synthesis and characterization of the rod-coil oligomer consisting of a molecular rod and a poly(ethylene oxide) with degree of polymerization of 12 (5) are presented. The rod-coil oligomer5 shows a crystalline phase with microphase segregation. However, the complexation of the rod-coil oligomer5 with LiCF₃SO₃ induces a thermotropic smectic liquid crystalline phase. In aqueous solution, the rodcoil oligomer5 shows various lyotropic mesophases such as lamellar, cubic and cylindrical micellar mesophases, depending on the oligomer concentration. These results characterized by differential scanning calorimetry and optical polarized microscopy are described.     

Thermotropic comblike polymers with lipobiphenyl side chains: Factors governing nature of mesophases

In this article we describe the thermotropic behavior of comblike polymers with three types of main chains (polyacrylamide, polymethacrylamide, and polystyrylamide), two lengths of spacers (10 or five methylene groups), and three types of mesogenic cores (biphenyl, carbonitrilbiphenyl, and 2-methyl-1-butoxybiphenyl). The spacers are always linked to the mesogens by an ester bond. All the polymers are smectic at room temperature and exhibit two different smectic phases as a function of temperature, except for the polymer with a styrylamide main chain and a carbonitrilbiphenyl mesogen that presents only one mesophase; but the type of smectic phases is governed by the nature of both the main chain and the substituent R of the biphenyl core. Polyacrylamide polymers exhibit only bilayer smectic phases whose type is determined by the nature of the substituent R of the biphenyl; the smectic phases are SI2 and SC2 for R = H, SC2 and SA2 for R = CN, and SF2 and SC2 for R = O—CH₂—CH(CH₃)—C₂H₆. On the contrary, polymethacrylamide and polystyrylamide polymers exhibit two perpendicular monolayer smectic phases, SB1 and SA1, except for R = CN where a SAd phase replaces the SA1 phase. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2407–2417, 1997     

Molecular packing and phase transitions of side-chain liquid crystalline polymethacrylates based on p-methoxyazobenzene

The phase structures and transition behaviors of a series of side-chain liquid crystalline (LC) polymethacrylates based on p-methoxyazobenzene (PMnAzs, n = 6, 8, 10, 12) were studied using differential scanning calorimetry, one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction, and Fourier transform infrared spectroscopic experiments. The LC phase transition of PMnAz follows the sequence of smectic A (SmA) ? nematic (N) ? isotropic (I). For PM10Az and PM12Az, the transition of SmA-to-N is not complete upon heating. In the low-temperature SmA phase, the polymers adopt a fully interdigitated side-chain packing with the smectic layer period almost identical to the side-chain length. For all the four samples, the first-order diffraction of the SmA structure only renders when the temperature approaches the transition of SmA ? N, with the intensity much lower than that of the second-order diffraction. The absence of the first-order diffraction at low temperatures is ascribed to the possible matching of the electron densities between the center portion of the side-chain sublayer and the main-chain sublayer of the SmA structure. Since only the mesogens from the same main-chain sublayer can stack parallel together, the distribution of the azobenzene domains may cause some sort of density undulation within the smectic layer. Among the samples, PM6Az presents the strongest undulation with some additional orders. We also examined the annealing effect on the H-aggregation of PMnAzs. It is found that isothermal annealing at a temperature slightly higher than the T_g of PM8Az and PM10Az can significantly enhance the UV absorption at 326 nm, indicating a further development of H-aggregation. However, for PM6Az and PM12Az, the UV–vis spectrum of the annealed sample is nearly identical to that without annealing.     

Voltammetric investigation of polyelectrolyte-Cu(II) complexes

The complexation behaviours of poly(N-vinylcarbazole) (PNVCz), poly(acrylic acid) (PAA) poly(itaconic acid) (PIA) and their copolymers, synthesized by using different initial monomer compositions, with Cu(II) ions were investigated by the voltammetric technique. Their solutions were prepared in THF-water mixture according to the water-insoluble nature of PNVCz and its copolymers. The polymeric ligand-Cu(II) interactions, i.e. complex formations were studied as a function of copper ion concentration and copolymer composition. It was observed that although the cyclic voltammogram (CV) of Cu(II) alone in THF-water mixture was characterized by one redox wave, which has an irreversible nature, it became more reversible in the presence of polymer. Further, the CV results indicated the presence of two different electron transfer mechanisms, depending on the n _COOH/n _Cu(II) ratio and the carboxyl content of the copolymers.     

