Liquid Crystalline Side Group Polymers Research Articles

Two-dimensional NMR study of slow phenyl-flips in liquid-crystalline side group polymers

Abstract Glass-forming liquid-crystalline group polymers were investigated by 2H 2D exchange NMR. In oriented systems, the exchange pattern of a single 2D spectrum yields the orientational distribution function with at least as high precision as a full rotation pattern of 1D spectra. In addition, important information about the geometry of the phenyl-flip motion is obtained. The 2D lineshapes are particularly sensitive towards possible slow motion of the flip axis which could be envisaged to fluctuate within the orientational distribution of the mesogenic group. However, the experimental spectra for a frozen nematic and a frozen smectic polysiloxane with an orientational distribution of width ±18·5° and ±12·5°, respectively show no indication of the corresponding features, proving that the flip axis is fixed within ± 3° even after a large number of flips.

Ferroelectric liquid-crystalline side group polymers Spacer length variation and comparison with the monomers

Abstract The phase behaviour and the ferroelectric properties of liquid-crystalline side group polyacrylates containing an (R)-4″(1-methylheptyloxy)-4′-biphenylyloxycarbonyl-4-phenoxy moiety are compared with the properties of their monomers. A S*C phase polymorphism including monolayer and bilayer structures was found for the polymers. Some of the S*C subphases, consisting of smectic mono- or bi-layers, do not exhibit ferroelectric properties. These unusual properties do not exist for the corresponding monomeric acrylates. Therefore, one has to take into account that the polymer chain exerts a strong influence on the phase behaviour and the ferroelectric properties.

Ferroelectric liquid crystalline polymers

Abstract The recent state and perspectives in the field of synthesis, phase behaviour and properties of ferroelectric liquid crystalline polymers are reviewed. Spontaneous polarization, pyroelectric effect and various relaxation processes in chiral tilted smectic phases of both side chain and combined (side group and main chain) liquid crystalline polymers are discussed.

2D-ELDOR detection of magnetization transfer of nitroxides in disordered solid polymers

Two-dimensional electron—electron double resonance (2D-ELDOR) experiments on nitroxide spin labels in solid liquid-crystalline side-group polymers have been performed employing narrow-band microwave excitation pulses followed by a rapid magnetic field step during a mixing time and detection at the new selected point of the EPR spectrum. Information about magnetization transfer throughout the full EPR spectrum is obtained by sweeping both pumping and detecting fields. In the two-dimensional representation of experimental ELDOR data, the different processes causing magnetization transfer through the EPR spectrum, i.e. electron spin diffusion, nuclear relaxation, and slow rotational motions lead to different patterns and can be distinguished by recording 2D-ELDOR spectra as a function of temperature. In the specific system studied, the 2D-ELDOR spectra show the dominance of magnetization transfer between states with close molecular orientations but different nitrogen nuclear spin projections caused by flips of nuclear spins. The results are discussed in terms of dynamic processes in glasses.

Order in thin films of a liquid crystalline polymer

Ordering effects of a side group liquid crystalline polymer PMA64 have been observed by the x-ray reflectivity technique. Thin films on float glass substrate are investigated as a function of temperature and film thickness. At 100 °C, a phase transition from a smectic-A to a nematic phase is observed. The layers of the smectic-A phase are oriented parallel to the surface giving rise to a Bragg peak which is coherently superimposed on Kiessig fringes. The Kiessig fringes are caused by interference of beams reflected at the polymer surface and the polymer–glass interface, while the Bragg peak originates from the electron density modulation perpendicular to the surface. As a function of film thickness, we observe a significant deviation of the integrated intensity of the Bragg peak as compared to the integrated intensity of a Bragg peak due to perfect periodic one-dimensional density modulations. A model which includes the influence of the interfaces as well as distortions of the first and second kind is used to describe this thickness dependence of smectic order in thin films of liquid crystalline polymers. The Bragg peak is lost at the smectic–nematic phase transition where we observe a significant roughening of the free surface. This effect is discussed with respect to molecular order.

