Oligooxyethylene Spacers Research Articles

Self-Assembled Liquid-Crystalline Ion Conductors: Odd-Even Effects of Flexible Spacers Binding a Carbonate Moiety and an Aliphatic Rod-Like Core on Phase Transition Properties and Ion Conductivities

Abstract Liquid-crystalline compounds consisting of mesogenic cores linked to cyclic carbonates through flexible spacers have been developed. These liquid crystals form complexes with lithium salts and self-assemble into nanostructures with well-defined ion pathways. It is found that the type and length of the intramolecular spacer affects the liquid crystallinity and ion conductivity of the materials. Mesogenic compounds based on alkylene-based spacers show odd-even effects on the liquid-crystalline properties of the compounds. The liquid crystals based on spacers with an even number of carbon atoms show liquid crystallinity in wider temperature ranges and higher ion conductivities as compared to the liquid crystals based on spacers with an odd number of carbon atoms. On the other hand, liquid crystals based on polar oligooxyethylene spacers are observed to show liquid-crystallinity in wider temperature ranges and higher ion conductivities as compared to the alkylene-based liquid crystals. The liquid crystals with more polar and more flexible spacers, that is, oligooxyethylene groups show higher ion conductivities than those of the liquid crystal with alkylene spacers. This enhanced behavior may be due to the increase in the fluidity of the ionic pathways. These findings may provide us with new designs of self-assembled ion conductors.

Efficient Cellular Knockdown Mediated by siRNA Nanovectors of Gemini Cationic Lipids Having Delocalizable Headgroups and Oligo-Oxyethylene Spacers.

The use of small interfering RNAs (siRNAs) to silence specific genes is one of the most promising approaches in gene therapy, but it requires efficient nanovectors for successful cellular delivery. Recently, we reported liposomal gene carriers derived from a gemini cationic lipid (GCL) of the 1,2-bis(hexadecyl dimethyl imidazolium) oligo-oxyethylene series ((C16Im)2(C2H4O)nC2H4 with n = 1, 2, or 3) and 1,2-dioleyol phosphatidylethanolamine as highly efficient cytofectins for pDNA. On the basis of the satisfactory outcomes of the previous study, the present work focuses on the utility of coliposomes of these gemini lipids with the biocompatible neutral lipid mono oleoyl glycerol (MOG) as highly potent vectors for siRNA cellular transport in the presence of serum. The (C16Im)2(C2H4O)nC2H4/MOG-siRNA lipoplexes were characterized through (i) a physicochemical study (zeta potential, cryo-transmission electron microscopy, small-angle X-ray scattering, and fluorescence anisotropy) to establish the relationship between size, structure, fluidity, and the interaction between siRNA and the GCL/MOG gene vectors and (ii) a biological analysis (flow cytometry, fluorescence microscopy, and cell viability) to report the anti-GFP siRNA transfections in HEK 293T, HeLa, and H1299 cancer cell lines. The in vitro biological analysis confirms the cellular uptake and indicates that a short spacer, a very low molar fraction of GCL in the mixed lipid, and a moderate effective charge ratio of the lipoplex yielded maximum silencing efficacy. At these experimental conditions, the siRNA used in this work is compacted by the GCL/MOG nanovectors by forming two cubic structures (Ia3d and Pm3n) that are correlated with excellent silencing activity. These liposomal nanocarriers possess high silencing activity with a negligible cytotoxicity, which strongly supports their practical use for in vivo knockdown studies.

Liquid-Crystalline Dye-Sensitized Solar Cells: Design of Two-Dimensional Molecular Assemblies for Efficient Ion Transport and Thermal Stability

Nanostructured liquid-crystalline (LC) electrolytes have been developed for efficient and stable quasi-solid-state dye-sensitized solar cells (DSSCs). Two types of ionic LC assemblies for electrolytes have been designed: (i) noncovalent assemblies of two-component mixtures consisting of I2-doped imidazolium ionic liquids and carbonate-terminated mesogenic compounds (noncovalent type) and (ii) single-component mesogenic compounds covalently bonding an imidazolium moiety doped with I2 (covalent type). These mesogenic compounds are designed with flexible oligooxyethylene spacers connecting the mesogenic and the polar moieties. The oligooxyethylene-based material design inhibits crystallization and leads to enhanced ion transport as compared to alkyl-linked analogues due to the higher flexibility of the oligooxyethylene spacer. The noncovalent type mixtures exhibit a more than 10 times higher I3– diffusion coefficient compared to the covalent type assemblies. DSSCs containing the noncovalent type liquid cryst...

