A new route for the preparation of liquid crystalline polyorganosiloxanes containing laterally linked mesogenic units on the main chains

A new route for the preparation of liquid crystalline polyorganosiloxanes containing laterally linked mesogenic units on the main chains (LLM-POS) is described. First, a novel polyorganosiloxane containing hydroquinone units on the main chains (HQ-POS) was synthesized by hydrosilylation polymerization. To avoid the oxygen silylation side reaction of phenolic groups, tetrahydropyranyl (THP) protective groups were used on the phenols taking part in the hydrosilylation reaction, the results indicating that THP groups are very stable and effective in hydrosilylation reactions. Then HQ-POS was further modified by a grafting reaction with 4- n -octyloxybenzoyl chloride, giving the desired LLM-POS, which has an increased molecular mass in comparison with similar polymers prepared by commonly used approaches. The titled LLM-POS was characterized by DSC, POM and XRD and shown to give smectic textures.     

Electrooptical properties of liquid crystalline side chain polymers with laterally attached mesogenic units

The electrooptical properties of side-chain liquid crystalline polymers were investigated for the case that the mesogenic units were attached laterally rather than longitudinally to a flexible chain backbone via flexible spacer units. The experimental finding is that these polymers display unusual electrooptical properties within the isotropic phase in the neighborhood of the transition into the nematic phase. The polymers are characterized by the occurrence of a fast and a slow electrooptical response both of which show a critical divergence of the Kerr constant and the Kerr relaxation time. In addition, they show deviations between the rise and the decay values of the Kerr constants and in certain cases also of the Kerr relaxation times. Finally an overshoot of the induced birefringence following a sudden stepwise increase of the applied electric field has been found for one of these polymers. All these features can be accounted for on the basis of a newly developed theoretical approach that considers the particular dipolar and optical polarization configurations of these polymers.     

Synthesis and X-ray investigation of liquid crystalline polymers containing laterally methyl-substituted tolane-based mesogenic side groups

A series of polymethacrylates containing laterally methyl-substituted 4-alkoxy-4-nitrotolane, 4-alkoxy-4'-cyanotolane, and 4-alkoxy-4'-trifluoromethyltolane as mesogenic side groups are presented. The thermal behaviours of the prepared compounds were characterized by differential scanning calorimetry, optical polarized microscopy and X-ray diffraction. All of the obtained methacrylate monomers exhibit no mesophase, while most of the synthesized polymers reveal enantiotropic mesomorphism. The polymer containing 4-propyloxy-2'-methyl-4'-nitrotolane side groups was the only one to show no mesomorphic behaviour. The spacer length and the nature of terminal group have a profound influence on the type of mesophase formed and the thermal stability. Incorporation of a lateral methyl-substituent into the mesogenic groups reduces the thermal stabilities of the mesophases. X-ray diffraction reveals that polymers with a smectic A or smectic E phase have the inclination to form a bilayer structure. Increasing the temperature within the smectic phase range, the intermolecular spacing increases while the layer spacing decreases. On the other hand, introducing a lateral substituent into the mesogenic side groups leads to increase in both layer and intermolecular spacing.     

Side-chain liquid crystalline polymers with silphenylene-siloxane main chains. I. Synthesis of silphenylene-siloxane polymers containing hydrosilane units

Siophenylene-siloxane polymers with repeating units containing hydrosilane, SiH, groups were synthesized for use as backbone polymers in side-chain liquid crystalline polymers. The polymerization of 1,4-bis (hydroxydimethylsilyl) benzene with a bis (Pyrrolidinyl) silane monomer formed a crosslinked polymer during the course of the reaction, while the use of a bis (ureido) silane monomer gave a polymer which crosslinked on storage after preparation. However, a soluble polymer could be prepared successfully by using a dichlorosilane as the comonomer. Polymers containing two and three Si? H groups in each unit were prepared by the last method. All Soluble polymers were characterized by gel permeation chromatography (GPC), infrared spectroscopy (IR) multinuclear NMR spectroscopy, and differential scanning calorimetry (DSC).     

