Liquid Crystalline Polysiloxanes Research Articles

Side chain liquid crystalline polysiloxane hydroxamic acids and their liquid crystalline behaviour

The synthesis and properties of side chain polysiloxane hydroxamic acids have been described. The N-p substituted phenyl hydroxamic acids were synthesized by reacting p - allyloxy benzoyl chloride and acryloyloxy sebacoyl chloride with N-arylhydroxylamines in toluene medium, rendered basic with aqueous suspension of sodium bicarbonate at 0 °C or lower. The synthesized N-phenyl substituted hydroxamic acids were attached to poly(methylhydrosiloxane) via hydrosilylation reaction in the presence of platinum catalyst The polysiloxane hydroxamic acids were characterized by melting point, FT – IR, NMR and Mass spectral techniques. The liquid crystalline behaviour of the side chain polysiloxane hydroxamic acids with allyloxy and acryloylsebacoyloxy spacer have been studied by optical.polansed microscopy and differential scanning calorimetry. Side chain liquid crystalline polysiloxane hydroxamic acids with allyloxy spacer (N-p substituted phenyl p-[(3-polysiloxane propyloxy) benzo] hydroxamic acids, (PHA – 1 to PHA −4) show nematic phases, while the second series with acryloylsebacoyloxy spacer (N-p-substituted phenyl (3-polysiloxane propanone) octyl carbonyloxy hydroxamic acids, (PHA – 5 to PHA – 8) show nematic as well as smectic phases. The liquid crystalline behaviour of the side chain polysiloxane hydroxamic acids with allyloxy and acrylsebacoyloxy spacer have been studied.

Design and Investigation of a Side-Chain Liquid Crystalline Polysiloxane with a Ntb-Phase-Forming Side Chain

A new mesogenic non-symmetric dimeric monomer with a terminal olefin function, forming a twist bend nematic (Ntb) as well as a nematic (N) phase, was synthesized, using an enhanced synthetic methodology, which avoids isomerization of the terminal double bond in the preparation of the dimer. This monomer was attached to a pentamethyldisiloxane group, resulting in the SmA LC phase behavior of the ensuing material. Linking the monomer to a siloxane main chain resulted in nematic phase behavior. Detailed studies with the Ntb phase forming dimer DTC5C7 show full miscibility of the dimer and the new LC polymer in the LC state, suggesting that the side-chain LC polymer forms a Ntb phase as the low-temperature nematic phase. Copolymerizing the monomer with a cyanobiphenyl-based monomer allows us to tune the glass transition and phase behavior further.

Cholesteric liquid crystalline polysiloxanes containing furan ring with selective reflection – synthesis and properties

ABSTRACT In this paper, first series of liquid crystal polymers (PF) synthesised by hydrosilylation of monomer containing furan group (MA), monomer containing cholesterol group (MB), monomer containing D (+)-camphoric acid group (MC) and monomer containing cyano-group (MD), catalysed by platinum catalyst. Another series of liquid crystal polymers (EF) is synthesised by the Dies-Alder reaction of the former series and cross-linker containing bismaleimide group. The results of Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance(1H NMR) showed the successful preparation of various monomers as well as polymers. The thermal properties of two series were characterised by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). We observed dramatic colour changes and Grand-jean textures of polymers using polarised optical macroscope (POM). The results of POM and selective reflection showed that both series of polymers are cholesteric liquid crystals. In the latter series, crosslinking by Diels-Alder reaction can make the liquid crystal better oriented, which can maintain their wonderful liquid crystal (LC) texture and selective reflection, and at the same time, it has a certain regulation effect on the appearance of cholesteric Grand-jean blue texture. The results of X-ray diffraction (XRD) further proved the two series of polymers are cholesteric liquid crystals.

High intrinsic thermally conductivity side-chain liquid crystalline polysiloxane films grafted with pendent difunctional mesogenic groups

Herein, the microscopic ordered aggregation morphologies of SCLCP films are investigated, and molecular structures with regular arrangement can increase heat transfer via suppressing the scattering of phonons, thus greatly improving the λ of SCLCPs.

