Synthesis and properties of cholesteric liquid crystalline elastomers

The synthesis of new side-chain cholesteric liquid crystalline elastomers, containing the flexible non-mesogenic crosslinking agent M-1 and the cholesteric monomer M-2, is described by a one-step hydrosilication reaction. The chemical structures of the monomers and network polymers obtained were confirmed by FT-IR spectroscopy. Their mesogenic 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 network polymers showed elasticity, reversible phase transitions, and cholesteric Grandjean texture. The experimental results demonstrated that the glass transition temperatures and isotropization temperatures of network elastomers decreased as the concentration of crosslinking units was increased, but the cholesteric phase was not disturbed.     

Synthesis and properties of polysiloxane side chain cholesteric elastomers

The synthesis of new side chain cholesteric liquid crystalline elastomers containing the flexible non-mesomorphic crosslinking agent M-1 and the cholesteric monomer M-2 by a one-step hydrosilylation reaction is described. The chemical structures of the obtained monomers and network polymers 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. The glass transition temperatures and isotropic temperatures of the mesomorphic elastomers decreased as the concentration of crosslinking units increased; in the mesomorphic region the liquid crystalline elastomers showed elasticity, reversible phase transitions and Grandjean texture. The flexible crosslinking agent did not disturb the cholesteric structure; moreover, it was beneficial for adjusting the helix of the cholesteric liquid crystalline polymers, and cholesteric elastomers P-6, P-7, show reversible selective reflection of visible light.     

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     

Synthesis and characterization of side chain cholesteric liquid crystalline elastomers derived from chiral bisolefinic crosslinking units

In this work we prepared a nematic monomer (4'-allyloxybiphenyl 4'-ethoxybenzoate, M₁), a chiral crosslinking agent (isosorbide 4-allyloxybenzoyl bisate, M₂) and a series of new side chain cholesteric liquid crystalline elastomers derived from M₁ and M₂. The chemical structures of the monomers and polymers were confirmed by FTIR and ¹H NMR spectroscopy. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X-ray diffraction. The effect of the content of the crosslinking unit on phase behaviour of the elastomers is discussed. Polymer P₁ showed a nematic phase, P₂-P₇ showed a cholesteric phase; P₆ formed a blue Grandjean texture over a broad temperature range 145-209.6°C, with no changed on the cooling. Polymers P₄-P₇, with more than 6 mol % of chiral crosslinking agent, gave rise to selective reflection. Elastomers containing less than 15 mol % of the crosslinking units displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that, with increasing content of crosslinking agent, the glass transition temperatures first fell and then increased; the isotropization temperatures and mesophase temperature ranges decreased.     

侧链胆甾液晶聚合物及弹性体的液晶性能研究

把胆甾液晶单体 4 烯丙氧基苯甲酸胆甾醇酯 (Mch)分别和向列液晶单体 4 烯丙氧基苯甲酰氧基 4′ 甲氧基苯 (Mn) ,向列液晶交联剂 2 叔丁基对苯二酚双 [4 (6 丙烯酰氧基己氧基 )苯甲酸酯 ](Mnc)接枝到聚硅氧烷链上 ,得到系列侧链液晶聚合物Pn 系列和液晶弹性体Pe 系列 .通过热分析、偏光显微分析和X 射线分析等手段分别研究了向列液晶单体和向列液晶交联剂对含同一胆甾液晶基元聚合物的影响 .结果表明 ,向列液晶单体的摩尔百分比在 80 %以下 ,液晶聚合物Pn 系列为胆甾型液晶 ,在研究的范围内 ,液晶弹性体Pe 系列也为胆甾型液晶 ,Pn 系列和Pe 系列都具有较宽的液晶相范围 ,热分解温度均在 2 80℃以上 .     

Side chain cholesteric liquid crystalline elastomers: synthesis and phase behaviour

A series of new side chain cholesteric liquid crystalline elastomers (P-2-P-6) containing the nematic crosslinking monomer 4-(10-undecen-1-yloyloxy)benzoyl-4'-allyloxybenzoyl-p-benzenediol bisate (M-1) and the cholesteric monomer 4-cholesteryl 4-(10-undecen-1-yloyloxy)benzoate (M-2) were synthesized. The chemical structures of the monomers and elastomers obtained were confirmed by FTIR and ¹H NMR spectroscopy. Their liquid crystalline properties and phase behaviour were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The effect of the crosslinking units on phase behaviour is discussed. Elastomers containing less than 20 mol % of the crosslinking units showed elasticity, reversible phase transitions and cholesteric Grandjean texture. The experimental results demonstrated that the glass transition and isotropization temperatures of P-2-P-6 increased with the increasing concentration of crosslinking unit M-1.     

