Ultrastructure studies of polystyrene-based side-chain liquid-crystalline copolymers containing charge transfer groups

A series of new side-chain liquid-crystalline copolymers has been prepared, and the thermal properties of the individual copolymers have been determined. These copolymers are derived from atactic polystyrene and contain both 4-methoxyazobenzene and 4-nitroazobenzene mesogens; these are linked through octyl spacers to the polystyrene backbone. All the copolymers exhibit a smectic phase that has been assigned smectic A on the basis of polarizing microscopy and x-ray diffraction studies. The glass transition temperatures of the polymers exhibit a linear dependence on composition, whereas the clearing temperatures and the associated entropies show significant deviations from such behavior. The smecticisotropic transition temperatures of the copolymers are higher than those of the composition-weighted averages for the corresponding homopolymers, whereas the entropies of transition are lower than expected. X-ray diffraction studies of fiber samples revealed that the director of the mesophase is oriented perpendicular to the fiber axis. The liquid-crystalline polystyrene containing 25 mol % nitro-substituted mesogen shows an unusual S_A-phase WAXS pattern. The copolymers were investigated further by ¹³C CP/MAS NMR spectroscopy, and the observed changes in the spectra are analyzed in terms of chemical composition and local electronic environment. The application of the interrupted decoupling technique revealed that the spacer contains a number of gauche defects. These observations lead us to suggest possible microstructural arrangements in the smectic phase. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of chiral liquid‐crystalline polysiloxanes containing fluorinated units and sulfonic acid groups

Chiral side‐chain liquid‐crystalline polysiloxanes ( PS‐1 , PS‐2 , PS‐3 , PS‐4 , PS‐5 , PS‐6 ) bearing fluorinated units and sulfonic acid groups were synthesized with poly(methylhydrogeno)siloxane, cholest‐5‐en‐3‐ol(3β)‐4‐(2‐propenyloxy)benzoate, and 3‐trifluoromethyl‐phenyl 3‐sulfo‐4‐undec‐10‐ enoyloxy‐benzoate. The effects of fluorinated units and sulfonic acid groups on characteristic of liquid‐crystalline properties were studied. PS‐1 , PS‐2 , and PS‐3 exhibited both smectic and cholesteric mesophases, while PS‐4 , PS‐5 , and PS‐6 exhibited only cholesteric mesophase. As the polymers contained more fluorinated units and sulfonic acid groups, segregation of the fluorinated segment to the surface and aggregation of hydrogen bonding should occur. Therefore, the highly ordered lamellar mesogen–siloxane matrix systems should be disturbed severely, suggesting that PS‐4 , PS‐5 , and PS‐6 show no smectic phase. The maximum reflection bands become broad and shifted slightly to long wavelength from PS‐1 to PS‐6 . Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of terminally carboxyl ethylene glycol monomethyl ethers-substituted side-chain liquid-crystalline polysiloxanes

Alkene monomers containing phenyl or biphenyl carboxylate benzoate ester based on a mesogenic group of varied lengths of carboxyl oligo (ethanediol) monomethyl ethers as the terminal were synthesized. They were grafted onto poly(methyl-hydrosiloxane) by the platinum-catalyzed hydrosilylation process. The thermal transition temperatures and mesophase textures of monomers and of polymers were characterized by using differential scanning calorimetry (DSC), x-ray diffraction, and polarized optical microscopy with a hot stage. The factors governing mesophase textures and thermal transition temperatures are discussed. © 1993 John Wiley & Sons, Inc.     

Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups

The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an S_A phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2793–2800, 1997     

Synthesis, structure and mesomorphic properties of side-chain chiral liquid crystalline polysiloxanes based on (S)-(+)-2-methyl-1-butanol derivatives

The synthesis of five chiral liquid crystalline monomers (M₁-M₅), and their corresponding side-chain polymers (P₁-P₅) based on (S)-(+)-2-methyl-1-butanol derivatives is described. The chemical structures of the monomers were confirmed by FT-IR, ¹H NMR, and elemental analyses. The structure-property relationships of the monomers and polymers obtained are discussed. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. All monomers showed a cholesteric phase. For M₂, M₃, and M₅, besides a cholesteric phase and a smectic A (S_A) phase, M₂ also revealed an enantiotropic chiral smectic C phase and a monotropic smectic B (S_B) phase, and M₃ also showed a S_B phase. The polymers P₁-P₅ exhibited a S_A phase, moreover, P₂, P₃ and P₅ also revealed a phase. The experimental results demonstrated that a flexible siloxane backbone and a long flexible spacer tended to exhibit a low glass transition temperature, high thermal stability, and wide mesophase temperature range.     

