Synthesis and characterization of diselenide crosslinked polymeric micelles via Diels–Alder click reaction

ABSTRACT

A well-defined amphiphilic block copolymer, poly (ethylene oxide)-b-(poly (furfuryl methacrylate) (PEO-b-PFMA) was prepared by single electron transfer living radical polymerization using tris(dimethylamino)ethyl amine (Me6TREN) as a ligand. The block copolymer formed sub-100 nm micelles in water with PEO as a shell and PFMA as a core. Diels–Alder click type reaction was employed to form core-crosslinked micelles using a diselenide-containing crosslinker without any catalyst. The block copolymer and micelles were characterized by gel permeation chromatography, nuclear magnetic resonance, Fourier-transform infrared spectroscopy, dynamic light scattering analysis and transmission electron microscopy. The stability of core-crosslinked micelles under reductive-oxidative condition was also investigated. The diselenide crosslinked micelles displayed good stability against extensive dilution but decomposed under the presence of hydrogen peroxide or glutathione. The redox responsive core-crosslinked micelles can be a promising carrier for drug delivery applications.     

Sorption properties of silica gel with adsorbed copolymers of 4-vinylpyridine and styrene with respect to Cu(II), Pb(II) and Fe(III) ions

Abstract

A number of new organo-mineral composites in different mass ratios of organic and inorganic components were obtained by adsorption on the silica gel surface of 4-vinylpyridine–styrene copolymer. The fact of the copolymer immobilization on the silica gel surface was confirmed by Fourier transform infrared spectroscopy (FTIR) spectroscopy and thermogravimetry combined with mass-spectrometry analysis. Thermogravimetric analysis was employed for estimation of copolymers mass content in the composite obtained. It has been established that all the synthesized composites exhibit sorption activity toward traces of Cu (II), Pb (II) and Fe (III) ions in neutral aqueous medium.     

Properties of liquid crystals and Cu2+ recognition based on Schiff bases

Two series of new Schiff base compounds were synthesized. For Schiff base compounds with a pyridine nitrogen atom in 4-position (7a–e), their supramolecular hydrogen bonding complexes show good liquid crystal properties. However, no liquid crystal property is observed for 8a–e. Results of theoretical calculations demonstrate that it is the intermolecular hydrogen bond of Schiff base compounds (8a–e) that prevents the formation of supramolecular hydrogen bonding. The Schiff base compounds, with terminal alkoxy chains, can recognize Cu²⁺ selectively with a color change. Nevertheless, others cannot recognize Cu²⁺.     

CCMM′98 Chemistry and Characterization of Mesophase Materials

Abstract

Although the International Liquid Crystal Conference in Strasbourg in July 1998 was a most notable exception, it is unfortunately true that the chemistry content of many liquid crystal meetings is painfully low. This fact, along with a strong desire to show the growing commonality of work in thermotropic and lyotropic liquid crystals, and in block copolymers, was enough to persuade a group of scientists in Bayreuth that it might be timely to organize a meeting primarily to present results on the chemistry and characterization of these mesophase materials. So, from 7–9 October 1998, around 100 delegates from the USA to Japan, via Europe, congregated in the old Fraconian city of Bayreuth for two-and-a-half days of synthesis and structure under the title CCMM′98.     

PMA‐b‐PAA‐controlled synthesis of one‐dimensional CaCO3 superstructures

Crystallization of calcium carbonate (CaCO₃) crystals by a gas‐liquid diffusion method has been carried out in aqueous solution using a double‐hydrophilic block copolymer (DHBC) poly(maleic anhydride)‐b‐poly(acrylic acid) (PMA‐b‐PAA). The as‐prepared products were characterized with X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), high‐resolution transmission electron microscopy (HRTEM) and infrared spectroscopic analysis (FT‐IR). Uniform one‐dimensional calcite micro/nanostructures with different morphologies are fabricated through an assembled process. The influence of PMA‐b‐PAA copolymer concentration on the morphology of calcite nano/microwires is investigated, which plays an important role in the morphological control of building blocks composed of one‐dimensional calcite crystals. The possible formation mechanism of one‐dimensional CaCO₃ crystals was discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Towards The Synthesis of Electroactive Block Copolymers Via Anionic-To-Ziecler-Natta Transformation Reactions

