Synthesis, structure and mesomorphism of new cholesteric monomers and smectic comblike polymers

Seven new cholesteric monomers (M-1−M-7) and the corresponding smectic comblike polymers containing cholesteryl groups (P-1−P-7) were synthesized. The chemical structures and purity were characterized by FT-IR, ¹H NMR, and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The mesomorphism was investigated by polarizing optical microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction. The specific optical rotation values of these monomers and polymers with the same numbers of phenyl ring and terminal groups were nearly equal, however, they decreased with increasing the aryl numbers in the mesogenic core. M-1−M-7 showed oily streak texture and focal conic texture, or fingerprint texture, or spiral texture of cholesteric phase. P-1−P-7 showed the smectic A phase. The melting, clearing, and glass transition temperatures increased, and the mesophase temperature ranges widened with increasing the aryl number in the mesogenic core. Surprisingly, although the molecular structures of M-6 and M-7 were similar to those of M-4, namely the mesogenic cores contained three phenyl rings, their phase behavior had a considerable difference, and T_m and T_i of M-6 and M-7 were less than those of M-4. In addition, M-6 and M-7 also showed an obvious glass transition. TGA showed that all the polymers had good thermal stabilities.     

Synthesis and properties of new chiral mesogenic monomers and side-chain smectic homopolymers containing (−)-menthyl groups

The synthesis of new chiral monomers (M₁−M₅) and the corresponding smectic homopolymers (P₁−P₅) containing menthyl groups is described. The chemical structures and purity were characterized by FT-IR, ¹H NMR and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The phase behavior and mesomorphism were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. The selective reflection property of light was studied with UV/visible/NIR. The monomers M₂−M₅ formed a chiral smectic C , and cholesteric or blue phase when a flexible linkage chain was inserted between the mesogenic core and the terminal menthyl groups by reducing the steric effect. M₁ showed no mesomorphism, while M₂−M₅ showed enantiotropic and cholesteric phases. Moreover, M₅ also exhibited a cubic blue phase on cooling. With increasing temperature, the selective reflection of light shifted to the long wavelength region at the phase range, and to the short wavelength region at the cholesteric phase range, respectively. The homopolymers P₁−P₅ all exhibited the batonnet textures of a smectic A phase. The melting, clearing, and glass transition temperatures increased, and the mesophase temperature ranges widened with increasing the aryl number in the mesogenic core.     

Study on new chiral liquid crystalline monomers and polymers containing menthyl groups

A series of new chiral monomers (M1–M4) and the corresponding siloxane polymers (P1–P4) containing menthyl groups were synthesised to establish the relationship between their structure and liquid crystalline properties. The effect of the mesogenic core rigidity and the spacer length on the phase behaviour of the monomers and polymers obtained in this study was discussed. The selective reflection of light for the chiral monomers was studied with UV-Vis spectrometer. Polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis were used to characterise the phase behaviour and thermal stabilities. It was found that these chiral monomers and polymers were beneficial for the formation of the mesophases when a flexible spacer was inserted between the mesogenic core and terminal menthyl groups. M1–M3 showed enantiotropic chiral smectic C phase and cholesteric phase, and monotropic cubic blue phase on cooling cycle. M4 only showed cholesteric phase. P1–P4 showed a smectic A phase. With increasing the mesogenic core rigidity or decreasing the spacer length, the corresponding melting temperatures, glass transition temperatures and isotropic temperatures all increased.     

Synthesis,structure and properties of new chiral liquid crystalline monomers and homopolysiloxanes containing menthyl groups

The synthesis is described of four new chiral liquid crystalline monomers (M₂–M₅ ) and their corresponding side‐chain homopolysiloxanes (P₂–P₅ ) containing menthyl groups. Chemical structures were characterised using FT‐IR or ¹H NMR spectra, and specific optical rotations were evaluated with a polarimeter. The phase behaviour and mesomorphic properties of the new compounds were investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy, UV/visible/NIR spectrocopy and X‐ray diffraction. The monomers and homopolymers with more aryl segments showed noticeably lower specific optical rotation value. The monomers M₂–M₅ formed a cholesteric or blue phase when a flexible spacer was inserted between the rigid mesogenic core and the terminal menthyl groups by reducing the steric effect. M₂–M₅ revealed enantiotropic cholesteric phase. Moreover, M₂ also exhibited a monotropic smectic A (SmA) phase, and M₄ also exhibited a cubic blue phase on cooling. The selective reflection of light shifted to the long wavelength region with increasing rigidity of the mesogenic core for M₂–M₅ . P₂–P₅ exhibited SmA phases, and the mesogenic moieties were ordered in smectic orientation with their centres of gravity in planes. Melting or glass transition temperature and the clearing temperature increased, and the mesophase temperature range widened with increasing rigidity of the mesogenic core.     

