Kerr effect in a laterally substituted side-chain liquid-crystalline polymer

The static and dynamic Kerr effects in a liquid-crystalline (LC) side-end polymer with a laterally substituted mesogenic fragment are studied. The characteristic relaxation times of the two different relaxation processes observed diverge at the same temperature. The main feature of the dynamic behavior of the polymer, e.g., the type of the electro-optical response is similar to that of side-on LC polymers.     

Crosslinkable liquid-crystalline combined main-chain/side-group polymers with low glass transition temperatures

Crosslinkable and crosslinked liquid-crystalline polymers with elastic properties were prepared from main-chain and combined main-chain/side-group polymers. These polymers exhibit nematic, smectic A, and smectic C phases. Polymers of these types with azoxybenzene as mesogen do not crystallize upon cooling. As a consequence, the liquid-crystalline phases are frozen in glassy around room temperature.     

Synthesis and thermal behavior of liquid-crystalline block copolymers containing both main-chain and side-chain mesomorphic blocks

A novel type of block copolymers comprising both side-chain and main-chain liquid-crystalline (LC) blocks in the same macromolecular structure was synthesized and studied. The former block was either one of two LC polymethacrylates containing an azobenzene mesogen with different substituents (block A), and the latter was a semiflexible LC polyester block (block B). Thermal, dynamic-mechanical, and X-ray diffraction data indicated that the two structurally different blocks were at least partly phase-separated within the glassy and LC states. The thermodynamic phase transition parameters of block A were not affected by copolymer composition. However, significant deviations of the thermodynamic parameters of block B were observed relative to those of the corresponding homopolymers. In particular, the normalized transition enthalpies of block B were much lower, suggesting the occurrence of a more or less diffuse interphase. An increase in the nematic-isotropic temperature was found at variance with previous results on most of the LC block copolymers, in which only one block was an LC component.     

NMR investigations on a liquid-crystalline side-chain siloxane polymer with a wide biphasic region

A polysiloxane bearing two different kinds of side chains has been studied by nuclear magnetic resonance and relaxation investigations. Both side chains contain the same mesogenic core but differ in their connection to the main chain: one of them is bound directly to the backbone, the other is linked to it via a ? (CH₂)₃? spacer. In this sample, the isotropic and mesomorphic phases coexist over a relatively wide range of temperatures. We have tried to explain this phenomenon by microphase separation. For the s_A –s_B transition a similar biphasic behaviour could not be observed with our methods. The order parameter has been estimated selectively for carbons in different parts of the side chain (spacer, wing group, mesogenic core). The behaviour of the order parameter in the mesomorphic regions of the biphase was observed, and a possible explanation is given.     

Optical investigations on a liquid-crystalline side-chain polymer with biaxial nematic and biaxial smectic A phase

A liquid-crystalline side-chain polymer with laterally incorporated naphthalene groups in the mesogenic moiety is investigated in binary mixtures with an optical uniaxial low-molar-mass liquid crystal. Mixtures with up to 50 mol-% content of the monomeric liquid crystal show a biaxial nematic phase. At lower temperatures a new biaxial smectic phase is observed, which corresponds to the smectic A phase. The angles between the optical axes are measured in dependence of temperature and mixture composition. Starting from the neat polymer, the angles decrease in the nematic as well as in the smectic phase with increasing mole fraction of the uniaxial liquid crystal. From the results a phase transformation uniaxial nematic to biaxial nematic can be inferred.     

Gas permeation through a side-chain liquid-crystalline polysiloxane-based membrane

A membrane was prepared by sandwiching the side-chain liquid-crystalline polysiloxane (LCP) 3 between two porous poly(propylene) (Celgard) films. Permeation properties for H₂, O₂, N₂, CH₄ and CO₂ through the side-chain LCP-based membrane was measured using a gaschromatographic method at several different temperatures corresponding to the different states of the side-chain LCP. The gas permeation behaviour depends strongly on the different states of the side-chain LCP. The plots of permeability versus reciprocal temperature show an abrupt change of the slope in the vicinity of the glass transition temperature (T_g) of the side-chain LCP for all five gases. The activation energy for permeation obtained at these different states exhibits different values. The value obtained in the liquid-crystalline state is the highest. Separation factors (P_O2/P_N2) and (P_CO2/P_CH4) exhibit an unusual behaviour when the temperature changes across T_g. They increase abruptly when the temperature increases and the phase changes from the glassy state to the liquid-crystalline state of the side-chain LCP. The fact that both permeability and selectivity increases with increasing temperature above the glass transition is attributed to the supermolecular arrangement of the liquid-crystalline state of the side-chain LCP.     