Self-assembly, liquid crystalline behavior and electrorheological performance of phthalocyanine-contaning polysiloxanes

Series of phthalocyanine-based ionic liquid-crystalline polysiloxanes (ILCPs) were self-assembled by bromo-polysiloxanes and zinc tetraaminophthalocyanine, and their chemical structure, thermal and liquid-crystalline (LC) behavior were characterized by various experimental techniques. The ILCPs exhibited hexagonal columnar phase and SmA phase. The effects of ionic phthalocyanine content and LC phase on the dielectric properties including dielectric constant and dielectric loss were investigated, which was closely related to their electrorheological (ER) effect. The ILCPs-based ER fluids (ERFs) were prepared by the ILCPs and silicone oil, and the ER performance was investigated at controlled test conditions. The ER effect increased with the increase of ionic phthalocyanine moieties for these ERFs. Furthermore, the ER efficiency of the ERFs at 330 K was much higher than that at 300 K at the constant conditions. The real-time response experiments of the ERFs was performed by switching alternately turned on or off the electric field, illustrating a synergetic rearrangement and orientation of the LC mesogens and the ionic phthalocyanine moieties along the direction of the electric field. Moreover, the ERFs showed good sedimentation property due to good compatibility between ILCPs’ polysiloxane matrix and the polysiloxane-based silicon oil.

Influence of chain interaction and ordered structures in polymer dispersed liquid crystalline membranes on thermal conductivity

Abstract Polymer dispersed liquid crystalline (PDLC) membrane with intrinsic thermal conductivity was prepared by dispersing liquid crystalline polysiloxane containing crosslinked structure (liquid crystalline polysiloxane elastomer (LCPE)) into polyvinyl alcohol (PVA). Chemical structures were characterized by Fourier transform infrared (FT-IR) and 1H-NMR, and microscopic structures were analyzed by polarizing optical microscope (POM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The thermal conductivity of PDLC membrane was characterized by hot disk thermal constants analyzer, and the tensile properties were measured by tensile testing machine. Thermal properties were characterized by differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA). The results show that LCPE was dispersed in PVA uniformly, and the mesogenic monomer of LCPE formed microscopic ordered structures in PDLC membrane. Meanwhile, hydrogen-bond interaction was formed between LCPE and PVA chain. Both microscopic-ordered structure and the hydrogen-bond interaction improved the phonon transmission path, and the thermal conductivity of PDLC membrane was up to 0.74 W/m⋅K, which was 6 times higher than that of pure PVA film. PDLC membrane possessed proper tensile strength and elongation at break, respectively 5.18 MPa and 338%. As a result, PDLC membrane can be used as thermal conductive membrane in electronic packaging and other related fields.

Effect of microscopic-ordered structures on intrinsic thermal conductivity of liquid-crystalline polysiloxane

Intrinsic insulating and thermal conductive polymers were prepared by synthesizing liquid-crystalline polysiloxanes elastomer (LCPE) with chemical cross-linking (0.83 W/m K and 0.81 W/m K). The microscopic-ordered structures were found in LCPE and considered affording high thermal conductivity. Chemical structures were observed by hydrogen nuclear magnetic resonance spectroscopy (1H-NMR) and fourier transform infrared (FT-IR) spectroscopy. Microscopic-ordered structures were analyzed by polarizing optical microscopy, scanning electron microscope and X-ray diffraction. Thermal conductivities were calculated according to equation: λ = α·ρ·Cp. Thermal properties were researched by differential scanning calorimeter and thermal gravimetric analyzer. The results revealed that LCPE showed high thermal conductivity because of the microscopic-ordered structures existing. The phonon scattering was suppressed and the mean free path of phonon was extended maximally. In addition, phonon conduction path was more complete. Our study provided a useful method to enhance the thermal conductivities of intrinsic thermal conductivity polymer themselves.

A series of novel side chain liquid crystalline polysiloxanes containing cyano‐ and cholesterol‐terminated substituents: Where will the structure‐dependence of terminal behavior of the side chain reappear?