Mesomorphic properties of side-chain cholesteric liquid-crystalline elastomers

New monomer cholesteryl 4-(10-undecylen-1-yloxybenzoyloxy)-4′-ethoxybenzoate (M₁), crosslinking agent biphenyl 4,4′-bis(10-undecylen-1-yloxybenzoyloxy-p-ethoxybenzoate) (M₂) and a series of side-chain cholesteric elastomers were prepared. The chemical structures of the monomers and elastomers obtained were confirmed by element analyses, FT-IR, and ¹H NMR. The mesomorphic properties and thermal stability were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. The influence of the content of the crosslinking unit on the phase behavior of the elastomers was examined. M ₁ showed cholesteric phase, and M ₂ displayed nematic phase. The elastomers containing less than 12 mol% of the crosslinking units revealed reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability.     

Synthesis, structure and mesomorphic properties of side-chain chiral liquid crystalline polysiloxanes based on (S)-(+)-2-methyl-1-butanol derivatives

The synthesis of five chiral liquid crystalline monomers (M₁-M₅), and their corresponding side-chain polymers (P₁-P₅) based on (S)-(+)-2-methyl-1-butanol derivatives is described. The chemical structures of the monomers were confirmed by FT-IR, ¹H NMR, and elemental analyses. The structure-property relationships of the monomers and polymers obtained are discussed. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. All monomers showed a cholesteric phase. For M₂, M₃, and M₅, besides a cholesteric phase and a smectic A (S_A) phase, M₂ also revealed an enantiotropic chiral smectic C phase and a monotropic smectic B (S_B) phase, and M₃ also showed a S_B phase. The polymers P₁-P₅ exhibited a S_A phase, moreover, P₂, P₃ and P₅ also revealed a phase. The experimental results demonstrated that a flexible siloxane backbone and a long flexible spacer tended to exhibit a low glass transition temperature, high thermal stability, and wide mesophase temperature range.     

Side-chain cholesteric liquid crystalline elastomers derived from a mesogenic crosslinking agent: I. Synthesis and mesomorphic properties

The synthesis of new side-chain cholesteric elastomers derived from a cholesteric monomer and mesogenic crosslinking agent is presented. The chemical structures of the monomers obtained were confirmed by elemental analyses, FT-IR, ¹H NMR, and ¹³C NMR. The mesomorphic properties and thermal stability were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. M₁ showed cholesteric phase, and M₂ displayed enantiotropic nematic phase and monotropic smectic phase. The elastomers containing less than 12 mol% of the crosslinking units revealed reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability.     

Synthesis and characterization of side-chain cholesteric elastomers derived from an isosorbide crosslinking agent

New liquid crystalline monomer 4-(4-ethoxybenzoyloxy)biphenyl-4′-[(10-undecylen-1-yloxy)-4′-ethoxy]benzoate (M ₁ ), chiral crosslinking agent isosorbide di-(10-undecylen-1-yloxybenzoate) (M ₂ ), and the corresponding elastomers were prepared. The chemical structures of M ₁ and M ₂ were characterized by Fourier transform infrared and ¹H-nuclear magnetic resonance. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction measurements. M ₁ exhibited typical threaded texture and droplet texture of nematic phase. The use of chiral crosslinking agent in the polymer networks could induce cholesteric phase. The elastomers containing less than 10 mol% of the chiral crosslinking units showed elasticity, reversible phase transition, wide mesophase temperature ranges, and high thermal stability. For the elastomers P ₂ –P ₄ , the glass transition temperature (T _g) increased; clearing temperature (T _i) and mesophase temperature range (ΔT) decreased with increasing content of the crosslinking unit.     

Side-chain cholesteric liquid crystalline polymers containing menthol and cholesterol—synthesis and characterization

A series of new cholesteric side-chain liquid crystalline polymers were prepared containing cholesteric 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 and X-ray diffraction measurements, and temperature-changing solidistic optical rotation. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectra. M₁ showed cholesteric phase during the heating and the cooling cycle. Polymer P₁ were chiral smectic A phase, whereas P₂–P₇ were cholesteric phase. Experimental results demonstrated that nonmesogetic chiral moity offered the possibility of application because of its lower glass-transition temperature, and the glass-transition temperatures and isotropization temperatures reduced, and the ranges of the mesophase temperature changed abruptly at first and then smoothly with increasing the content of chiral agent.     

