Discotic liquid-crystalline side chain polymers with inositol derivatives as mesogens

The synthesis of monofunctionalized myo- and scyllo-inositol derivatives and their attachment as side groups on a polysiloxane backbone are described. All polymers with scyllo-inositol mesogens show liquid-crystalline behaviour. In contrast to this the myo-inosital mesogens containing polymers exhibit no liquid-crystalline phases.     

Photoreactive Langmuir–Blodgett–Kuhn multilayer assemblies from functionalized liquid-crystalline side chain polymers,I. Homopolymers containing azobenzene chromophores

Stable monomolecular layers of a liquid-crystalline homopolymer bearing azobenzene chromophores in the mesogenic side groups could be prepared at the water–air interface by slow compression at room temperature. From the area per monomer unit of A₀≈0.25 nm² a structural model with tightly packed azobenzene groups oriented nearly parallel to the surface normal was deduced. After transfer to a solid support in a Y-type mode the obtained Langmuir–Blodgett–Kuhn (LBK) multilayer assemblies of varying thicknesses (from a double layer to a thick film of d = 238 nm, capable of guiding optical modes) were prepared and analyzed by X-ray reflection and optical evanescent wave techniques. A monolayer thickness of d₀ = 2.52 nm, as well as the anisotropic index of refraction of these layers, could thus be evaluated. Photo-isomerization by UV-irradiation (at λ = (360±30)nm) was examined by UV-VIS absorption spectroscopy. X-ray reflectivity data of samples illuminated for 30 min showed a complete loss of the layered structure of the LBK samples. As a result strongly light-scattering films were obtained. Surface plasmon microscopy was used to demonstrate the usefulness of this photo-induced order–disorder transition for optical information storage.     

Thermotropic liquid-crystalline polymers. XXVII. Reentrant nematic phase of side chain liquid-crystalline polymers and their optical properties

The phase diagrams of side chain liquid-crystalline acrylic copolymers with cyanobiphenyl mesogenic groups are described. These copolymers are shown to form a reentrant nematic phase. The main regularities of the reentrant behaviour of polymer systems are studied. Certain peculiarities of the electric field induced orientation phenomena are discussed.     

Effect of sulfonic acid containing mesogens on liquid-crystalline behavior of polysiloxane-based polymers

A series of liquid-crystalline polysiloxanes synthesized by cholest-5-en-3-ol (3beta)-10-undecenoate and 4'-octanoyloxy-biphenyl-4-yl 4-allyloxy-3-sulfo-benzoate were prepared in a one-step reaction with sulfonic acid group contents ranging between 0 and 2.73 wt %. All the polymers displayed smectic mesophases with a large temperature range for the mesophases. With an increase of sulfonic acid containing mesogens in the polymers, the temperature of the glass transition did not change greatly, while the temperature of the clear point decreased. The hydrogen-bonding mesogen aggregates in the domains disturb the liquid-crystalline molecular mobility and orientation, leading to a decrease in temperature from the mesophase to the isotropic transition. Unlike the polymers containing lower sulfonic acid mesogens, some polymers showed a dendritic texture of the SmB* phase, indicating that the sulfonic mesogens enhanced the rigid moieties of the supermolecular structure of the liquid-crystalline phases. All the polymers displayed sharp and strong peaks at low angles around 2theta approximately 2.6 degrees and broad peaks at wide angles around 2theta approximately 17 degrees in X-ray measurements. The intensity of the strong peak at low angles in the X-ray profiles decreased with an increase of sulfonic acid mesogens in the polymer systems.     

Mesomorphic and luminescent properties of side chain nematic liquid-crystalline polymers containing Ir(III)

Iridium-containing liquid-crystalline polymers were obtained by graft copolymerisation using poly(methylhydrogeno)siloxane, 1-methyl-4-(4-(4-vinylcyclohexyl)cyclohexyl)benzene (M₁) and an iridium complexes monomer (Ir-M₂). The series of polymers contained different molecular fractions of Ir-M₂ from 0% to 1.2%. All of these polymers showed mesomorphic behaviours. The introduction of small amount of iridium ions endowed liquid-crystalline polymers with luminescent properties. The chemical structures were characterised by IR and ¹H NMR. The mesomorphic properties and phase behaviour were investigated by differential scanning calorimetry, thermal gravimetric analysis, polarising optical microscopy and X-ray diffraction. With an increase of iridium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) decreased. All polymers showed typical nematic marble textures, which was confirmed by X-ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of iridium complexes units did not change the liquid-crystalline state of polymer systems. With Ir³⁺ ion contents ranging between 0.6 and 2.4 mol%, luminescent intensity of polymers gradually increased.     