Effect of ionic aggregates of sulphonate groups on the liquid crystalline behaviours of liquid crystalline elastomers

A series of siloxane-based liquid crystalline elastomers containing biphenyl benzoate mesogenic units and ionic Brilliant Yellow moieties was synthesized. The chemical structures and liquid crystalline properties of the samples were characterized by FTIR, ¹H NMR, DSC, POM and XRD. The effective crosslink density of the ionic elastomers was determined by swelling experiments in organic/buffer mixtures. All the polymers displayed a smectic mesophase. It was shown that the glass transition and melting point temperatures of the polymers increased slightly with increasing content of ionic and mesogenic groups in the polymers, while the liquid crystal mesophase region decrease slightly.     

Synthesis and characterization of liquid crystalline elastomers bearing fluorinated mesogenic units and crosslinking mesogens

Several new side‐chain liquid crystalline (LC) polysiloxanes and elastomers ( IP ‐ VIP ) bearing fluorinated mesogenic units and crosslinking mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a fluorine‐containing LC monomer 4′‐undec‐10‐enoyloxy‐biphenyl‐4‐yl 4‐fluoro‐benzoate and a crosslinking LC monomer 4′‐(4‐allyloxy‐benzoxy)‐biphenyl‐4‐yl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, ¹H‐NMR, EA, TGA, DSC, POM and XRD. The effect of crosslinking mesogens on mesomorphic properties of the fluorinated LC polymers was studied as well. The obtained polymers and elastomers were soluble in many solvents such as toluene, tetrahydrofuran, chloroform, and so forth. The temperatures at which 5% weight loss occurred (T_d) were greater than 250°C for all the polymers, and the weight of residue near 600°C increased slightly with increase of the crosslinking mesogens in the fluorinated polymer systems. The samples IP , IIP , IIIP and IVP showed both smectic A and nematic phases when they were heated and cooled, but VP and VIP exhibited only a nematic mesophase. The glass transition temperature (T_g) of polymers increased slightly with increase of crosslinking mesogens in the polymer systems, but the mesophase–isotropic phase transition temperature (T_i) and smectic A–nematic mesophase transition temperature (T_S‐N) decreased slightly. It suggests that the temperature range of the mesophase became narrow with the increase of crosslinking mesogens for all the fluorinated polymers and elastomers. In XRD curves, the intensity of sharp reflections at low angle decreased with increase of crosslinking mesogens in the fluorinated polymers systems, indicating that the smectic order derived from fluorinated mesogenic units should be destroyed by introduction of more crosslinking mesogens. Copyright © 2008 John Wiley & Sons, Ltd.     

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, ^1?H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.     

Synthesis and characterization of a series of side chain chiral smectic liquid crystalline elastomers

A series of new chiral smectic liquid crystalline elastomers was prepared by graft polymerization of a nematic monomer with a chiral and non-mesogenic crosslinking agent, using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by FTIR and ¹H NMR. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X-ray diffraction. Monomer M₁ showed a nematic phase during heating and cooling. Polymer P₀ exhibited a smectic B phase; elastomers P₁-P₃ showed the smectic A phase, P₄-P₆ showed a chiral smectic C(SmC*), and P₇ displayed stress-induced birefringence. Elastomers containing less than 15 mol % M₂ displayed elasticity, reversible phase transitions with wide mesophase temperature ranges, and high thermal stability. With increasing content of the crosslinking unit, glass transition temperatures first increased, then fell, then increased again; isotropization temperatures and mesophase temperature ranges steadily decreased.     