Styrene/acetylene diblork copolymers have been prepared by alkylating Ti(OBu)₄ with polystyryl lithium (Li/Ti = 3) in THF followed by exposure to acetylene. Homopolystyrene can be separated from the soluble, blue-violet diblock copolymer by extraction with 10% THF/acetone, the latter being soluble in THF. Infrared spectroscopy confirmed the presence of polystyrene and (CH)_x components. Gel permeation chromatography of copolymers in which the (CH)_x portion has been converted to poly(l,2-dibromoethylene unambiguously demonstrates that block copolymers have been synthesized. The yields of block copolymer based on the total weight of polystyryl Li used initially is estimated to be ca 5%.     

Optical Field Induced Scattering in Polymer Dispersed Liquid Crystal Films

Abstract

Polymer dispersed liquid crystals are composite materials consisting of inclusions of liquid crystalline materials dispersed in a polymer binder. If the refractive indices of the constituent liquid crystal and polymer are appropriately matched, then films of these materials may be switched between an optically scattering state and a non–scattering transparent state^1?2 by the application of electric fields which reorient the liquid crystal in the inclusions. In this paper we discuss the response of these materials to intense laser radiation, and examine the mechanisms associated with optical field induced reorientation.     

Mechanochromic Photoluminescent Liquid Crystals Containing 5,5′-Bis(2-phenylethynyl)-2,2′-bithiophene

5,5′-Bis(2-phenylethynyl)-2,2′-bithiophene derivative 1 containing dendritic moieties linked through amide groups was synthesized. Compound 1 exhibits a rectangular columnar phase on slow cooling from the isotropic liquid. In contrast, a cubic phase is formed as a metastable liquid-crystalline phase by rapid cooling of the isotropic melt. Mechanical shearing induces a cubic–columnar phase transition, accompanied by the change of a photoluminescent color from yellow-green to green. The infrared spectra of 1 suggest that the mechanical stimuli can induce the partial dissociation of the hydrogen bond. This may lead to more disordering of the π-stacks of chromophores.     

Thermotropic Liquid-Crystalline Polymers,Re-Entrant and Discotic Liquid Crystals. A Bibliography for 1977–1984

This bibliography contains bibliographic data of books and papers concerning the thermotropic liquid-crystalline polymers, re-entrant and discotic liquid crystals for 1977–1984 years. The bibliography of the thermotropic liquid-crystalline polymers contains also bibliographic data of papers describing both the thermotropic and lyotrophic behavior of the liquid-crystalline polymers, liquid-crystalline melts, solutions of thermotropic liquid-crystalline polymers, solutions of polymer chains in a nematic solvent and some polymerization problems. In this bibliography are included also bibliographic data of papers which according to the citation in the literature are important for the study of both the thermotropic and lyotropic liquid-crystalline polymers. In the bibliography of the re-entrant liquid crystals (at atmospheric pressure) are included the papers published after the first work in this field of Cladis (Phys. Rev. Lett. 35, 48–51 (1975)) up to the end of 1984 year. Similarly, in the bibliography of the discotic liquid crystals are included the papers published after the first work of Chandrasekhar, Sadashiva and Suresh (Pramana 9, 477–480, (1977)) also up to the end of 1984 year.     

Infrared Spectroscopic Studies of Homologous Cholesteric Liquid Crystals

Abstract

Infrared (500–2500 cm^?1) spectra of cholesteryl alkyl carbonates (methyl, ethyl and oleyl) have been examined in the solid (cholesteryl methyl carbonate and cholesteryl ethyl carbonate) and liquid crystalline (cholesteryl oleyl carbonate) states. An attempt has been made to correlate the variation in the intensities and frequency shifts with the molecular structures. The shift in the carbonyl frequency in the case of cholesteryl oleyl carbonate may be correlated with the affect on the coplanarity with benzene ring.     