侧基含偶氮基的硅氧烷梳状聚合物的光致变色性

本文研究了对十一烯酰胺基偶氮苯及其硅氧烷均聚、共聚的梳状聚合物在溶液或薄膜状态下的光致变色性和热回复性。它们的反、顺异构体组分比随光照时间趋于某稳定值, 该稳定的组分比与照射光波长有关。光异构反应是可逆的。比较了异构反应速率和异构转换率, 以聚硅氧烷共聚物PSII3A[侧基比(M1/M2)=1/9, M1是对十一烯酰基偶氮苯, M2是对十一烯酰氧对氧基苯酯]为最佳。升高温度能增进热回复异构。     

Synthesis of side chain liquid-crystalline polysiloxane containing trans-cyclohexane-based mesogenic side groups

The synthesis and characterization of nine new side chain liquid-crystalline polysiloxanes containing one cyclohexyl ring and another 2-4 aromatic rings in their mesogenic side groups are described. All synthesized polymers displayed nematic mesomorphism. Most of the polymers showed a very wide mesomorphic temperature range. The mesogenic core length has profound influence on the phase transitions of the polymers. The mesomorphic temperature range increased with increasing mesogenic core length.     

Synthesis of side chain liquid-crystalline polysiloxane containing trans-cyclohexane-based mesogenic side groups

Abstract

The synthesis and characterization of nine new side chain liquid-crystalline polysiloxanes containing one cyclohexyl ring and another 2-4 aromatic rings in their mesogenic side groups are described. All synthesized polymers displayed nematic mesomorphism. Most of the polymers showed a very wide mesomorphic temperature range. The mesogenic core length has profound influence on the phase transitions of the polymers. The mesomorphic temperature range increased with increasing mesogenic core length.     

Liquid-crystalline monomers, dimers and side group polymers containing phenylpyrimidine mesogens

Phenylpyrimidine derivatives were used to synthesize monomers, dimers and side group polymers. Only a few monomers and dimers show liquid-crystalline behaviour whereas almost all of the polysiloxanes, polyacrylates and polymetha-crylates prepared possess enantiotropic Hquid-crystalline phases. The structure of the main chain and of the mesogenic unit as well as the length of the spacer and of the terminal groups were modified. The relation between structure and phase behaviour is discussed.     

Main chain liquid crystalline polymers with laterally linked organometallic mesogens

The synthesis and characterization of the phase behaviour of a homologous set of polymers of 1,m-diamino-n-alkanes with bis[4-(4-alkoxybenzoyloxy)-2-hydroxybenzaldheyde]copper(II) is reported. The structural peculiarity of these polymers, which is indicated in the title, stems from the presence of metal-complexed salicylideneaminato segments connected via the nitrogen atoms. Calorimetric analysis, polarizing optical microscopy, X-ray diffraction and dynamic viscosity measurements indicate the occurrence of nematic mesomorphism for all the polymers-including two structural analogues containing Ni(II) or Pd(II) in place of Cu(II).     

Mesomorphic polyacrylates containing isomeric methyl-substituted azobenzene mesogens

The synthesis and characterization are reported of two new series of structurally isomeric polyacrylates containing the azobenzene moiety spaced away from the backbone by a hexamethylene spacer and substituted in 4-position with linear alkoxy groups (C₁? C₆, C₁₀) and with a lateral methyl group in 2′- or 3′-position. Thermal optical and X-ray analyses of the prepared polymer samples, with molecular weight ranging from 50 × 10³ to 35 × 10⁴ Dalton (M?_w/M?_n = 2?3), provide evidences for the establishment of liquid crystalline behavior in the melt in a fairly broad range of temperature. In any case, quenching from the mesophase allows for the lock-in of the liquid crystalline structure in the glassy state. The presence of the lateral methyl-substitutents causes a drop as high as 50–100 K. in the stability of the mesophase with respect to the corresponding samples of the methyl-unsubstituted series. A parallel depletion of the smectogenic character is also observed. Typical even-odd effects on the isotropization temperature and relevant thermodynamic parameters have been detected along with the formation of interdigitated smectic structures.     

Molecular simulation and experimental characterisation of monotropic and enantiotropic polymers containing azobenzene and diphenyl mesogens

Molecular simulation techniques have been applied to previously synthesised liquid crystalline polymers containing azobenzene and diphenyl mesogenic groups within the chain. Single chains and amorphous unit cells of aromatic polymers with a degree of polymerisation of 4–16 and containing propylene and diethyletheric (oxydiethylene) spacers were used. The energy was minimised and then molecular dynamics were performed for 1000 ps at seven temperatures between 10 and 600 K. The axial ratio or coefficient of asymmetry was calculated from computer-generated structures. The predictive capability of the orientational order parameter was used to estimate the degree of orientation and the liquid crystalline–isotropic transition temperature of the polymers. The simulated results for the monotropic polymers agreed very well with Maier–Saupe mean field theory and experimental data, though the enantiotropic polymer did not show a good agreement. The predicted glass transition and decomposition temperatures of the simulated polymers are also reported.     

Main chain liquid crystalline polymers with laterally linked organometallic mesogens

The synthesis and characterization of the phase behaviour of a homologous set of polymers of 1,m-diamino-n-alkanes with bis[4-(4-alkoxybenzoyloxy)-2-hydroxybenzaldheyde]copper(II) is reported. The structural peculiarity of these polymers, which is indicated in the title, stems from the presence of metal-complexed salicylideneaminato segments connected via the nitrogen atoms. Calorimetric analysis, polarizing optical microscopy, X-ray diffraction and dynamic viscosity measurements indicate the occurrence of nematic mesomorphism for all the polymers-including two structural analogues containing Ni(II) or Pd(II) in place of Cu(II).     