A delocalizable cationic headgroup together with an oligo-oxyethylene spacer in gemini cationic lipids improves their biological activity as vectors of plasmid DNA.

Lipoplex nano-aggregates constituted of plasmid DNA (pDNA) pEGFP-C3 and mixed cationic liposomes, consisting of several percentages of a gemini cationic lipid (GCL) of the 1,2-bis(hexadecyl imidazolium) oxyethylene series, referred to as (C16Im)2(C2O)n, with oxyethylene spacers (n = 1, 2 or 3) between the imidazolium cationic groups and the DOPE zwitterionic helper lipid, have been characterized by various biophysical and biological approaches carried out at several GCL compositions (α), and either the mass or the effective charge ratio of the lipoplex. The electrochemical study by ζ-potential confirms that the three GCLs yield a 10% lower effective charge than the nominal one, while compacted pDNA yields only a 25% effective negative charge. The SAXS study reveals, irrespective of the spacer length (n) and effective charge ratio (ρeff), the presence of two lamellar structures, i.e., one (Lα,main) in the whole GCL composition and another (Lα,DOPE,rich) with higher periodicity values that coexists with the previous one at low GCL composition (α = 0.2). The cryo-TEM analysis shows two types of multilamellar structures consisting of cationic lipidic bilayers with pDNA sandwiched between them: a cluster-type (C-type) at low α = 0.2 and a fingerprint-type (FP-type) at α≥ 0.5, both with similar interlamellar spacing (d) in agreement with the Lα,main structure determined by SAXS. Transfection efficacies (TEs) of each lipid mixture were determined in four different cell lines (HEK293T, HeLa, Caco-2 and A549) at several α and ρeff values in the absence and presence of serum (FBS). The optimized formulations (α = 0.2 and ρeff = 2.0) substantially transfect cells much better than a commercial transfection reagent, Lipofectamine 2000 and previously studied efficient lipoplexes containing other cationic head groups or spacers both in the absence and presence of serum. The activity of optimized formulations may be attributed to the combination of several factors, such as: (a) the fusogenic character of DOPE which results in higher fluidity of the lipoplexes at α = 0.2, (b) the coexistence of two lamellar structures at α = 0.2 that synergizes the TE of these lipid vectors, and mainly (c) the higher biocompatibility of the GCLs reported in this work due to the presence of two imidazolium cationic groups together with an oligo-oxyethylene spacer. The length of the spacer in the GCL seems to have less impact, although (C16Im)2(C2O)n/DOPE-pDNA lipoplexes with n = 1 and 3 show higher gene transfection than n = 2. All the optimum formulations reported herein are all highly efficient with negligible levels of toxicity, and thus, may be considered as very promising gene vectors for in vivo applications.

Binding of Gemini Bisbenzimidazole Drugs with Human Telomeric G-Quadruplex Dimers: Effect of the Spacer in the Design of Potent Telomerase Inhibitors

The study of anticancer agents that act via stabilization of telomeric G-quadruplex DNA (G4DNA) is important because such agents often inhibit telomerase activity. Several types of G4DNA binding ligands are known. In these studies, the target structures often involve a single G4 DNA unit formed by short DNA telomeric sequences. However, the 3′-terminal single-stranded human telomeric DNA can form higher-order structures by clustering consecutive quadruplex units (dimers or n-mers). Herein, we present new synthetic gemini (twin) bisbenzimidazole ligands, in which the oligo-oxyethylene spacers join the two bisbenzimidazole units for the recognition of both monomeric and dimeric G4DNA, derived from d(T2AG3)4 and d(T2AG3)8 human telomeric DNA, respectively. The spacer between the two bisbenzimidazoles in the geminis plays a critical role in the G4DNA stability. We report here (i) synthesis of new effective gemini anticancer agents that are selectively more toxic towards the cancer cells than the corresponding normal cells; (ii) formation and characterization of G4DNA dimers in solution as well as computational construction of the dimeric G4DNA structures. The gemini ligands direct the folding of the single-stranded DNA into an unusually stable parallel-stranded G4DNA when it was formed in presence of the ligands in KCl solution and the gemini ligands show spacer length dependent potent telomerase inhibition properties.