Preparation and characterization of side-chain liquid crystalline polymers containing chenodeoxycholic acid residue

A series of new side-chain liquid crystalline polymers containing chenodiol residue derived from 24-[4′-hydroxybiphenyl-4-yl-4-(allyloxy)benzoyloxy]-3α,7α-di{n-[4′-(4-ethoxybenzoyloxy)biphenyl-4-yloxy]-n-oxoalkanoyloxy}-5β-cholane was designed and prepared. The chemical structures of the monomer and polymer were confirmed by Fourier transform infrared and ¹H NMR spectra. The mesomorphic properties of monomer and polymer were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. The side-chain liquid crystalline polymers revealed wide mesophase temperature range and high thermal stability, and they showed nematic liquid crystalline phase. The influence of flexible space group length on thermal properties and specific rotation was examined.     

Synthesis and thermal properties of side-chain liquid crystalline polyethers with racemic and chiral backbone

Racemic and chiral [(4-cyano-4′-biphenyl)oxy] and [(4-methoxy-4′-biphenyl)oxy]methyloxiranes were prepared from racemic epichlorohydrin or racemic and chiral glycidols and polymerized in dimethylsulfoxide (DMSO) with Bu^tOK as the initiator system. Initial phase identifications were made by differential scanning calorimetry (DSC) and optical microscopy techniques and confirmed by X-ray diffraction measurements. Upon heating, all the monomers show only a crystal–isotropic phase transition. The racemic and chiral [(4-cyano-4′-biphenyl)oxy]methyloxiranes exhibit a nematic and a cholesteric monotropic phase, respectively. Methoxybiphenyl substituted polyethers are crystalline and insoluble in virtually all common solvents. Cyanobiphenyl substituted polyethers are soluble under the same experimental conditions and show enantiotropic liquid crystalline properties. The racemic polymer exhibits a nematic phase, while the optically active polymer forms a cholesteric phase.     

Synthesis and phase behavior of side‐chain liquid‐crystalline polymers containing malachite green lactone groups

New side‐chain liquid‐crystalline polymers containing both cholesteric and thermochromic side groups were synthesized. Their chemical structures were confirmed with elemental analyses and Fourier transform infrared, proton nuclear magnetic resonance, and carbon‐13 nuclear magnetic resonance spectra. The mesogenic properties and phase behavior were investigated with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The effect of the concentration of dye side groups on the phase behavior of the polymers was examined. The polymers showed smectic or cholesteric phases. Those polymers containing less than 20 mol % dye groups had good solubility, reversible phase transitions, wider mesophase temperature ranges, and higher thermal stability. The experimental results demonstrated that the isotropization temperature and mesophase temperature ranges decreased with an increasing concentration of dye groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3870–3878, 2004     

Monotropic smectic A to double layer smectic C transition of biphenyl containing liquid crystal acetylene

5-[（4’-Heptoxy-4-biphenylyl）carbonyloxy]-1-pentyne（A-3,7） was synthesized and the phase structures and transitions were investigated by differential scanning calorimetry（DSC）,wide angle X-ray diffraction（WAXD）,polarized light microscopy（PLM） and the molecular packing in the crystal and liquid crystalline phases were simulated by molecular dynamic simulation.The results showed that the sample formed thermodynamically metastable SmA and SmC₂ phases before crystallized during cooling and the crystal phase directly transformed into isotropic phase during heating.     

光致变色液晶高分子的研究(Ⅰ)─含胆甾介晶基无侧链聚硅氧烷及其单体的液晶行为

用POM、DSC和WAXD研究了十一烯酸胆甾酯及含胆甾介晶基元侧链聚硅氧烷的液晶行为。单体呈现明甾相的油条及螺旋织构,单致变近晶相的扇形织构和固-固相变。均聚物显示S_A相的扇形织构。     

Side‐chain cholesteric liquid‐crystalline elastomers derived from smectic crosslinking units: Synthesis and phase behavior