Transitional properties of liquid-crystalline side-chain polymers derived from poly(p-hydroxystyrene)

A series of liquid-crystalline polystyrene derivatives with ω-(4-(4-fluorophenylazo)phenoxy)-alkoxy pendant groups have been synthesized and characterized. Homologues with four or more methylene units in the spacer chain exhibit smectic liquid-crystalline phases, while the homologue with three methylene units forms an amorphous glass. The smectic A-isotropic (S_A-I) transition temperatures show a marked odd-even effect as a function of the parity of the spacer chain. This odd-even behaviour is also found in the variation of ΔS/R at the S_A-I transition across the series. A marked hysteresis between the transition temperatures determined on heating and the transition temperatures determined on cooling is observed. A molecular interpretation of these phenomena is proposed.     

Solution behaviour of a liquid-crystalline side-group polymer

Dilute and semidilute solutions of fractions of a liquid-crystalline side-group polymer were investigated by means of size-exclusion chromatography (SEC), static light scattering (LS), density and viscosity measurements. The mass-average molar mass ranged from M?_w = 1 · 10⁵ g · mol^?1 to 1,5 · 10⁶ g · mol^?1. Large discrepancies were found between the molar mass determined through SEC and through LS. Strong interactions between the mesogenic groups can be assumed by the results of density and LS measurements. Due to the determined characteristic ratio of C_∞ = 19,5 a similar chain stiffness as a poly(alkyl methacrylate) of equal length of the side chain is observed. In semidilute solutions an excess low-angle scattering (ExLAS) occurs which increases at higher concentrations. The dependence of the reduced osmotic modulus [M?_w/(RT)](?π/?c)_T on the parameter x = A₂ · M?_W · c was studied.     

Synthesis of side-chain liquid-crystalline polysalts with a poly(methylsiloxane) backbone

The synthesis and thermal properties of side-chain liquid-crystalline polysiloxanes, incorporating quaternized pyridyl groups, are described. The polymers are obtained by hydrosilylation of poly(hydrogenmethylsiloxane) with a protected alcohol. Reaction of the deprotected polysiloxanes with 4-(hydroxymethyl)pyridine and subsequent reaction with mesogenic alkyl bromides of different structure yielded the desired poly[(6-{N-[ω-(4′-alkoxy-4-biphenylyloxy)alkyl]-4-pyridiniomethoxy}hexyl)methylsiloxane bromide]. Four different types of polymers are prepared with either octyl or dodecyl alkyl chain, and with either methoxy or S-2-methyl-1-butoxy as an alkoxy group. Degrees of quaternization up to 80% are obtained. First results of their liquid-crystalline behaviour investigated by optical polarizing microscopy and differential scanning calorimetry are reported.     

Preparation of side-chain liquid-crystalline polymers via pyridylphenol hydrogen bonding

A series of side-chain liquid-crystalline polymers via pyridyl-phenol hydrogen bonding complexation was prepared by using non-liquid-crystalline precursors, such as poly[(4-vinylpyridine)-co-(butyl acrylate)] and 4-(4′-nitrophenylazo)phenol, 4-(4′-methoxyphenylazo)phenol or 4-(phenylazo)phenol. The association by hydrogen bonding was confirmed by means of FTIR. While the hydrogen bonds are weakened, and some dissociation occurs at the isotropization temperature, complete dissociation needs much higher temperature. The hydrogen bonds re-form as the complex is cooled to room temperature. The nematic liquid crystallinity of the polymer complexes was shown by means of wide-angle X-ray diffraction (WXRD) and polarized optical microscopy (POM). The different substitution groups of azophenol give isotropization temperatures of the polymer complexes in the following sequence:  NO₂ >  H >  OCH₃.     

Side-Chain liquid-crystalline polymers containing a siloxane spacer, 2. Effects of mesogenic groups on the thermal properties of side-chain liquid-crystalline polymers containing a disiloxane unit in the spacer

A series of side-chain Iiquid-crystalline polymers was prepared containing disiloxane units in the spacer. The polymers consist of a polymethacrylate backbone and several kinds of mesogenic side groups. For the synthesis of the desired monomers, silanol compounds carrying a mesogenic groups were prepared as the intermediates. The polymers were obtained by ordinary free-radical polymerization. As the mesogenic groups, linear-type p- or p′-substituted phenyl and biphenylyl benzoates, p- or m-substituted benzoyloxybiphenyl groups and laterally attached biphenylyl benzoate-type mesogens were chosen, and the structural effects on the thermal properties of the polymers were investigated. In the case of linear-type mesogens, only when triple-core mesogens were introduced a stable smectic mesophase was observed with a wide range of phase stability, while on mesophase was observed for the linear double-core and the laterally attached mesogens. On the other hand, a highly ordered smectic phase was observed for polymers having linear-type triple-core mesogens with p-alkoxy and m-cyano end groups. Furthermore, it was revealed that the introduction of a disiloxane unit in the spacer lowered the temperature range of the mesophase, in comparison with polymers having an alkylene spacer with the same backbone component and mesogens.     

