Synthesis and characterization of side‐chain liquid‐crystalline elastomers containing cholesterol

A series of new smectic and cholesteric liquid‐crystalline elastomers were prepared by graft polymerization of mesogenic monomer with the chiral and nonmesogenic crosslinking agent using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectra. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. M₁ showed cholesteric phase during the heating and the cooling cycle. Polymer P₁, elastomers P₂ and P₃ exhibited smectic phase, elastomers P₄? P₆ showed chiral smectic C phase, P₇ showed cholesteric phase, and P₈ displayed stress‐induced birefringence. The elastomers containing less than 15 mol % M₂ displayed elasticity and reversible phase transition with wide mesophase temperature ranges. Experimental results demonstrated that the glass transition temperatures, the isotropization temperatures, and the mesophase temperature ranges decreased with increasing content of the crosslinking unit. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 383–390, 2005     

Synthesis and characterization of a series of smectic liquid crystalline elastomers

A series of new smectic and cholesteric liquid crystalline elastomers was prepared by graft polymerization of mesogenic monomer with the chiral and nonmesogenic crosslinking agent using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance spectra (¹H‐NMR). The mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction measurements (XRD). M₁ showed smectic (S_B, S_C, S_A) and nematic phases during the heating and the cooling cycles. Polymer P₀ and elastomer P₁ exhibited smectic B phase, elastomers P₂–P₅ showed smectic A phase, P₆ and P₇ showed cholesteric phase, and P₈ displayed stress‐induced birefringence. The elastomers containing less than 15 mol % M₂ displayed elasticity and reversible phase transition with wide mesophase temperature ranges. Experimental results demonstrated that the glass transition temperatures decreased first and then increased; melting temperatures and the isotropization temperatures and the mesophase temperature ranges decreased with increasing content of crosslinking unit. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 498–506, 2005     

Synthesis and structure of polysiloxane liquid crystalline elastomers with a mesogenic crosslinking agent

A new mesogenic crosslinking agent M‐1 was synthesized to minimize the perturbations of a nonmesogenic crosslinking agent for liquid crystalline elastomers. The synthesis of new side‐chain liquid crystalline elastomers containing a rigid mesogenic crosslinking agent M‐1 and a nematic monomer M‐2 is described by a one‐step hydrosilylation reaction. The chemical structures of the obtained monomers and elastomers were confirmed by ¹H NMR and FTIR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the crosslinking units on the phase behavior is discussed. The elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and nematic‐threaded texture. However, when the crosslinking density reached 21.6 mol %, the mesophase of polymer P‐8 disappears. The adoption of a mesogenic crosslinking agent diminishes the perturbation of a nonmesogenic crosslinking agent on mesophase of liquid crystalline elastomers, and isotropic temperature and a mesomorphic temperature range slightly decreased with increasing content of the crosslinking agent. In addition, X‐ray analysis shows nematic polydomain network polymers can transform into smectic monodomain by stress induction, leading to the orientation formation macroscopically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1736–1742, 2004     

Bistable light scattering effects in a (side chain liquid crystalline polymer)/(low molecular weight liquid crystal) composite and in a ferroelectric liquid crystalline polymer

The electro-optical effects and aggregation states of liquid crystalline polymer (LCP)/ low molecular weight liquid crystal (LC) composite and ferroelectric liquid crystalline copolymer (FLCP) have been investigated. The nematic LCP was observed to be miscible with the nematic LC over wide ranges of concentration and temperature. The binary mixture showed an induced smectic phase in the range of 80/20-20/80 mol%. The electro-optical effects of the LCP/LC composite in an induced smectic phase could be classified into the turbid (light- scattering) and the transparent states upon application of AC and DC electric fields, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal in the chiral smectic C phase of FLCP. The reversible transparent-opaque (light scattering) change was observed in the chiral smectic C state upon application of DC and AC electric fields, respectively. Both transparent and light-scattering states of the LCP/LC composite and the FLCP could be maintained, even after the electric field had been turned off (memory effect). The bistable effects of LCP/LC composite and FLCP are opposite under the same conditions. A novel type of electro-optical effect on light scattering was obtained for liquid crystalline polymer in the smectic states.     