Novel bent-shaped liquid crystalline compounds: III. Synthesis of Schiff base liquid crystal dimers

A group of new bent-shaped mesomorphic compounds with two identical mesogens (Schiff base), which have 2-hydroxy-1,3-dioxypropylene (–OCH₂CH(OH)CH₂O–) as a short spacer unit, and different lengths of terminal alkoxy chains (–OC_nH_2n+1; n = 5–10, 12), are synthesized. Transition temperatures and phase characterization were studied by DSC, POM and XRD analyses. The dependence of phase transition temperatures on the terminal alkoxy chain lengths is discussed. With the increase in the terminal chain lengths, the thermal stability of the smectic mesophases of these liquid crystals was increased, and the smectic–isotropic transition temperatures in this series showed an even–odd effect.     

Interpolymer interactions and miscibility in poly(n‐butyl methacrylate‐co‐methacrylic acid)/poly(styrene‐co‐N,N‐dimethyl acrylamide) blends

The miscibility of poly(n‐butyl methacrylate‐co‐methacrylic acid) containing 18 mol % methacrylic acid (BMAM‐18) and poly(styrene‐co‐N,N‐dimethyl acrylamide) containing 17 mol % N,N‐dimethyl acrylamide (SAD‐17) was investigated with viscometry, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The DSC analysis showed a single glass‐transition temperature for all the blends, indicating that these copolymers were miscible over the entire composition range. The glass‐transition temperatures of these blends were higher than those calculated with the additivity rule. This was characteristic of the presence of specific interactions. The interactions between BMAM‐18 and the tertiary amide of SAD‐17 were studied with FTIR spectroscopy, which revealed that hydrogen‐bonding interactions occurred between the hydroxyl groups of BMAM‐18 and the carbonyl amide of SAD‐17. A new band characterizing these interactions appeared around 1613 cm^?1. The quantitative results showed that the fraction of the associated amide increased with an increase in the amount of the acidic BMAM‐18 copolymer. Although BMAM‐18 and SAD‐17 led to homogeneous solutions in butan‐2‐one, as the concentration of N,N‐dimethyl acrylamide increased to 32 mol % [as within the poly(styrene‐co‐N,N‐dimethyl acrylamide) containing 32 mol % N,N‐dimethyl acrylamide], complexation occurred when this latter compound was mixed with BMAM‐18 in butan‐2‐one. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2717–2724, 2006     

A novel technique for the preparation of secondary fatty amides II: The preparation of ricinoleamide from castor oil

The butyl amide of ricinoleic acid (N-n-butyl-12-hydroxy-(9Z)-octadecenamide) was prepared from a neat mixture of castor oil andn-butylamine (fatty ester/amine molar ratio, 1:1.3). No catalyst was required. The identity and purity of the amide was assessed by thin-layer chromatography and confirmed by elemental analysis and by infrared and C¹³ nuclear magnetic resonance spectroscopy. High product yields were achieved at 45 and 65°C in 48 and 20 h, respectively. The reaction was inhibited by the addition of trimethylpentane and dioxane, but not by water. An attempt was made to prepare the amide from methyl ricinoleate, rather than castor oil; even after 10 d only partial conversion was achieved. Attempts to prepare the amide from methyl-n-butylamine, rather thann-butylamine, were also unsuccessful. The ease with which secondary fatty amides can be produced from an oil that consists primarily of the glycerol esters of hydroxylated fatty acids indicates that the described procedure has industrial utility.     

Synthesis and Thermotropic Studies of Two Novel Series of Kinked Liquid Crystals: 2-(4′-Alkoxybiphen-4-yl)-6-methylquinolines and 2-(6-Alkoxynaphthalen-2-yl)-6-methylquinolines

Two novel homologous series of kinked (Z-shaped) liquid crystalline compounds were synthesized using a short two-step reaction. Yields of 30%–40% and 51%–57% were obtained for 2-(4′-alkoxybiphen-4-yl)-6-methylquinolines (nO-PPQMe, n = 3–8) and 2-(6-alkoxynaphthalen-2-yl)-6-methylquinolines (iO-NpQMe, i = 3–7), respectively. Spectral analyses agreed with the expected structures. The thermotropic behaviors of these compounds were investigated using polarized optical microscopy and differential scanning calorimetry. An enantiotropic nematic phase appeared to be the main mesophase in these two series of kinked liquid crystalline compounds, and an additional enantiotropic smectic C phase appeared when n = 8.     

