Liquid Crystalline Side Group Research Articles

Constituent Isomerism-Induced Quasicrystal and Frank–Kasper σ Superlattices Based on Nanosized Shape Amphiphiles

Naturally, subtle variations in the chemical structures of constituent molecules may significantly affect their multiscale spatial arrangements, properties, and functions. Deceptively simple spheri...

3C10 セグメント化スペーサーを有する側鎖型液晶性高分子の合成及び熱物性II : セグメント鎖長の影響

3C10 セグメント化スペーサーを有する側鎖型液晶性高分子の合成及び熱物性II : セグメント鎖長の影響

A Theory of Microphase Separation in the Melt of Diblock Copolymers with Smectic Liquid Crystalline Side Groups

We develop a theory of microphase separation in a melt of flexible AB block copolymers with liquid crystalline side groups (C) attached to the B block using the strong segregation approximation. Wi...

Shear-Induced Alignment of Smectic Side Group Liquid Crystalline Polymers

Large amplitude oscillatory shear (LAOS) is frequently capable of generating macroscopic alignment from an initially random orientation distribution in ordered polymer fluids. Side-group liquid crystalline polymers are of special interest in that the flow field may couple differently to the polymer backbone and the mesogen ordering. We report combined rheological and in situ X-ray scattering investigations of LAOS-induced alignment in smectic side-group LCPs. Synchrotron X-ray scattering is used to study orientation development using a rotating disk shear cell in which orientation is tracked within the flow-vorticity (1−3) plane. In all cases, we find that shear promotes anisotropic orientation states in which the lamellar normal tends to align along the vorticity direction of the shear flow (“perpendicular” alignment). We examine the effects of shear strain amplitude and polymer backbone molecular weight on the ability of LAOS to induce alignment. Rheological measurements of the dynamic moduli reveal that large amplitude shearing in the smectic phase causes a notable decrease in the modulus. X-ray and rheological data demonstrate that increasing strain promotes higher degrees of orientation, while increasing molecular weight impedes development of smectic alignment.

Effect of Mesophase Order on the Dynamics of Side Group Liquid Crystalline Polymers

Rheology and X-ray scattering were employed to probe the viscoelastic properties and structural transitions of model cyano-biphenyl-based side-group liquid−crystalline polymers (SGLCPs) with molecular weights ranging from 91 to 1900 kg/mol. Temperature-dependent rheological data show a rapid change in dynamics over a small temperature range. Small-angle X-ray scattering reveals these changes to be associated with an isotropic to smectic transition with an appreciable biphasic region. The presence of a biphasic region is attributed to inhomogeneity in chain structure resulting from incomplete attachment of mesogens to every monomeric unit in the SGLCP polymer. While isotropic and smectic phase data may be separately time−temperature shifted to create master curves for the individual phases, we argue against attempts to achieve superposition between the two phases in the high-frequency regime, since smectic ordering may not simply slow the dynamics but also increase the modulus of the sample. Molecular weight has a strong influence on rheology in the isotropic phase, where an entanglement plateau emerges; however, the smectic-phase rheology is dominated by the layer structure and is fairly insensitive to molecular weight.

Sn-containing liquid crystalline side group homopolymers with two glass transitions

Three homologous tin-containing homopolymers with a terminal CN-dipole in the side group have been synthesized and characterized by dynamical calorimetry, polarization microscopy, X-ray and dielectric methods. AFM was used to evaluate the texture at room temperature. Four different phase transitions were detected by DSC. The high temperature phases were identified by polarization microscopy as SmA and SmC. AFM-measurements show focal-conic domains at room temperature and confirm so the smectic nature of all phases. X-ray measurements on nonoriented samples give hints to a phase segregation on nanometer scale. Dielectric investigation and temperature-modulated DSC (TMDSC) confirm clearly phase separation by appearance of two glass transitions related to the liquid order of the main chains and the liquid crystalline of the side groups.

Photoreorientation in Liquid Crystalline Side-Group Polysiloxane with Azobenzene Derivative Admixture

ABSTRACT The photoreorientation effect in thin films of a liquid crystalline side-group polysiloxane with an azobenzene derivative admixture of the pseudo-stilbene type is presented. The film is introductory homogenously aligned in a typical liquid crystal cell of 3 µm in thickness due to rubbed polyimide coatings. The molar concentration of the azobenzene derivative, calculated per monomeric mesogenic units of the polysiloxane, is equal to 0.021 M/M and corresponds to 2 wt%. The exposure with linearly polarized light results in a reorientation of the azobenzene derivative and the 4′-cyano biphenyl side groups of the liquid crystalline polymer perpendicular towards the electric field vector of the incident light. Caused due to the reorientation process the degree of order is decreased from 0.73 to 0.44.

