Self-assembled bent-core side-chain liquid crystalline polymers

The synthesis of H-bonded bent-core side-chain liquid crystal polymers carried out by two alternative synthetic routes and their properties are reported.     

Development of thermotropic liquid crystalline polymers

Wholly aromatic, thermotropic liquid crystalline (LC) terpolyesters made from 6-hydroxy-2-naphthoic acid (HNA) and 4,4′-biphenol (BP) as key components have been prepared and evaluated for utility as high performance fiber precursors. The processability and fiber properties of a specific composition (1) made from both HNA and BP were compared with those of a more well-known LC terpolyester made from p-hydroxybenzoic acid, tere- and isophthalic acids and BP (Ekonol^® type). The advantages of polymer 1 and its high-modulus fiber are described.     

Photoresponsive liquid crystalline and amorphous polymers

Isomerization processes of azobenzene dyes dissolved in a glassy polymeric matrix or attached in glassy amorphous or liquid crystalline polymers to the backbone as side groups are induced by light. The isomerization process, in turn, causes the dye to reorient provided that polarized light is used: the long axis of the dye is oriented perpendicular to the polarization direction in the stationary case. Such a reorientation gives rise to strong modifications of the optical properties. This contribution is concerned with the analysis of the correlation between the nature of the azobenzene dyes, the isomerization, reorientation and modulations discussed above and with possible applications in the optical holographic storage. Considered are, in particular, dye/matrix combinations giving rise to nonlinear holographic responses, two photon holography, transient holographic modes applicable for holographic displays and the optical switching of other than optical properties.     

Viscoelastic properties of liquid crystalline polymers

The viscoelastic properties of main-chain liquid-crystalline polymers are reviewed with an emphasis on the main differences that these materials show with respect to the behaviour of ordinary polymers. The distinction between the anomalies directly arising from the material anisotropy and those which are related to the polydomain structure is also emphasised.     

Lyotropic liquid crystalline epoxide-amine addition polymers

A new type of amphiphilic polymer is described. It is built up from a hydrophilic main chain and hydrophobic n-alkyl chains directly attached to the monomer units. With this chemical constitution the formation of micelles and micellar aggregates is expected, where the hydrophobic side chains are organised on a convex surface. The polymers are synthesised by the polyaddition of tetra-, hexa- and octaethylene diglycidyl ether and n-dodecyl- and n-hexadecyl amine. Polymers are synthesised by systematic variation of the hydrophilic/lipophilic balance (HLB). Although the HLB of the polymers is varied, only a uniform polymorphism is observed in aqueous solutions. A broad miscibility gap and a hexagonal phase at polymer concentrations of 70–80 wt.% polymer exist. Due to the new head-type constitution of the polymers, the hexagonal phase is expected to be of the inverse type.     

Structural models for some crystalline and liquid crystalline polymers

Structural models for the crystalline and liquid crystalline smectic phase are presented for polymethylsiloxanes with mesogenic side groups and for some crystalline and lyotropic liquid crystalline cholesteric phases of cellulose derivatives. Optical and X-ray methods have been applied in these investigations.     

Advances in liquid crystalline conjugated polymers

We review advances in liquid crystalline (LC) conjugated polymers by focusing on (i) ferroelectric and (ii) photoresponsive LC conjugated polymers. In Part 1, LC polyphenylene derivatives were synthesized through substitution of fluorine‐containing chiral LC groups into side chains. Poly(para‐phenylene) [ P1 ] and poly(meta‐phenylene) [ P2 ] derivatives showed chiral smectic C phases responsible for ferroelectricity. They exhibited quick response to electric field, giving switching times of <1 s between two bistable states. The spontaneous polarization (P_S) of P2 remained unchanged even after the electric field became zero, affording the residual polarization (P_R) whose value was the same as that of P_S. This indicates that P2 has a potential memory function based on FLC nature. In Part 2, poly(para‐phenylenevinylene) [ P5 ] and poly(bithienylene‐phenylene) [ P6 ] derivatives were synthesized by introducing dithienylethene moieties into side chains. Drastic quenching of fluorescence occurred when the photoresponsive moiety changed from an open form to a closed one upon an irradiation of ultraviolet light. The quenched fluorescence was recovered through a photoisomerization from the closed form to the open one. Macroscopically aligned P6 film exhibited a linearly polarized fluorescence with significant anisotropy. Reversible quenching and emitting behavior in anisotropic fluorescence was controlled by the photochemical switching. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2463–2485, 2009     

Rigid rod polymers from liquid crystalline phthalocyanines

A number of alkoxy-substituted silicon-dihydroxy-phthalocyanines have been synthesized which form discotic mesophases depending on the side chain length. Metal salt catalyzed polycondensation only gives oligomers while polymer synthesis from activated monomers leads to reasonable high molecular weigths. Indications for the existence of mesophases in this polymer are given.     