Dimeric 1,3-Phenylene-bis(piperazinyl benzimidazole)s: Synthesis and Structure–Activity Investigations on their Binding with Human Telomeric G-Quadruplex DNA and Telomerase Inhibition Properties

Ligand-induced stabilization of G-quadruplex structures formed by the human telomeric DNA is an active area of research. The compounds which stabilize the G-quadruplexes often lead to telomerase inhibition. Herein we present the results of interaction of new monomeric and dimeric ligands having 1,3-phenylene-bis(piperazinyl benzimidazole) unit with G-quadruplex DNA (G4DNA) formed by human telomeric repeat d[(G(3)T(2)A)(3)G(3)]. These ligands efficiently stabilize the preformed G4DNA in the presence of 100 mM monovalent alkali metal ions. Also, the G4DNA formed in the presence of low concentrations of ligands in 100 mM K(+) adopts a highly stable parallel-stranded conformation. The G-quadruplexes formed in the presence of the dimeric compound are more stable than that induced by the corresponding monomeric counterpart. The dimeric ligands having oligo-oxyethylene spacers provide much higher stability to the preformed G4DNA and also exert significantly higher telomerase inhibition activity. Computational aspects have also been discussed.

Contribution of 1H NMR to the investigation of the adsorption of cationic Gemini surfactants with oligooxyethylene spacer group onto silica

The present study aims to investigate the behavior of a series of cationic Gemini surfactants with a hydrophilic spacer at liquid–gas and solid–liquid interfaces, with particular emphasis on the effect of spacer length. Gemini surfactants containing two quaternary ammonium groups bound by an ethylene oxide spacer chain, referred to as 12-EO x -12 with x = 1 , 3 , 7 and 12 were synthesized. Surface tension measurements were used to show that the hydrophilic spacer with oxyethylene moieties was not fully extended at the air–water interface. With increasing the spacer group size, it became sufficiently flexible to adopt a particular conformation with a loop at the water side of the interface. A combined study by adsorption isotherm measurements and 1H NMR spectroscopy allowed a detailed description of the adsorption mechanism of these investigated 12-EO x -12 surfactants, with NMR providing more precise information on the conformation of hydrophilic spacer at the solid–liquid interface. Binding to the silica surface involved one cationic headgroup for the surfactants with a short spacer and the two headgroups for the ones with a long spacer. The number of charged surface sites was estimated by considering the dimeric surfactant as a “molecular ruler.” The small density of adsorption sites gave rise to the formation of pinned surface micelles.

Syntheses and Coordination Properties of (Thia)Calix[4]Arenes Bearing Single ω-Quinolin-8-Yl-Oligooxyethylene Pendant

Four mono-quinolin-8-yl-substituted (thia)calix[4]arenes via oligooxyethylene spacers (1a–b and 2a–b) were synthesised conveniently in one step. Their structures and conformations were characterised by 1H NMR and ESI-MS spectra. Their coordination properties were studied by fluorescence spectra titration in CH3CN. All of them can form stable 1:1 complex with Zn(II) and Mg(II) ions, respectively. The stability constants of thiacalix[4]arene (2a and 2b) derivatives are higher than those of the calix[4]arene analog (1a and 1b).

Gel formation in cationic polymerization of divinyl ethers. III. Effect of oligooxyethylene chain versus oligomethylene chain as central spacer units