Preparation and study of a thermo-responsive membrane using binary liquid crystal mixtures of cholesteryl cetyl ether and cholesteryl oleyl carbonate

A facile method for the synthesis of thermotropic liquid crystalline cholesteryl cetyl ether (CCE) was carried out from cholesterol and cetyl alcohol using montmorillonite K-10 as an acid catalyst. The aim of this study was to investigate the use of liquid crystalline blends of CCE and cholesteryl oleyl carbonate (COC) with appropriate crystal to smectic phase temperature (T _c?Cs) just above body temperature as a temperature-modulated drug permeation system. Using 30/70?mol ratio of COC/CCE, a mixture of desirable phase transition temperature was obtained. The phase transition behavior of COC/CCE binary liquid crystalline mixture was established by differential scanning calorimetry and polarizing optical microsopy. The COC/CCE-embedded cellulose nitrate membrane was used by an in vitro drug penetration studies. Paracetamol and mesalazine were chosen as hydrophobic and hydrophilic drug models, respectively. Paracetamol permeability through the membrane was higher at temperatures above the phase transition of liquid crystal (LC) blends (39?°C) than its permeability below the phase transition temperature of liquid crystal blends (30?°C). The drug penetration through LC-embedded cellulose membrane was influenced by the pore size of the membrane and therefore the adsorbed amount of LC. There was no penetration of mesalazine through that membrane presumably, due to the differences in hydrophilicity of LC-embedded membrane and permeated drug.     

A Spramolecular Star-Like Polymer

This study reports the creation of star-like chain architecture through complexation of a mono-amino terminated poly(ethylene oxide) (PEO-NH₂) with a macrocyclic compound, 4-sulfonic calix[n]arene (n=4 and 8) (SCA-n). The complexes were prepared in aqueous solution to render proton transfer from the sulfonic acid groups in SCA-n to the amino groups in PEO-NH₂, and thereby generated 4- and 8-arm star-like complexes with the PEO arms attached to the SCA-n cores via ionic bonding. Formation of the complexes was verified by titration, solubility test, and dilute solution viscometry. The intrinsic viscosities ([]) of the complexes in toluene were 60% higher than that of neat PEO-NH₂, showing that the star-like structure retained in nonpolar solvents. On the other hand, PEO arms dissociated from the cores in water, so that the complexes and neat PEO-NH₂ displayed similar []. The star-like supramolecules showed a SAXS peak associated with the core-core correlation in the melt with the inter-core distance of 7.3 nm. The concentration fluctuation in the melt was completely destroyed upon the crystallization of PEO arms. In the semicrystalline state, the SCA-n cores were excluded from the crystal lattice and resided in the interlamellar amorphous regions. Measurements of the crystal thickness by SAXS indicated that the PEO chains in the crystals were once- and twice-folded in neat PEO-NH₂ and the complexes crystallized at 40°C, respectively.     

Studies on the Radiochemical Degradation of Tetraethylhexyl Diglycolamide and Ethylhexylphosphoric Acid in n-Dodecane Solution

The organic solvent phase composed of N,N,N’,N’-tetra-2-ethylhexyl diglycolamide (TEHDGA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) in n-dodecane (n-DD) is regarded as a promising candidate for single-cycle separation of americium (III) from high-level liquid waste. The radiochemical degradation of a solution of TEHDGA + HDEHP/n-DD was investigated by irradiating the solvent to various absorbed dose levels of γ-radiation. The neat extractants or a solution of extractants in n-dodecane were irradiated in the presence and absence of nitric acid. The degree of degradation was assessed by measuring the variation in the extraction behavior of Am(III), Eu(III) and other metal ions in irradiated solvent systems. The distribution ratio of americium and europium decreased with increase of absorbed dose. The presence of n-dodecane enhanced the radiolytic degradation of the solvent; however, the role of nitric acid during degradation was insignificant. The recovery of Am(III) and Eu(III) from the irradiated solvent system was studied. The recovery of Am(III) was quantitative in 3 contacts; however, the separation factor of Eu(III) over Am(III) during stripping decreased marginally with increase of absorbed dose.     

