Synthesis of thermotropic liquid crystal polyimide and its properties

Thermotropic liquid crystal polyimide which has neither an ester linkage nor a carbonate linkage was prepared by the polymerization of 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) and 1,3-bis[4-(4′-aminophenoxy)cumyl)]benzene (BACB). This polyimide shows the liquid crystal phase at 549-593 K. Mixing this liquid crystal polyimide or copolymerizing BACB decreases the melt viscosity of the thermoplastic polyimide (Aurum). © 1994 John Wiley & Sons, Inc.     

Ionic thermotropic liquid crystal dendrimers

The synthesis and characterization of two families of ionic liquid crystal dendrimers consisting of the ammonium salts of the commercially available poly(amidoamine) (G = 0-5) and poly(propylene imine) (G = 1-5) dendrimers and three long-chain carboxylic acids are reported. The liquid crystalline behavior was investigated by means of differential scanning calorimetry, polarizing light optical microscopy, and X-ray diffractometry. The thermal stability of the ionic materials was further studied by NMR. Most of the dendrimers show lamellar mesomorphism, and two of them exhibit columnar mesomorphism. On the basis of the experimental results, we propose models both at the molecular level and in the mesophase for all the materials.     

Polymer-dispersed liquid crystal composites for bio-applications: thermotropic,surface and optical properties

Polymer-dispersed liquid crystal (PDLC) systems based on polysulfone as carrying matrix and 4-cyano-4?-pentylbiphenyl (5CB) liquid crystal (LC) were obtained as thin transparent films. The PDLC films were prepared by solvent- and thermally induced phase separation methods, with various compositions in the two components. Information on the phase separation was obtained by polarised light optical microscopy, differential scanning calorimetry and scanning electron microscopy. The PDLC composites show well-defined droplets of submicrometric size, around 650 nm for a medium content of LC and around 250 nm for a low one. The droplets show a radial configuration and a homeotropic alignment of the LC molecules within. By contact angle measurement and surface free energy calculations, it was established that self-assembling of aliphatic units of the two composite components, at droplet interface, is the driving force of the homeotropic alignment. Moreover, these data indicated the potential biocompatibility of the studied composites. The photophysical behaviour shows a better light emission of the PDLCs containing bigger droplets.     

Lyotropic structures in a thermotropic liquid crystal

We have investigated the nature of didodecyldimethylammonium bromide (DDAB)/water aggregates dispersed in 4-n-pentyl-4'-cyanobiphenyl thermotropic liquid crystal (5CB). The structure of this microemulsion has been probed by small-angle neutron and X-ray scattering experiments far above the nematic-to-isotropic phase transition temperature of the solvent. Our data show that the stability of this system is controlled by strong attractive van der Waals interactions between spherical inverted micelles. These interactions also explain why other swollen mesophases in related cosurfactant/DDAB/water/5CB phase diagrams are not observed. When approaching the isotropic-to-nematic phase transition, scattering experiments additionally confirm the predominance of an increasing attractive interaction due to the 5CB paranematic fluctuations.     

Synthesis and spinning of a thermotropic liquid crystal copolyester containing a semirigid cycloaliphatic spacer

A thermotropic, liquid crystalline copolyester, based on 2-chlorohydroquinone, 1,4-cyclohexanedimethanol and terephthaloyl chloride, has been synthesized and melt spun. The cyclohexanedimethylene moiety acts as a semirigid spacer, introducing flexibility while preserving the thermotropic nature of the polymer. Melt-spun fibers were observed to have a high degree of molecular alignment owing to the nematic nature of the melt. Both polymer and fiber properties have been characterized. Characterization techniques used to this end include elemental analysis, hot-stage polarized light microscopy, scanning electron microscopy, dilute solution viscometry, Fourier transform infrared spectroscopy, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1473–1480, 1998     

A mixed cyclodextrin‐biphenyl thermotropic liquid crystal: Synthesis,liquid‐crystalline properties,and supramolecular organization