AbstractCationic polymerizations of two series of divinyl ethers were carried out to clarify the effects of their central spacer chain structure on their crosslinking polymerization behavior. One series of the monomers involves divinyl ethers with an oligooxyethylene central spacer chain: diethylene glycol divinyl ether (O‐3), triethylene glycol divinyl ether (O‐4), tetraethylene glycol divinyl ether (O‐5), pentaethylene glycol divinyl ether (O‐6), and heptaethylene glycol divinyl ether (O‐8) (see Scheme 1). The other series includes divinyl ethers with an oligomethylene central spacer chain: 1,4‐butanediol divinyl ether (C‐4), 1,6‐hexanediol divinyl ether (C‐6), and 1,8‐octanediol divinyl ether (C‐8). Cationic polymerizations of these monomers were carried out with the hydrogen chloride/zinc chloride (HCl/ZnCl2) initiating system in methylene chloride (CH2Cl2) at −30 °C ([Monomer]0 = 0.15 M; [HCl]0 = 5.0 mM; [ZnCl2]0 = 0.5 mM). The polymerizations of the oligomethylene‐based divinyl ethers C‐6 and C‐8 caused gel formation at high monomer conversions (∼90%), whereas C‐4 formed soluble polymers even at almost 100% monomer conversion. The oligooxyethylene‐based divinyl ethers O‐3, O‐4, O‐5, and O‐6 underwent gel‐free polymerizations up to 100% monomer conversion and O‐8 did so at least up to ∼80% conversion. The content of unreacted pendant vinyl groups of the obtained soluble polymers was measured by 1H NMR spectroscopy. In the polymerizations of the oligomethylene‐based divinyl ethers (C‐4, C‐6, and C‐8), the vinyl contents of the polymers decreased monotonously with increasing monomer conversion, and their number‐average molecular weights (Mn's) and polydispersity ratios (Mw/Mn's) increased considerably just before the gelation occurred. On the contrary, the vinyl contents of the polymers obtained from the oligooxyethylene‐based divinyl ethers (O‐3, O‐4, O‐5, O‐6, and O‐8) decreased steeply even in the early stage of the polymerizations and almost all the pendant vinyl ether groups were consumed in the soluble polymers at the final stage of the polymerizations. The oligooxyethylene spacer units adjacent to the pendant unreacted vinyl ether groups may solvate intramolecularly with the carbocationic active center to accelerate frequent occurrence of intramolecular crosslinking reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3729–3738, 2004

Ferroelectric liquid crystalline polymers based on mesogens with halogen-containing terminal groups

A new series of halogen-containing side chain ferroelectric liquid crystal polymers was synthesized. Mesophases were characterized by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction and molecular simulation. The behaviour of the liquid crystalline phase was investigated with variation of chiral centres, spacer units and grafted ratios. It was found that the thermal stability and temperature range of the chiral smectic C phase decreased with increasing length of the oligo-oxyethylene spacer, and decreasing mesogenic group content. The bulky substituent attached to the chiral centre reduces molecular packing in smectic liquid crystal phases, which disturbs the orientation of the side chain liquid crystal polymer. Furthermore, the influence of molecular structure on electrooptical properties of FLCPs has been studied by broad band dielectric spectroscopy (from 0.1 to 1 × 106 Hz).

Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers

A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.

Synthesis and hydrophobic association of poly(N,N-dimethylacrylamide) end-functionalized with perfluorocarbon and hydrocarbon groups

Polydimethylacrylamides (PDMAs) end-functionalized with hydrophobic groups were synthesized by the reaction of cesium salts of one- or two-ended living PDMA anion with octadecanoyl and perfluorooctanoyl chlorides and with α-phenylacrylate monomers containing an octadecyl group attached via oligooxyethylene spacers to the acrylate functionality. Size exclusion chromatography or NMR studies indicated that the end functionalizations were nearly quantitative. Reduced viscosity measurements were consistent with predominantly dimeric association of the perfluorooctanoyl-end-functionalized PDMAs. The association of the two-ended, perfluorooctanoyl- and octadecanoyl-functionalized polymers was more extensive and consistent with pairwise association. Furthermore, the presence of oligoethylene oxide spacers between the octadecyl and α-phenylacrylate groups greatly enhanced the hydrophobic association of bis(octadecyl)-end-functionalized PDMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1403–1418, 2001

Correlation of the thermal properties of main-chain liquid crystalline polymers with the symmetry and anisometry of their mesogens

Several series of liquid crystalline poly[aroyl-bis(oxyarylates)] with oligomethylene (n = 6 and 10) and oligooxyethylene (n = 2; 3; 4 and -) spacers were synthesized. The structure of their mesogenic groups was varied by replacement of central or terminal units by those with reduced symmetry. The polymers were invetigated by methods, such as differential scanning calorimetry, polarizing optical microscopy and in some selected cases by X-ray diffraction methods using synchrotron radiation. An absence of transesterification during measurements at elevated temperatures was proved by 13 C NMR spectroscopy. The formation of smectic melts was demonstrated for all the polymers with high symmetry of the mesogenic group. A lower symmetry leads to a decrease of crystallinity of the polymers and to the appearance of a nematic phase in their melts. Comparative analyses of their thermal properties were made in order to determine the contribution of each single unit of the mesogenic groups on the thermal properties of the polymers.