Synthesis and properties of chiral azo-liquid crystalline terpolymer containing cyano mesogenic units

A series of side-chain cholesteric polysiloxanes (PQ) were synthesised with poly(methyl--hydrogeno)siloxane, cholesterol (4-allyoxybenzoate) (M₁), and 4-hydroxyphenyl-4(allyloxy) phenylpropanoate (M₂), 4-allyloxy-4 ‘-cyanobiphenyl (M₃). Then azo-containing chiral liquid crystalline polymer (PZ) were synthesised with PQ and 4-(4-hexyloxyphenylazo) benzoic acid (M₄) by esterifying catalysed by 4-dimethylaminopyridine which is a new synthetic way. The chemical structures of monomers and polymers were confirmed by conventional spectroscopic methods and test methods for liquid crystal properties. The photo-induced isomerisation of the polymer is investigated by UV–vis spectroscopy. Weight lost temperatures (5%) for all polymers were greater than 298°C. The results showed that the introducing of azo moieties makes the polymer more stable on thermo dynamics. The transition temperatures of the polymers PQ and PZ exhibited some regularity as the change of ingredients of polymers. PQ series showed Grandjean textures and PQ₁–PQ₅ exhibited blue selective reflection in the visible light region. PZ₁–PZ₅ also showed Grandjean textures and the texture colour of the polymer turned to red and colourful with green and blue due to increasing contents of azo moiety, and yellow selective reflection in the visible light region were observed. The molecular design introducing shorter and harder part into chiral polymerisation system is favourable to the appearance of selective reflection. All polymers turned out right-handed optical activity due to having the same cholesteric group, the photo-responsive behaviours of the PZ series were also investigated.     

Model studies towards liquid crystalline dendrimers with mesogenic repeat units throughout the structure

Model studies towards liquid crystal dendrimers in which the mesogenic units are based on alkoxyalkylbiphenyls and repeat through the structure are described; the parent monomers show smectic mesophases demonstrating the suitability of the motifs.     

Synthesis and thermotropic behaviour of liquid crystals containing tolane-based mesogenic units

Tolane-based liquid crystal materials with three different terminal groups: trifluoromethyltolanes, cyanotolanes, and nitrotolanes, and with different chain lengths of alkenyloxy groups, have been synthesized. The phase behaviour of these liquid crystal materials has been characterized by differential scanning calorimetry, optical polarized light microscopy and X-ray diffraction. The mesophase behaviour of the materials was shown to be significantly influenced by the polarity of the terminal groups. The trifluoromethyltolanes exhibit an enantiotropic smectic E mesophase and the cyanotolanes exhibit a monotropic nematic mesophase. The most polar among the three types of liquid crystal material; the nitrotolanes do not display any liquid crystalline phases, except for the homologue with an eleven methylene unit chain.     

Synthesis and thermotropic behaviour of liquid crystals containing tolane-based mesogenic units

Abstract

Tolane-based liquid crystal materials with three different terminal groups: trifluoromethyltolanes, cyanotolanes, and nitrotolanes, and with different chain lengths of alkenyloxy groups, have been synthesized. The phase behaviour of these liquid crystal materials has been characterized by differential scanning calorimetry, optical polarized light microscopy and X-ray diffraction. The mesophase behaviour of the materials was shown to be significantly influenced by the polarity of the terminal groups. The trifluoromethyltolanes exhibit an enantiotropic smectic E mesophase and the cyanotolanes exhibit a monotropic nematic mesophase. The most polar among the three types of liquid crystal material; the nitrotolanes do not display any liquid crystalline phases, except for the homologue with an eleven methylene unit chain.     

Synthesis and mesomorphic properties of new liquid crystalline stilbene derivatives containing vinyloxyalkoxy chains

New liquid crystalline stilbene derivatives containing vinyloxyalkoxy chains 1 (n=5, 7, 9, 11) have been synthesised. Their mesomorphic properties have been studied by polarising optical microscopy and differential scanning calorimetry. It is interesting to note that even their alcohol precursors showed liquid crystalline behaviour. The effect of terminal alkoxy chain length and UV irradiation on the mesomorphic behaviour is discussed.     

Synthesis and liquid crystalline structures of poly(L-lysine) containing undecanamidobiphenyl units in the side chains

In order to obtain liquid crystalline comb-like poly(L-lysine) bearing biphenylyl mesogenic groups in their side chains, we synthesized the 11-(biphenyl-4-carboxamido)undecanamidoL-lysine (KC10φφ) from L-lysine by a five step procedure and transformed the KC10 φφ into its polymerizable cyclic derivative (the N-carboxyanhydride or NCA derivative) by the action of diphosgene. We homopolymerized the NCA of KC10 φφ to obtain the polymer pKC10 φφ and copolymerized it with the NCA of trifluoroacetyl-L-lysine (Kt) to obtain block copolymers pKt-pKC10 φφ of various compositions. X-ray diffraction studies demonstrated the existence of mesophases for our homopolymers and copolymers, resolved the structure of the mesophases and established the influence of temperature and the composition of the copolymers on the structure of the mesophases. Homopolymers pKC10 φφ exhibit, as a function of temperature, three phases (CrE_d, SmB_d and SmA_d) deriving from the β -pleated sheet structure of polypeptides and proteins. The presence of a pKt block in copolymers pKt-pKC10 φφ transforms the smectic CrE_d structure into a SmA_d structure and, when the content of pKt block increases, into a bidimensional hexagonal structure similar to that of the homopolymers pKt.     