A well‐defined structure liquid crystal heptakis [6‐deoxy‐6‐(1‐H‐1,2,3‐triazol‐4‐yl)(methyl)6‐(4‐methoxybiphenyl‐4′‐yloxy) hexanoyl]‐β‐cyclodextrin (H6B‐β‐CD) was synthesized from propargyl 6‐(4‐methoxybiphenyl‐4′‐yloxy) hexanoate (P6B) and heptakis (6‐deoxy‐6‐azido)‐β‐cyclodextrin ((N₃)₇‐β‐CD) by click reaction. The chemical structure of H6B‐β‐CD was confirmed by ¹H NMR, FTIR, and MALDI‐TOF MS. The thermal stability of the compound was investigated by thermogravimetric analysis (TGA). The liquid crystalline behavior was studied by differential scanning calorimetry (DSC), polarizing optical microcopy (POM), and wide‐angle X‐ray diffraction (WAXD) measurement. These investigations have shown that the supramolecular structure of H6B‐β‐CD are consisted of a large scale ordered lamellar structure and a small scale ordered structure (SmE) at low temperature region. As the temperature increases, the small scale structure becomes disordered relatively in the first instance, from smectic E to smectic A. Then, the lamellar structure collapses and nematic phase and isotropic phase are observed in sequence. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2838–2845, 2010     

Synthesis,liquid crystallinity,and mechanical properties of thermotropic polyquinolines

Thermotropic liquid-crystalline polyquinolines with high molecular weights, i.e., poly[2,2′-(α,ω-dioxyphenylene (or -dioxybiphenylene) alkane)-6,6′-(4,4′-dioxybiphenyl)-bis(4-phenylquinoline)]s (P-H-B1Mns or P-H-B2Mns), were synthesized by polycondensation of 4,4′-bis(4-amino-3-benzoylphenoxy)biphenyl and α,ω-bis(4-acetophenoxy (or -acetobiphenoxy))alkanes. For P-H-B1Mn series, the T_m and T_i were in the range of 129–230°C and 156–254°C, respectively, while for the P-H-B2Mn series, those were 182–275°C and 217–309°C, respectively. The introduction of both the dioxybiphenylene group and an alkylene spacer induced thermotropic liquid crystallinity in the polyquinoline, although the introduction of the alkylene spacer alone did not induce it. In addition, polyquinolines substituted with methyl, methoxy, and chloro groups exhibited larger mesophase temperature ranges as well as higher T_ms and T_is than the unsubstituted ones. Tensile strengths of these thermotropic polyquinolines were considerably high in the range of 770 to 1170 kgf/cm². © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 749–759, 1998     

Phase behavior of nanoparticles in a thermotropic liquid crystal

In this work, we describe the outstanding behavior of a nanocomposite system composed of the thermotropic liquid crystal 5CB doped with nanoparticles of the magnetic iron oxide maghemite (gamma-Fe(2)O(3)). We show that the I-N transition is associated with a reversible gathering of nanoparticles inside droplets of the ferronematic phase coexisting with a nonmagnetic nematic host phase.     

Control of liquid crystal alignment on polystyrene nanorod arrays

Herein we demonstrate that the alignment of liquid crystals on a nanopatterned substrate can be controlled by the small variation of the size of the nanostructure. We fabricate hexagonally packed uniform polystyrene nanorod arrays and investigate the orientation of liquid crystals on the patterned surface. Homeotropic alignment is found on larger or longer rod arrays (diameter > 55 nm or length > 113 nm), while random alignment of liquid crystals is observed on smaller or shorter rod arrays. The change of liquid crystal orientation occurs with the small variation of the nanorod diameters or lengths.     

A surfactant-encapsulated polyoxometalate complex towards a thermotropic liquid crystal

A novel surfactant-encapsulated terbium-substituted heteropolyoxotungstate complex [L1]13[Tb(SiW11O39)2].30H2O (SEC-1) bearing mesomorphous groups was successfully prepared by the ionic self-assembling route, exhibiting characteristic thermotropic liquid-crystalline behavior.     

A mixed fullerene-ferrocene thermotropic liquid crystal: synthesis, liquid-crystalline properties, supramolecular organization and photoinduced electron transfer

Grafting of a ferrocene-containing liquid-crystalline malonate derivative to C60 led to the mixed fullerene-ferrocene material 1 which gave rise to a smectic A phase. Cholesterol was used as liquid-crystalline promoter. X-ray diffraction experiments and volumetric measurements indicated that 1 is organized in double layered structures. The corresponding supramolecular organization within the mesomorphic lamellar phase is characterized by a microsegregation of the different units (ferrocene, fullerene, and cholesterol) in distinct sublayers. In such a smectic A phase, C60 imposes the arrangement of the other molecular moieties. Photophysical studies revealed that electron transfer occurs from the donor ferrocene to the electron accepting fullerene. The formation of a long-lived radical pair, with lifetimes of the order of several hundred nanoseconds, was confirmed by time-resolved spectrometry, especially in the near infrared region, in which the radical anion of the fullerene moiety displays its characteristic fingerprint absorption.     

