Thermotropic liquid-crystalline peptide derivatives: oligo(glutamic acid)s forming hydrogen-bonded columns

We report on new thermotropic liquid-crystalline oligo(amino acid) derivatives forming columnar structures. These are based on branched oligo(glutamic acid)s and 2-(3,4-dialkyloxyphenyl)ethyl moieties. An oligo(glutamic acid) derivative, alpha,gamma-bis(L-glutamoyl) L-glutamic acid tetra[2-(3,4-dioctadecyloxyphenyl)ethyl]ester, shows a hexagonal columnar phase, whilst a glutamic acid derivative, alpha,gamma-bis[2-(3,4-dioctadecyloxyphenyl)ethyl] L-glutamate, does not show a mesophase. Hydrogen bonds formed by the oligo(glutamic acid) moieties should contribute to the induction of the columnar liquid-crystalline properties. In addition, we have examined the effects of the molecular chirality of the oligo(glutamic acid) parts and the functionalisation at the focal position of the taper shaped molecules on the liquid-crystalline properties of the compounds.     

Liquid-crystalline polymers for fibres

Recent advances in the development of liquid-crystalline polymers for fibres are reviewed. The discussion of lyotropic systems concentrates upon poly(p-phenylene terephthalamide) and its copolymer with 3,4′-oxydiphenylene terephalamide units. The discussion of thermotropic systems identifies specific problems restricting the development of fibres and suggests some possible means of improvement.     

Liquid-Crystalline Behaviour in the n-Alkyl Gluconamides and Other Related Carbohydrates

Many alkyl derivatives of carbohydrates are used as detergents for cell wall membranes. This study describes the liquid-crystalline properties of a number of these systems. The combination of a hydrophilic carbohydrate moiety and a hydrophobic aliphatic substituent leads to the formation of both thermotropic and lyotropic liquid-crystal mesophases. Materials with this structural combination are suspected to form interdigitated bilayer smectic A phases. The central core region of the layer is held together by dynamic hydrogen-bonding between the neighbouring carbohydrate moieties, whereas the terminal aliphatic chains create fluidity between layers.     

Preparation and properties of polymides from 3,4′- and 4,4′-oxydianiline and various aliphatic and aromatic diacids

Aromatic-aliphatic polyamides of high molecular weight were prepared by the direct polycondensation of 3,4′- and 4,4′-oxydianiline with aliphatic diacids with 4-10 methylene groups in a triphenyl phosphite/pyridine system. Polyamides prepared from 3,4′-oxydianiline are characterized by greater solubility, lower melt temperatures, and lower glass transition temperatures than are those from 4,4′-oxydianiline. Aromatic polyamides from 3,4′- and 4,4′-oxydianiline and isophthalic and terephthalic acids were also prepared and characterized.     

Synthesis and Characterization of Poly(ether amide)s Containing Phthalazinone Moieties

Soluble aromatic polyamides containing phthalazinone moieties were prepared. Those polymers were obtained from the solution polymerization of a new diacid containing phthalazinone moieties with various diamines. The new monomer, 2-(4-carboxyphenyl)-4-(4-carboxyphenoxy)phenyl-1(2H)phthalazinone(Ⅳ) was synthesized in a two-step reaction sequence. 2-(4-Cyanophenyl)-4-(4-cyanophenoxy)phenyl-1(2H)phthalazinone (Ⅲ) was prepared via the condensation reaction of 4-(4-hydroxyphenyl)-1(2H)phthalazinone (Ⅰ) with p-chlorobenzonitrile (Ⅱ). After (Ⅲ) was hydrolyzed, (Ⅳ) was acquired. The synthesized polyamides were characterized by means of viscosimetry, DSC, FT-IR, 1H NMR and EA. The polyamides have a high glass transition temperature which can be as high as 316 ℃. The polyamides also have good solubilities in some organic solvents.     

Liquid-Crystalline Behaviour in the n-Alkyl Gluconamides and Other Related Carbohydrates

Abstract

Many alkyl derivatives of carbohydrates are used as detergents for cell wall membranes. This study describes the liquid-crystalline properties of a number of these systems. The combination of a hydrophilic carbohydrate moiety and a hydrophobic aliphatic substituent leads to the formation of both thermotropic and lyotropic liquid-crystal mesophases. Materials with this structural combination are suspected to form interdigitated bilayer smectic A phases. The central core region of the layer is held together by dynamic hydrogen-bonding between the neighbouring carbohydrate moieties, whereas the terminal aliphatic chains create fluidity between layers.     

Shapes of Micelles and Molecular Geometry Synthesis and Studies on the Phase Behaviour, Surface Tension and Rheology of Rigid Rod-Like Surfactants in Aqueous Solutions

Amphiphiles with rigid rod-like hydrophobic moieties have been synthesized in order to investigate the effect of the packing restraints of such moieties on the micellar association behaviour of amphiphiles in aqueous solution. Investigations of the phase behaviour of amphiphile/water mixtures reveal that liquid-crystalline phases exist in defined temperature and concentration regimes and that they are all lamellar, regardless of the hydrophilic-hydrophobic balance of the amphiphile. For these lyotropic liquid-crystalline phases a polymorphism is observed which is similar to the polymorphism of thermotropic smectic liquid crystals. Surface tension measurements indicate critical micelle concentrations of the amphiphiles in dilute solutions which are similar to those of conventional surfactants. From rheological measurements it can be assumed that the variation of temperature and/or concentration of the solution does not influence the micellar shape. This is in contrast to the behaviour of non-ionic surfactants having a flexible hydrophobic group.     