Synthesis and properties of dimesogenic liquid crystalline side group polymers

Liquid crystalline polymalonates with side groups consisting of two different mesogenic units separated by alkylene spacers from each other and from the polyester backbone have been prepared. According to microscopic observations, DSC measurements and X-ray studies, all polymers display smectic phases.

Synthesis and properties of functionalized polymers

This paper describes the rational design of four different types of functionalized polymers with interesting material properties. (i) Liquid crystalline (LC) side-group polymers with a high spontaneous polarization in the ferroelectric chiral smectic C∗ phase can be prepared by a proper selection of the chiral groups. The additional functionalization with non-linear optical chromophores makes these materials interesting for non-linear optics. (ii) Chiral LC polymers, which are functionalized with crosslinkable groups, can be converted into LC elastomers. The mechanical orientability of these elastomers leads to new piezoelectric materials. (iii) The incorporation of ferrocene units into a LC matrix allows the reversible formation of LC ionomers by a redox reaction. This leads to a gelation of the LC polymer system. (iv) The curing (dense crosslinking) of a polymer matrix is one possibility to stabilize the polar order of dye molecules, which is necessary for frequency doubling. This can lead to large and stable non-linear optical coefficients.

Thermotropic Liquid Crystalline Side Group Polymers as Stationary Phases in High Performance Liquid Chromatography. II. the Mechanism of Separation

Abstract Liquid crystalline side group polymers support coated on silica gels have been applied as stationary phases in high performance liquid chromatography. It has been possible to show that also in liquid chromatography, separations based on the mesophase structure can be observed in analogy to gas chromatography. From results of separations in which temperature, flow rate, sample concentration and the solvent strength of the mobile phase were varied, this work derives views on the fundamental mechanisms involved. In addition, it will be shown that different mechanisms are probably involved in the separation of steroids and dinitrobenzene isomers on these stationary phases.

Thermotropic Liquid Crystalline Side Group Polymers as Stationary Phases in High Performance Liquid Chromatography. I. the Temperature Dependence

Abstract Till now, thermotropic liquid crystalline side group polymers have been rarely used in gas chromatography and have never been applied as stationary phases in high performance liquid chromatography. This work presents the results of temperature-dependent measurements on surface modified silica gels serving as stationary phases. These silica gels have been coated with polyacrylates with mesogenic side groups of phenyl benzoate type and various spacer lengths. Steroids and dinitro-benzene isomers were used as sample substances for testing the chromatographic properties of these stationary phases. It will be shown that chromatographic characteristics correlate with the phase transition temperature of the liquid crystalline polymers.

Synthesis and phase behaviour of liquid-crystalline side group polyesters

Abstract Several series of liquid-crystalline side group polymers with a polyester backbone structure have been synthesized using mesogenic diethylmalonate and 1,3-propanediol derivatives. The structures of the polymer backbone and the mesogenic units have been varied systematically. As shown by differential scanning calorimetry, polarizing microscopy and X-ray diffraction, the side group polyesters exhibit nematic and/or smectic mesophases. Polyesters synthesized from mesogenic diethylmalonate derivatives can tolerate long non-mesogenic segments in the polymer main chain without losing their liquid crystal properties. X-ray studies suggest that some of the smectic polymers exhibit interdigitated bilayer SA phases.

A comparative study of individual and collective rotational motion in mixtures of liquid crystalline side group polymers and low-molecular-weight mesogens

La variation avec la temperature de la frequence F de la relaxation dielectrique Delta et de la viscosite rotationnelle γ de melanges du polysiloxane (−Si(Me)(R)O−) n (R=(CH 2 ) 4 -OPh-CO 2 -Ph-OMe) avec un nematogene est determinee surtout par la variation du coefficient de diffusion rotationnelle qui est decrite par la formule de Vogel-Fulder. L'effet du potentiel nematique sur F et γ est decrit par les theories de Martin-Meier-Saupe et Hess