Effect of the different rigidity of the chiral crosslinker on phase behaviors of side‐chain chiral liquid crystalline elastomers

In the present work, the phase behaviors of two series of side‐chain liquid crystalline elastomers ( PI and PII series) derived from the same nematic liquid crystalline monomer and the different rigidity of chiral bisolefinic crosslinking units have been compared and studied extensively, and the effect of the different rigidity of crosslinker on the phase behavior of elastomers has been discussed. The chemical structure of the monomers and polymers obtained were confirmed by FTIR and ¹H NMR spectroscopy. The phase behaviors were investigated by differential scanning calorimetry, polarizing optical microscopy measurement, thermogravimetric analyses, and X‐ray diffraction measurement. The two series of elastomers showed smectic or cholesteric phases. When the amount of different crosslinking units was less than 15 mol %, both of the elastomers displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. It is shown that the isotropization temperature values of PII series are higher than those of PI series, and the glass transition temperature values of PII series varied smoothly and that of PI series changed smoothly first and then abruptly with increasing the contents of crosslinkers with different rigidity. In addition, PI series showed an interesting change in LC texture near clearing point, but PII series did not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study on the Optical and Mesomorphic Properties of Cholesteric Side-Chain Liquid Crystalline Elastomers Containing a Nematic Cross-Linking Agent

To study the effect of the content of the nematic cross-linking units on the mesophase behaviors, the optical and mesomorphic properties of liquid crystalline elastomers (LCEs), aseries of LCEs have been synthesized by hydrosilylation reaction with poly(methylhydrogeno)siloxane, a cholesteric liquid crystalline monomer, and a nematic cross-linking agent. The chemical structures and properties of the synthesized LCEs have been investigated by use of various techniques. Homopolymer P₀ bearing only cholesteric component displays a smectic A phase, but elastomers P₁-P₅ containing different content of nematic cross-linking units show a cholesteric mesophase. The reflection wavelengths of theLCEs show a weak temperature dependence at lower temperatures but a strong temperature dependence at higher temperatures. Furthermore, the maximum reflection wavelengths of the LCEs can be stabilized over a wide temperature range when the LCEs are heated, suggesting that the helical structure and pitch of the cholesteric phase can be stabilized with a polymer network.     

Isothermal Phase Transitions in Ceramic Lead Zirconate

Constant temperature permittivity measurements of ceramic lead zirconate near 230°C revealed that the paraelectric to ferroelectric, ferroelectric to antiferroelectric, and antiferroelectric to paraelectric phase transitions were isothermal transformations. On heating, the antiferroelectric phase transformed into a paraelectric phase. Cooling produced a transformation from the paraelectric into an intermediate ferroelectric phase which existed over a temperature range of about 5°C. On further cooling, the ferroelectric transformed into the antiferroelectric phase. Thermal expansion, relative permittivity, and dissipation factor data are reported.     

Electrical performance and ferroelectric phase transition characteristic in different oriented 0.73PMN-0.27PT single crystals

The electrical and optical properties of (001)- and (110)-oriented 0.73 Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃ single crystals are systematically investigated at various temperatures, both of which present a series of ferroelectric phase transition processes. Dielectric performance measurements reveal that the ferroelectric phase transition occurs over a temperature range, rather than at one temperature point. By testing the ferroelectric hysteresis P–E curves as well as bipolar and unipolar electric field-induced strain S–E curves, the values of remnant polarization, coercive field, maximum strain, and converse piezoelectric constant d₃₃^* change considerably near the phase transition temperatures. Simultaneously, the 0.73PMN-0.27PT single crystals with (001)- and (110)-orientations under a low electric field show ultrahigh d₃₃^* values of 3540 and 2817 pm/V, respectively, which can be attributed to the electric field-induced monoclinic and orthorhombic phases, respectively. The series of ferroelectric phase transitions upon heating, that is, from rhombohedral ferroelectric to monoclinic/orthorhombic, followed by from monoclinic/orthorhombic to tetragonal, and finally from tetragonal to cubic paraelectric, are further investigated via polarized light microscopy and Raman spectroscopy.     