Thermal properties of some fully aromatic thermotropic liquid crystal polyesters

Wholly aromatic liquid crystalline main chain polyesters derived from terephthalic acid, phenyl- or (1-phenylethyl)hydroquinone modified with either 3,4′- or 4,4′-dicarboxydiphenylether and p-hydroxybenzoic acid, have been prepared by acidolysis and thermally investigated. All prepared polyesters exhibit excellent thermal stability up to about 400°C, however, the (1-phenylethyl)hydroquinone polyesters generally showed lower stability. Melting points could be decreased to around 200°C without any decrease in the thermal stability or the nematic range.     

Solubilization of thermotropic liquid crystal compounds in aqueous surfactant solutions

We study the micellar solubilization of three thermotropic liquid crystal compounds by immersing single drops in aqueous solutions of the ionic surfactant tetradecyltrimethylammonium bromide. For both nematic and isotropic drops, we observe a linear decrease of the drop size with time as well as convective flows and self-propelled motions. The solubilization is accompanied by the appearance of small aqueous droplets within the nematic or isotropic drop. At low temperatures, nematic drops expell small nematic droplets into the aqueous environment. Smectic drops show the spontaneous formation of filament-like structures which resemble the myelin figures observed in lyotropic lamellar systems. In all cases, the liquid crystal drops become completely solubilized, provided the weight fraction of the liquid crystal in the system is not larger than a few percent. The solubilization of the liquid crystal drops is compared with earlier studies of the solubilization of alkanes in ionic surfactant solutions.     

Infrared study of phase transitions in thermotropic liquid crystal polyesters

Three samples of semiflexible thermotropic liquid-crystalline polyesters based on mesogenic aromatic triads and a decamethylene spacer have been investigated by IR spectroscopy at various temperatures between room temperature and 290°C. The crystal-to-liquid crystal (either nematic or smectic) phase transition was accompanied by fairly strong spectral variations, whereas slight, but significant, changes in the IR profiles were detected at the liquid crystal-to-isotropic transition. By comparing the results obtained with the spectral behavior recorded for corresponding structural analogs of low molar mass, it was possible to attribute the spectral variations observed in the polymer samples to a decrease in intermolecular interactions rather than to conformational changes. The thermal transitions indicated by IR spectra were in good agreement with the analogous data obtained by calorimetric or optical microscopy techniques.     

Crosslinked liquid crystal polymers from liquid crystal monomers: Synthesis and mechanical properties

Difunctional acrylates and methacrylate monomers have been made which are high order smectic liquid crystal (or crystalline) at room temperature. This report discusses materials with the following structure: F–S–M–S–F, where F is a functional group, acrylate or methacrylate (A or M); S is a spacer (CH₂)_n(n), and M is a mesogen—in this case 4,4′-dioxybiphenyl (B). They are codified as BnA or BnM where n is the number of methylenes in the spacer. High conversion with high T_g can be obtained when polymerizing in the smectic state because the reactive end groups are concentrated in a small volume and can react well with little or no diffusion. B2A, B3A, B6A, B11A, and B3M were polymerized in the smectic state and compared to polymers made at temperatures where the monomers were isotropic. High conversion was obtained below final T_g—even then, probably because the polymers were ordered. All the polymers were studied by WAXD and dynamic mechanical spectroscopy. Solid-state NMR on B3A showed that there was very high conversion of the double bonds at all temperatures. B3A photopolymerized in the smectic state (60–76°C) produced a crystalline polymer with T_g = 185°C (1 Hz). When photopolymerized at 85°C, above the isotropization temperature (T_i), a poorly organized polymer was obtained with a T_g of 155°C (1 Hz). Monomers with an odd number of methylene groups as spacers were crystalline after polymerization. With an even number of methylene groups, they lost most of their crystallinity on polymerization below T_i, but retained a low order smectic structure. Similar structures were obtained with all the monomers when they were polymerized above T_i. There was little effect of polymerization temperature on T_g when the spacers had an even number of methylene groups. © 1993 John Wiley & Sons, Inc.     

