Synthesis and mesomorphic properties of cholesteric elastomers based on chiral mesogenic crosslinking agent

Six chiral monomers ( M ₁? M ₆), and their corresponding polymers ( P ₁, P ₄) and elastomers ( P ₂, P ₃, P ₅, P ₆) derived from chiral mesogenic crosslinking agent were synthesized. The chemical structures of M ₁? M ₆ were confirmed by FTIR and ¹H NMR spectroscopy. The structure‐property relationships of M ₁? M ₆ and P ₁? P ₆ were discussed. Their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), polarizing optical microscopy (POM), and X‐ray diffractometer (XRD) measurements. All monomers obtained, except M ₂ and M ₅, showed typical oily streaks texture and focal conic texture of cholesteric phase on heating and cooling cycles. The selective reflection of cholesteric monomers and elastomers shifted to the short wavelength region with increasing temperature. The elastomers P ₂ and P ₅ did not reveal the mesomorphic properties, and P ₃ and P ₆ showed cholesteric phase. TGA showed that P ₁? P ₆ had a high thermal stability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Europium‐containing cholesteric liquid crystalline polymers in the side chain

Europium‐containing cholesteric liquid crystalline polymers were graft copolymerized using poly(methylhydrogeno)siloxane, cholesteryl 4‐(allyloxy)benzoate (M₁), cholesteryl acrylate (M₂), and a europium complexes monomer (M₃). The chemical structures of the monomers were characterized by Fourier transform infrared and ¹H‐nuclear magnetic resonance. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermo gravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. With an increase of europium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) and mesophase temperature range (ΔT) decreased. All polymers showed typical cholesteric Grandjean textures, which was confirmed by X‐ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of europium complexes units did not change the liquid crystalline state of polymer systems; on the contrary, the polymers were enabled with the significant luminescent properties. With Eu³⁺ ion contents ranging between 0 and 1.5 mol %, luminescent intensity of polymers gradually increased and luminescent lifetimes were longer than 0.45 ms for the polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40866.     

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     

Mesomorphic properties of cholesteric side‐chain liquid crystalline polysiloxanes and elastomers

A series of crosslinked liquid crystalline polymers and corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization. Their liquid crystalline properties were characterized by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The results showed that the crosslinking obtained in the isotropic state and the introduction of nonmesogenic crosslinking units into a polymeric structure could cause additional reduction of the clearing point (T_i) of the crosslinked polymers, compared with the corresponding uncrosslinked polymers. The crosslinked polymers (P‐2–P‐4) with a low crosslinking density exhibited cholesteric phases as did the uncrosslinked polymers. In contrast, a high crosslinking density made the crosslinked polymer P‐5 lose its thermotropic liquid crystalline property. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 773–778, 2004     

Preparation of novel acrylate‐based liquid crystalline polymers and the photoinduced alignment behavior of their films

Two acrylate monomers containing both mesogenic biphenyl group and photoreactive cinnamoyl group as well as different length of flexible spacers (i.e., n‐[4′‐(n‐cinnamoyloxyalkoxy)biphenyl‐4‐yloxy]alkyl acrylate, n = 4 (A4OO4C) and 6 (A6OO6C)) were synthesized for the first time. Their corresponding polymers (i.e., PA4OO4C and PA6OO6C) were obtained by free radical polymerization using AIBN as an initiator. The monomer A4OO4C showed smectic liquid crystalline phase and a clear fan texture was observed under optical polarizing microscope. However, no liquid crystalline phase was found for A6OO6C. In contrast, PA4OO4C showed no liquid crystalline phase while PA6OO6C showed a clear nematic schlieren texture during the cooling process. The optical polarized microscope of E5 cast on the top of the polymer film also showed the alignment. Furthermore, the irradiation of the polymer films by LP‐UV light led to the cycloaddition of the cinnamoyl groups, resulting in the simultaneous alignment of the biphenyl groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4565–4572, 2006     

Main‐chain liquid‐crystalline polymers containing azobenzene mesogen having long lateral aliphatic side chain: effect of copolymerization on thermal and phase behaviors

Homo‐ and copolyesters of derivatives of hydroxyazobenzenecarboxylic acid with various percentage compositions of m‐hydroxy benzoic acid (m‐HBA)/p‐hydroxy benzoic acid (p‐HBA) were synthesized and characterized. The properties of the copolyesters were compared with their corresponding homopolyesters. The solubility of the copolyesters with m‐HBA increased because of the decrease in the rigidity of the polymer chain attributed to the introduction of nonlinear molecules, whereas the solubilities of the copolyesters with p‐HBA changed only slightly compared to their corresponding homopolyesters. Thermal and phase behaviors of the polymers were characterized by TGA, DSC, and polarizing light microscopy (PLM) methods. Above 30% composition of m‐HBA, the thermal stability of the copolyesters with m‐HBA decreased compared to that of the homopolyester P1, whereas the copolyesters of p‐HBA possessed greater thermal stability than that of their homopolyesters at all compositions. The introduction of the long, flexible alkyl side chain laterally to the backbone of the azobenzene moiety drastically reduced the transition temperature of the homopolyester, but without destroying the mesophase. The effect of copolymerization on liquid‐crystalline behavior and transition temperature of the copolymers was discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1976‐1982, 2004     