Broadband dielectric spectroscopy on side group liquid crystal polymers

Abstract Dielectric studies on three liquid-crystalline side group polymers were performed in the temperature range from 100 K to 450 K and in the frequency range from 10−1 Hz to 107 Hz. All samples exhibit an α relaxation with a WLF dependence of the activation energy as well as a β relaxation, which are comparable in the glassy state. Their mean relaxation times, their relaxation time distribution, in its asymmetry and half-width, and their activation energies are nearly unaffected by the spacer length, terminal group and/or main chain. These findings are supported by N.M.R. measurements. A third relaxation process occurring close to the clearing point is also observed and assigned to the cooperative rotation of the side group around the main chain.

Synthesis and characterization of liquid-crystalline side group polymers with benzylideneaniline as mesogenic moiety

Abstract Two new thermotropic liquid-crystalline side group polymers were synthesized, characterized and compared with the liquid-crystalline monomeric analogues. Some packing features of these polymeric liquid crystals are discussed. Investigations were carried out by differential calorimetry (D.S.C.), polarization microscopic observation and X-ray diffraction on non-aligned and magnetic field-aligned samples in the wide and small angle region. The synthesized polymers contain as mesogenic moiety a benzylideneaniline group which is attached in the 4 position via a hexamethylene spacer to a poly-methacrylate backbone. The benzylideneaniline group is substituted in 4′ position with an ethoxy or butoxy group (PEt or PBu). The monomeric analogues are denoted MEt and MBu. The two polymers show a phase sequence crystalline-smectic A-nematic-isotropic. The liquid-crystalline temperature range is observed between 90 and 150°C. The monomeric MEt exhibits only a monotropic nematic, MBu an enantiotropic nematic and a smectic A phase.

Highly ordered main chain in a liquid crystalline side-group polymer

Le groupe lateral mesogene derive du butoxy-4' phenyl hydroxy-4 benzoate, est lie a la chaine polymethacrylate par des «spacers» de 6 unites methylene

Structure‐property relations in linear and crosslinked liquid crystalline polymers

AbstractThis paper reviews structure‐property relations in liquid crystalline side group polymers, as investigated by X‐ray scattering of fibres, by small angle X‐ray scattering in solution, by dielectric relaxation measurements and by melt rheology, as well as synthetic ways to “combined liquid crystalline polymers”. The synthesis of liquid crystalline elastomers from side group, main chain and combined liquid crystalline polymers is described. First structure‐property relations are discussed.

Orientational Ordering of Dyes in the Glassy State of Liquid-Crystalline Side Group Polymers

Abstract Liquid-crystalline side group copolymers containing dyes can be macroscopic-ally oriented and the orientation can be locked-in below the glass transition temperature. The order parameters of anthraquinone dyes and a trisazo dye in nematic and smectic glasses were determined by optical absorption measurements. The dyes have higher degrees of order in the smectic glass than in the nematic glass. A comparison of order parameters of covalently bonded dyes with order parameters of monomeric dyes dissolved in the corresponding homopolymers demonstrates the influence of covalently anchoring the dye to the polymer.

Evidence for a liquid-liquid transition in a liquid crystalline side group polymer obtained by Brillouin spectroscopy and dsc

Hypersonic and calorimetric investigations of a liquid crystalline side group polymer are presented. The existence of a liquid-liquid transition above the nematic-isotropic transition is established.

Structures of liquid crystalline side group polymers oriented by drawing

AbstractThe fiber patterns of a series of liquid crystalline polymers were analysed. For polymers with smectic phases and for polymers with long spacers and nematic phases, the mesogenic groups orient perpendicularly to the polymer main chains which are parallel to the fiber axis. The fiber pattern indicate a short range order of the mesogenic groups analogous to that in low‐molecular weight liquid crystals. For polymers with short spacer groups and nematic phases qualitatively different fiber patterns are found. These fiber patterns are indicative for a special nematic phase formed by ribbon‐like molecules.