High-resolution characterization of liquid-crystalline [60]fullerenes using solid-state nuclear magnetic resonance spectroscopy

Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of fullerene-containing thermotropic compounds using solid-state natural abundance (13)C NMR experiments under stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic, liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional (13)C experiments, while two-dimensional separated local-field experiments were used to measure the (1)H- (13)C dipolar couplings in mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate fast around the symmetry axis on the characteristic NMR time scale of approximately 10 (-4) s.     

Synthesis of novel and regioselectively mesogen-incorporated thermotropic liquid crystals from cellulose derivatives

Regioselectively mesogen-incorporated cellulose derivatives, in which the hydroxy group at C-6 is displaced by a bulky and rigid mesogenic group such as {4-[(4-methoxyphenoxy)carbonyl]phenoxy}acetate or [(4′-cyanobiphenyl-4-yl)oxy]acetate, and the C-2 and C-3 groups are displaced by octanoyl or lauroyl groups, were synthesized. Thermogravimetric and differential scanning calorimetric analyses of the final products, along with polarized optical microscopic observations, revealed that the obtained cellulose derivatives have a thermotropic liquid-crystalline nature and transition from the mesomorphic to the isotropic phase over a wide range of temperatures. These derivatives could be considered to be main-chain liquid-crystalline cellulosic polymers.     

Polyimides and polyamides with semiflexible spacers

Thirteen polyimides and three polyamides were synthesized with alternating rigid and semiflexible polymethylene units along the chain backbone. Derivatives of the pyromellitic species served as rigid segments in the polyimides and the sulfanilamide group was incorporated in the rigid segments of the polyamides. These systems were examined for a thermotropic liquid–crystalline phase. None was detected, probably because of the high crystalline melting temperatures of these polymers.     

Supramolecular liquid-crystalline materials: molecular self-assembly and self-organization through intermolecular hydrogen bonding

Supramolecular liquid-crystals are molecular complexes formed from different and independent molecular species through specific molecular interactions such as hydrogen bonding. We have recently developed new types of H-bonded liquid-crystalline materials obtained by molecular self-assembly processes: (1) doubly H-bonded liquid-crystalline complexes through a molecular recognition process between 2,6-bis(acylamino)pyridines and benzoic acids, (2) liquid-crystalline polymer blends involving an H-bonding interaction between poly(4-vinylphenol) and a thermotropic main-chain polyester containing a lateral pyridyl substituent, (3) liquid-crystalline networks built through hydrogen bonds between multifunctional H-bonding components. These new materials may bridge a gap between liquid crystals and supramolecular systems.     

Liquid crystallinity,IR analysis,and mechanical properties of thermotropic polyamides having alkylene spacers

Thermotropic polyamides with high molecular weights were synthesized by melt polycondensation of 3,3′-disubstituted-4,4′-biphenylenediacetamides with α,o-diphenoxyalkane-4,4′-dicarboxylic acids. Methyl, methoxy, and chloro groups were used as 3,3′-substituents. IR measurements revealed that there are hydrogen-bonded carbonyls and free carbonyls the intensities of which depended on the polymer structure and the temperature. The thermotropic liquid crystallinity of the polyamides is assumed to occur by a decrease in intermolecular hydrogen bondings between carbonyls and amide NH's which was caused both with 3,3′-substitutions of the biphenylene moiety and with introduction of long alkylene spacers in the polymer backbone. In addition, mechanical properties of the thermotropic polyamides were measured on the molded dumbbell-type specimen. The 3,3′-dichloro polyamides showed medium tensile strengths and moduli in the range of 500–890 kgf/cm²a nd 19.0 × 10³ to 27.0 × 10³ kgf/cm², respectively. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of liquid-crystalline side group polymers with benzylideneaniline as mesogenic moiety

Two new thermotropic liquid-crystalline side group polymers were synthesized, characterized and compared with the liquid-crystalline monomeric analogues. Some packing features of these polymeric liquid crystals are discussed.

Investigations were carried out by differential calorimetry (D.S.C.), polarization microscopic observation and X-ray diffraction on non-aligned and magnetic field-aligned samples in the wide and small angle region.

The synthesized polymers contain as mesogenic moiety a benzylideneaniline group which is attached in the 4 position via a hexamethylene spacer to a poly-methacrylate backbone. The benzylideneaniline group is substituted in 4′ position with an ethoxy or butoxy group (PEt or PBu). The monomeric analogues are denoted MEt and MBu. The two polymers show a phase sequence crystalline-smectic A-nematic-isotropic. The liquid-crystalline temperature range is observed between 90 and 150°C. The monomeric MEt exhibits only a monotropic nematic, MBu an enantiotropic nematic and a smectic A phase.     

