Liquid crystalline lonomers. I. Main-chain liquid crystalline polymer containing pendant sulfonate groups

Liquid crystalline polymers containing sodium sulfonate groups pendant to the polymer backbone were synthesized by an interfacial condensation reaction of brilliant yellow, a sulfonate-containing monomer, with 4,4′-dihydroxy-α,α′-dimethyl benzalazine and a 50/50 mixture of sebacoyl and dodecanedioyl dichlorides. Polymers containing up to ca. 4 mol% brilliant yellow were characterized by elemental analysis and ultraviolet spectroscopy. The polymers were thermally stable to about 300°C, and they exhibited a broad nematic mesophase region of 70–100°C. The solution viscosity behavior in chloroform suggested that intramolecular associations of the sulfonate groups occurred at low polymer concentrations and intermolecular associations predominated at higher concentrations.     

Study on the thermotropic liquid crystalline polycarbonates. IV. Synthesis and properties of liquid crystalline poly(imide-carbonate)s

Two series of novel thermotropic liquid crystalline poly(imide-carbonate)s were prepared by melt polycondensation from various arylene or alkylene bis(phenylcarbonate)s by using N,N′-bis(hydroxyethyl)pyromellitimide and N,N′-bis(hydroxypropyl)pyromellitimide as monomers. Thermotropic liquid crystalline properties were characterized by a polarizing microscope with a heating stage and a differential scanning calorimeter (DSC). Nematic melts were found for the synthesized aromatic poly(imide-carbonate)s. In order to investigate whether the pyromellitimide unit could be used as a mesogenic unit for preparing LC polymers, a series of aliphatic poly(imide-carbonate)s was prepared in this study. However, no significant LC textures were found under the observation by polarizing microscope. It was suggested that the aspect ratio of the pyromellitimide unit was too short to form liquid crystalline poly(imide-carbonate)s. In addition, it was interesting that the aliphatic poly(imide-carbonate)s with a longer spacer (n = 3) in the pyromellitimide unit showed better crystallinity. Thermostabilities of all synthesized poly(imide-carbonate)s were measured by thermogravimetric analysis (TGA). © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of photochromic liquid‐crystalline copolymers containing both spironaphthoxazine and cholesteryl groups

Photochromic liquid‐crystalline copolymers consisting of a photochromic monomeric unit containing both a spironaphthoxazine group and an undecamethylene spacer, and a liquid‐crystalline monomeric unit containing both a cholesteryl group and a decamethylene spacer were prepared to investigate the effect of the thermal properties of the photochromic monomeric unit on the mesomorphic order of the side chain of the related copolymers. The photochromic liquid‐crystalline copolymers containing a photochromic liquid‐crystalline monomeric unit showed only a smectic phase. On the other hand, the photochromic liquid‐crystalline copolymers containing a photochromic non‐liquid‐crystalline monomeric unit showed a chiral nematic phase (cholesteric phase). The photochromic chiral nematic liquid‐crystalline copolymer containing 14 mol % photochromic monomeric unit reflected visible light around 104 °C. To lower the temperature range of reflection of visible light, cholesteryl oleyl carbonate was used as a chiral nematic plasticizer for the photochromic chiral liquid‐crystalline polymer systems. Photo‐induced pitch change of the mixture by means of UV irradiation was investigated and it was concluded that the pitch change observed under UV irradiation was mainly induced by thermal effect in the case of our system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 887–894, 2000     

主链型高分子液晶向列相向错观察的进展

综述了主链型高分子液晶向列相向错在实验观察方面的进展。从纹影织构的观察和展曲、弯曲弹性常数相等条件下的二维曲率弹性理论出发探讨了向错结构的几何特征。简要涉及了弹性常数不相等对向错的影响、向错核心的本质和反转墙的观察;给出了拓扑强度s高达4的高阶向错的实验观察结果;归纳出描绘向错周围指向矢场的主要实验方法:1)片晶装饰;2)条带织构装饰;3)表面微裂纹装饰。本文对上述方法进行了讨论和比较,列举了一些电子显微镜和光学显微镜照像的图例。     

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

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

Synthesis and mesomorphic properties of novel fishbone-like liquid crystalline polysilsesquioxanes VI. Fishbone-like,ester-based liquid crystalline polysilsesquioxanes