Synthesis and thermal properties of bismaleimides with mesogen aromatic amide–ester and flexible polymethylenic group

Four bismaleimides with mesogen “amide–ester” aromatic and flexible polymethylenic group variable length (8 ≤ n ≤ 11) were synthesized in two stages, producing yields exceeding 80%. These bismaleimides (BMIs) were obtained after several purifications by dissolution—precipitation in dimethylformamide–methanol (1/4) with over 94% purity (high‐performance liquid chromatography). These pure BMIs were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elemental analysis and studied by differential scanning calorimetry, thermogravimetric analysis, polarized light microscopy, and X‐ray diffraction. Solubilities and thermal properties show effects of parity. The even BMIs are more difficult to solubilize than the odd BMI. The melting points of the even BMI (approximately, 220°C) are far higher than those of odd BMI (approximately, 160°C). Crosslinking temperatures of even BMI are close to 230°C, whereas odd BMI crosslinking temperatures are higher (approximately, 250°C). Even BMIs give rise to a liquid crystal state upon melting. Under the same conditions, odd BMIs give rise to an amorphous state; however, after crosslinking, the four bismaleimides give rise to an ordered liquid crystal state of smectic type. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Smectic polyester/layered silicate nanostructured hybrids: Effect of modified nanoclay in the phase transitions

The effect of incorporating different proportions of a layered silicate nanofiller into poly(diethylene glycol p,p’-bibenzoate) has been analysed. On cooling from the isotropic melt, this thermotropic main-chain liquid-crystalline polymer exhibits a smectic mesophase which is able to crystallise rather slowly by long time annealing. The results show that the nanocomposites exhibit a higher stability against thermal decomposition in oxidative atmosphere. The intercalation of polymeric chains into the clay layers is deduced from X-ray diffraction, although part of the initial silicate structure is preserved. The DSC results indicate a clear nucleation ability of the clay for both mesophase formation and crystallisation from the mesophase. The effect in this crystallisation is of major importance, causing a reduction of the time necessary to attain 50% of the total transformation by a factor of more than 4. Additional information was obtained from microhardness measurements.     

Quantification of the complexation of protein with neutral water borne polymer by fluorescence spectroscopy

The complexation of bovine serum albumin (BSA) with poly(N-isopropylacrylamide) (PNIPAM) in an aqueous system (pH 7) has been investigated by means of fluorescence spectroscopy. Through analyzing the change of fluorescence intensity of protein chromophores caused by complexation, a quantitative mathematical equation has been established and the average number of bound proteins per neutral polymer (n_b) can be calculated accurately without destroying the dynamic equilibrium of aqueous complex system. At the same time, with the help of this equation, the extreme value of n_b can also be calculated when PNIPAM concentration is low enough. Compared with traditional calculation methods, this method has the advantages of rapid detectability, high sensitivity, accuracy and extensive applicability. Thus, it is a better way to study the complexation of protein with polymer.     

Hydrothermal alteration of sedimentary organic matter in the presence and absence of hydrogen to tar then oil

Hydrothermal alteration (hydrous pyrolysis) experiments, in the absence and presence of H₂ (reductive), were conducted on organic matter from marine and lacustrine sediments. The experiments were carried out at discrete temperatures from 150 °C to 350 °C to assess the yields and compositions of the bitumen (tar) formed and subsequently at higher temperatures the oil generated. The yield of bitumen was observed to increase with increasing temperatures. Under hydrous pyrolysis conditions with hydrogen, the yield increases by an order of magnitude and immature lacustrine organic matter shows the highest yield. Bitumen, the extractable organic matter at temperatures below 250-300 °C, contains mainly polar compounds, an unresolved complex mixture (UCM) of branched and cyclic compounds, with low amounts of saturated hydrocarbons. The polar compounds include n-alkanoic acids, n-alkanedioic acids, n-alkanols, isoprenoid ketones and methyl alkanoates. At temperatures above 300 °C, the bitumens transform into petroleum products with saturated hydrocarbons (n-alkanes and biomarkers) and UCM as the major components (>95% of total yield). The degree of maturation of the generated oil increases with increasing temperature under both pyrolysis conditions to full maturity at >350 °C. Although, the bitumen yield is much higher under conditions with added hydrogen, the maturity of the generated oil is lower than with just hydrous pyrolysis.