Effect of a lateral substituent on the mesomorphic properties of ferroelectric side chain liquid crystalline polysiloxanes

The synthesis of side chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and (S)-2-methylbutyl 4-\\[(4-oxybiphenyl-4-yl)carbonyloxy]-3-fluorobenzoate mesogenic side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for all synthesized monomers and polymers. All three precursor olefinic monomers reveal cholesteric and smectic A phases. The olefinic monomer which contains two oligooxyethylene units in the spacer is the only one which reveals a twist grain boundary A phase and a blue phase, besides the cholesteric and smectic A phases. All three polysiloxanes present enantiotropic smectic A and chiral smectic C phases. The mesomorphic behaviours of the monomers and polymers are compared with those of the corresponding monomers and polymers without the lateral fluoro substituent. The results seem to demonstrate that incorporating a lateral fluoro substituent in the mesogenic cores of the monomers affects not only the mesophase thermal stability, but also the nature of the mesophases formed. However, incorporating a lateral fluoro substituent in the mesogenic cores of the polymers affects only the thermal stability of the mesophases formed. The lateral fluoro substituent has a more profound effect on the mesomorphic behaviour for the monomers than that for the polymers.

Synthesis and Thermal Properties of Ferroelectric Side-Chain Liquid-Crystalline Polysiloxanes Based on Naphthyl Biphenylcarboxylate Mesogenic Groups and Oligooxyethylene Spacers

In this work, three series of ferroelectric side-chain polysiloxanes containing oligooxyethylene spacers and (S)-2-methyl-1-butyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates, (R)-1-methylheptyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates, and (2S,3S)-2-chloro-3-methylpentyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates mesogenic groups were synthesized. The mesomorphic behaviors of three series of ferroelectric side-chain liquid-crystalline polysiloxanes were also studied using differential scanning calorimetry, optical polarizing microscopy, and high-resolution X-ray diffraction measurements. Some of these side-chain polysiloxanes containing four phenyl rings of ester cores (i.e., −Ph−Ph−COO−naphthyl−) and chiral heptyl tail present a smectic A (SA), and a chiral smectic C (Sc*) phase (around 100 °C). Another two series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tail reveal a cholesteric (N*), an SA phase and an Sc* phase. The polymer PS12NC derivative with one unit of oxyethylene spacer (n = 1) of PSn2NC series reveals a N* phase, a twist grain boundary A (TGBA) phase, and a Sc* phase. X-ray investigations reveal that the packing of mesogenic groups for PS02NA, PS02NB, PS02NC with the shortest spacers (n = 0) exhibit a bilayer (two-layer) packing structures. Moreover, polymer PS32NA, PS32NB, PS32NC with the longest spacer chain (n = 3) reveal a monolayer packing structure. However, these two types of packing structure appear simultaneously in PS12NA (n = 1), PS12NC (n = 1), PS12NB (n = 1), and PS22NB (n = 2), depending on the chiral tail length. Results obtained in this study again demonstrate that the tendency toward chiral smectic C mesomorphism increases as the rigidity of phenyl ester mesogens increases via the flexible oligooxyethylene spacers system. Furthermore, the thermal stability of the chiral smectic C mesophase is determined by the flexibility of the chiral tail.

Synthesis and characterization of new ferroelectric liquid crystals containing a phenyl biphenyl carboxylate mesogenic group and oligooxyethylene spacers

Abstract Two series of ferroelectric liquid crystals containing a phenyl biphenyl carboxylate mesogenic group and oligooxyethylene spacers were synthesized. The mesomorphic behaviours of the compounds were characterized using differential scanning calorimetry (DSC), optical polarizing microscopy (POM) and powder X-ray diffraction measurements. These series all contain a smectic A (SA), a chiral smectic C (SC) and a crystal E (Cr E) phase sequence. The ordered smectic Cr E phase was observed for the short spacer chain (n = 0, 1, 2) homologues of the two series. Moreover, the mesomorphic properties are discussed as a function of the oligooxyethylene spacer length, and the position of the aromatic core rings. These results indicate that the structures with a rigid part (biphenyl group) closer to the flexible spacer chain (oxyethylene unit) tend to form the symmetrical smectic SA and Cr E phases.