Synthesis and mesomorphic properties of side‐chain cholesteric liquid‐crystalline polymers containing menthyl groups

A series of new cholesteric liquid‐crystalline polysiloxanes ( P₁ – P₅ ) derived from menthyl groups were synthesized. The chemical structures of the monomers and polymers were characterized with Fourier transform infrared, ¹H‐NMR, ¹³C‐NMR, and elemental analyses. The mesomorphic properties and thermal behavior were investigated with differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis, and X‐ray diffraction measurements. The influence of the polymer structure on the thermal behavior was discussed. The monomer diosgeninyl 4‐allyloxybenzoate exhibited a typical cholesteric oily‐streak texture and a focal‐conic texture. Polymers P₁ – P₅ showed thermotropic liquid‐crystalline properties. P₁ displayed a smectic fan‐shaped texture, P₂ – P₅ showed a cholesteric Grandjean texture, and P₆ and P₇ did not show mesomorphic properties. The experimental results demonstrated that the glass‐transition temperature and the clearing temperature decreased, and the mesomorphic properties weakened with an increasing concentration of menthyl units. Moreover, P₁ – P₅ exhibited wide mesophase temperature ranges and high thermal stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5559–5565, 2006     

Synthesis and characterization of side‐chain cholesteric liquid‐crystalline polymers derived from steroid substituents

A series of new cholesteric liquid‐crystalline polysiloxanes derived from steroid substituents were synthesized. The chemical structures of the monomers or polymers obtained were characterized by FTIR, element analyses, ¹H NMR, and ¹³C NMR. Their mesogenic properties and thermal stability were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. Monomers exhibited typical cholesteric focal‐conic or spiral texture. The polymers P ₁? P ₆ showed cholesteric phase and P ₇ displayed smectic phase. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of nonmesogenic crosslinking units on the mesogenic properties of side‐chain cholesteric liquid crystalline elastomers

A series of cyclosiloxane‐based cholesteric liquid crystalline elastomers were synthesized by using cholest‐5‐en‐3‐ol(3β)‐4‐(2‐propenyloxy)benzoate and a soft nonmesogenic crosslinking agent, acryloyl‐hexyl acrylate. The polymers were prepared in a one‐step reaction with the crosslinking contents ranging between 0 and 5.6 weight %. The effective crosslink density (M_c) was determined by swelling experiments employing Flory–Rehner models. All the polymers exhibited thermotropic LC properties and revealed a cholesteric phase. With increase of the crosslinking component in the polymers, the melting behavior disappeared and the enthalpy of transition decreased. But the temperature of glass transition and clear point changed little and did not show uptrend or downtrend. Reflection spectra of the cholesteric mesophase of the polymers showed that the reflected wavelength became broad and shifted to long wavelength with increase of the soft crosslinking component in the polymer systems. All these results originate from the effect of the soft nonmesogenic chemical crosslinking. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 625–631, 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     

Investigation of liquid crystalline and photocrosslinkable poly[4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamate]s

Three series of liquid‐crystalline‐cum‐photocrosslinkable polymers were synthesized from 4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamates (x = ? H, ? OCH₃ and ? CN; m = 6, 8 and 10) by free radical solution polymerization using azobisisobutyronitrile as an initiator in tetrahydrofuran at 60 °C. All the monomers and polymers were characterized using intrinsic viscosity, and FTIR, ¹H NMR and ¹³C NMR spectroscopy. The liquid crystalline behavior of these polymers was examined using a hot stage optical polarizing microscope. All the polymers exhibited liquid crystalline behavior. The hexamethylene spacer‐containing polymers exhibited grainy textures; in contrast, the octamethylene and decamethylene spacer‐containing polymers showed nematic textures. Differential scanning calorimetry data confirmed the liquid crystalline property of the polymers. Thermogravimetric analysis revealed that all the polymers were stable between 236 and 344 °C in nitrogen atmosphere and underwent degradation thereafter. As the methylene chain length increases in the polymer side‐chain, the thermal stability and char yield of the polymers decrease. The photocrosslinking property of the polymers was investigated using the technique of exposing the polymer solution to UV light and using UV spectroscopy. The crosslinking reaction proceeds via 2π–2π cycloaddition reactions of the ? CH?CH? of the pendant cinnamate ester. The polymers containing electron‐releasing substituents (? OCH₃) showed faster crosslinking than the unsubstituted polymers and those containing electron‐withdrawing substituents (? CN). Copyright © 2007 Society of Chemical Industry     

