Preparation and liquid-crystalline properties of toluene-4-sulphonyl urethane of hydroxypropylcellulose

A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of M_w = 60000 g mol^-1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase.     

High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals

High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals is examined. Reactions proceed regiospecifically to afford single products in case of all 3-substituted glycals. Upon heating or even after standing at room temperature adducts undergo retro-addition to give starting glycals. Various aspects of the cycloaddition are discussed, especially ret-ro-reaction and rearrangement of β-lactams to α,β-unsaturated amides.     

Phase transitions of hydroxypropylcellulose liquid-crystalline solutions in magnetic field

The phase transitions and the phase state of hydroxypropylcellulose-DMAc and hydroxypropylcellulose-ethanol solutions both under an applied magnetic field and in its absence have been studied via the cloud-point method, polarization microscopy, and polarization-photoelectric measurements. The magnetic field changes the structure of solutions and increases the phase transition temperature. The higher the field strength, the more pronounced this effect. As the molecular mass of the polymer grows, the ability of its macromolecules to orient in the magnetic field tends to increase. Hydroxypropylcellulose solutions fall into the family of memory systems. When the magnetic field is switched off, the orientation of macromolecules and the increased phase transition temperature are preserved for many hours.     

Orientational properties of liquid-crystalline 4-n-alkyloxybenzilidene-4'-fluoroanilines

The orientational order of 4-n-hexyloxybenzilidene-4'-fluoroaniline, (FAB-OC6) and its 4-n-heptyloxy analogue, (FAB-OC7), studied by means of ²H NMR and ¹⁹F NMR is reported. The entire temperature range of the liquid-crystalline phases (S_B, S_A and N for FAB-OC6, S_B and S_A for FAB-OC7) have been investigated. The results are discussed in relation to previous X-ray diffraction measurements. The chemical shift tensor components of the fluorine bond, evaluated from the ¹⁹F NMR spectra are compared with previous results.     

The synthesis of optically pure β-lactams derived from sugars. High-pressure [2+2] cycloaddition of toluene-4-sulphonyl isocyanate to glycals.

[2+2] Cycloaddition of toluene-4-sulphonyl isocyanate to glycals 1 - 4 at room temperature under 10 kbar pressure gave respective β-lactams 5 - 8 in good yields. The reaction proceeds regio- and stereospecifically to afford the four-membered ring in position trans to the acetoxy group at C-3 of the glycal moiety.     

Synthesis and liquid-crystalline properties of pyrans

4-Alkoxy-N-{4-[5,6-dihydro-2H-pyran-4-yl)methyloxy]phenylcarbomoylmethyloxybenzylidene}anilines are synthesized. They exhibit properties of smectic and nematic liquid crystals.Bashkir State University, Ufa 450074. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 896–897, July, 1994. Original article submitted May 23, 1994.     

Self-assembly and liquid-crystalline properties of 5-fluoroalkylporphyrins

We report three crystal structures of a synthetic 5-fluoroalkylporphyrin molecule that was programmed for self-assembly. All the X-ray structures of zincated and free-base porphyrins Zn2 b, Zn5 a, and 2 b revealed rigorous pi-pi stacking and extremely hydrophobic interactions. Other the other hand, the strong aggregation of 5-fluoroalkylporphyrins in solution was also found. Interestingly, the regular nanopore formation of the 5-fluoroalkylporphyrin was visualized by atomic force microscopy (AFM). Importantly, the 5-fluoroalkylporphyrins possess liquid-crystalline properties that were confirmed by using a combination of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) techniques. By comparison, the self-assembly of non-fluorine-containing porphyrins with similar structure showed much lower aggregation ability, as investigated by NMR techniques. Additionally, no birefringent mesophase was observed for the non-fluorine-containing porphyrin.     

Preparation and properties of 4-nitrosoquinolines

4-Nitrosoquinoline ( 2a ) and 4-nitroso-7-chloroquinoline ( 2b ) were prepared from the parent hydroxyzines. Their characteristic nmr spectrum were recorded. These highly reactive compounds condense readily with 2,3-dimethyl-1,3-butadiene and with aniline.     

Anchoring properties of a nematic liquid crystal on anisotropic hydroxypropylcellulose films

Thin solid films of hydroxypropylcellulose (∼15-30 µm) prepared from liquid crystalline and isotropic aqueous solutions are used as liquid crystal alignment layers. Using the standard nematic liquid crystal 5CB we measured the interface properties of these solid films as a function of the polymer concentration in the aqueous precursor solution, expressed in terms of zenithal and azimuthal anchoring orientations and extrapolation lengths. The hydroxypropylcellulose thin films are found to induce a planar orientation of 5CB independently of the polymer concentration, with the alignment along the polymer backbone. The zenithal anchoring strength is found to be strong and essentially independent of the temperature far from the nematic-isotropic transition, with an extrapolation length ξ_θ≈50 nm. The zenithal anchoring becomes weaker near the nematic-isotropic transition, as expected. The azimuthal anchoring strength is found to be intermediately weak and strongly dependent on the polymer concentration, with an extrapolation length varying from ξ_θ≈250 nm to ξ_ϕ≈500 nm. These films are particularly interesting since their surface topography and morphology may be tuned by varying a few parameters in the film preparation process, such as the polymer concentration in the aqueous solution.     