ABSTRACTA series of polysiloxane side chain liquid crystal polymers with strong polarity cyano substitution‐terminated achiral side chains and cholesterol‐terminated chiral side chains was successfully synthesized via thiol‐ene click chemistry. 1H‐NMR, FT‐IR, and thermogravimetric analysis were used to confirm their chemical structures and thermal stabilities. Their phase transition behaviors and phase structures were systematically investigated by a combination of analysis methods such as differential scanning calorimetry, polarized optical microscopy, and X‐ray. Results revealed that attributing to the decisive role of the polarity interaction, all the polymers only developed a monolayer interdigitated SmA phase in which the period arrangement was determined by the cyano‐terminated side chains, the increased content of cholesterol‐terminated chiral side chains (Xchol) just expanded the distance between neighboring molecules within a layer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1765–1772

PB12 側鎖型液晶性ポリシロキサンのER効果に及ぼす側鎖末端基の影響(化学・材料)

PB12 側鎖型液晶性ポリシロキサンのER効果に及ぼす側鎖末端基の影響(化学・材料)

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

ABSTRACTA 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.

My way to George Gray and liquid crystal polymers

This article has allowed me the pleasant opportunity to recall the outstanding scientist and remarkable person – Professor George Gray – who played an important role in my scientific career. My first acquaintance with George was virtual, only thanks to his monograph ‘Molecular Structure and the Properties of Liquid Crystals’ (1962), which triggered the development of liquid crystals science in many countries, including the former Soviet Union. However, our first face to face meeting was held in 1981 during the Liquid Crystal Conference in Tbilisi – the capital of the Georgian Republic of Soviet Union. This personal acquaintance laid the foundations of our long term friendship, based not only on the mutual scientific interest of liquid crystals, but also on the merely (pure) human warm relationship. This article describes the evolution of our relationship starting with my visit to Hull University in 1984 and our further meetings at the European and International Conferences in the period 1987–2002. The most impressive research of George’s activity is associated with the synthesis of cyanobiphenyl derivatives and his fundamental approach to the synthesis of liquid crystalline polysiloxanes with the side mesogenic groups; these are discussed in detail. The principle of creation of liquid crystalline (LC) ‘comb-shaped’ (side chain LC) polymers suggested by us in seventies in comparison with the preparation of LC polysiloxanes are considered. The Author of this article is extremely grateful for the opportunity to have met Prof. George Gray who was a humble person and whose warm and welcoming smile will be forever preserved in my memory.

Synthesis and characterization of fluorine-containing cholesteric liquid crystalline polysiloxanes bearing trifluoromethyl-substituted mesogens

A series of side-chain liquid crystal (LC) polysiloxanes were synthesised with Poly(methylhydrogeno)siloxane, 4ʹ-(undec-10-enoyloxy) biphenyl – 4 – yl 4- (trifluoromethyl) benzoate (Mth) and a chiral nematic (N*) LC monomer 1-allyl 10-(cholesteryl)-decanedioate (Mch). The chemical structures and LC properties of the monomers and polymers were characterised by FTIR, 1H-NMR, differential scanning calorimetry, thermogravimetric analysis, POM and X-ray diffractometer. Mch is monotropic N* LC. The homopolymer derived from monomer Mch is enantiotropic N* LC. Monomer Mth is a smectic A liquid crystal. The copolymers derived from Mch and Mth are N* LCs. The temperatures at which 5% weight loss occurred are greater than 300°C for all the fluoro-containing polymers, and the residue weights of the samples at 600°C increased slightly as the content of trifluoromethyl mesogens increased in the polymers. The glass transition temperatures of the polymers increased as trifluoromethyl mesogens increased, too. The N*–I phase transition temperatures show a negative deviate from ideal or linear behaviour. The values of the enthalpy changes for the cholesteryl containing polymers are rather low and this is attributed to the biaxiality of cholesteryl moiety which tends to reduce the change in the orientational order at the N*–I transition. Compared to the monomers, the polymers show wider mesophase region.