Liquid crystalline properties of cholesteric elastomers based on a mesogenic monomer containing menthyl groups

A new chiral mesogenic monomer (M_LC) based on menthyl groups and the corresponding cholesteric elastomers (LCE₁–LCE₃) were prepared. Their chemical structures and purity were characterized by Fourier transform infrared, nuclear magnetic resonance and elemental analyses. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis and X‐ray diffraction. The selective reflection of light for M_LC was characterized with ultraviolet/visible/near infrared. The effect of the content of crosslinking units on the liquid crystalline behaviour of LCE₁–LCE₃ is discussed. The experimental results show that the chiral monomer and the corresponding elastomers containing menthyl groups can show mesomorphism when a flexible linkage chain is inserted between the mesogenic core and the bulky terminal menthyl fragments to reduce the steric effect. M_LC exhibited a chiral smectic C phase, a cholesteric phase and a cubic blue phase. LCE₁–LCE₃ with a low content of crosslinking units showed a cholesteric phase because of the introduction of the nematic crosslinking unit. With increasing content of crosslinking units, the corresponding glass transition temperature increased, while the clearing temperature decreased. Thermogravimetric analysis showed that LCE₁–LCE₃ have good thermal stability. Copyright © 2012 Society of Chemical Industry     

Synthesis and characterization of ferroelectric side chain liquid crystal polymers bearing banana-shaped chiral mesogens

A series of ferroelectric liquid crystal polymers having banana-shaped side chain mesogens were synthesized through photo-polymerization of epoxide moiety. 2,5-disubstituted-thiophene sub-unit was used in synthesizing the banana-shaped monomers. These liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). Mesomorphism was investigated as a function of spacer units. All the synthesized low molar mass banana-shaped compounds exhibit smectic blue phase, but chiral smectic C phase could be observed only on compounds having longer spacer. The clearing temperature of low molar mass compounds fluctuated a little when spacer length varies. All polymers exhibit cholesteric mesophase and an observable glass transition. These liquid crystalline compounds reveal strong photoluminescence at visible region (λ_max = 475 nm for M9EPX) and have potential use in polarized organic light emitting diode materials.     

Effect of the length of the carbochain on the phase behavior of side‐chain cholesteric liquid‐crystalline elastomers

In this study, we prepared two series of new side‐chain cholesteric liquid‐crystalline elastomers (PI and PII) derived from the same chiral bisolefinic crosslinking units and different nematic liquid‐crystalline monomers. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and ¹H‐NMR spectroscopy. The phase behavior properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. The effect of the length of the carbochain on the phase behavior of the elastomers was investigated. The polymers of the PI and PII series showed similar properties. Polymer P₁ showed a nematic phase, P₂–P₇ showed a cholesteric phase, and P₄–P₇, with more than 6 mol % of the chiral crosslinking agent, exhibited a selective reflection of light. The elastomers containing less than 15 mol % of the crosslinking units displayed elasticity, a reversible phase transition with wide mesophase temperature ranges, and a high thermal stability. The experimental results demonstrate that the glass‐transition temperatures first decreased and then increased; the isotropization temperatures and the mesophase temperature ranges decreased with increasing content of crosslinking agent. However, because of the different lengths of the carbochain, the glass‐transition temperatures and phase‐transition temperatures of the PI series were higher than those of the PII series, and the PI and PII elastomers had their own special optical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1204–1210, 2005     

Side‐chain copolymers containing smectic monomer and chiral reagent—Synthesis and characterization