Two novel kinds of fishbone-like, ester-based, liquid crystalline, random copolysilsesquioxanes, LC₁-CH₃-P and LC₂-CH₃-P, have been synthesized for the first time by stepwise coupling polymerization (SCP) from trichlorosilane monomers (RSiCl₃) containing mesogenic ester groups, using three main steps including preaminolysis, hydrolysis and polycondensation. Two new monomers 4-(11-trichlorosilylundecloyloxy)phenyl 4-methoxybenzoate (M₁) and 4-(3-trichlorosilylpropoxy)phenyl 4-methoxybenzoate (M₂) have been synthesized by hydrosilylation reaction of trichlorosilane and the mesogens 4-n-undecenoyloxyphenyl 4-methoxybenzoate and 4-allyloxyphenyl 4-methoxy-benzoate, respectively, in the presence of dicyclopentadienylplatinum(II) chloride (Cp₂Ptcl₂) catalyst. The structures and mesomorphic properties of LC₁-CH₃-P and LC₂-CH₃-P were investigated by FTIR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, gel permeation chromatography, polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. It is proposed from the characterization data that these two polymers not only have an ordered ladder-like, double main chain, but also show thermotropic smectic behaviour with high clearing points and wide mesophase ranges (ΔT), which may hold promise for potential applications as highly stable gas chromatographic stationary phases.     

Synthesis and thermal transitions of a soluble,main chain,nematic liquid crystalline polymer exhibiting a kinetically trapped,disordered structure

An aromatic copolyester composed of 25 mol % phenyl hydroquinone, 10 mol % isophthalic acid, 40 mol % chloroterephthalic acid, and 25 mol % t-butyl hydroquinone (PICT) has been synthesized. This amorphous, glassy polymer is soluble in common organic solvents such as methylene chloride. Thin, solution-cast films may be prepared which are in a metastable, vitrified, optically isotropic state. On first heating of an isotropic film at 20°C/min in a calorimeter, one glass transition is observed at low temperature (approximately 49°C) and is ascribed to the glass/rubber transition of the metastable, isotropic polymer. This thermal event is followed by a small exotherm due to the development of order during the scan, which results in a second T_g at approximately 125°C. This T_g is associated with the glass/rubber transition of the ordered polymer. Nematic order can be developed by thermal annealing. The lower T_g increases toward the upper T_g as annealing time is increased. For an initially isotropic film annealed at 90°C, the increase of the lower T_g with annealing time and the increase in birefringence observed by optical microscopy are governed by similar kinetics. Isotropization occurs in the temperature range of 250–300°C. The nematic polymer is slightly more dense than its isotropic analog. No detectable differences between isotropic and nematic samples were observed in rotating frame proton spin lattice relaxation times. © 1996 John Wiley & Sons, Inc.     

Highly stable rigid main‐chain nonlinear optical polymers with nematic phase: Effect of liquid‐crystalline phase on nonlinear optical response

Nonlinear optical (NLO) rigid main‐chain polyesters containing azobenzene mesogens with high thermal and temporal stabilities were synthesized from derivatives of hydroxyphenylazobenzoic acid. The NLO properties of the homopolymer, poly[4‐(4‐hydroxy‐3‐methyl phenyl)azo]benzoic acid, and copolymers of 4‐[(4‐hydroxy‐3‐methylphenyl)azo]benzoic acid, 4‐[(4‐hydroxy‐2‐methylphenyl)azo]benzoic acid, and 4‐[(4‐hydroxy‐2‐pentadecyl phenyl)azo]benzoic acid (PSCpHBA) with p‐HBA were measured by the Maker fringe technique. The thermal and liquid‐crystalline (LC) phase behaviors of the polymers were examined by differential scanning calorimetry, a thermal‐stimulated polarization current, and polarized light microscopy. The polymers except PSCpHBA exhibited nematic‐threaded and Schlieren textures. The LC orientations give rise to an enhanced NLO response. The polymers had high thermal and temporal stabilities for second‐harmonic generation activity because of their rigid aromatic backbone. This study suggests that the rigid aromatic main chain exhibiting an LC phase is a promising simple method to synthesize highly stable NLO polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1527–1535, 2003     

Synthesis and properties of reactive liquid crystal monomers and side-chain liquid crystalline polymers

Two nematic liquid crystal (LC) monomers containing double bonds in the side chain were designed and synthesised. Length of the side groups varied from 1 to 2 methylene units. The side-chain polymers were synthesised by hydrosilylation reaction. The molecular structures of the intermediates and the LC monomers were characterised by Fourier transform infrared, elemental analysis and nuclear magnetic resonance spectroscopy. The thermal phase behaviour of the monomers and polymers were investigated by differential scanning calorimetry and polar optical microscopy coupled with hot stage. The LC monomers showed only one nematic mesophase in the cooling process. And, the two polymers exhibit an enantiotroppic nematic mesophase either in the heating or in the cooling process.     