Synthesis and liquid crystalline structures of poly(L-lysine) containing undecanamidobiphenyl units in the side chains

In order to obtain liquid crystalline comb-like poly(L-lysine) bearing biphenylyl mesogenic groups in their side chains, we synthesized the 11-(biphenyl-4-carboxamido)undecanamidoL-lysine (KC10 ϕϕ) from L-lysine by a five step procedure and transformed the KC10 ϕϕinto its polymerizable cyclic derivative (the N-carboxyanhydride or NCA derivative) by the action of diphosgene. We homopolymerized the NCA of KC10 ϕϕto obtain the polymer pKC10 ϕϕand copolymerized it with the NCA of trifluoroacetyl-L-lysine (Kt) to obtain block copolymers pKt-pKC10 ϕϕof various compositions. X-ray diffraction studies demonstrated the existence of mesophases for our homopolymers and copolymers, resolved the structure of the mesophases and established the influence of temperature and the composition of the copolymers on the structure of the mesophases. Homopolymers pKC10 ϕϕexhibit, as a function of temperature, three phases (CrE_d, SmB_d and SmA_d) deriving from the β-pleated sheet structure of polypeptides and proteins. The presence of a pKt block in copolymers pKt-pKC10 ϕϕtransforms the smectic CrE_d structure into a SmA_d structure and, when the content of pKt block increases, into a bidimensional hexagonal structure similar to that of the homopolymers pKt.     

An efficient synthesis of liquid crystalline gigantocycles combining banana-shaped and rod-like mesogenic units

The synthesis of monodisperse gigantocycles with 63, 87, and 147 ring atoms on the gram scale is described. These molecules were assembled from terphenylene derivatives and long, flexible chains which were mainly aliphatic, with terminal alkyne groups. The latter allowed for ring formation through oxidative alkyne dimerization in high yield (80-87%). The combination of a rod-like and a banana-shaped mesogen connected by flexible chains within the backbone of a ring gives rise to nematic and smectic mesophases.     

Evidence for a new ferroelectric switching liquid crystalline phase formed by a carbosilane based dendrimer with banana-shaped mesogenic units

The first carbosilane dendrimer with peripheral bent-core mesogenic units is reported. This material forms a liquid crystalline phase which is stable over a wide temperature range and forms an LC glass on cooling. Polarizing microscopy, X-ray diffraction, and dielectric and electrooptic investigations reveal the presence of a novel liquid crystalline phase, in which the molecules are tilted and adapt a polar order within the layers, but without long-range correlation between the layers. By applying external electric fields, switching into a ferroelectric organization can be achieved. Once formed the ferroelectric states are stable and can be switched between the different polarization states.     

Photoreactive main chain liquid crystalline polyesters containing oxadiazole and bis(benzylidene) cycloalkanone units

Photoreactive main chain liquid crystalline polyesters containing oxadiazole and bis(benzylidene)cycloalkanone moieties were synthesized and characterized by structural, thermal, mesomorphic, and optical measurements. The bis(benzylidene) cycloalkanone chromophores in the main chain can constitute both as a mesogen and photoreactive center, whereas 1,3,4‐oxadiazole is a well‐known fluorophore. The thermal properties of polymers were found to be inversely proportional not only to the spacer length but also to ring‐size of cycloalkanones. Hot stage polarized optical microscopic investigations displayed enantiotropic nematic liquid crystalline phases and development of grainy to schlieren textures depends on the length of flexible spacer in the polymer backbone which was in accordance with DSC analysis. Both photoisomerization and photodimerization are observed from the absorption spectra and discussed. The fluorescence spectra in solution state at various concentrations showed that the polymers show blue‐emission maxima and the Stokes shifts being 48–49 nm. The energy transfer occurred when increasing the concentration of the solution. The band gap energies calculated from the absorption spectra are in the range of 3.17–3.41 eV. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5760–5775, 2008     

Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T _g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T _g and T _m of the polymers.     

Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T_g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T_g and T_m of the polymers.     

Side-chain liquid crystalline polymers with silphenylene-siloxane main chains. III. Synthesis and characterization of polymers with phenyl benzoate mesogenic groups

Side-chain liquid crystalline (SCLC) silphenylene-siloxane polymers with a phenyl benzoate mesogenic group and polymethylene spacers were prepared and characterized, and their properties were compared with those of equivalent SCLC polymers, SCLCPs, with a biphenyl mesogenic group. With identical spacers and terminal substituents, the melting temperatures of the former were much lower, but the isotropization temperatures were lowered to a lesser extent, than those of the latter, and, consequently, a more thermally stable nematic phase was obtained for the former. Both types of SCLCPs formed nematic phases, while polymethylsiloxanes with the same side-chain mesogens exhibited smectic phases with wider temperature ranges. The lower thermal stability of the mesophases in the silphenylene-siloxane SCLCPs compared to those of the SCLC polymethylsiloxanes can be attributed to both the rigidity of the backbone and the greater separation of the side-chains along the main chains of the former.     