UV curable coatings with mesogenic side groups

Copolymers having liquid crystalline (LC) side groups were prepared by ultraviolet (UV) photo-polymerization of acrylic monomers with mesogenic groups, acrylic monomers, and acrylic oligomers. These copolymers were evaluated as coatings on metal substrates in view of enhancement of film hardness and flexibility. A non-LC copolymer, i.e., a copolymer without mesogenic units, was used as control. Extraordinary balances of elongation and hardness have been obtained from the coatings consisting of copolymers with an LC side group.

Synthesis and Phase Behavior of Side-Group Liquid Crystalline Polymers in Nematic Solvents

A model system of side-group liquid crystalline polymers (SGLCPs) with systematically varied molecular weight (from 78 to 420 kg/mol; PDI ≤ 1.16) and spacer length (8−12 atoms long) was prepared by polymer analogous synthesis. Matching the structure of the mesogenic units to that of the nematic solvent produced excellent solubility, even at molecular weights an order of magnitude greater than in prior literature on SGLCP solutions. Addition of up to 10 wt % polymer did not affect the ordinary and extraordinary refractive indices of the nematic host (4-pentyl-4‘-cyanobiphenyl, 5CB), indicating that the order parameter was not significantly affected by the polymer.

Synthesis and investigation of photophysical and photochemical properties of new side-group liquid crystalline polymers containing coumarin moieties

Four coumarin (2-oxo-2H-1-benzopyran) containing liquid crystalline polymethacrylates possessing the same monomer formula but different linkage directions and/or construction directions of their mesogens into the same main-chain were prepared and investigated. Each of the four polymers exhibits a smectic A liquid crystalline phase. The change of construction and/or linkage directions significantly affected their liquid crystalline properties. Especially, the change of the construction directions of the mesogens caused different photophysical and photochemical properties.

Nuclear Magnetic Resonance Spectroscopy in Macromolecular Science

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nuclear Magnetic Resonance Spectroscopy in Macromolecular Science

AbstractA historical overview of the role of NMR spectroscopy in macromolecular science in general and its coverage in “Macromolecular Chemistry and Physics” in particular is given. In the early days physics‐application to study molecular dynamics, partial alignment of macromolecules and phase separation prevailed, deduced from broad‐line solid‐state NMR. Only somewhat later, high‐resolution NMR in solution was established as an important tool for elucidating the chain microstructure. In the future, these two aspects are expected to merge. Side group liquid crystalline polymers: 2H NMR has elucidated alignment and dynamics of these complex materials.magnified imageSide group liquid crystalline polymers: 2H NMR has elucidated alignment and dynamics of these complex materials.

Study of phase transitions in liquid crystalline side group polymers via photon transmission method

Photon transmission measurements were applied to study the phase transitions of an acrylate monomer, 3-(4-cyanobiphenyl-4′-oxy)propyl acrylate (LC3), its homopolymer (PLC3) and its graft copolymer (GLC3) with polytetrahydrofuran grafts. In PLC3 drastic decrease in the transmitted light intensity was attributed to a first-order isotropic–nematic phase transition. The phase transitions were also confirmed by DSC and polarizing microscopy. No phase transition was observed in GLC3. This method was not able to detect the isotropic–nematic phase transition in GLC3, probably because of the small size of the phase separated domains in this graft copolymer. The isotropic–nematic transition of GLC3 was identified by polarizing microscopy only by the appearance of a weak diffuse birefringence on cooling.

X-ray investigations on some liquid crystalline methacrylic polymers with ω-hexyloxysalicylaldimine side groups carrying p -alkyl or p -alkyloxy terminal substituents

X-ray diffraction data for four different liquid crystalline side group methacrylic polymers based on the ω-hexyloxysalicylaldimine moiety with p-alkyl or p-alkyloxy terminal substituents are presented. For the decyloxy, dodecyloxy and octyl derivatives, a smectic C2 phase occurs over a broad temperature range, while for the tetradecyl derivative a complex behaviour was observed on cooling from the isotropic state. In this last case a smectic Ad phase arises, changing to a smectic C2 phase and a further smectic Cd phase. A possible explanation for the observed phenomena is presented.

Synthesis and photoluminescence property of polyacetylenes containing liquid crystalline side groups

A series of new side-chain liquid crystalline (LC) polyacetylenes containing 4-(trans-n-alkylcyclohexanylcarbonyloxy)phenyl 4-alkynyloxybenzoate side groups were synthesized by using [Rh(nbd)Cl]2, WCl6 and MoCl5 as polymerization catalysts. The synthesized polymers were characterized by differential scanning calorimetry, optical microscopy and X-ray diffraction measurements. The monomers showed a nematic phase while all polymers revealed the nematic, smectic A and smectic C phases. X-ray diffraction measurements proved that all the polymers show an interdigitated bilayer structure. The optical properties of the polymers were investigated by UV-vis and photoluminescent spectroscopies. The polymer films emitted green-blue photoluminescence at about 500 nm.