Synthesis of side-chain liquid-crystalline polyethers by chemical modification of polyepichlorohydrin

Copolymers derived from polyepichlorohydrin (PECH), bearing pendant mesogenic units are obtained by chemical modification of atactic samples of PECH with sodium 4-cyano-4′-biphenoxide. Rate and yield of substitution are strongly dependent on the molecular weight of the used PECH. A substantial rise (ΔT ～ 110°C) of glass transition temperature with the percentage of incorporated cyanobiphenyl groups is observed. Copolymers with an amount of substitution higher than 60% present thermotropic liquid-crystalline behaviour and form nematic phases. Chemical modification of PECH offers a simple method for the synthesis of new liquid-crystalline polyethers whose transition temperatures can be adjusted by varying the amount of substitution.     

Synthesis and characterization of some new photochromic side-chain liquid-crystalline polymers

The synthesis and characterization of a series of liquid-crystalline copolymethacrylates containing side chains with both azobenzene and benzanilide moieties is described. The phase behaviour of the polymers is discussed in dependence of their copolymer composition. The copolymers are suitable for optical investigations on the photochemical trans-cis isomerization of the azo group.     

Orientational behaviour of polymer blends containing a liquid-crystalline component

This paper describes the orientational behaviour of polymer blends containing a side-group liquid-crystalline polymer (LCP). The macroscopic orientation of the LC phase in these blends, and the possibility to freeze in this state are of technical interest. The orientation of LCP-containing blends through mechanical forces depends on a variety of structural, thermal, energetical and also morphological properties, which are strongly dependent on the kinetical and thermal history. This report describes the optical- and scanning electron microscopy (SEM), X-ray diffraction and interfacial tension studies of the liquid-crystalline polyacrylate 1a and the poly(methacrylate) 1b in poly(methyl methacrylate) (PMMA) and polycarbonate matrices. 1a droplets in thermoplastic matrices can be oriented macroscopically during fibre-drawing, but, as a result of higher interfacial tension between the components, 1b -containing blends can not.     

Nematic-nematic immiscibility and induced smectic a phases in mixtures with liquid-crystalline side-chain polymers

Two non-ideal kinds of behaviour for solutions of liquid-crystalline side-chain polymer (LC polymer) solutes in nematic solvents of low molecular weight (LMW) are investigated, viz. immiscibility and induced smectic A phases. The former property already observed in the nematic state of some polysiloxanes is extended to polymethacrylates (or polyacrylates) leading to the conclusion that immiscibility is strongly influenced by the chemical structure of the whole macromolecule. The latter property responds in the same way as the former to molecular modifications, suggesting that they can be connected somehow.     

Synthesis and properties of liquid-crystalline side-chain polymers containing β-diketonato transition metal complexes

Polymers ( 5-7 ) containing β-diketonato metal complexes of Cu²⁺, Ni²⁺ and Co³⁺ were synthesized from new thermotropic liquid-crystalline poly(acrylate ester)s ( 4 ) with a mesogenic bidentate β-diketone in the side chain, and the liquid-crystalline properties were examined by differential scanning calorimetry (DSC), X-ray diffraction and polarizing microscopy. The mesophase of 4 is an enantiotropic smectic A phase showing a batônnet and focal conic fan texture in polarizing microscopy. Polymers 5a-c containing a bis(β-diketonato) copper(II) complex also exhibit an enantiotropic smectic A phase, and polymer 5d prepared from the vinyl monomer 8 shows a nematic phase. Concerning the complexes of polymers 6 and 7 with nickel(II) and cobalt(III), only 6a and 7a containing a small amount of metal-chelating β-diketonate units exhibit liquid-crystalline behavior like the parent polymer 4 . It was found that the fourcoordinated square planar bis(β-diketonate)copper(II) acts as the mesogen; both nickel(II) and cobalt(III) complexes do not work as mesogens and rather hinder the liquid crystallinity of 4 . The electron spin resonance (ESR) spectra of 5a and 5b change markedly along with the transition from the smectic A phase to the isotropic one. The broadening and simplification of the spectra for the isotropic phase indicates increased interaction between neighboring bis(β-diketonato)copper(II) complexes and substantial electron spin-spin interaction. The ESR spectra of 5c and 5d also imply this increased interaction between neighbouring complexes and spin-spin interaction regardless of the phase transition.     