Photochromic liquid crystalline structures containing azobenzene moieties

Novel liquid crystalline photochromic materials of the type 4-R-C₆H₄-N=N-C₆H₄-O(CH₂)_n-N(CH₂CH₂OH)₂, where R is NO₂, H, CN, O-n-C₈H₁₇, phenyl, 4-O₂NC₆H₄, were prepared. Some of them are photoconductive. These materials were used for the preparation of light-sensitive polymers in which the photoactive moieties were attached to polyurethane chain. Photochromism of these compounds is based on trans-cis isomerization of azobenzene group. An example of the photochromic activity is presented on solid solution of one material (R = O-n-C₈H₁₇, n = 5) in poly(methyl methacrylate) matrix.     

Photochromic liquid-crystalline copolymers containing crown ether groups

An approach was developed for the synthesis of new multifunctional photosensitive liquid-crystalline copolymers of the acryl series containing azobenzene, ionophoric, and mesogenic groups in the same macromolecule. The phase behavior of the copolymers was studied. Most of these copolymers were demonstrated to form nematic mesophases. An increase in the concentration of crown-containing groups to 26 mol.% leads to amorphization of the copolymers. The influence of complexation of the crown ether groups of the copolymers with potassium perchlorate on the mesomorphic properties of the systems was investigated. A comparative study of the photooptical properties of the copolymers in solution and thin films was performed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2332–2242, December, 2007.     

Methylacrylate polymers with photochromic side chains containing heterocyclic sulfonamide substituted azobenzene

Methylacrylate monomers containing azobenzene groups with heterocyclic sulfonamide: sulfisomidyne (4-amino-N-[2,6-dimethylpyrimidyn-4-yl]benzenesulfonamide) and sulfamethoxazole (4-amino-N-[5-methylisoxazol-3-yl]benzenesulfonamide) substituents were synthesized. The monomers were used for preparation of homopolymers and copolymers with butyl 2-methylacrylate and 2-ethylhexyl acrylate. The materials obtained showed photochromic properties manifested by trans-cis isomerization of the side chain azobenzene fragments induced by illumination with unpolarized and polarized light. The decrease of the absorbance of the E(trans) form at ≈450 nm was observed and the materials tested were in form of thin films deposited onto glass.The isomerization of the polymers carried out during ellipsometric measurements showed the reversibility of the process in repeated illumination cycles with green laser light. The change of refractive index caused by illumination was in the range ≈0.005-0.008 as determined by ellipsometry.     

Synthesis and nonlinear optical properties of side chain liquid crystalline polymers containing azobenzene push–pull chromophores

Azobenzene monomeric precursors bearing piperazine as donor moiety with different withdrawing groups and derived side chain polymethacrylates have been prepared and characterized. Monomers having terminal cyano or nitro groups, and the corresponding polymers, exhibited smectic A phases. Linear and nonlinear optical properties of every monomer and thin films of the cyano polymer ( pol‐PZ‐CN ) have been also studied. UV‐vis spectroscopy revealed out‐of‐plane orientation in the as prepared films, as confirmed by waveguide refractive index measurements. Moreover, absorption spectra indicated the presence of azo aggregates in these films. The initial molecular arrangement has been modified by applying thermal annealing within the mesophase range and UV‐blue irradiation. Although thermal annealing resulted in a significant amplification of the out‐of‐plane optical anisotropy due to thermotropic self‐organization of side chain azo moieties, irradiation with 440 nm light induced some disruption of aggregates. The nonlinear optical response of Corona poled films has been studied by second harmonic generation measurements, and the influence of the molecular arrangement on the nonlinear d_ij coefficients has been analyzed. The more efficient poling corresponded to preirradiated films. In any case, a noticeable degree of polar order (70% of the initial d₃₃ value) remained for several months after the poling in films kept at RT. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 232–242, 2010     

Coexistence of two different side chain packing structures in a smectic phase of liquid-crystalline side chain polymers

Ten varieties of liquid-crystalline side chain polymers, poly(cholesteryl-ω-(methacryloyloxy)alkanoates) (pChMO-n, n = 1, 2, 3, 4, 5, 7, 9, 10, 11 and 15; the carbon number of the alkyl chain), were studied by differential scanning calorimetry and small angle X-ray scattering. On and after the first cooling run from the isotropic state, these polymethacrylates gave the same smectic phase. X-ray investigations showed that pChMO-n with short spacers (n = 1-7) has a two layer (bilayer) S_A packing structure, and pChMO-n with a longer spacer (n= 15) has a single layer (monolayer) S_A packing structure. However, these two types of packing structure appear simultaneously in pChMO-n (n = 9s-11) below their phase transition temperature. To clarify the manner of the coexistence of the two different structures the smectic layer spacing and X-ray diffraction patterns were examined by small angle X-ray scattering at various temperatures.