侧基甲壳效应和甲壳型液晶高分子

侧链液晶高分子体系里,液晶基元可以通过尾接或腰接的方式与主链相连.一般认为,在液晶基元与主链间插入一段长度合适的＂柔性间隔基＂可有效实现主、侧链间的动力学去偶合,从而有利于侧基液晶基元之间的有序排列.作为一类特殊的腰接型侧链液晶高分子,甲壳型液晶高分子中体积较大的侧基（如棒状液晶基元）通过非常短的间隔基或仅通过一个碳-碳键直接横挂至主链上,这导致了强烈的甲壳效应,使得主链被迫伸展.因此,可从与＂柔性间隔基＂完全不同的角度出发,充分利用主链和侧基间的偶合作用,设计甲壳型液晶高分子.本文综述了腰接型侧链液晶高分子中的侧基甲壳效应、甲壳型液晶高分子中由主链与侧基相互作用所导致的特殊构象以及液晶相结构.研究表明,侧基甲壳效应在调控甲壳型液晶高分子的形状、尺寸以及螺旋结构等方面有重要作用.甲壳型液晶高分子可作为刚-柔嵌段共聚物的刚性链段,也可作为主/侧链结合型液晶高分子的主链部分参与到多层次分级超分子有序结构的构筑之中.     

Main-chain biodegradable liquid crystal derived from cholesteryl derivative end-capped poly(trimethylene carbonate): synthesis and characterisation

Main-chain biodegradable liquid crystal derived from cholesteryl derivative end-capped poly(trimethylene carbonate) was investigated. The novel liquid crystal was synthesised via ring-opening polymerisation of trimethylene carbonate initiated by cholesteryl derivative with an alkyl spacer and end primary hydroxyl group, without any catalyst. The chemical structure of resulting polymers was verified by ¹H NMR. Liquid crystalline properties were validated by X-ray diffraction, differential scanning calorimetry, and polarising optical microscopy. The results showed that all the synthesised polymers Chol-(CH₂)₂-(TMC)_n exhibited mesomorphism in particular temperature ranges because of the introduction of the cholesteryl derivative moiety.     

Columnar phases of achiral vanadyl liquid crystalline complexes

Two liquid crystalline vanadyl complexes have been studied by frequency domain dielectric spectroscopy over the range 10 mHz to 13 MHz. The materials exhibit two or three columnar phases denoted Col_ro, Col_rd, and Col_hd that were identified by X-ray diffraction. In the higher temperature Col_rd phase, a relaxation process in the kHz range is observed that is attributed to the reorientation about the molecular short axis. A pronounced dielectric relaxation process shows up in the low temperature Col_ro phase at hertz and sub-hertz frequencies. This slow relaxation is assigned to reorientation of the molecular dipoles within the polar linear chains, which are aligned along the column's axis. Triangular wave switching studies at low frequency reveal processes inside the Col_ro phase which are most probably due to ionic/charges relaxations but a ferroelectric switching for an achiral discotic system cannot be ruled out completely. Below the Col_ro phase there is an orientationally disordered crystalline Cr_x phase with disordered side chain dipoles. A dielectric relaxation process connected with the intramolecular relaxation of the alkoxy side chains, similar to the beta-process of polymers, has been found in the lower temperature Cr_x phase.     

Synthesis,characterization and properties of N‐maleimide side‐chain liquid crystalline copolymers

A homologous series of side‐chain liquid crystalline (SCLC) poly{[N‐[10‐((4‐(((4′‐n‐hexyloxy)benzoyl)oxy)phenoxy)carbonyl)‐n‐decyl]maleimide]‐co‐[N‐(n‐octadecyl)maleimide]} [(ME6)‐co‐(MI‐18)] random copolymers with various MI‐18 contents have been synthesized and their properties studied. The high content in threo‐disyndiotactic sequences of the maleimide main chain seems responsible for the stability of the highly ordered smectic mesophase. The relationship between structure and composition on thermotropic mesophase was investigated by polarizing optical microscopy, differential scanning calorimetry, and X‐ray diffraction. For copolymers with mesogenic unit contents less than ～0.655 molar fraction the transition from (S_A) texture to isotropic (I) is maintained, as shown by the T_Cl, ΔH_Cl and ΔS_Cl amounts and intermolecular spacing 4.42–4.53 Å and intralayer correlation lengths of 44.2–45.2 Å. The layer thickness does not appreciably depend on copolymer composition. However, copolymers with non‐mesogenic comonomer MI‐18 molar contents larger than >0.655 molar fraction X(M), are no longer liquid crystalline materials, despite its packing is preserved without any detectable appearance of birefringence. Thermodynamic boundaries of the liquid crystalline state have been established through a phase diagram. The properties of this n‐hexyloxy pendant group‐based series are compared to those of the analogous materials containing methoxy pendant groups (ME1), and differences are accounted for in terms of the local side‐chain packing within the mesophase. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Heterocyclic pyridine-based liquid crystals: synthesis and mesomorphic properties

A series of new calamitic liquid crystals, 4-{[(pyridin-4-yl)methylidene]amino}phenyl 4-alkoxybenzoates comprising a heterocyclic (pyridine) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were synthesised and characterised. This series consists of nine members wherein the members differ by the length of alkoxy chain (C_nH_2n+1O–, where n = 2, 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviours were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first three members of the series (n = 2, 4 and 6). As the alkoxy chain increased to n = 8 and n = 10, the nematic phase appeared together with an additional smectic A (SmA) phase. When moving from n = 12 until the highest members (n = 18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA).     