Synthesis and characterization of liquid crystalline elastomers bearing fluorinated mesogenic units and crosslinking mesogens

Several new side‐chain liquid crystalline (LC) polysiloxanes and elastomers ( IP ‐ VIP ) bearing fluorinated mesogenic units and crosslinking mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a fluorine‐containing LC monomer 4′‐undec‐10‐enoyloxy‐biphenyl‐4‐yl 4‐fluoro‐benzoate and a crosslinking LC monomer 4′‐(4‐allyloxy‐benzoxy)‐biphenyl‐4‐yl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, ¹H‐NMR, EA, TGA, DSC, POM and XRD. The effect of crosslinking mesogens on mesomorphic properties of the fluorinated LC polymers was studied as well. The obtained polymers and elastomers were soluble in many solvents such as toluene, tetrahydrofuran, chloroform, and so forth. The temperatures at which 5% weight loss occurred (T_d) were greater than 250°C for all the polymers, and the weight of residue near 600°C increased slightly with increase of the crosslinking mesogens in the fluorinated polymer systems. The samples IP , IIP , IIIP and IVP showed both smectic A and nematic phases when they were heated and cooled, but VP and VIP exhibited only a nematic mesophase. The glass transition temperature (T_g) of polymers increased slightly with increase of crosslinking mesogens in the polymer systems, but the mesophase–isotropic phase transition temperature (T_i) and smectic A–nematic mesophase transition temperature (T_S‐N) decreased slightly. It suggests that the temperature range of the mesophase became narrow with the increase of crosslinking mesogens for all the fluorinated polymers and elastomers. In XRD curves, the intensity of sharp reflections at low angle decreased with increase of crosslinking mesogens in the fluorinated polymers systems, indicating that the smectic order derived from fluorinated mesogenic units should be destroyed by introduction of more crosslinking mesogens. Copyright © 2008 John Wiley & Sons, Ltd.     

Liquid crystal polymers containing macroheterocyclic ligands. III. Side chain liquid crystalline polymethacrylates containing mesogenic units based on diarylacetylenes and benzo-15-crown-5

The synthesis and polymerization of 4′-[4-ethynyl-1-(11-methacryloylundecan-1-yloxy) benzene] benzo-15-crown-5 ( 8 ), 4′-[4-ethynyl-4′-(11-methacryloylundecan-1-yloxy) biphenyl] benzo-15-crown-5 ( 15 ), 4′-[2-ethynyl-6-(11-methacryloylundecan-1-yloxy) naphthalene] benzo-15-crown-5 ( 24 ), and 4′-[2-ethynyl-6-(11-methacryloylundecan-1-yloxy)naphthalene]-5′-ethylbenzo-15-crown-5 ( 35 ) is described. The synthesis and characterization of 4′-[4-(4-ethynyl-1-(2-ethynyl-6-(6-hydroxyhexan-1-yloxy)naphthathalene)benzene]) benzo-15-crown-5 ( 29 ) is also presented. Both monomers and polymers were characterized for their mesomorphic behavior. 8 , poly( 8 ), and 15 are crystalline. Due to the insolubility of 15 , poly( 15 ) could not be synthesized. 24 is crystalline, while poly( 24 ) displays a monotropic nematic mesophase. 29 exhibits also a monotropic nematic mesophase. 35 is crystalline, while poly( 35 ) displays an enantiotropic nematic mesophase which is kinetically controlled due to its close proximity to the glass transition temperature.     

Liquid crystalline properties of a series of thermotropic copolyesters containing both mesogenic and nonmesogenic units

A series of copolymers containing triad ester mesogenic units, with pendent n-octyl substituents, and triad ester nonmesogenic units, both with flexible spacer groups, was prepared and characterized for the effect of the nonmesogenic unit content on transition temperatures and thermodynamic parameters. The mesophase temperature range increased, but temperature, enthalpy, and entropy of isotropization decreased in a linear manner with increasing nonmesogen comonomer content. The entropy of isotropization is considered to be a quantitative measure of the degree of order of the nematic phase, but this order may include both the amount and the order parameter of the mesophase if, as proposed, both the isotropic and nematic phase exist below the isotropization temperatures of the copolymers.