New side‐chain cholesteric liquid‐crystalline elastomers containing cholesteryl 4‐allyloxybenzoate as cholesteric mesogenic units and biphenyl 4,4′‐bis(10‐undecen‐1‐ylenate) as smectic crosslinking units were synthesized. The chemical structures of the olefinic compounds and polymers obtained were confirmed by element analysis, Fourier transform infrared, proton nuclear magnetic resonance, and carbon‐13 nuclear magnetic resonance spectra. The mesogenic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the concentration of the crosslinking unit on the phase behavior of the elastomers was examined. The elastomers containing less than 17 mol % of the crosslinking units revealed elasticity, reversible mesomorphic phase transition, wider mesophase temperature ranges, and higher thermal stability. The experimental results demonstrated that the glass‐transition temperature, isotropization temperature, and mesophase temperature ranges decreased with an increasing concentation of the crosslinking unit. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5262–5270, 2004     

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

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

High performance benzoxazine monomers and polymers containing furan groups

Furan‐containing benzoxazine monomers, 3‐furfuryl‐3,4‐dihydro‐2H‐1,3‐benzoxazine (P‐FBz) and bis(3‐furfuryl‐3,4‐dihydro‐2H‐1,3‐benzoxazinyl)isopropane (BPA‐FBz), were prepared using furfurylamine as a raw material. The chemical structures of P‐FBz and BPA‐FBz were characterized with FTIR, ¹H NMR, elemental analysis, and mass spectrometry. Formation of furfurylamine Mannich bridge networks in the polymerizations of P‐FBz and BPA‐FBz increased the cross‐linking densities and thermal stability of the resulting polybenzoxazines. P‐FBz‐ and BPA‐FBz‐based polymers also exhibited high glass transition temperatures above 300 °C, high char yields, and low flammability with limited oxygen index values of 31. The dielectric (D_k = 3.21–3.39) and mechanical properties (high storage modulus of 3.0–3.9 GPa and low coefficient of thermal expansion of 37.7–45.4 ppm) of the P‐FBz‐ and BPA‐FBz‐based polymers were superior or comparable to other polybenzoxazines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5267–5282, 2005     

Interfacial tension of blends containing thermotropic liquid crystalline polymers

A method is proposed to determine the interfacial tension of immiscible blends containing a liquid crystalline polymer (LCP) and a flexible-molecule polymer, under flow conditions. The method is based on Taylor's theorem for immiscible fluids, i.e., that a suspended drop of liquid A in liquid matrix B is deformed in shear or elongational flow in proportion to the ratio of interfacial to viscous stresses. Taylor's theorem, as originally derived, applies to low concentrations, Newtonian fluids and small deformations. Thus, the theorem was modified to account for “Power Law” fluids in elongational flow and large deformations, more applicable to the system under investigation. The elongational viscosities of the LCP and the flexible polymer (polycarbonate) as a function of elongational rate were determined using converging type flow. The two polymers exhibited a Power-Law behavior in elongational flow and, hence, the experimental constitutive equations of state were used to quantify the viscous stresses. The interfacial stresses were modified for large deformations by taking into consideration the deformed shape and hence increased surface area of the elongated LCP particle. Using the modified expression, the interfacial tension of LCP and PC was determined to be in the range of 5–6.6 dyne/cm.     

Synthesis and mesomorphic evaluation of new calamitic liquid crystals containing benzothiazole core

The design and synthesis of new calamitic benzothiazole-based liquid crystals,2-[4-（4-alkyloxybenzoyloxy）-phenyl]ben-zothiazoles are presented.The target compound was characterized using spectroscopic techniques,such as FT-IR,NMR(¹H and ¹³C),microanalysis and EI-MS.The liquid crystalline behaviours of these compounds were thoroughly examined by differential scanning calorimetry and polarizing optical microscope techniques.These materials exhibited enantiotropic nematic phase with high thermal stability（>168℃）.Smectic A phase starts to emerge as monotropic（metastable） phase from C10 member and changes into enantiotropic（stable） phase from C12 and persists up to C16 members.     

Properties of blends containing two liquid crystalline polymers

Blends containing two, wholly aromatic, naphthalene-based liquid crystalline polymers (LCPs) are studied. Experimental results show that the viscosities of the resulting blends are lower than the parent LCPs over the entire shear-rate range investigated. The orientation development following capillary flow demonstrates, that over a defined blend composition range, some blends have higher orientability than the constituent polymers. This is further manifested in the tensile and flexural properties of injection-molded specimens. A detailed analysis indicates that in the composition range where synergistic effects are observed in orientation development as well as in mechanical properties, only one glass transition temperature is detected. This suggests that “miscibility” is desirable for obtaining maximum properties in these blend systems.