V. P. Shibaev

Thermotropic liquid crystalline polymers

SummaryLiquid crystalline comb-like polymers with spontaneous polarization are described.

Liquid crystalline dendrimer of the fifth generation: From lamellar to columnar structure in thermotropic mesophases

The structure of a liquid crystalline (LC) carbosilane dendrimer of the fifth generation bearing 128 terminal cyanobiphenyl mesogenic groups has been studied. This dendrimer was synthesized by a hydrosilylation reaction and then the cyanobiphenyl mesogenic groups were chemically linked to the dendritic matrix via a-OOC-(CH2)10-Si(CH3)2OSi(CH3)2-spacer. Structural studies carried out by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction methods revealed unusual phase behaviour. At room temperature the dendrimer forms a lamellar (smectic A) phase which develops in-plane ordering above 40C.This is due toa tendency to form columns ofmolecules which areprobably perpendicular to the layers. Above 121C the material transforms into another more disordered mesophase which is probably a disordered hexagonal columnar phase. The proposed structures and molecular packing in these different types of mesophase are discussed.

Phase diagrams and optical properties of new menthyl-containing LC copolymers forming chiral mesophases

New comb-shaped LC copolymers based on phenyl benzoate and menthyl-containing monomers were synthesized. Phase behaviour, optical properties and structure of the synthesized copolymers with different compositions were studied. Specific features of the development of helical nematic and smectic mesophases (N*, NB*, Ncyb*, Nre*, SmA*, SmF*, blue phases) were revealed. Special attention was paid to studying the structure and optical properties of the new chiral NB* mesophase. For this unusual type of mesophase, a model accounting for the arrangement of the mesogenic group is suggested. It is stressed that the subscript B does not mean biaxial (a biaxial N phase is usually denoted Nb) and B refers to the hexagonal ordering of the side groups, similar to that in a SmB phase. An alternative nomenclature would be Nh, where subscript h refers to hexagonal as in Colh0 for a hexagonally ordered columnar phase of a discogen.

Liquid-crystalline polymers: Past, present, and future

The main steps of the evolution in studies related to the design and investigation of the structure and properties of thermotropic LC polymers containing mesogenic groups are discussed. The principal attention is focused on the results of experiments performed at the Laboratory of Chemical Transformations of Polymers, Faculty of Chemistry, Moscow State University, which was established and guided by Academician N.A. Plate from 1966 to 1985 and then supervised by V.P. Shibaev, the author of this review. Historical evidence is presented to demonstrate the contribution of Russian scientists to the development of approaches to the synthesis and study of chiral and electro- and photocontrollable comb-shaped LC polymers and related composites. The concept of preparing multifunctional LC copolymers and LC networks containing mesogenic, chiral, photochromic, and functional (including ionophoric) groups that can undergo hydrogen bonding, form complexes with metal ions, and interact with nanoparticles is scrutinized. Specific features of the structural organization of polymer mesophases are covered. The data on multifunctional comb-shaped LC polymers, LC ionomers, and LC dendrimers are examined, and the problems concerning the design of light-controllable LC copolymers and polymer photochromic composites and networks are reviewed. Some applied aspects of using LC polymers are considered: specifically, approaches to creation of lasers based on cholesterics and photo- and electroactive media in optics and photonics, systems for data recording and storage, holography, display technology, and other fields.

Induction of the cholesteric mesophase in hydrogen-bonded blends of polymers with a low molecular mass chiral dopant

A family of new hydrogen bonded complexes based on comb-shaped LC copolymers containing alkyloxy-4-oxybenzoic acid mesogenic fragments and chiral dopant molecules, derivatives of pyridine-4-carboxylic acid has beenprepared. At concentrations of chiral groups in the range 1± 25 mol%, induction of the cholesteric phase is observed. The temperature .

Twisting power of bridged binaphthol derivatives: comparison of theory and experiment

The twisting ability of a novel series of bridged binaphthol derivatives with substituents of various lengths and chemical nature in the 6,6-positions, recently synthesized and used as dopants in nematic solvents, is investigated with the help of the model based upon surface- helicity tensors. Structures of the low energy conformers of these compounds have been generated by molecular mechanics calculations. Their orientational behaviour and the coupling between anisotropy in the alignment and molecular chirality, which are at the origin of the helical twisting power, are analysed on the basis of the anisometry and the chirality of the shape.

Thermotropic liquid crystalline polymers—19. Peculiarities of the liquid crystalline structure of cholesterol-containing polymers☆

Abstract Phase transitions and structure of cholesterol-containing polymers, poly(cholesteryl-ω-acryloyloxyalkanoates) and poly(cholesteryl-ω-methacryloyloxyalkanoates), were examined by differential scanning calorimetry. X-ray studies and polarization microscopy. The polymers are shown to form smectic and cholesteric mesophases. Models for the packing of macromolecules in the liquid crystalline state are suggested. The cholesteric structure of the polymers is characterized by layer ordering in the arrangement of mesogenic groups. The cholesteric mesophase of the polymers was found to exhibit selective light reflection in the u.v.-region and circular dichroism.

Ferroelectric liquid-crystalline polymethacrylates

Abstract The ferroelectricity in the chiral smectic C phase of two comb-shaped liquid-crystalline polymers with a methacrylic main chain, phenyl benzoate side groups and chiral fragments of different types have been studied using the pulse pyroelectric method. The spontaneous polarization, pyroelectric coefficient and some relaxation times associated with two different molecular motions have been evaluated.

Thermotropic liquid-crystalline polymers XXVI. Synthesis of comb-like polymers with oxygen containing spacers and a study of their phase transitions

Abstract Synthesis of new liquid-crystalline comb-like polymers with oxygen-containing spacers and mesogenic cyanbiphenyl groups is described. Liquid-crystalline homo-polymers of acrylates and methacrylates, their copolymers and liquid-crystalline polysiloxane are obtained. It is shown that the incorporation of oxygen atoms in spacer leads to decrease of the clearing temperature. The mesophase types of the homopolymers and copolymers are determined.

Induced Cholesteric Liquid Crystal Polymer as a New Medium for Optical Data Storage

Induced cholesteric LCP material is suggested for optical data storage and its main parameters are measured.