Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, ^1?H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.     

Mesomorphic and luminescent properties of side chain nematic liquid-crystalline polymers containing Ir(III)

Iridium-containing liquid-crystalline polymers were obtained by graft copolymerisation using poly(methylhydrogeno)siloxane, 1-methyl-4-(4-(4-vinylcyclohexyl)cyclohexyl)benzene (M₁) and an iridium complexes monomer (Ir-M₂). The series of polymers contained different molecular fractions of Ir-M₂ from 0% to 1.2%. All of these polymers showed mesomorphic behaviours. The introduction of small amount of iridium ions endowed liquid-crystalline polymers with luminescent properties. The chemical structures were characterised by IR and ¹H NMR. The mesomorphic properties and phase behaviour were investigated by differential scanning calorimetry, thermal gravimetric analysis, polarising optical microscopy and X-ray diffraction. With an increase of iridium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) decreased. All polymers showed typical nematic marble textures, which was confirmed by X-ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of iridium complexes units did not change the liquid-crystalline state of polymer systems. With Ir³⁺ ion contents ranging between 0.6 and 2.4 mol%, luminescent intensity of polymers gradually increased.     

Synthesis and characterization of side‐chain liquid crystalline polymers bearing cholesterol mesogen

A series of new norbornene carboxylic cholesteryl ester monomers with and without alkyl spacers, NBCh, and NBCh‐n , respectively, were synthesized. New side‐chain liquid crystalline homopolymers, PNBCh and PNBCh‐n , were cleanly prepared using NBCh and NBCh‐n , respectively, with Grubbs 2nd generation catalyst. Molecular and structural characterization of monomers and polymers were carried out by nuclear magnetic resonance, NMR, Fourier transform infrared, FT‐IR, spectroscopy, and gel permeation chromatography, GPC. The thermal and liquid crystalline properties of the homopolymers were investigated by differential scanning calorimetry, DSC, thermogravimetric analysis, TGA, and polarized optical microscopy, POM. Small angle and wide angle X‐ray studies of PNBCh‐n in powder and fiber states not only confirmed the formation of smectic A mesophases, but also established their morphologies. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2690–2701, 2009     

Luminescent Iridium-containing liquid crystalline polymers in the side chain

Luminescent liquid crystalline polymers consisting of Iridium attached to polysiloxanes are prepared. 4-Cyanophenyl 4-(allyloxy) benzoate (M₁) and an Iridium complex (Ir-M₂) grafted to poly(methylhydrogeno)siloxane are used for the preparation of the Iridium-containing liquid crystalline polymers. The chemical structures are characterised by Fourier transform infrared spectroscopy and ¹H NMR. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing <1.2 mol% of the Iridium ions reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. The introduction of the Iridium ions does not change the liquid crystalline state of polymer systems; on the contrary, the polymers are enabled with the luminescent properties. With the Iridium ion contents ranging between 0.3 and 1.2 mol%, luminescent intensity of polymers gradually increased. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase.     

Static and dynamic properties of smectic liquid crystal side chain polymers

On the basis of models for the conformation of liquid crystal side chain polymers in the smectic phase, some dynamic aspects of such systems are considered using the reptation approach. The overall diffusion constants of the polymer along and perpendicular to the director of the side chains are derived.     

Properties of optically addressed liquid crystal spatial light modulators studied by mach-zehnder interferometry

In this work optically addressed liquid crystal spatial light modulators are experimentally investigated. Local reorientation of molecules in the modulator and local changes of effective refractive index n_eff (x,y) are induced by modulated light intensity I (x,y). We present preliminary results of measurements of phase shifts in optically addressed liquid crystal panels using a Mach-Zehnder interferometer. Experiments were performed for the panels filled with nematic and dye-doped nematic liquid crystals. Optical addressing was realized by Ar+ laser beam (λ = 514.5 nm) while the reading beam was supplied by He-Ne laser (632.8 nm). The operation voltage was in the range 4 - 20 V. The total phase shift under the influence of addressing light for the studied systems was 2 - 6 pagr;, sensitivity to the addressing light ∼ μW/cm² per 2π phase change and speed of response to the light was 20 ms - 30 s with total recovery time 0.5 - 120 s.     

Twisted smectic A phases in side chain liquid crystal polymers

The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type II superconductors.     

Twisted smectic A phases in side chain liquid crystal polymers

Abstract

The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type II superconductors.     