The liquid-crystalline properties of selected cellulose derivatives

The liquid-crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4-methoxyphenylacetoxy cellulose (4MPAC), and p-tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t-butyldimethylsilyl cellulose (TBDMSC), are reported. Hot-stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials. PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH₂Cl₂. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid-crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.     

Synthesis and properties of thermotropic liquid-crystalline polyesters containing 9,10-diphenylanthracene moiety in the main chain

We synthesized thermotropic liquid-crystalline polyesters in which 9,10-diphenylanthracene moieties are incorporated into the main chain type of polyester forming the chiral smectic C (Sm C*). The polymers were prepared by the isopropyltitanate-catalyzed reaction of biphenyldicarboxylic acid and the corresponding diols, with different ratios of diol of 9,10-diphenylanthracene moiety to the alkane diols (1, 5, and 10 mol %) under nitrogen atmosphere. The polymers exhibited thermotropic liquid crystals despite the presence of a bulky diphenylanthracene moiety in the main chain. The circular dichroism spectra revealed that a Sm C* phase was formed in the polymer with 1 mol % of anthracene moiety, although only an Sm A phase was formed in the other polymers. This is the first example of a Sm C* polyester containing a diphenylanthracene moiety in the main chain. Furthermore, we measured the optical properties of the polymers and found that they exhibited very high fluorescent efficiency. The fluorescence spectra of the thin film differed from that of a CH₂Cl₂ solution.     

含X-型和棒型两种液晶基元的主链型共聚酯

采用高温溶液缩聚方法,合成了一系列不同配比的含X-型和棒型两种液晶基元的主链型芳族共聚酯。经检测,所有样品均具有热致液晶性。本文对这类共聚酯的液晶行为进行了研究。     

Synthesis,characterization, and water sorption properties of new aromatic polyamides containing benzimidazole and ethylene oxide moieties

New polyamides, containing a benzimidazole side group and ethylene oxide moieties in the structural repeat unit, were synthesized by low‐temperature polycondensation. The aim of this design was to obtain polyamides that were more soluble in common organic solvents and hence had better processability than benzimidazole polyamides while maintaining the water sorption properties characteristic of the latter. The results showed that the number of ether linkages of the repeat unit played an important role in the glass‐transition temperature and in the water sorption properties, the polyamides with one or two ethylene oxide units being more hydrophilic than benzimidazole polyamides. However, the length of the ethylene oxide chain played a minor role in the solubility because the second member of the series, with two ether linkages (i.e., one ethylene oxide unit), reached the same level of solubility as those polyamides with more ethylene oxide moieties. No crystallinity was observed by X‐ray and calorimetric measurements for the new polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 112–121, 2005     

Liquid-crystalline side chain polymers by chemical modification of poly(chloroalkylvinylether)s

The synthesis of polyalkylvinylethers with pendant 4-cyano-4'-oxybiphenyl groups gives thermotropic liquid-crystalline polymers. The new method developed here consists of the living cationic polymerization of chloroalkylvinylethers and the subsequent modification of the polymer by the mesogenic groups. The liquid-crystalline polymers have a controlled degree of polymerisation and narrow molecular weight distributions. The influence on the mesomorphic properties of various parameters such as the degree of polymerization, the spacer length and the proportion of the mesogenic side chain content has been investigated. Binary phase diagrams with low molar mass analogues are also reported and the properties of both neat materials and binary mixtures are compared.     

New thermotropic liquid crystals derived from thiophenes

Properties of new homologous series of low molecular mass thermotropic liquid crystals containing non-linear mesogenic cores, 2,5-thiophene (T) and 2,2'-bithio-phene (BT), are presented for the purpose of refining molecular structural prerequisities for liquid crystallinity. Herein we focus on the effect of core linearity on mesophase stability. The bis(p-alkoxyphenyl) dicarboxylate derivatives containing the bent T and kinked BT central units are found to form enantiotropic liquid crystal phases with nematic and smectic polymorphism, depending on the length of their terminal chains. All members of the non-linear T and BT homologous series have narrower mesomorphic temperature ranges than the corresponding compounds with linear central units (p-phenylene and 4, 4'-biphenyl); liquid crystallinity is not found in the analogous m-phenylene derivatives. This finding is consonant with the established principles of prolate mesogen structural requirements, i.e. core linearity is closely related to liquid crystal phase formation and deviation from core linearity lowers mesophase stability. The results of this study indicate that the 2,5-thiophene and 2,2'-bithiophene moieties with non-linear structures are viable mesogenic core units and may be substituted for p-phenylene units in conventional liquid crystal molecules. Moreover, these moieties should be particularly useful for modifying the transition temperatures of liquid-crystalline polymers.     

Understanding the rheological behavior and processing of complex polymer systems from a molecular point of view

The rather complex rheological behavior of block copolymers and thermotropic liquid-crystalline polymers is illustrated, putting emphasis on transient shear flow and stress relaxation behavior.