Synthesis and characterization of a series of side chain chiral smectic liquid crystalline elastomers

A series of new chiral smectic liquid crystalline elastomers was prepared by graft polymerization of a nematic monomer with a chiral and non‐mesogenic crosslinking agent, using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by FTIR and ¹H NMR. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X‐ray diffraction. Monomer M ₁ showed a nematic phase during heating and cooling. Polymer P ₀ exhibited a smectic B phase; elastomers P ₁–P ₃ showed the smectic A phase, P ₄–P ₆ showed a chiral smectic C(SmC*), and P ₇ displayed stress‐induced birefringence. Elastomers containing less than 15?mol?% M ₂ displayed elasticity, reversible phase transitions with wide mesophase temperature ranges, and high thermal stability. With increasing content of the crosslinking unit, glass transition temperatures first increased, then fell, then increased again; isotropization temperatures and mesophase temperature ranges steadily decreased.     

Synthesis and properties of two new series of isomeric liquid crystalline polyesters with conjugated double bonds

Two homologous series of flexible main chain liquid crystalline polyesters with isomeric mesogenic groups containing conjugated double bonds, were synthesized and studied by differential scanning calorimetry and optical microscopy. One series (S1) has the p-phenylene-diacryloyloxydibenzoyl moiety as a mesogenic unit. The other (S2) has the terephtaloyl dioxydicinnamoyl moiety as a mesogenic unit. The reactivity of the conjugated double bonds of the p-phenylenediacryloxy unit, at the temperature of mesophase formation, impedes the stability of liquid crystalline mesophases of polymers of series (S1). Two low molecular weight analogues of polymers were also prepared and their properties compared with those of polymers of similar structure. The two model compounds form stable smectic mesophases over a wide range of temperatures, which shows the high mesomorphogenic ability of both mesogenic units.     

Synthesis and characterization of side chain cholesteric liquid crystalline elastomers derived from chiral bisolefinic crosslinking units

In this work we prepared a nematic monomer (4′‐allyloxybiphenyl 4′‐ethoxybenzoate, M₁ ), a chiral crosslinking agent (isosorbide 4‐allyloxybenzoyl bisate, M₂ ) and a series of new side chain cholesteric liquid crystalline elastomers derived from M₁ and M₂ . The chemical structures of the monomers and polymers were confirmed by FTIR and ¹H NMR spectroscopy. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X‐ray diffraction. The effect of the content of the crosslinking unit on phase behaviour of the elastomers is discussed. Polymer P₁ showed a nematic phase, P₂ –P₇ showed a cholesteric phase; P₆ formed a blue Grandjean texture over a broad temperature range 145–209.6°C, with no changed on the cooling. Polymers P₄ –P₇ , with more than 6?mol?% of chiral crosslinking agent, gave rise to selective reflection. Elastomers containing less than 15?mol?% of the crosslinking units displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that, with increasing content of crosslinking agent, the glass transition temperatures first fell and then increased; the isotropization temperatures and mesophase temperature ranges decreased.     

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 liquid‐crystalline poly(ethyleneimine)s with cyanobiphenyl groups

A series of polyethyleneimine‐based side‐chain liquid‐crystalline polymers substituted with different ratios of cyanobiphenyl as pendent mesogenic groups has been synthesized in which the spacer length varies between two and six methylene units. The structures of the synthesized polymers are confirmed by infrared and ¹H nuclear magnetic resonance spectroscopy. The thermal properties of these polymers have been investigated using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. The results indicate that the thermal behaviour of the polymers is strongly dependent on the degree of substitution. Polymers containing more than 69% of mesogenic groups exhibit nematic‐type thermotropic liquid‐crystalline behaviour with schlieren textures. Below this limit, the polymers are amorphous. Polymers with a higher degree of substitution present the crystalline states. The phase transition temperatures increase and the mesomorphic temperature ranges widen with increasing degree of substitution. The clearing temperatures decrease as the spacer length increases. An odd–even effect in the clearing temperatures is observed and the odd members display the higher values.     

Side chain cholesteric liquid crystalline elastomers: synthesis and phase behaviour

A series of new side chain cholesteric liquid crystalline elastomers (P-2–P-6) containing the nematic crosslinking monomer 4-(10-undecen-1-yloyloxy)benzoyl-4′-allyloxybenzoyl-p-benzenediol bisate (M-1) and the cholesteric monomer 4-cholesteryl 4-(10-undecen-1-yloyloxy)benzoate (M-2) were synthesized. The chemical structures of the monomers and elastomers obtained were confirmed by FTIR and ¹H NMR spectroscopy. Their liquid crystalline properties and phase behaviour were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The effect of the crosslinking units on phase behaviour is discussed. Elastomers containing less than 20?mol?% of the crosslinking units showed elasticity, reversible phase transitions and cholesteric Grandjean texture. The experimental results demonstrated that the glass transition and isotropization temperatures of P-2–P-6 increased with the increasing concentration of crosslinking unit M-1.     