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.     

Transport properties of a side-chain liquid-crystalline polymer. Poly(4-acryloyloxy biphenyl)

The transport properties of a side-chain liquid-crystalline polymer forming a smectic A phase have been investigated using dichloromethane as a permeant. Samples differing in the isotropization enthaoly were analyzed. A. Correlation between this thermal parameter and sorption has been found, while the diffusion coefficient is substantially the same in all samples. The results obtained can be explained in terms of a biphasis model in which a disordered permeable phase is present within the liquid-crystalline phase, which is impermeable to the diffusant molecules.     

Transport properties of a thermotropic liquid-crystalline polyester

Transport properties of a thermotropic liquid-crystalline polymer with the mesogenic group in the main chain were analyzed. Different samples were examined as films obtained by pressure molding and rapid quenching to 0°C. Thermal and transport parameters of the quenched films were measured. The results show that the isotropization enthalpy and sorption coefficient are interdependent, while the diffusion coefficient is substantially constant in all the samples analyzed. These results suggest that the permeable component behaves in the same way in the different samples but is present in different amounts, the transport phenomena occurring in amorphous, or less ordered, interphase regions within impermeable mesomorphic and crystalline domains.     

Mesomorphic properties of side-chain cholesteric liquid-crystalline elastomers

New monomer cholesteryl 4-(10-undecylen-1-yloxybenzoyloxy)-4′-ethoxybenzoate (M₁), crosslinking agent biphenyl 4,4′-bis(10-undecylen-1-yloxybenzoyloxy-p-ethoxybenzoate) (M₂) and a series of side-chain cholesteric elastomers were prepared. The chemical structures of the monomers and elastomers obtained were confirmed by element analyses, FT-IR, and ¹H NMR. The mesomorphic properties and thermal stability were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the content of the crosslinking unit on the phase behavior of the elastomers was examined. M ₁ showed cholesteric phase, and M ₂ displayed nematic phase. The elastomers containing less than 12 mol% of the crosslinking units revealed reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability.     

Rheological and thermal properties of a commercial liquid-crystalline polyesteramide

A commercial main-chain liquid-crystalline, naphthalene-based polyesteramide, was studied by three experimental techniques: extrusion capillary rheometry, dynamic viscoelasticity, and differential scanning calorimetry (DSC). From capillary rheometry a maximum at 360°C was observed in viscosity temperature curve. This result is compared with literature data for other thermotropics, and the possibility of a transition from a nematic to an isotropic phase is considered. The results obtained from dynamic viscoelasticity and DSC agree, and reveal the existence of a glass transition at 128°C (by DSC) and 137–147°C (by viscoelastic measurements, depending on frequency) as well as melting at 282°C. Annealing below 230°C produces two types of crystals, whereas annealing above this temperature gives rise to only one type of crystal, the melting temperature of which can be, depending on annealing time, as high as 340°C. The results are compiled in a phase diagram with six regions, four of them corresponding to the solid state, one to a liquid mesophase, and one to an isotropic phase.     

Mesophase structure and some properties of liquid-crystalline organoelement polymers

The structure and physico-mechanical properties of polyphosphazene, poly(trimethylvinylsilane) and blends of polyphosphazene with polyethylene were studied. It was shown that these organoelement homopolymers form mesophase structure which can be described as condis-crystal, and mesophase polymers are effective modifiers when mixed as blends with polyethylene, allowing to make processing more effective and obtain composites with improved mechanical properties.     

The thermotropic and lyotropic liquid-crystalline properties of acetoacetoxypropyl cellulose

Acetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid-crystalline phases. DSC and hot-stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ₀ of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x-ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ₀ for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.     

Micellar and liquid-crystalline properties of bicyclic fragment-containing cationic surfactant

NMR spectroscopy is employed to study the aggregation of a cationic surfactant, 4-aza-1-cetyl-1-azoniabicyclo[2.2.2]octane bromide, in aqueous solutions. Self-diffusion coefficients are determined for micelles and monomers and the hydrodynamic radius and aggregation number are calculated for micelles. Polarization microscopy data demonstrate that the examined compound is an amphotropic substance. It is found that the lyotropic liquid-crystalline system is characterized by a wider temperature range of mesophase existence as compared to the thermotropic system.