A. I. Alexandrov

Structure of polymers with phenyl benzoate side groups by X-ray evidence

Abstract Structure of four polymers were studied: poly-p-methacryloyloxy phenyl esters of p-n-hexyloxy benzoic acid (PMB-6), p-n-heptyl benzoic acid (PMH-7) and p-n-heptyl - trans-cyclohexane carboxylyc acid (PMC-7) and poly-p-n-hexyloxy phenyl ester of pmethacryloyloxy benzoic acid (PM-06). Diffractions parameters and polymer organization were discussed in terms of both crystallinity and paracrystal. The structural organization of PMB-6, PMH-7 and PM-06 was interpreted on the basis of block model. Structure of PMC-7 assumed to be organized similar to cybotactic nematics.

Influence of Meso-Substituted Porphyrins Molecular Structure on Their Mesogenity

The study of 27 new meso-substituted free-base and metal complexes of tetraphenylporphyrins with substitution by alkoxygroups (from -OC4H9 to -OC16H33) in para-, meta-, or ortho-position has been carried out. Out of 11 synthesized free-base alkoxysubstituted tetraphenylporphyrins – 4 possess mesomorphic state of columnar type and 1 – lyotropic mesomorphism in binary systems with toluene, benzene or chloroform. The important role of substituents position in phenyl rings of porphyrins was determined. It was established, that metal complexes (Cu, Ni, Zn, Ag, Pd, SnCl2, ZnOAc, VO) of mesogenic free-base porphyrins does not display liquid crystal properties.

A New Chiral LC Acrylate that Exhibits Pyroelectricity

Abstract The new material (R)-4-(5-acryloyloxy-4-methylpentanoyloxy)-4′-octanoyloxy biphenyl has been synthesised and characterised by POM, DSC, X-ray diffraction, IR dichroism, pyro- and piezoelectric techniques. The acrylate was shown to exhibit direct isotropic to smectic H* phase transition. The natural texture of the H* phase separates from the isotropic phase in the form of bâtonnets and rounded domains, the latter develop into a mosaic. The mesophase was found to align in a thin cell of KBr plates with homeotropic anchoring independently of the type of surface treatment. The molecular organisation in the H* phase strongly favours fast and efficient polymerisation when the initial orientation retains upon the reaction. The structure of the crystal and H* phases is mono-layer, the molecules pack monoclinic in antiparallel fashion with long-range polar ordering. The pyroelectric coefficient was found to be very high in the crystal (γ = 2.0÷2.9 nC/cm2·K) and H* (γ = 2.9÷1.0 nC/cm2·K) phases. The direct...

Structure of Films Formed from Lyotropic Liquid Crystal Phases of Dyes. 1. Benzopurpurin - 4B

Abstract The films aligned by drawing thin lyotropic liquid crystal layers of benzopurpurin-4B were investigated by X-ray and electron diffraction methods. The analysis of diffraction data was carried out by straigh-forward (Patterson synthesis) and model procedures. The film structure is crystalline on the microlevel. Molecules ar packed in monoclinic lattice (a=27A, b=7. 2A, c=59.5A, β =141°) corresponding to space group C2/c. This model explains the type geometry of molecular aggregates in the lyotropic liquid crystal phase of benzopurpurin-4B.

Synthesis and phase behaviour of poly(propylene imine) dendromesogens of lowest generations

ABSTRACT Liquid crystal poly(propylene imine) dendrimers of the zero (D0) and the first (D1) generations were synthesised and structurally characterised by elemental analysis, FT-IR and nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MALDI-ToF). The phase behaviour of all the compounds was studied using polarisation microscopy and differential scanning calorimetry. Their structures were investigated by X-ray diffraction method by direct magnetic field influence. Analysis of diffraction patterns was carried out using the paracrystal model of Hosemann and the Fonk cluster model. Structural simulation and diffraction calculations on the models were used for determining the layer structure parameters of the dendrimers. Temperature behaviour of the structural parameters was considered in the interval from room temperature to isotropic melting temperature. It was determined that only the dendrimer of zero generation can be oriented by magnetic field. The schemes of phase transformations of the dendrimers look like: Cr→159°С→Sm-C→274°С→I for D0 and G→55–66°С→Sm-F→108°С→Sm-C→274°С→I for D1. Graphical Abstract

New chiral LC acrylates: Polar ordering in crystal and smectic phases

Abstract Two mesogenic acrylates derived from (R)-5-bromo-4-methylpenta-noic acid, having biphenyl moiety, have been synthesised and characterised by POM, DSC, X-ray, pyro- and piezoelectric techniques. The only real difference in molecular structure of the compounds is that the one contains terminal octyloxy group (1) and the other has octanoyloxy group (2). Crystal structures of the acrylates were shown to be precursors of tilted smectic phases. Both compounds are manomorphic exhibiting either smectic I* phase (1) or smectic crystal H* phase (2). 1 crystallises in non-polar space group while the crystallisation of 2 yields crystals with a polar axis. Good correlations were found in electric responses between the crystalline phases and mesophases of both the acrylates.

Layered Structure of Some Mesogenic Monomers and Polymers in Thin Films and Bulk Samples

Abstract X-ray diffraction and structural simulation were performed to elucidate the structure of Langmuir-Blodgett (LB) films fabricated from monomeric and polymeric monolayers of some mesogenic compounds and corresponding bulk samples. The multilayer structure of LB films of nematic-forming compounds (parasubstituted dibenzo-18-crown-6) was shown to be not quasi-two-dimensional. It is unstable and displays a tendency for the transformation into a three-dimensional crystalline structure. LB films of smectic-forming monomers and polymers (parasubstituted biphenyi and phenylbenzoate) have quasi-two-dimensional multilayer structure, which differs in many aspects from layered structures of bulk smectic and crystalline phases.

Effect of the composition on the structure and ferroelectric properties of side chain liquid crystalline copolyacrylates

Abstract The structure and physical properties of two side chain liquid crystalline polyacrylates are discussed, one bearing biphenyl core and chiral carbon atom in the flexible spacer, and the other a phenyl benzoate core. The biphenyl version displays two smectic phases of S*F and S*F types and no ferroelectric switching. The phenyl benzoate variant displays a single SC phase. The copolymerisation of the two monomers led to polymeric materials exhibiting a S*c polymorphism and composition dependent structural features. Only the copolymer of equimolar composition displayed a strong piezoelectric response in the S*F phase and ferroelectric behaviour in the lower temperature S*c modification.

X-Ray Study of Some Liquid Crystal Homo- and Copolymers

Abstract The structure of liquid crystal homo- and copolymers based on chiral and achiral monomers was investigated by X-ray diffraction. All investigated polymers have tilted smectic phases with bilayer structures but their X-ray patterns show some features of intensity distribution in reflections related to both the orientation manners and the ratio of the chiral and achiral components. The correlation between the structure of comb-shaped molecules and the chirality of smectic phases is considered using experimental X-ray data, molecular simulation and diffraction calculations from structure models.

Electron Diffraction Study on the Structure of Some Comb-Like Polymers in Glassy State

Abstract Electron diffraction from liquid crystalline polymers with direct connection of mesogenic side groups to main chain has been investigated. The polymers exhibit crystalline phase as local inclusions which form by crystallization of macromolecule fragments. The content of the crystalline phase is about 2%.