A series of new chiral side‐chain liquid‐crystalline polymers were prepared containing smectic‐nematic monomer and nonmesogenic chiral monomer. All polymers were synthesized by graft polymerization using polymethylhydrosiloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analyses, and X‐ray diffraction measurements. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared, proton nuclear magnetic resonance spectra (¹H NMR). M₁ showed smectic (S_B, S_C) and nematic phase on the heating and the cooling cycle. Polymers P₀–P₂ were in chiral smectic A phase, while P₃–P₅ were in cholesteric phase, P₆ has bad LC properties, and P₇ has no LC properties. Experimental results demonstrated that nonmesogenic chiral moiety and LC mesogenic with long carbochain offered the possibility of application because of its lower glass transition temperature, and the glass transition temperatures and isotropization temperatures and the ranges of the mesophase temperature reduced with increasing the contents of chiral agent. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and mesomorphic properties of a new side‐chain,chiral smectic,liquid‐crystalline elastomer

The synthesis of the new chiral monomer 4‐(10‐undecylen‐1‐yloxy)biphenyl‐4′‐[(S)‐2‐methyl‐1‐bu‐ toxy]benzoate (M₁), the nematic crosslinking agent biphenyl 4,4′‐bis(10‐undecylen‐1‐yloxybenzoate) (M₂), and the corresponding liquid‐crystalline elastomer is described. The chemical structures of the chiral monomer and crosslinking agent have been characterized with Fourier transform infrared, elemental analyses, and proton and carbon‐13 nuclear magnetic resonance spectra. The mesomorphic properties have been investigated with differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction. Monomer M₁ shows different smectic phases (smectic A, chiral smectic C, and smectic B) and a cholesteric phase, and M₂ exhibits a nematic phase. The liquid‐crystalline elastomer shows smectic A and chiral smectic C phases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4234–4239, 2006     

Synthesis and X-ray diffraction of ferroelectric liquid crystalline polysiloxanes containing 4′-(2-chloro-3-methylpentanoyloxy)-4-alkanyloxybiphenyl side groups

Summary The synthesis and characterization of side-chain liquid crystalline polysiloxanes containing (2S,3S)-4-(2-chloro-3-methylpentanoyloxy)-4-alkanyloxybiphenyl side groups are presented. All the obtained polymers exhibit smectic mesomorphism. Those polymers containing a spacer length longer than 8 methylene units reveal respectively enantiotropic S_A, S _* ^C and S_B phases. The result demonstrates that the tendency toward the S _* ^C phase increases with increasing the spacer length.     

Synthesis and characterization of chiral side‐chain liquid‐crystalline polymer containing menthol ester

The synthesis of new chiral side‐chain liquid‐crystalline polysiloxanes containing p‐(allyoxy)benzoxy‐p‐chlorophenyl (ABCH) as mesogenic units and undecylenic acid menthol ester (UM) as chiral nonmesogenic units is presented. The chemical structures of monomers and polymers are confirmed by IR spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) are used to measure thermal properties of those polymers. Mesogenic properties are characterized by polarized optical microscope (POM), DSC, and small‐angle X‐ray diffraction. Analytic results revealed that polymers P₀–P₆ are thermotropic liquid‐crystalline polymers with low glass transition; Polymers P₂–P₆ exhibit chiral smectic liquid‐crystalline properties with marble texture, optical rotation, and a sharp reflection at low angles in X‐ray diffraction; polymers P₀, P₁ only exhibit smectic liquid‐crystalline properties without chirality; and P₇ only exhibits chirality without liquid‐crystalline properties. All the polymers exhibit good thermal stability with temperature of 5% mass loss over 297°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2845–2851, 2003     

Synthesis and phase behavior of chiral side‐chain liquid‐crystalline polysiloxanes containing two mesogenic groups

The synthesis of chiral side‐chain liquid‐crystalline polysiloxanes containing both cholesteryl undecylenate (M_I) and 4‐allyloxy‐benzoyl‐4‐(S‐2‐ethylhexanoyl) p‐benzenediol bisate (M_II) mesogenic side groups was examined. The chemical structures of the obtained monomers and polymers were confirmed with Fourier transform infrared spectroscopy or ¹H‐NMR techniques. The mesomorphic properties and phase behavior of the synthesized monomers and polymers were investigated with polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis (TGA). Copolymers IIP–IVP revealed a smectic‐A phase, and VP and VIP revealed a smectic‐A phase and a cholesteric phase. The experimental results demonstrated that the glass‐transition temperature, the clearing‐point temperature, and the mesomorphic temperature range of IIP–VIP increased with an increase in the concentration of mesogenic M_I units. TGA showed that the temperatures at which 5% mass losses occurred were greater than 300°C for all the polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2670–2676, 2002     