Comparison of the Molecular Dynamics of a Liquid Crystalline Side Group Polymer Revealed from Temperature Modulated DSC and Dielectric Experiments in the Glass Transition Region

Temperature modulated DSC (TMDSC) in the frequency range from 10–3 Hz to 3.4 10–2 Hz and dielectric spectroscopy in the frequency range from 10–2 Hz to 106 Hz is employed to analyze the temperature dependence of the relaxation rates of the α- and of the δ-relaxation of a liquid crystalline polymethacrylate having a derivative of (p-alkoxy-phenyl)-benzoate as mesogenic unit in the side group. Especially the molecular assignment of the α-relaxation was discussed controversial in the literature up to now. By applying a temperature derivative method it was found that the temperature dependencies of the relaxation rates of the dielectric α-relaxation and of the dynamic glass transition measured by TMDSC can be described by Vogel/Fulcher/Tammann laws with the same Vogel temperature. Therefore it is argued that the dielectric α-relaxation of liquid crystalline polymers is rather due to the dynamic glass transition related to the segmental dynamics of the backbone than to the transverse dipole component of the mesogenic unit.

Shear-induced band texture of side group liquid crystalline polymers

The shear-induced band texture of conventional end-on fixed side group liquid crystalline polymers (LCPs) has been investigated by using polarizing optical microscopy (POM), small angle light scattering (SALS) and infra-red dichroism techniques. The band spacing is about 1 μm, which increases very slightly on increasing the temperature of shearing and is independent of shearing rate within the range studied. The band texture is not seen to exhibit an interchange of dark and bright bands on rotation of the sample with respect to the polarizer/analyser, but a typical periodical structure is reflected by the SALS patterns of the band texture. The relaxation behaviour of the bands indicates that the band texture formed here is the result of the orderly aligning of domains exhibiting the focal-conic texture, and this is totally different from the case of main chain LCPs where the band texture is substantially an optical effect of the periodic zigzag or sinusoidal structure of parallel aligned microfibrils. Infra-red dichroism and rotating parallel-plate shearing measurements show that the axes of the backbone of the polymer tend to orient in the shearing direction and the end-on fixed mesogenic side groups tend to align perpendicular to the shearing direction.

Liquid crystalline coumarin polymers, 1. Synthesis and properties of side-group liquid crystalline polymers with coumarin moieties

This paper deals with two series of novel side-group liquid crystalline polymers containing coumarin (2H-1-benzopyran-2-one) moieties. Several kinds of polymethacrylates of Series I (Fig. 1) containing a 7-benzoyloxycoumarin unit in the side group with or without substituent at 3 or 4 position of coumarin ring were prepared, in order to study the influence of spacers, tail groups and the positions of the tail groups on their liquid crystalline properties. Three polymethacrylates (Series II, Fig. 1) containing a phenyl 7-octyloxycoumarin-3-carboxylate unit, which consisted of a turned ester group between the aromatic rings in the central unit of side group as compared to Series I, were also prepared. The investigation of the thermal behavior of the two series indicated that the structure of the side-group significantly affected the liquid crystalline properties of the polymers. It was found that the polymers in Series I with substituents at the 3 position of the coumarin ring exhibited mesophase with a wide temperature range, whereas the polymers with substituents at the 4 position showed no mesophase. In addition, each polymer of Series I tended to exhibit a glassy state, whereas each polymer of Series II tended to exhibit a crystalline state. This would be due to the different interactions of side groups of the polymers in Series I and II. It was also revealed that the UV-Vis absorption and fluorescence spectra were influenced by their mesogenic structures and chromophore aggregations. Furthermore, the preliminary results about the emission spectra suggested that the annealing of the polymer film had a great influence on its fluorescence property.

Gas-influenced surface and bulk properties of a liquid crystalline side-group polymer

A preliminary study on the influence of gas sorption on the surface and the bulk properties of a liquid crystalline (LC) side-group polyacrylate PAC-6 is reported. For the first time the gas-induced enrichment of mesogenic side groups at the surface is observed, while the reproducible temperature-scanning surface tension in the high viscous smectic phase is enabled through the plasiticization of gas. Selected experiments demonstrate that the gas-influenced surface and bulk properties of the LC polymer are widely comparable with those of low-molecular-weight ones. The surface tension and the phase transitions depend strongly on the LC phase state, temperature, gas type and gas pressure. At higher pressures, the CO2-induced pretransitional surface excess order is confirmed in the nematic and isotropic phases of PAC-6. Furthermore, our experiments imply a reversible, physical gas sorption in PAC-6.

A tin-containing liquid crystalline polymer with two glass temperatures

A tin-containing liquid crystalline side group polymer was synthesized and characterized. Two glass transitions were detected by calorimetric investigations. The X-ray pattern corresponds to a smectic C order of the side groups and a disordered isotropic main chain. Dielectric measurements show two relaxation ranges which are influenced by the glass transitions and a fast local process. The low frequency mechanism can be related to the reorientation of the side groups and the higher glass transition temperature. The second is connected with the α-relaxation of the main chain and freezes in at lower temperatures.