Dielectric properties of ternary melt processed blends

Thermal, morphological and dielectric properties of conductive thermoplastic blends based on polystyrene, styrene–butadiene–styrene block copolymer and doped polyaniline have been investigated with special emphasis on the effect of doped polyaniline concentration. Blends were prepared by melt blending using an internal mixer. Morphological studies by scanning electron microscopy of cryofractured surfaces indicated that thermoplastic matrix had a better miscibility with the presence of copolymer as compatibilizer and also good dispersability and structuring of doped polyaniline particles within polystyrene. A reduction in impedance from 26 to 2 MΩ at 10 Hz, with the increasing polyaniline content is also observed. The blends can be used for antistatic applications. From the fit to the impedance spectroscopy data we obtained the relaxation strength, the depression angle and the relaxation.     

Synthesis and characterization of new nematic liquid crystalline compounds-based thiophene units

Four new liquid crystalline thiophene compounds (M1?M4) with a long flexible spacer were prepared. Their structures were characterized by Fourier transform infrared and proton nuclear magnetic resonance. The mesomorphism and thermal stability were investigated with differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The photo-physical properties were evaluated using ultraviolet/visible spectroscopy and photoluminescence. M1?M4 all showed thermotropic mesogenic properties with excellent thermal stability, and exhibited nematic threaded texture, droplet texture, and Schlieren texture on heating and cooling cycles. The effect of flexible spacer and terminal groups on mesomorphic and spectroscopic property is discussed. The experimental results demonstrated that the tendency toward melting temperature (Tm) decreased, while isotropic temperature (Ti) increased with increasing the flexible spacer length. In CHCl₃ solution, these thiophene compounds displayed an intense broad absorption band peaking within 230–340 nm and a maximum fluorescent emission wavelength at 426–439 nm.     

New fabrication approach to develop a high birefringence photo-crosslinked film based on a sulfur-containing liquid crystalline molecule with large temperature dependence of birefringence

ABSTRACT

We present a new fabrication approach to achieve a high birefringence film by means of photopolymerization based on an alkylthio-containing rod-like liquid crystalline molecule exhibiting large temperature dependence of birefringence. We designed a new reactive mesogen having alkylthio linkages (BPM–S). It was found that BPM–S had a larger increment of birefringence with decreasing temperature, relative to commercially available alkoxy analog LC242. This result could be thought to be due to enhanced intermolecular attractive interaction for an alkylthio mesogen implied by the proximity of laterally neighboring molecules and cybotactic nematic tendency based on wide-angle X-ray measurement. The uniaxially-aligned photo-polymerized film for BPM–S showed higher birefringence than that for LC 242.     

X-ray Analysis of Chiral Thermotropic Liquid Crystal Copolyesters Based on Linear and Nonlinear Aromatic Ester Triads

A series of chiral thermotropic liquid crystalline copolyesters, based on linear mesogenic triads and nonlinear nonmesogenic triads consisting of two p-oxybenzoyl units coupled by a terephthaloyl or phthaloyl residue respectively, is studied by X-ray diffraction. Complementary data of differential calorimetry and polarizing microscopy are presented. The degree of crystallinity is found to depend significantly on the relative content of the nonlinear counit and to vary with thermal history. The occurrence of cholesteric phases is established, whose stability and breadth can be modulated on the basis of appropriate chemical compositions. The structural data of the investigated copolymer samples are compared with those previously obtained for an analogous series of copolymer samples based on the same linear aromatic triad and an isomeric triad containing a central isophthaloyl residue.

Keywords: liquid crystalline polymers, chiral thermotropic polymers, cholesteric copolyesters, 4,4'-(terephthaloyldioxy)dibenzoate mesogen, X-ray diffraction     

Structural transformations in solid and liquid n-butanol from FTIR spectroscopy

Abstract

FTIR spectra of n-butanol were registered for temperatures from ?100 °С to 40 °С during heating of the sample and from 40 °С to ?170 °С during its cooling. Structural changes at phase transitions solid–liquid and liquid–solid were detected. At n-butanol cooling below the melting point the initial crystalline structure was not achieved. Instead of it, a super-cooled liquid or amorphous phase was obtained. Quantum-chemical simulation of 27 n-butanol rotational conformers were provided via ROCBS-QB3 method. According to the calculations, the most stable conformer is TG′t. Comparison of calculated in the anharmonic approximation IR spectra of possible monomers and dimers of n-butanol with experimentally registered spectra showed that there are no monomers and dimers in the studied sample, and the structure of n-butanol in the condensed state is formed by bigger clusters.     