Phase behavior of side‐chain liquid‐crystalline elastomers and their precursors containing para‐nitro azobenzene

Side‐chain liquid‐crystalline copolymethacrylates (PMm's), containing para‐nitro azobenzene as the mesogenic group and 2‐hydroxylethyl methacrylate (HEMA) as a comonomer, were synthesized by radical polymerization, and their corresponding liquid‐crystalline elastomers (LCEm's) were prepared through chemical crosslinking. All of the polymers (PMm's) and the elastomers studied showed enantiotropic smectic A phases; the clearing temperature (T_i) of the PMm polymers decreased with increasing amount of HEMA, and the T_i of the corresponding LCEm's decreased compared to that of their precursors. Small‐angle X‐ray scattering studies on the copolymers quenched from their liquid‐crystalline phases indicated that the characteristic distance increased with increasing amorphous component content and thus, the amorphous components were in between the smectic layers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2275–2279, 2003     

Synthesis and phase behavior of nematic liquid‐crystalline elastomers derived from smectic crosslinking agent

A mesogenic crosslinking agent M‐1 was synthesized to minimize the perturbations of nonmesogenic crosslinking agent for liquid‐crystalline elastomers. The synthesis of side‐chain liquid‐crystalline elastomers containing a rigid mesogenic crosslinking agent M‐1 and a nematic monomer M‐2 was described by a one‐step hydrosilylation reaction. The chemical structures of the obtained monomers and network polymers were confirmed by Fourier transform infrared and ¹H‐NMR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the crosslinking units on the phase behavior was discussed. The liquid‐crystalline elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and threaded texture. The experimental results demonstrated that isotropic temperature and liquid‐crystalline range of polymers P‐1–P‐7 decreased a little as the concentration of crosslinking agent M‐1 increased, and the use of mesomorphic crosslinking agent M‐1 promotes the arrangement of liquid‐crystalline units from P‐1 to P‐5. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1712–1719, 2005     

Synthesis and characterization of side-chain liquid crystalline polymers and oriented elastomers containing terminal perfluorocarbon chains

Several novel chiral side-chain liquid crystalline (LC) polysiloxane resins containing epoxy groups and mesogenic components have been graft copolymerized by a one-step hydrosilylation reaction with poly(methylhydrogeno)siloxane, an epoxy monomer 2-(allyloxymethyl)oxirane, and chiral fluorinated liquid-crystalline monomers 4′-(4-(allyloxy)benzoyloxy)biphenyl-4-yl 6-(perfluorooctanoyloxy)hexahydrofuro[3,2-b]furan-3-yl adipate and 4′-(4-(undec-10-enoyloxy)benzoyloxy)biphenyl-4-yl 6-(perfluorooctanoyloxy)hexahydrofuro[3,2-b]furan-3-yl adipate. The synthesized epoxy resins are cured using 4,4′-diaminodiphenyl-methane in mesophase state under a magnetic field to obtain crosslinked oriented elastomers. The chemical structures, LC properties and surface morphology of the monomers, the resins and the liquid crystalline elastomers (LCEs) are characterized by use of various experimental techniques such as FTIR, ¹H NMR, EA, TGA, DSC, POM, and X-ray measurements. The mesomorphic properties of the synthesized resins and corresponding oriented elastomers are influenced by the terminal perfluorocarbon chains components effectively. The resins show chiral nematic and chiral smectic C phases (), and are frozen in their corresponding oriented elastomers. The LC phases are verified by X-ray measurements, and the orientational order parameters of the oriented LCEs are calculated as well.