Influence of main chain on the phase behaviors of side-chain liquid-crystalline polymers with triphenylene mesogens of long alkyl tail substituents

A series of side-chain liquid-crystalline polymers (SCLCPs) containing triphenylene mesogen, in which the long alkyl tail Tp connected directly with main chain, were synthesized successfully. The chemical structures of the monomers were confirmed by ¹H NMR and mass spectrometry. The phase behaviors of polymers were investigated by a combination of techniques, including DSC, POM, 1D/2D WAXD, and SAXS. The experimental results suggested that the type of main chain played an important role in the LC phase structures of these polymers. Because of the steric effects of side chains and the coupling effects between the Tp moieties and the main chains, all the polymers exhibited columnar phase. However, the SCLCPs with poly(vinyl benzene methyl ether) or polynorbornene backbone displayed hexagonal columnar phase, while those with polyacrylate or polymethacrylate backbone presented columnar nematic phase, and the one with poly(vinyl benzoate) main chain showed rectangular columnar phase. Moreover, the clearing temperatures (Ti) changed with change in main chain. Especially, the Ti of the SCLCP with polymethacrylate backbone was above 300 °C. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 754–766     

Synthesis and characterization of side-chain liquid-crystalline poly(ether ester)s having p-substituted biphenyl mesogenic side groups

Several novel mesogenic spiro-orthoester monomers such as 1,6,10-trioxaspiro[4,5]decanes 4 , containing biphenyl mesogens at the C-8 positions of the five- and six-membered spirocyclic ring, through the alkylene spacers of different lengths were prepared by condensation reaction of the corresponding biphenyl mesogenic 1,3-propanediol 3 with 2,2-diethoxytetrahydrofuran, with 50–75% yields. Through cationic double ring-opening polymerization, carried out with boron trifluoride etherate as an initiator (5 mol % vs. monomer) in bulk at 150°C, spiro-orthoester monomers 4 afforded a novel class of side-chain thermotropic LC polymers with a poly(ether ester) as the main chain 8 . The liquid-crystalline properties of the spiro-orthoester monomers and the resulting polymers were examined by differential scanning calorimetry and optical polarized microscopy. Biphase separation was observed in the side-chain liquid-crystalline poly(ether ester)s upon annealing in the broad isotropic region. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2439–2455, 1998     

Chiral side-chain liquid crystalline polysiloxanes bearing fluorinated mesogens and cholesteryl groups

A series of chiral side-chain liquid crystalline (LC) polysiloxanes bearing fluorinated mesogens were synthesized with a cholesteric LC monomer and a fluorinated nematic LC monomer. They were characterized by use of various experimental techniques, and effect of fluorinated mesogens on characteristic of LC polysiloxanes was studied as well. In photoluminescence spectra, a narrow and a broad peak occur at around 270-317 nm, originated, respectively, from fluorinated phenyl groups and the conjugated xenene structure. The specific rotation analysis of all polymers showed negative values, but absolute values were lower than those of the chiral monomers. All polymers showed smectic LC phase with very wide temperature ranges on heating and cooling cycles. Especially, only polymers bearing more fluorinated component exhibited smectic-cholesteric phase transition when they were heated. As the polymers contained more fluorinated mesogens, segregation of the fluorinated segment to the surface should occur at mesomorphic temperature. The highly ordered lamellar mesogen-siloxane matrix systems should be disturbed severely by separation of fluorinated mesogens, suggesting mesogenic orders transition from lamellar smectic to cholesteric phase.     

Synthesis and thermal behaviours of side-chain liquid-crystalline poly[N-(4-methoxyazobenzene-4′-oxyalkyl)ethyleneimine]

A series of side-chain liquid-crystalline polymers, poly[N-(4-methoxyazobenzene- 4′-oxyalkyl)ethyleneimine](PEnZO), has been synthesised in which the number of methylene units in spacers varies from two to six. The structures of the synthesised monomers and polymers were confirmed by infrared (IR) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. The thermal properties of these polymers have been investigated using differential scanning calorimetry (DSC), polarising optical macroscopic (POM) X-ray diffraction and thermogravimetric analysis (TGA). The test results indicated that the obtained polymers exhibited thermotropic liquid-crystalline mesomorphism of nematic type with schlieren textures. It was observed that the thermal behaviours of the polymers were strongly dependent on the degree of substitution and the length of spacers. Polymers containing less than 57% of mesogenic groups did not exhibit mesogenic phase and resembled amorphous polymer. A more pronounced odd–even effect in the melting points and their enthalpy changes was observed on increasing the spacer length in which the odd members displayed lower values, which were also slightly dependent on the substitution degree of polymers. The mesomorphic temperature ranges of odd members were wider than those of even members. The decomposition temperatures of copolymers were near 230°C.     