Synthesis and characterization of new ferroelectric liquid crystals containing a (2S)-2-[6-(4-hydroxybiphenyl-4′-carbonyloxy)-2′- naphthyl] propionate mesogenic group and oligo(oxyethylene) spacers

Abstract Three series of ferroelectric liquid crystals containing a (2S)-2-(6-(4-hydroxybiphenyl-4′-carbonyloxy)-2″-naphthyl)propionate mesogenic group and oligo(oxyethylene) spacers were synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC), optical polarized microscopy (POM), and X-ray powder diffraction measurements. Some of these materials containing four phenyl rings of ester cores (i.e. -Ph-Ph-COO-naph-) and chiral heptyl tail exhibited a rich mesomorphic behaviour, a blue phase (BP), a cholesteric phase (Ch), a smectic A (SA), a twist grain boundary A (TGBA), and a chiral smectic C (SC*) phase. Another series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tails revealed only a SA phase and a SC* phase. Moreover, a crystal E phase was observed in the short spacer chain (n = 0 or 1) homologues of three series of compounds. Also, the mesomorphism properties were discussed as a function of spacer units, num...

Broad liquid crystalline temperature range of ferroelectric liquid crystals

Abstract Novel ferroelectric liquid crystalline compounds, containing the (S)-2-methyl-l -butyl (4-hydroxybiphenyl-4′-carbonyloxy)biphenyl-4-carboxylate mesogenic group and an oligooxyethylene spacer, were synthesized. The mesomorphic properties of these materials were investigated by differential scanning calorimetry (DSC), optical polarizing microscopy (POM) and powder X-ray diffraction measurement. The results indicate that all members of this series exhibit a very broad temperature mesophase range (reaching a maximum around 210°C) including a blue phase (BP), cholesteric (Ch), twist grain boundary A (TGBA), chiral smectic C (S∗c), and smectic X (Sx) phases. The mesomorphic properties are discussed and a comparison is made with three phenyl rings of ester core analogues.

Synthesis and characterization of new series of ferroelectric liquid crystals containing oligooxyethylene spacers

Abstract Four series of ferroelectric liquid crystals containing oligooxyethylene spacers have been synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). The properties of the liquid crystalline phase were investigated as a function of spacer units, numbers of core aromatic rings, and different terminal asymmetric moieties. It was found that (i) the phase transition temperature decreased with the increasing oligooxyethylene spacer unit, (ii) the liquid crystalline phases were enhanced in three phenyl ring system than in two phenyl ring system, and (iii) ferroelectric liquid crystals containing different terminal asymmetric moieties exhibited novel mesophase phenomena. A twist grain boundary phase (TGBA phase) was observed in some compounds of this study. Furthermore, a wide temperature chiral smectic Crange including room temperature was achieved.

Synthesis of liquid-crystalline polysiloxanes and polymethacrylates with broad temperature ranges of the chiral smectic C phase

The synthesis of side-chain liquid crystalline polysiloxanes and polymethacrylates containing oligooxyethylene spacers and 4-(S)-2-methyl-l-butyl (((4-hydroxybiphenyl-4'-yl)carbonylloxylbenzoate mesogenic side groups is presented. Differential scanning calorimetry, optical polarizing microscopy, and X-ray diffraction measurements reveal chiral smectic mesomorphism for all polymers. All three polysiloxanes present enantiotropic smectic A and chiral smectic C phases. The chiral smectic C phase covers a very broad temperature range (about 200 C). Among polymethacrylates prepared in this study, the polymethacrylate which contains three oxyethylene units in its spacer is the only one revealing smectic A and chiral smectic C phases. The results seem to demonstrate that the tendency toward a chiral smectic C phase increases with increasing the flexibility of the polymer backbone and the oligooxyethylene spacer can increase dramatically the thermal stability of the chiral smectic C phase, 3161