Phase behaviour of lyotropic liquid crystalline side chain polymers in aqueous solutions

Amphiphilic lyotropic liquid crystalline surfactants are synthesized displaying 10-undecenoic acid as hydrophobic and ethyleneglycol units as hydrophilic parts of the molecules. By addition reaction of the monomeric surfactants with poly [oxy(methylsilylene)], the surfactants are attached as side chains to the siloxane main chain. The phase behaviour of a polymer-water system and the corresponding monomer-water system is investigated by polarizing microscopy. The monomeric surfactant exhibits a liquid crystallineM ₁-phase of hexagonally packed, rod-like micelles in a concentration range of 49 to 70% surfactant. The liquid crystalline state of the polymeric surfactant is more stable, which is indicated by a broader temperature- and concentration range (35%–90% polymer surfactant). At lower concentration aM ₁-phase exists, which is separated by a cubic phase from a lamellarG-phase at higher concentration of the polymer surfactant. Compared to the monomeric system, the increased stability of the polymeric mesophase can be understood by the restriction of motions of the amphiphiles due to the linkage to the polymer main chain.Dedicated to Prof. Dr. F. H. Müller.The authors are greatly indebted to Wacker Chemie, D-Burghausen, FRG for kindly delivering the poly(hydrogensiloxane).     

Supramolecular side chain liquid crystal polymers II. Interaction of mesogenic acids and amorphous polymers

The thermal behaviour of blends of a low molar mass mesogenic acid, 6-(4-n-butyloxy-4'-oxybiphenyl)hexanoic acid (BOBPOHA) with polystyrene, poly(2-vinylpyridine) and poly(4-vinylpyridine) has been characterized. BOBPOHA exhibits a monotropic smectic A phase and is essentially immiscible with polystyrene. Thus, the transition temperatures of the acid are independent of blend composition. In contrast, the thermal properties of the acid are strongly modified on blending with poly(2-vinylpyridine) and poly(4-vinylpyridine). Molecular mixing occurs in these blends below approximately 0.2 mol fraction of acid. This miscibility is driven by the formation of hydrogen bonds between the pyridyl and acid moieties. At higher concentrations of acid, phase separation occurs. Liquid crystallinity is not observed in the miscible blends while in the immiscible blends mesomorphic behaviour is attributed to regions of phase separated acid.     

Properties of side chain liquid crystal and amorphous polymers. Applications to non-linear optics

Comb-like liquid-crystalline polymers exhibit many unique properties that challenge not only basic research but also numerous technological opportunities. They combine (partly) the properties of orientation of low molecular weight liquid crystals with the rigidity of polymers. For example, they can be oriented in the mesomorphic state and the structure frozen in a glassy state. These polymers with functionalized pendent groups lead to potential applications in the field of nonlinear optics, or in the domain of electro-optical displays. Other polymers like polysilanes show interesting properties such as photo-conductivity. This paper describes the properties and applications of some new side chain liquid-crystalline polyacrylates and their amorphous copolymers. It also describes the photo-conductive properties of polysilanes and their applications in spatial light modulators with liquid crystals. In the first part of this paper, we describe the properties of liquid crystal copolymers and amorphous polyacrylate copolymers with cyanobiphenyls and/or pendent groups with a large hyperpolarizability. Their different properties are compared with some recent results from the literature. These amorphous copolymers allow one to obtain, after poling in an electric field, high optical non-linear coefficients. We have used these copolymers for the manufacture of an electro-optic modulator working at 1·3 μm in the frequency range of 1 GHz. Applications to second harmonic generation at 1·06 μm are also discussed. In the second part of this paper we describe the photo-conductive properties of polysilanes and the realization and performance of an organic spatial light modulator for optical correlation.     

Amino acid derivatives, VIII [1]: synthesis and antimicrobial evaluation of α-amino acid esters bearing an indole side chain

A series of peptide and dipeptide derivatives conjugated with an indole residue were synthesized. The prepared compounds were tested for antimicrobial activity against two different bacterial and one antifungal species displaying different degrees of antimicrobial activities or inhibitory actions. Correspondence: Adel A.-H. Abdel-Rahman, Department of Chemistry, Faculty of Science, Menoufia University, Shebin El-Koam, Egypt.     

Amino acid derivatives,IX [1]: synthesis and antimicrobial evaluation of α-amino acid esters bearing a tryptophane side chain

A series of peptide and dipeptide derivatives conjugated with a tryptophane residue were synthesized. The prepared compounds were tested for antimicrobial activity against four different bacterial species displaying different degrees of antibacterial activities or inhibitory actions. Correspondence: Adel A.-H. Abdel-Rahman, Department of Chemistry, Faculty of Science, Menoufia University, Shebin El-Koam, Egypt; Wael A. El-Sayed, National Research Centre, Department of Photochemistry, Cairo, Egypt.     