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

A series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.     

A method for reproducible preparation of chiral polysiloxanes with regular repeat units as stationary phases for capillary gas chromatography

Trifluoroethyl ester-functionalized polysiloxanes can be prepared by block condensation of 3-dichloromethylsilyl-2-methylpropionic acid 2′,2′,2′-trifluoroethyl ester with 1,5-bis(diethylamino)hexamethyltrisiloxane or with disodium tetramethyldisiloxane-1,3-diolate. The functionalized polysiloxanes may serve as supports for a variety of selector groups; for instance, nucleophilic displacements with L-valine-t-butylamide or L-α-naphthylethylamine lead to chiral polysiloxanes in high yields and with high reproducibility. Imidazole accelerates the rate of nucleophilic displacement. Capillary columns coated with such chiral polysiloxanes exhibit high enantioselectivity and thermostability.     

Synthesis and properties of new chiral mesogenic monomers and side-chain smectic homopolymers containing (−)-menthyl groups

The synthesis of new chiral monomers (M₁−M₅) and the corresponding smectic homopolymers (P₁−P₅) containing menthyl groups is described. The chemical structures and purity were characterized by FT-IR, ¹H NMR and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The phase behavior and mesomorphism were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. The selective reflection property of light was studied with UV/visible/NIR. The monomers M₂−M₅ formed a chiral smectic C , and cholesteric or blue phase when a flexible linkage chain was inserted between the mesogenic core and the terminal menthyl groups by reducing the steric effect. M₁ showed no mesomorphism, while M₂−M₅ showed enantiotropic and cholesteric phases. Moreover, M₅ also exhibited a cubic blue phase on cooling. With increasing temperature, the selective reflection of light shifted to the long wavelength region at the phase range, and to the short wavelength region at the cholesteric phase range, respectively. The homopolymers P₁−P₅ all exhibited the batonnet textures of a smectic A phase. The melting, clearing, and glass transition temperatures increased, and the mesophase temperature ranges widened with increasing the aryl number in the mesogenic core.     

On the liquid-crystalline properties of methacrylic polymers containing 4′-(4-alkyloxyphenyl)azobenzene mesogens

In this article, we report on the synthesis and thermotropic behaviour of methacrylic polymers containing 4′-(4-alkyloxyphenyl)azobenzene mesogens attached to the backbone through n-alkyloxy spacers of 6 or 10 methylene groups. Polymerisations were carried out via free radicals using azobisisobutyronitrile (AIBN) as initiator. Chemical structures of polymers and their precursors were characterised by ¹H NMR spectroscopy. Thermogravimetric analysis showed that azopolymers are thermally stable up to temperatures around 300°C. The thermotropic liquid-crystalline (LC) behaviour was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). Results indicate that all synthesised mesogens, monomers and polymers developed two or more orthogonal LC phases in wide temperature ranges. Mesogens and monomers developed nematic and smectic phases, whereas polymers exhibited only smectic phase. In polymers, the arrangement of mesogens depends on the relative length of the spacer and the terminal flexible chain; two distinct structural models were proposed based on chemical interactions and steric constrains. The trans–cis photoisomerisation of monomers and polymers in solution was also studied. High cis-isomer contents (>80%) were reached in relative short irradiation times despite the steric constrains imposed by the polymer backbone.     

Optical anisotropy of a photoreacted side-chain liquid-crystalline polymer induced by linearly polarized UV light

Linearly polarized (LP) UV photoreaction of a photo-crosslinkable side-chain liquid-crystalline polymer (SLCP) containing photoreactive cinnamoyl and biphenyl mesogenic groups ( 1 ) was studied. The optical anisotropy of the polymer film was induced by the LP-UV photoreaction and was investigated by the temperature-controlled polarized UV absorption spectroscopy and polarized FT-IR measurements. The reorientation of the nonreacted mesogenic groups along to the Ê direction of the incident LP-UV light during the photoreaction occurred at the LC temperature range of the polymer, and the induced birefringence Δn was about 0.02. Because of the high-density photo-crosslinking, the LP-UV photoreacted film showed orientational stability up to 160°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1521–1526, 1998     

Optical and mesomorphic properties characterisation of chiral liquid crystalline copolysiloxane exhibiting cholesteric and blue phases

A series of liquid crystalline polymers (LCPs) have been synthesised by two cholesteric monomers M₁, M₂ and a nematic monomer M₃. The chemical structures and liquid crystalline properties of the monomers and polymers have been characterised by FTIR, ¹H-NMR, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction measurements and polarising optical microscopy. All LCPs show a high thermal stability with wide mesophase temperature ranges. For polymer P₁ bearing only cholesteric LC monomers component, it shows a cholesteric phase, whereas others display a blue phase besides a cholesteric phase. The formation of the blue phase is based on the structures of the polymers and the produced biaxial helix. The glass transition temperature and isotropic temperature of the polymers decrease on heating cycle with increasing the content of M₃ in the polymers. The specific rotation values of the polymers are temperature-sensitive. The reflection spectra of polymers P₁–P₆ show that the maximum reflected wavelengths shift to long wavelength with increasing the content of M₃ in the polymer systems. The frequency and intensity of the bands change sharply at the temperature where cholesteric phase changes to blue phase, but they show a weak dependence on temperature in the blue phase.     