Studies on the mesomorphic properties of ferrocenylene‐based organophosphorous liquid‐crystalline polymers containing phenyl and biphenyl pendant units

The synthesis, mesomorphic character, and effect of spacers in ferrocene‐containing main‐chain liquid‐crystalline polymers are reported in this article. Two different monomers containing ferrocene and phenyl/biphenyl phosphate groups possessing even numbers of spacers from 2 to 10 were prepared and polymerized by polycondensation at room temperature. All the polymers gave birefringent melt except one. The identification of the mesophase was transparent with an increase in spacers. The effect of substitution in the side chain with regard to bulkiness and spacers were studied with thermogravimetric analysis and differential scanning calorimetry. The results reveal that the thermal stability of the polymers increased with the increasing bulkiness of the side chain and decreased with increasing spacer length. The incorporation of the phosphorous moiety also had a considerable effect on the glass‐transition temperature. Char yield of the polymer decreased with increasing methylene chain length, and it did not vary much with the size of the pendent groups. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 831–841, 2002     

Synthesis and phase behavior of new cholesteric liquid‐crystalline copolymers containing chiral mesogenic groups derived from menthol derivatives

The synthesis of a new chiral mesogenic monomer ( M₁ ), a nematic monomer ( M₂ ), and a series of side chain cholesteric copolymers ( P₂ – P₆ ) containing the mesogenic menthyl groups is described. The chemical structures of the compounds were confirmed by FTIR and ¹H NMR. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. M ₁ showed an enantiotropic cholesteric phase, and M₂ revealed a nematic phase. The homopolymers P₁ and P₇ , respectively, displayed a chiral smectic A (S_A) phase and a nematic phase, while the copolymers P₂ – P₆ exhibited the Grandjean texture of the cholesteric phase. T_g, T_i, and ΔT of P₁ – P₇ increased with increasing the concentration of M₂ in the polymers. All of the obtained polymers displayed very good thermal stability and the wide mesophase temperature range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Investigation on stilbene‐ and azobenzene‐based liquid crystalline organophosphorus polymers

Two series of combined liquid crystalline polyphosphates bearing dual photoreactive mesogenic units (stilbene and azobenzene/α‐methylstilbene and azobenzene) were synthesized by solution polycondensation method. The structures of the synthesized polymers were confirmed by various spectroscopic techniques. Thermogravimetric analysis reveals that they are stable between 230 and 320°C. Differential scanning calorimetry studies were done to study the liquid crystalline property, and glass‐transition, melting, and isotropization temperatures for all the polymers. Polarizing optical microscope shows the birefringent melt for all the polymers exhibiting liquid crystalline property. The photochemical response was studied by UV–visible and fluorescence spectroscopy for all the polymers. The photocrosslinking reaction of the stilbene containing polymers was ascertained by spectroscopic and photolysis studies. The rate of the switching time for the conversion of trans to cis form of azobenzene unit was investigated by UV spectroscopy. The terminal substituents in the side chain affects the texture of liquid crystalline phase for all the polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Optical properties of ethyl‐cyanoethyl cellulose/poly(acrylic acid) cholesteric liquid crystalline composite films

Ethyl‐cyanoethyl cellulose [(E–CE)C]/poly(acrylic acid) (PAA) composite films were prepared by photopolymerizing acrylic acid (AA) in (E–CE)C/AA cholesteric liquid crystalline solutions. With the selection of suitable concentrations, (E–CE)C/PAA composite films showed vivid colors due to the selective reflection property of the cholesteric phase. It was found that the wavelength of reflection was a function of the concentration of (E‐CE)C, and the reflectivity was increased with increasing thickness of the film. The selective reflection of the composite holds well upon heating at temperatures below 160°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 213–217, 2004     

Synthesis and liquid‐crystalline properties of poly(4‐vinylpyridinium) bromides N‐substituted with dialkyloxyterphenyl groups