Synthesis and thermal properties of side-chain liquid-crystalline poly(glycidyl ethers) with racemic and chiral backbone

Oxiranes bearing a 4-cyanobiphenyl-4′-oxy mesogenic group with spacers of different length have been synthesized from glycidyl p-toluenesulfonate or epichlorohydrin (racemic or optically active). These monomers were polymerized with anionic initiators (CsOH, tBuOK

1 tBu: tert-butyl, Et: ethyl.

) or a chelate initiator (AlEt₃/H₂O/acetylacetone ). A transfer of chirality from the polymer backbone to the mesophase is observed for polyethers with a short spacer. A cholesteric phase is observed for the optically active polymer while the racemic polymer is nematic. Increasing the length of the spacer leads to a smectic mesophase. However, in that case, the effect of the chiral centre of the polymer backbone on the mesomorphous properties is not detected.     

Synthesis of novel sulfonyl-containing liquid-crystalline side-chain poly(vinyl ethers)

The synthesis of some new liquid-crystalline polymers with sulfonyl-containing mesogenic groups is described. 4-[(S)-(-)-2-MethylbutyIsulfonyl]-4′-[(11-vinyloxy)undecyloxy]biphenyl ( 10 -11), 4-[(S)-(-)-2-methylbutylsulfonyl]-4′-[8-(vinyloxy)octyloxy]biphenyl ( 10 -8), 4-[(S)-(-)-2- methylbutylsulfonyl]biphenyl 4-[11-(vinyloxy)undecyloxy]benzoate ( 12 -11), 4-[(S)-(-)-2-methylbutylsulfonyl]biphenyl 4-[8-(vinyloxy)octyloxy]benzoate ( 12 -8), 4-[(S)-(-)-2-methylbutyloxy]-4′- [11-(vinyloxy)undecylsulfonyl]biphenyl ( 18 -11) and 2-[11-(vinyloxy)undecyloxy]-6-{4-[(S)-(-)-2- methylbutylsulfonyl]phenyl}naphthalene ( 23 -11) were all synthesized, and polymerized with the initiating system CF₃SO₃H/S(CH₃)₂ in CH₃Cl₃ at 0°C. Monomers 10 -11, 10 -8, 18 -11 and 23 -11 are crystalline, while both 12 -11 and 12 -8 show an enantiotropic smectic A phase. All polymers exhibit the same thermotropic behaviour as their corresponding monomers, except poly( 23 -11) which exhibits an enantiotropic smectic A (s_A) and a monotropic chiral smectic C phase (S*_C).     

Ionic conductivity and morphology of polymer electrolytes based on a side-chain liquid-crystalline polysiloxane containing oligooxyethylene spacers and 6-cyano-2-naphthyl benzyl ether mesogens

Solid polymer electrolytes with different stoichiometries were prepared from solvent-cast mixtures of alkali metal salts with the side-chain liquid-crystalline polysiloxane 2 . Differential scanning calorimetry, optical polarizing microscopy, X-ray diffraction, and conductivity measurements revealed that both morphology and conductivity of the obtained complexes are dependent on the salt content. For the complexes formed from 2 with LiSO₃CF₃, the formation of a homogeneous phase occurred approximately at the mole ratio LiSO₃CF₃ to oxyethylene unit of 1/2. The conductivity of the complex gradually increases with increasing mole ratio LiSO₃CF₃/OCH₂CH₂. The highest conductivity at ambient temperature achieved was 4,8 · 10^?6 S · cm^?1, which corresponds to the complex with a mole ratio LiSO₃CF₃/OCH₂CH₂ of 1/1. For all complexes obtained the temperature dependence of the conductivity displays an unusual behaviour in the temperature range belonging to the glassy and glass transition states of the polymer and an Arrhenius-type behaviour in the temperature range belonging to the liquid-crystalline state of the polymer. For the complexes formed from 2 with various alkali metal salts, the conductivity decreases in the order LiSO₃CF₃ > LiClO₄ > NaClO₄ > LiBr > KClO₄. This indicates that LiSO₃CF₃ is more effectively ionized by the oxyethylene units than the other salts.     

Side-chain liquid-crystalline polymers containing a siloxane spacer, 1. Synthesis of side-chain liquid-crystalline polymers containing siloxane bond in the spacer unit

Side-chain liquid-crystalline polymers containing siloxane bond in the spacer units were prepared. For the synthesis of the desired monomers, novel silanol compounds carrying a mesogenic group were prepared as the intermediates. The polymers were obtained by ordinary free-radical polymerization. As the mesogenic groups, p- or p′-cyano-substituted biphenyl group, phenyl and biphenylyl benzoates were chosen, and the structural effects on the thermal properties were investigated. Introduction of a disiloxane group in the side chain resulted in a decrease of T_g which was more marked for longer siloxane units. Furthermore, only when a terphenylene-type mesogen was introduced, a stable smectic mesophase was observed with wide range of phase stability.