Synthesis and properties of side-chain liquid crystalline polymers grafted with chiral dimers containing cholesteryl groups

ABSTRACT

Two series of novel side-chain liquid crystal (LC) polysiloxanes grafted with chiral liquid crystalline dimers containing cholesteryl mesogens were synthesised. The chemical structure and LC properties of comonomers and polymers were characterised by FTIR, ¹H-NMR, DSC, TGA, POM and XRD. M₁ and M₂ were chiral nematic (N*) dimers, and M₃ was an achiral LC monomer displaying nematic mesophase in a narrow mesomorphic temperature range, while the copolymers exhibited N* mesophase whose mesomorphic temperature ranges were much wider than those of the comonomers. Moreover, the glass transition temperatures and isotropization temperatures of the polymers all decreased with decreasing the dimer components. Reflection spectra showed that P_a series tend to attain wide-band selective reflection at long wavelengths, while P_b series were more potential at short wavelengths with narrow bandwidths. Decreasing the dimer components led the wavelength of the selective reflection to blue shift, which was an abnormal phenomenon in chiral mixture system.     

Crosslinking of a fibrous sample to a macro-oriented mesomorphic network

Preliminary results on the synthesis and characterization of anisotropic networks, oriented on a macroscopic scale, are reported. Fiber samples of segmented thermotropic liquid-crystalline polymers bearing the oxypentenyl lateral substituent have been crosslinked via thermally activated radical reaction. This was made possible by immersion of fiber samples in dichloromethane containing t-butylperoxybenzoate as activating agent, thus allowing its diffusion in the samples. Subsequent annealing at 145°C brings us to an anisotropic network with no loss of the original orientation. A mesophase is stabilized and no structural modification is observed by heating samples from room temperature up to 400°C, where thermal decomposition takes place. Crosslinked fibers exhibit good tensile properties, at both room temperature and at 150°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 433–438, 1998     

Synthesis of novel tri-podal mesogenic alkenes and side-chain polysiloxanes

Low molecular weight tri-podal biphenyl- and benzoate-type mesogens [C₆H₅C₆H₄O(CH₂)₅SiMe₂CH₂CH₂SiMe₂]₃CH (4), [C₁₁H₂₃O(C₆H₄)₂O(CH₂)₅SiMe₂]₃CH (5) and [MeOC₆H₄OC(O)C₆H₄O(CH₂)₅SiMe₂]₃CH (6) (C₆H₄ = 1,4-phenylene) were obtained, from branched silyl substituted methane precursors [CH₂CH(Me)₂Si]₃CH (1) and (HMe₂Si)₃CH (2). The biphenyl-containing ones (4) and (5) were converted into terminal alkenes, which were subsequently hydrosilylated with poly(methylsiloxanes). The polymer derived from (5) exhibited mesomorphic properties. Such systems have the potential to significantly increase the density of liquid crystal rod-like structures in side chains of linear polymers (or dendritic liquid crystal polymers).     

Nanostructured ion-conductive films: Layered assembly of a side-chain liquid-crystalline polymer with an imidazolium ionic moiety

An ion-conductive mesogenic monomer with an imidazolium ionic moiety has been designed to obtain self-assembled materials forming ionic layers. Self-standing polymer films are prepared by in situ photopolymerization of the monomer that forms homeotropic monodomain on a normal glass substrate in the smectic A phase. Macroscopically oriented, layered nanostructures are formed in the film. The ionic conductivity parallel to the smectic layer has been measured for the oriented film. In the smectic A phase at 150 °C, the magnitude of conductivity is about 10⁻² S cm⁻¹. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3486–3492, 2003     

Synthesis and mesomorphic properties of chiral fluorinated liquid crystals

Some fluorinated chiral liquid crystals were synthesized and the compounds characterized by IR, ¹H NMR, ¹⁹F NMR and mass spectroscopy and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry and polarizing optical microscopy. Nearly all of the compounds synthesized are liquid crystals with an enantiotropic cholesteric phase. Some of them exhibit a blue phase. Lateral tetrafluoro substitution decreases the clearing point and molecular polarity affects the formation of liquid crystalline phases.