Relaxation processes in oriented liquid crystalline polymers

A review is presented of research on oriented thermotropic liquid crystalline polymers undertaken at Leeds University. A range of main-chain polyesters has been studied based on 1,4-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid as the primary monomers. By using a combination of dynamic mechanical, dielectric and NMR measurements insight has been gained into the molecular motions associated with the three principal relaxation processes. The behaviour in tension, for stresses parallel and perpendicular to the principal orientation direction, has been related to that in shear by use of mechanical models.     

Electromechanical effects in ferroelectric liquid crystalline polymers

Electric fields can induce mechanical vibrations in planar aligned sandwich cells of ferroelectric liquid crystals. Measurements on a polysiloxane and a polyacrylate side chain polymer proved that the electromechanical effect also exists in ferroelectric liquid crystalline polymers. The main characteristics of the electromechanical responses of these polymers are described and compared to the response of low molecular weight ferroelectric liquid crystals. According to the proposed interpretation, the vibrations in the direction parallel to both the smectic layers and cell substrates are due to coupling between the director rotation and the flow, while the resonances in the vibrations normal to the plates are connected to layer deformations.     

Electro-optical properties of ferroelectric liquid crystalline polymers

Ferroelectric liquid crystalline polymers (FLCPs) were synthesized. These ferroelectricities were confirmed directly by measuring polarization reversal currents and other electro-optical properties. The smectic layer structure of FLCP was also studied. A chevron structure similar to that of low molecular weight FLC was observed even in an FLCP cell; but the zigzag defects were not so sharp, which means that it is easy to obtain a good orientation even in large-area displays.     

Piezochromic fluorescence in liquid crystalline conjugated polymers

Liquid crystalline diphenylacetylene polymer derivatives showed piezochromic fluorescence via order-to-disorder phase transition.     

Amphiphilic mesogen‐jacketed liquid crystalline polymers: Design,synthesis, and self‐assembly behaviors

We synthesized a series of amphiphilic mesogen‐jacketed liquid crystalline (LC) polymers with a biphenyl side‐chain mesogen containing a carboxylic acid group on one side and an octyloxy group on the other, and the number of methylene units between the biphenyl core and the exterior carboxylic acid group was varied to adjust the mesophases and the amphiphilic nature. The polymers were obtained through conventional radical polymerizations and characterized by a combination of different techniques such as thermogravimetric analysis, differential scanning calorimetry, polarized light microscopy, and X‐ray scattering. The results revealed that the polymer without any methylene spacer, POBP‐0C, did not exhibit LC properties while POBP‐1C (n = 1) and POBP‐7C (n = 7) formed double layer smectic A (S_A) phases. The hydrogen bonding among the carboxylic acid groups and the segregation between the carboxylic acid groups and the alky chains played important roles in forming the mesophases. In addition, the solution self‐assembly behaviors were also preliminarily investigated through the fluorescent probe technique and transmission electron microscopy, and vesicles with uniform sizes were observed. The weak hydrophilicity and large degree of freedom of the carboxylic acid group and the relative rigidity of the polymer chain due to the “jacketing” effect were responsible for the formation of the structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Thermotropic liquid crystalline polymers. I. Cholesterol-containing polymers and copolymers

An approach to the creation of thermotropic cholesterol-containing liquid crystalline polymers by the chemical binding of cholesterol molecules with side chains of comblike polymers is presented. This type of structure permits a decrease in the steric hindrances provided by the backbone chains for the purpose of realizing the liquid crystalline state. A number of new cholesteric esters of poly(N-methacryloyl-ω-aminocarbonic acid)s (PChMAA-n) with different side-chain lengths (n = 2–11) as well as a series of copolymers of ChMA-n with n-alkylacrylates and n-alkylmethacrylates have been synthesized. The experimental evidence of liquid crystalline structure formation in these polymers in glass, viscoelastic, and fluid states is discussed. Molecular and supermolecular structures of cholesterol-containing comblike polymers have been studied and the model of macromolecular packing in the liquid crystalline state is proposed. It is shown that the existence of a layered order of side methylene groups together with ordering of cholesterol groups is necessary to the production of the liquid crystalline state in these polymers.