Poly(4‐vinylpyridine)s (P4VPs) fully and partially quaternized with dialkyloxyterphenyl groups were synthesized and characterized. These new polymers developed both liquid‐crystalline (LC) properties and a light emission (luminescence) in the blue region. The mesomorphic behavior of the polymers was initially characterized by differential scanning calorimetry and polarizing optical microscopy and was further corroborated by X‐ray diffraction analyses. The X‐ray diffraction patterns showed in the low‐angles region several equidistant diffraction peaks (d₀₀₁, d₀₀₂, d₀₀₃, …) and in the wide‐angles region a broad peak typical of nonordered mesophases. From d₀₀₁ and the length of the monomers, we deduced that the molecular arrangement in the mesophase corresponded to a double‐layered stacking of molecules with mesogens tilted with respect to the smectic plane and the backbones sandwiched between. In this arrangement, the different parts of mesogens are segregated from one another in layered domains. The longer smectic periods observed for copolymers indicated that the nonsubstituted pyridine cycles were sandwiched between two smectic layers. The emission spectra of these polymers were characterized by a broad signal centered at 365 nm. The combination of LC properties with luminescence in the polymers is interesting for the preparation of thin films with aligned emitters, particularly for linearly polarized light emission. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and phase behavior of cholesteric liquid crystal polymers containing glutamic acid in main‐chain

Four polymers (P₀–P₃) containing peptide chain as polymer backbone were synthesized by condensation reaction with bis(trichloromethyl)carbonate and triethylamine. The chemical structures of the monomers M₀–M₃ were confirmed by FTIR and ¹H‐NMR. The structure–property relationships of the monomers and polymers are discussed. Their phase behavior and optical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. Monomers M₁–M₃ and polymers P₁–P₃ displayed cholesteric phases. The results demonstrated that the melt temperature and clear point of monomers (M₁–M₃) and polymers (P₁–P₃) decreased with the increase of the flexible spacer length in the side‐chain, and the mesophase temperature range of the polymers increased with the increase of the flexible spacer length. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of α‐methylstilbene‐ and azobenzene‐based thermotropic liquid crystalline polymers

A series of combined liquid crystalline poly(bis‐4,4′‐oxy‐α‐methylstilbene‐4‐substituted (X) phenylazo‐4′‐phenyloxydecylphosphate ester)s bearing photoreactive mesogenic units were synthesized. FTIR and ¹H NMR spectroscopy confirmed the structures of these polymers. The inherent viscosities of the polymers were found to be in the range 0.45–0.65 dL g^?1. Polarizing optical microscopy (POM) exhibited birefringent liquid crystalline melt properties. The thermal properties of all of the polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The photochemical properties of these polymers were studied by UV‐visible and fluorescence spectroscopy. The influence of the photoinduced E–Z (trans–cis) isomerization of the various terminal substituents of the side‐chain azobenzenes was investigated. The kinetics of the photoisomerization process reveal the switching times for the conversion between the trans‐ and cis‐ forms of the azobenzene units. The photo‐optical properties of these polymers exhibited layered smectic phases and showed good photoinduced properties in their mesomorphic states. Copyright © 2005 Society of Chemical Industry     

Synthesis and characterization of side‐chain cholesteric liquid‐crystalline polysiloxanes containing different space groups

A series of liquid‐crystalline (LC) polysiloxanes were synthesized by two different cholesteric monomers, cholest‐5‐en‐3‐ol(3β)‐10‐undecenoate and cholesteryloxycarbonylmethyl 4‐allyloxybenzoate. The chemical structures and LC properties of the monomers and polymers were characterized by various experimental techniques, including Fourier transform infrared spectroscopy, ¹H‐NMR, elemental analysis, differential scanning calorimetry, and polarized optical microscopy. The specific rotation absolute values increased with increasing rigid spacers between the main chain and the mesogens. All of the polymers exhibited thermotropic LC properties and revealed cholesteric phases with very wide mesophase temperature ranges. With a reduction in the soft‐space groups in the series of polymers, the glass‐transition temperature and the isotropic temperature increased slightly on heating cycles. Reflection spectra of the cholesteric mesophase of the series of polymers showed that the reflected wavelength shifted to short wavelengths with decreasing soft‐space groups in the polymers systems, which suggested that the helical pitch became shorter with increasing rigid‐space groups. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of fillers on the mechanical response of an amorphous liquid‐crystalline polymer

A semirigid and amorphous commercial liquid‐crystalline copolyester (Rodrun) was filled with mica and calcium carbonate (up to 25 wt %) by direct injection molding. The fillers led to decreases in the processability, as observed by torque increases, but maintained the thermal resistance of Rodrun. The effects of the two fillers on the modulus of elasticity, ductility, and tensile strength were the same or very similar. The decrease in the tensile strength (20% for a 10% filler content) was compensated by a generally slight increase in the modulus of elasticity, whatever the filler content was. This balance of properties found in these new liquid‐crystalline‐polymer‐based materials and the important savings that the fillers bring may spread the applications of these materials' matrices. © 2003 Wley Periodicals, Inc. J Appl Polym Sci 88: 998–1003, 2003