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     

Thermoplastic and thermoset main chain liquid crystal polymers prepared from biphenyl mesogen

Main chain liquid crystal thermoplastic polyesters and thermosetting epoxy resins were prepared using biphenyl mesogens. The melting points of the polyesters were effectively decreased by incorporating flexible methylene spacers into the polymer main chain. The liquid crystal epoxy resins exhibit high glass transition temperature, low thermal expansion coefficients, high dielectric strengths, and low dielectric loss. They are suitable for the preparation of self-reinforcing molecular composites. © 1993 John Wiley & Sons, Inc.     

Synthesis and nonlinear optical properties of side chain liquid crystalline polymers containing azobenzene push–pull chromophores

Azobenzene monomeric precursors bearing piperazine as donor moiety with different withdrawing groups and derived side chain polymethacrylates have been prepared and characterized. Monomers having terminal cyano or nitro groups, and the corresponding polymers, exhibited smectic A phases. Linear and nonlinear optical properties of every monomer and thin films of the cyano polymer ( pol‐PZ‐CN ) have been also studied. UV‐vis spectroscopy revealed out‐of‐plane orientation in the as prepared films, as confirmed by waveguide refractive index measurements. Moreover, absorption spectra indicated the presence of azo aggregates in these films. The initial molecular arrangement has been modified by applying thermal annealing within the mesophase range and UV‐blue irradiation. Although thermal annealing resulted in a significant amplification of the out‐of‐plane optical anisotropy due to thermotropic self‐organization of side chain azo moieties, irradiation with 440 nm light induced some disruption of aggregates. The nonlinear optical response of Corona poled films has been studied by second harmonic generation measurements, and the influence of the molecular arrangement on the nonlinear d_ij coefficients has been analyzed. The more efficient poling corresponded to preirradiated films. In any case, a noticeable degree of polar order (70% of the initial d₃₃ value) remained for several months after the poling in films kept at RT. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 232–242, 2010     

Biomaterials made of bile acids

The use of natural compounds in the preparation of new materials can improve the biocompatibility of the materials and avoid any potential toxicity of the degradation products when used for biomedical applications. Bile acids are amphiphilic molecules biosynthesized in the liver. They are used to prepare various polymers and oligomers. These polymers made of bile acids are promising materials in both biomedical and pharmaceutical fields.     

Self-assembly properties of bile acid derivatives of l-cysteine,l-valine and l-serine alkyl esters

Comprehensive self-assembly studies for nine bile acid amides of amino acid esters are reported. The number of the hydroxyl groups attached to the steroidal skeleton and the character of the amino acid ester moiety were used as variables when examining the self-assembly properties of the compounds. Two of the compounds were shown to undergo self-assembly leading to organogelation. In addition, preliminary self-assembly studies in aqueous mixtures of polar organic solvents were conducted. Microscopic methods (optical microscopy and scanning electron microscopy) were utilised in order to gain a deeper insight into the self-assembled structures. Furthermore, single-crystal X-ray structures for three of the compounds were solved.     

Molecular dynamics and ordering of side chain liquid crystal polymers as studied by paramagnetic resonance

Abstract

Molecular dynamics of side chain liquid crystalline polymers (LCP) and their components were studied using the technique of paramagnetic resonance. A cigar shape spin probe (COL) and a nearly spherical spin probe (TPL) were used to study the motions and order of the LCPs. Computer simulations of the observed spectra were performed. Both rotational correlation times and order parameters were extracted from these simulations. We found that LCPs containing 30 per cent and 50 per cent of mesogenic side chains had about the same viscosity as indicated by nearly equal tumbling times at the same temperature. In addition, the LCPs motion is considerably slower than that of the monomeric liquid crystal indicating that the spacer couples the motions of the side chains to those of the main chain. Rotations about axes perpendicular to the side chain are slowed more than rotations about an axis parallel to the side chain. DSC measurements were employed to study the phase transitions. The 30 and 50 per cent LCPs displayed first order NS_A transitions, but the 50 per cent LCPs transition was much weaker, in agreement with McMillan's theory which predicts a first order transition for T _NS/T _NI>0.87 (observed ratios are 0.98, 0.90 and 0.86 for 30, 50 and 100 per cent LCPs, respectively). The 30 per cent LCP has a very short nematic range so that the nematic order, which is not saturated at the NS transition, can couple with the smectic order. This was indicated by a sharp change in slope of the order parameter versus temperature plot as the smectic is entered. The LCPs studied formed a highly ordered glass when cooled in a 1 T field. If one could find a LCP with similar ordering properties whose glass temperature is well above room temperature, then one would have a useful binder for the manufacture of haze-free polymer dispersed liquid crystal displays.