偶氮苯为探针的液晶聚合物聚集形态研究

利用紫外-可见光谱,对比研究了尾挂侧链液晶聚合物和腰挂侧链液晶聚合物在结晶相和液晶相转变过程中的液晶基元取向情况.研究表明,石英基材表面倾向于诱导偶氮液晶基元垂直于基材排列;观察到了在液晶态尾挂侧链液晶聚合物和腰挂侧链液晶聚合物的不同取向行为.在室温下重新结晶数天后,腰挂液晶聚合物的紫外可见光谱缓慢回复.     

Synthesis and crosslinking of biphenyl and naphthalene liquid‐crystalline polyethers with pendant full‐saturated and vinyl‐terminated aliphatic chains

Two series of vinyl‐terminated, side‐chain liquid‐crystalline polyethers containing 4,4′‐biphenyl and 2,6‐naphthalene moieties as mesogenic cores with several contents of vinyl crosslinkable groups were synthesized by chemically modifying poly(epichlorohydrin) with mixtures of saturated and vinyl‐terminated mesogenic acids. In most cases the degree of modification was over 90%. The polymers were characterized by chlorine analysis, IR and ¹H and ¹³C NMR spectroscopies, viscometry, size exclusion chromatography/multi‐angle laser light scattering, and thermogravimetric analysis. The liquid‐crystal behavior of all the synthesized polymers was examined by differential scanning calorimetry, polarized optical microscopy (POM), and X‐ray diffraction on mechanically oriented samples. The crosslinking of most polymers was done by peroxide‐type initiators, which generally led to liquid‐crystal elastomers. The mesophase organization was maintained on the crosslinked materials, as confirmed by POM and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3384–3399, 2003     

Mesomorphic properties of liquid crystalline polysiloxanes and elastomers based on a tri-vinyl crosslinker

A series of crosslinked liquid crystalline polymers and the corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization; their liquid crystalline properties were characterized by DSC, POM and X-ray measurements. The results show that the crosslinking obtained in the isotropic state leads to a reduction of the clearing point (T_c) of the crosslinked polymers, as compared with the corresponding uncrosslinked polymers. The crosslinked polymers with low crosslinking density (P₁-P₇) exhibit nematic mesogenic phases, as do the uncrosslinked polymers. In contrast, a high crosslinking density leads to the crosslinked polymers P₈ and P₉ losing their thermotropic liquid crystalline phases; they instead exhibit stress-induced orientation.     

Synthesis and crosslinking of vinyl‐terminated biphenyl and naphthalene liquid‐crystalline poly(epichlorohydrin) derivatives: Effect of nonmesogenic nonvinylic units on the mesogenic properties

Two series of vinyl‐terminated side‐chain liquid‐crystalline polyethers containing ethylene oxide or glycidyl aromatic carboxylates as spacers were synthesized. The mesogenic cores were 4,4′‐biphenyl or 2,6‐naphthalene moieties. The polymers were synthesized by chemically modifying poly(epichlorohydrin) or poly(epichlorohydrin)‐poly(ethylene oxide) with the corresponding mesogenic carboxylic acids or with mixtures of these acids and the nonmesogenic non‐crosslinkable analogous 4‐biphenyl‐ and 2‐naphthalenecarboxylic acids. In most cases the degree of modification achieved was higher than 90%. The polymers were characterized by chlorine analysis, IR, and ¹H and ¹³C NMR spectroscopies; viscosimetry; size exclusion chromatography; multi‐angle laser light scattering; and thermogravimetric analysis. The liquid‐crystal behavior, shown by most polymers, was examined by differential scanning calorimetry, polarized optical microscopy (POM), and X‐ray diffraction on mechanically oriented samples. The crosslinking of most polymers was done by peroxide‐type initiators that led to liquid‐crystal thermosets or elastomers. The freezing of the mesophase organization on the crosslinked materials was confirmed by POM and X‐ray diffraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3893–3908, 2002