Cholesteric Cyclohexane-Containing Side-Chain Liquid-Crystalline Polysiloxanes

Two new kinds of Cholesteric cyclohexane-Containing Side-Chain Liquid-Crystalline Polysiloxanes (PAand PB) were synthesized via hydrosilylation reaction of polymethyl hydrogen siloxane with cyclohexane mesogenic monomers (MAand MB). The yield of PA, PBwere 71.6%, 82.5% and 81.0%, respectively. The molecular structures of MAand MB, PAand PBwere investigated by Fourier transform infrared spectroscopy (FTIR) and hydrogen-nuclear magnetic resonance spectra (1H-NMR). The corresponding liquid crystalline phase type was also observed by polarizing optical microscopy (POM) and X-ray diffraction (XRD). The liquid crystalline phase behavior and thermal properties of the polymers were analyzed by differential scanning calorimetry (DSC). Results showed that MAand MBexhibited multicolor platelet texture of a blue phase and cholesteric phase, and the Tmand Tiof MAand MBincreased with the increasing flexible chain length. The mesophase temperature range of PAand PBwas broader than that of MAand MB. PAexhibited a rare nematic phase----spherulite texture of polymeric smectic A phase. PBwere of cholesteric and nematic---- cholesteric phase. The Tmand Tiof PAand PBincreased with the increasing flexible spacer groups.

Synthesis and characterization of a graft side-chain liquid crystalline polysiloxane

A graft side-chain crystalline polymer PI with polysiloxane as backbone and a liquid crystal polymer, poly{6-(4′-octyloxyphenyl-4″-benzoyl)hexyl acrylate}, as side chain has been synthesized via atom transfer radical polymerization (ATRP) technique. Attaching mesogenic polymers to the polysiloxane main chain through ATRP technique brings about the high density of mesogenic units and avoids the subsequent crosslinking reaction by the residual Si–H in the traditional hydrosilylation. The properties of the graft liquid crystal polymer PI was studied in detail by TGA, DSC, POM and XRD. Thermal analysis shows that the polymer PI has wider mesophase temperature ranges with a high thermal stability in comparison to its mesogenic monomer.

Liquid Crystalline Polymer–Co Nanorod Hybrids: Structural Analysis and Response to a Magnetic Field

This work deals with the structural analysis of side-chain liquid crystalline polysiloxanes, doped with magnetic cobalt nanorods, and their orientational properties under a magnetic field. These new materials exhibit the original combination of orientational behavior and ferromagnetic properties at room temperature. Here we show that, within the liquid crystal polymer matrix, the cobalt nanorods self-assemble in bundles made of nanorod rows packed in a 2-dimensional hexagonal lattice. This structure accounts for the magnetic properties of the composites. The magnetic and orientational properties are discussed with respect to the nature of the polymer matrix.

Synthesis and properties of novel chiral side-chain liquid crystalline polysiloxanes containing different chiral pendant groups

Two novel chiral liquid crystalline monomers, and a series of their corresponding chiral side-chain polymers (P1–P7) based on poly(methylhydrogeno)siloxane have been prepared. The chemical structures and liquid crystalline properties of the synthesized monomers and polymers have been investigated using various experimental techniques. Thermal analysis shows that all polymers have wide mesophase temperature ranges with a high thermal stability. With the increase of M2 molar ratio in the polymer systems, the isotropic phase transition and glass transition temperatures of all polymers increase, and the temperature ranges of N* phase and mesophase become broad. The effect of cholesteryl mesogens on mesophase behaviors, optical properties, and molecular arrangement of LC polysiloxanes and their advanced applications have also been discussed. For homopolymer P1, it shows a single SA phase. With increasing the content of M2 in the polymer systems, P2 and P3 reveal a SA–N* phase transition when they are heated, and P4–P7 reveal a N* phase. For N* phase polymers P4–P7, the reflection wavelengths exhibit blue shift, suggesting that the pitch decreases with a decrease in the amount of the smectic domains induced by the M1. The reflection wavelengths of P4–P7 are almost across the entire visible region when they are heated, which offer stremendous potential for various optical applications. For P2 and P3, the reflection wavelengths show a very steep change around the temperature of the SA–N* phase transition, which can be used as thermally sensitive liquid crystal devices requiring fast response, such as sensors, and thermally induced tuning.