New hydrocarbon side chain liquid crystalline polysiloxane polymers: Synthesis,characterization, and thermotropic behavior

A series of new and high-purity hydrocarbon liquid crystal monomers were synthesized through the acylation reaction, deoxygenation reaction, and Grignard reaction. ¹H-NMR spectra and elemental analyses were used to examine their purity. The liquid crystalline polysiloxane polymers were obtained by grafting the monomers onto poly(methylhydrosiloxane). The thermal transition temperature, mesomorphic properties, and mesophase textures of the monomers and the polymers were determined by differential scanning calorimetry (dsc), polarized optical microscopy, and X-ray diffraction analysis. Moreover, we observed the even–odd effect of the smectic/isotropic transition temperature with the length variation of the substituents. In this study, we found by X-ray diffraction that the liquid crystalline polysiloxane polymers undergo a transition from smectic B to smectic E mesophase. However, dsc has difficulty detecting the phase transition process. By considering the spin–lattice relaxation time (T₁), we can systematically explain the relation between the flexibility of the substituent with the smectic/isotropic transition temperature. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2849–2863, 1998     

Synthesis and liquid crystalline properties of thermotropic homo- and copolycarbonates

Nondirect-type thermotropic homo- and copolycarbonates which have flexible spacers between mesogens and carbonate linkages (-mesogenic unit-flexible spacer-carbonate link-flexible spacer-) were derived from dihydroxyalkyleneoxy derivatives containing biphenyl, i.e., 4,4′-bis (ω-hydroxyalkyleneoxy)biphenyl (Ia and Ib), as mesogens and the structure-liquid crystallinity relationships were evaluated by thermal analysis and with polarizing microscope. Homopolycarbonates with high molecular weight were prepared from (Ia) and (Ib), and alkylene diphenyl dicarbonates (II) by melt polycondensation. The polymers form mesomorphic phases and exhibit linear decrease of phase-transition temperatures with increment of alkylene spacer lengths without displaying odd-even number fluctuations. They show lower phase-transition temperatures and narrower mesomorphic temperature ranges than analogous direct-type (-mesogenic unit-functional group-flexible spacer-) biphenyl-containing polycarbonates \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm OMOC}({\rm O}){\rm O}({\rm CH}_2)_m {\rm OC}({\rm O})\rlap{--})_x $\end{document} and polyesters \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm OMOC}({\rm O})({\rm CH}_2)_m {\rm C}({\rm O})\rlap{--})_x $\end{document}, but have wider temperature ranges than nondirect-type (-mesogenic unit-flexible spacer-functional group-flexible spacer-) biphenyl-containing polyesters \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm O}({\rm CH}_2)_n {\rm OMO}({\rm CH}_2)_n {\rm OC}({\rm O})({\rm CH}_2)_m {\rm C}({\rm O})\rlap{--})_x $\end{document}. These results indicate that by the incorporation of alkylene segments between mesogens and carbonate linkages the polymers having reasonable phase-transition temperatures and wider mesophasic temperature ranges can be obtained. Copolycarbonates were prepared from mixtures of (Ib) and 1,4-bis(2-hydroxyethyleneoxy)benzene (IV), nonmesogenic moiety, taken in definite molar ratio in feed and (II) (m = 2 and 4). These copolymers except polymers having only nonmesogenic moiety show liquid crystalline mesophases and have wider phase-transition temperature ranges than the homopolymers. Maximum temperature ranges are observed in the copolymers of composition ratio of 1 : 1. Stable mesophases can be obtained over the entire range of compositions, even though the copolymers contain nonmesogenic units in the backbones.     

Synthesis and characterization of thermotropic amphiphilic liquid crystals: semiperfluoroalkyl-ß-D-glucopyranosides

As part of our study of the mesomorphic properties of glucopyranosides containing fluorinated chains, this paper focuses on an investigation of the liquid crystalline behaviour of nonaromatic compounds. The synthesis of eight single-tailed materials which contain a semiperfluoroalkyl chain linked to the polar glucose head group is described. Using polarized optical microscopy, DSC and X-ray diffraction all the materials were found to show only monomesomorphism, a smectic A phase with bimolecular layers. The thermal behaviour is discussed in comparison with the previously reported data on the series of parent compounds.