Conformational Mobility and Phase Transitions in Alkyloxybenzoate of Cholesterol

Abstract

The structural particularities of polymorphic modifications and cholesterol liquid crystal phase have been investigated by theoretical and experimental IR spectroscopy methods. The spectra were recorded in the interval of temperatures 293–523 K within the range of 600–3600 cm^?1. The frequencies of normal modes and intensities in the IR spectra have been calculated for the alkyloxybenzoate of cholesterol conformers, which may be realized under certain temperatures. Comparison of results of theoretical modelling and recorded spectra confirmed suggestion about conformational mobility basically defined with changing of steroid kennel orientation comparatively stayed part of molecule in the different phase state.     

Synthesis of a BDT-based small-molecule acceptor with dye end groups for organic photovoltaic cell application

ABSTRACT

An acceptor-donor-acceptor (A–D–A)-type small molecule, BDT-IN, having a benzo[1,2-b:4,5-b']dithiophene (BDT) unit as its electron-donating core (D) and an 1,3-indanedione (IN) unit as its electron-withdrawing end group (A), was synthesized by Knoevenagel condensation. The BDT-IN film showed broader UV absorption with a greater red shift (λ_max = 622 nm) than that of the BDT-IN solution (λ_max = 570 nm). The organic photovoltaic cells were fabricated with an ITO/PEDOT:PSS/poly(3-hexylthiophene): BDT-IN/LiF/Al configuration, and showed a power conversion efficiency of 0.23%.     

Synthesis of Novel Ionic Liquid Crystalline Pyrrole Derivatives Having a Viologen Moiety

Abstract

A novel liquid crystalline N-substituted pyrrole having an ionic viologen side chain was synthesized, and was polymerized by a FeCl₃ method. Thermotropic liquid crystalline behavior of the pyrrole and the polymerized material were investigated by DSC, thermo-controlled polarizing optical microscopy, and XRD. The pyrrole derivatives showed two smectic phases between isotropic and crystalline (solid) phases. Viologen functions of redox and cation-radical generation for the pyrrole derivatives were confirmed by cyclic voltammetry with UV-Vis spectroscopy.     

Design and synthesis of large-pore p6mm mesoporus zirconia thin films templated by a novel block copolymer

A novel poly(butadiene-b-ethylene oxide) (PB-PEO) block copolymer was employed as the structure-directing agent for the preparation of large-pore, mesoporous for zirconia with two-dimensional (2D) hexagonal (p6mm) mesostructure through evaporation-induced self-assembly (EISA) approach. The presented materials, calcined at 400 °C and 500 °C, were characterized in detail by X-ray diffraction, transmission electron microscopy, and nitrogen sorption. The results showed that the mesoporous zirconia possesses a large-pore diameter, high BET surface area, and large-porosity. A probable formation mechanism was also presented in this work.     

Birefringence of binary liquid crystalline mixtures of MBBA and PPMAECOBA in TCM,interferometric assessment

Abstract

The mutual influence of two mesogenic components, namely a nematic liquid crystal N-(p-methoxy-bezylidene)-butylaniline (MBBA) and a lyotropic liquid crystal poly-(phenyl-methacrylic) ester of cetyloxybenzoic acid (PPMAECOBA) in tetra-chloromethane (TCM) is studied in this paper. The ordinary and extraordinary refractive indices of the mixtures, nematic liquid crystal and lyotropic liquid crystal were measured at 589.3?nm with a Rayleigh interferometer and some electro-optical parameters were computed. The main refractive indices, the birefringence, the main normalized polarizabilities and their difference are dependent on the mixture volumetric concentrations, proving the existence of the collective orientational interactions between the two types of liquid crystals.