Effect of fluorinated nematic mesogens on phase behaviors and optical properties of chiral liquid crystalline polysiloxanes

A series of new chiral side-chain liquid crystalline polymers (P1–P7) have been synthesized with poly(methylhydrogeno)siloxane, two chiral liquid crystalline monomers, cholesteryl-4-allyloxybenzoate (M1) and cholesteryl 4-(10-undecylen-1-yloxy) benzoate (M2), and a nematic liquid crystalline monomer, 4-(trifluoromethyl)phenyl 4-(undec-10-enoyloxy)benzoate (M3). The chemical structures and liquid crystalline properties of the synthesized polymers have been investigated by FTIR, 1H-NMR, differential scanning calorimetry (DSC), polarizing optical microscopy (POM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). All chiral polymers show wide mesophase temperature ranges and a high thermal stability with decomposition temperatures (T d) at 5 % weight loss greater than 300 °C. P1–P4 display a single cholesteric phase, but P5–P7 containing more fluorinated units show a smectic A (SA) phase besides a cholesteric phase. The optical properties of the polymers have been characterized by circular polarization spectra and optical rotation analysis. The cholesteric polymers P3 and P4 exhibit different colors at room temperature, and the color can remain over 24 months. The maximum reflection bands of polymers P1–P4 shift to long wavelength with increasing the content of M3 in the polymer systems. For P5–P7, the reflection wavelengths change sharply around the temperature of the SA–Ch phase transition. The specific rotation value of P2 smoothly decreases from −8.2° to −0.29° when it is heated, but the specific rotation value of polymer P7 changes from negative value to positive value on heating cycle. The optical properties of the polymers offer tremendous potential for various optical applications.

Electrorheological Effect and Electro‐Optical Properties of Side‐on Liquid Crystalline Polysiloxane in a Nematic Solvent

The electrorheological (ER) effect and the electro-optical properties of a ''side-on'' liquid crystalline polysiloxane (PS) are investigated. A large ER effect is observed and the response to the shear stress of neat PS in the nematic phase is shown to be affected by the shear rate. PS is also mixed with a low-molar nematic liquid crystal (5CB) in order to improve the response behavior to the applied electric field. The rheological properties of such mixtures are highly dependent on the concentration of 5CB. The composites respond faster to the applied electric field and have improved electro-optical properties. This study offers a new perspective on the development of liquid crystal materials for the ER effect.

Influence of two liquid crystalline polysiloxanes with different average molecular weight as new β-nucleator on crystallization structure of isotactic polypropylene

Two liquid crystalline polymers (LC-N1 and LC-N2) with different average molecular weight were designed and synthesized as a new β-nucleator in isotactic polypropylene (iPP). The main aim of this work was to investigate the influence of LC-N1 and LC-N2 on the crystallization structure and β nucleating activity of the iPP with wide angle X-ray diffraction and polarized optical microscopy. The β nucleation activity not only depended on the nucleator content, mesogenic molecular structure, and thermal processing history, but also on average molecular weight of the liquid crystalline polymers. LC-N1 or LC-N2 has been found to be an effective β-nucleator for the iPP. The experimental results indicated the relative content of β-crystal first increased and then decreased with increasing the nucleator content or crystallization temperature. The addition of LC-N1 or LC-N2 could provide a large number of nuclei, enhance the crystallization rate, reduce the spherulite size, and lead to a more uniform morphology; moreover, the colorful β-crystal was also induced. In addition, LC-N2 with higher average molecular weight is more effective than LC-N1 in inducing β heterogeneous nucleation under same crystallization conditions.

A nematic liquid crystalline polymer as highly active novel β-nucleating agent for isotactic polypropylene

A nematic liquid crystalline polysiloxane has been found to be a novel nucleating agent (LCP-NA2) to induce the formation of β-crystals in isotactic polypropylene (iPP). Wide angle X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy were used to evaluate the nucleating activity of LCP-NA2. The effect of LCP-NA2 content, crystallization temperature, and time on the crystallization structure, morphology, and thermal behavior of the iPP was discussed. The results indicated that the nucleating activity mainly depended on LCP-NA2 content and thermal history of processing. The addition of LCP-NA2 could provide a large number of nuclei and lead to a more uniform morphology, along with a change in the nucleation and crystal growth mechanism. The relative content of β-crystal increased with increasing LCP-NA2 content or crystallization temperature, reached a maximum value of 70 % when LCP-NA2 content and crystallization temperature were 1.0 wt% and 125 °C, and then decreased with a further increase of LCP-NA2 content or crystallization temperature. In addition, a different polymorphic behavior had been observed between pure iPP and LCP-NA2/iPP blends under the same thermal treatment.