Thermal expansion of liquid crystalline amphiphilic di-block copolymer observed by simultaneous DSC-XRD

Phase transition process of PEO_m-b-PMA(Az)_n was investigated by the simultaneous DSC-XRD measurement using the synchrotron radiation facility. Four endothermic DSC peaks were observed during heating process. These DSC peaks were assigned to the melting of PEO, the transition from SmX, which is a mixture of super-cooled SmC and crystal, to SmC, from SmC to SmA, and from SmA to isotropic liquid state as determined by XRD profiles. In SmC phase, the liner expansion coefficient calculated from the spacing variation of the smectic layer distance was larger than that of the other phases. This result reflected the fact azobenzene moieties in the long-side chains of PMA(Az)_n forming the smectic layers and then they were tilted and stood up during the heating process.     

Tailoring the liquid crystalline property via controlling the generation of dendronized polymers containing azobenzene mesogen

The first‐ and second‐generation dendronized polymers containing azobenzene mesogen were designed and successfully synthesized via free radical polymerization. The chemical structures of the monomers were confirmed by elemental analysis, ¹H NMR, and ¹³C NMR. The molecular characterizations of the polymers were performed with ¹H NMR and gel permeation chromatography. The phase structures and transition behaviors were studied using differential scanning calorimetry, polarized light microscopy, and small‐angle X‐ray scatter experiments. The experiment results revealed that the first‐generation dendronized polymer exhibited liquid crystalline behavior of the conventional side‐chain liquid crystalline polymer with azobenzene mesogen, that is, the polymer exhibited smectic phase structure at lower temperature and nematic phase structure at higher temperature. However, the second‐generation dendronized polymers exhibited more versatile intriguing liquid crystalline structures, namely smectic phase structure at lower temperature and columnar nematic phase structure at higher temperature, and moreover, the phase structure still remained before the decomposition temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1149–1159, 2010     

Synthesis of novel (-)-menthol-based azobenzene chiral liquid crystals and effect of terminal alkyl chains on mesomorphic behaviour

ABSTRACT

A series of novel azobenzene chiral liquid crystals (Mt4AZOnB) containing (-)-menthyl were successfully synthesised. Terminal alkyl chains of the molecules varied from methyl to hexyl. The chemical structures were characterised by Fourier transform infrared and ¹H-NMR spectra. Liquid crystalline behaviour of the chiral liquid crystals was characterised by differential scanning calorimetry and polarising optical microscopy. The effect of terminal alkyl chains on mesomorphic and photoisomerisation behaviour of azobenzene-based liquid crystals is discussed. The lower members (n = 1, 2, 3, 4) are monotropic and only the higher members (n = 5, 6) show enantiotropic behaviour. These compounds show a distinct odd-even effect for the phase transition temperature when the parity of the terminal chain is varied.     

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.     

Synthesis,mesomorphic behaviour and optoelectronic properties of phosphorus-based thermotropic liquid crystalline dendrimers

A new series of thermotropic phosphorus-based liquid crystalline (LC) dendrimers based on a thiophosphoryl-phenoxymethyl(methylhydrazono) core (thiophosphoryl-PMMH) up to the fifth generation has been synthesised by solution condensation of aldehyde groups, surface-functionalised thiophosphoryl-PMMH dendritic substrates of generation numbers G_0.5 to G_5.5, with the appropriate molar equivalents of the pro-mesogenic n-hexadecylaniline mono-functional building block. Their chemical composition has been confirmed by ¹H/¹³C/³¹P nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis. Optical properties have been studied by ultraviolet-visible absorption, photoluminescence spectroscopy and polarised optical microscopy, and thermal characteristics by differential scanning calorimetry. Electrical studies have been made using the current-voltage characteristics of organic light-emitting diodes consisting of multi-layered indium tin oxide/dendrimer/aluminium tris(8-hydroxyquinoline)Al architecture. It has been demonstrated that the molecular engineering approach adopted can successfully lead to phosphorus-containing dendritic organic semiconductors (OSCs) which show tunable mesomorphic behaviour (extension of the observed smectic mesophase) and (opto) electronic properties, owing to their peripheral decoration with a tunable number of azomethine-based optically active chromophoric units. This rare combination of ‘tunable by design’ properties makes this series of thermostable thiophosphoryl-PMMH-based LC dendrimers a particularly appealing class of OSCs for use in optically and/or electronically active layers of (opto)electronic devices such as light-emitting diodes, field-effect transistors, solar cells and lasers.