刚柔相嵌液晶高分子的赝二级相变温度

讨论了刚柔相嵌液晶高分子的向列相－各向同性相转变与其分子结构的关系，给出了该一级相变的赝二级相变温度Ｔ与这类液晶高分子的液晶基元和间隔基的长度，柔顺性（相关长度）以及它们之间的相互作用的关系的解析表示式，分析了液晶基元与间隔基连接处的表观弯曲（接口效应）对Ｔ的影响，文中的结论与实验相符。     

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.     

近晶C(Sc)相串型液晶高分子的合成与表征

以２，５ 二（对烷氧基苯甲酰氧基） 对苯二酚和不同结构的脂族二酰氯为单体，采用低温溶液缩聚的方法，合成了一系列新的液晶基元垂直于分子主链的Ｓｃ相串型液晶高分子．单体的结构通过元素分析、ＩＲ、１Ｈ ＮＭＲ和ＭＳ等方法确证．聚合物通过ＧＰＣ、ＤＳＣ、ＴＧ、ＷＡＸＤ和偏光显微镜等方法测试表征．研究发现，所有的聚合物加热至各自的熔点以上都能形成液晶态，在液晶态可以观察到纹影或焦锥织构．通过变温Ｘ 射线衍射证明它们为Ｓｃ相．所有聚合物的熔点（Ｔｍ）和液晶态的清亮点（Ｔ１）随分子中末端烷氧基增大和柔性间隔段长度增加逐渐降低，液晶态温度范围变窄．     

一系列含T-型二维液晶基元的液晶高分子配体的合成

以４,４′ （α,ω 亚烷基二酰氧）二苯甲酰氯和２,４ 二羟基 ４′ 烷氧基偶氮苯为单体,通过溶液聚合,合成了一系列新的含Ｔ 型二维液晶基元的液晶高分子配体．单体的结构通过元素分析、ＩＲ、１Ｈ ＮＭＲ和ＭＳ等方法确证．高分子配体通过ＧＰＣ、ＤＳＣ、ＴＧ、ＷＡＸＤ和偏光显微镜等方法测试表征,发现所有的高分子配体加热至各自的熔点以上都能形成液晶态,在液晶态可以观察到向列型的丝状织构和纹影织构．它们的熔点（Ｔｍ）和液晶态的清亮点（Ｔｉ）随分子中末端烷氧基增大和柔性间隔段长度增加呈规律性变化．特别值得一提的是,发现末端不含取代基的高分子配体也能产生液晶态,这对该类高分子液晶态生成的机制与液晶态的织构提供了一个新的研究课题［１］．     

含不同柔性链的(甲基)丙烯酸酯类液晶高分子的合成及其液晶行为研究

通过改变侧链中柔性间隔基的长度,合成了一系列含有两个手性中心的侧链液晶（甲基）丙烯酸酯类聚合物.红外、核磁和GPC表征各中间体、单体及聚合物的结构和分子量.通过DSC和热台偏光显微镜系统地研究了单体和聚合物的液晶态织构.结果表明,含有六个碳的柔性间隔基的丙烯酸酯类聚合物表现为近晶SA和手性近晶SC^＊液晶相.     

侧链聚硅氧烷液晶高分子的合成与表征及应用研究

液晶高分子既具有独特的液晶性 ,又具有高分子的良好材料性能 ,引起了人们的广泛注意[1～ 9] .侧链液晶高分子大多可以作为功能材料 ,对它们的研究有很大的理论与现实意义 .以往报道的此类化合物的介晶基元大多是通过烷氧基与间隔基相连[10 ] .我们以催化活性很高的铂络和物为催化剂 ,通过硅氢加成反应制备了间隔基与介晶基元通过酰氧基相连的两种侧链聚硅氧烷液晶高分子 ,并对它们的性质进行了初步表征 .发现它们具有很好的液晶性 .已有研究表明侧链聚硅氧烷液晶在气相色谱分离结构近似的物质方面 ,具有易涂渍、选择性及热稳定性优于低分子…     

含聚乙二醇柔性间隔段的主链型液晶聚酯的合成

分子结构与液晶行为间的关系是液晶性高分子物理问题研究的核心,通常的液晶性高分子中除液晶性基元外还引入一些相对来说很柔顺的链段,称作柔性间隔段．这是因为人们认识到高分子的液晶行为不只决定于液晶性基元的结构,也受到这些基元间以及基元和间隔段间相互作用的影...     

热致型光敏液晶高分子在液晶场中光交联反应的研究

研究了具有肉桂酸酯侧链基的热致型液晶高分子的光交联行为．结果表明，在２０ｍｉｎ紫外光照射的条件下，形成液晶相的液晶高分子膜的光交联凝胶百分率要明显高于尚未形成液晶相的同种高分子膜．对形成液晶相的高分子膜，在环境温度低于液晶各向同性温度Ｔ时，温度对光交联凝胶百分率的影响甚微．这表明，由于液晶高分子中致介单元的聚集和有序排列形成的微区结构也影响了大分子链侧基肉桂酸酯的聚集状态．从而使其光化学性质发生变化．     

单取代侧链液晶聚炔的相结构

侧链液晶聚炔由于具有潜在的导电性能和液晶性能而得到越来越多的关注。本文综述了单取代侧链液晶聚炔主链的立体构型与构象及形成的柱状相结构、近晶相、溶致液晶相及外场中形成的相结构。旨在介绍主链构象、间隔基长度、液晶基元的结构和尾链长度等因素对其相结构的影响。     

聚甲基丙烯酸-对-甲氧基偶氮苯烷氧基酯的合成及柔性间隔基对液晶行为的影响

通过甲基丙烯酸钾盐与溴化物的反应合成了一系列柔性间隔基长度不同的甲基丙烯酸 对 甲氧基偶氮苯烷氧基酯（ＰＭＡＡＺＯｎ,ｎ＝２,３,４,５,６）,然后聚合成相应的聚合物．用１Ｈ ＮＭＲ和ＩＲ表征了聚合物的结构,ＧＰＣ测定了分子量,ＤＳＣ和偏光显微镜观测了液晶高分子的相行为和织构．研究了间隔基长度对织构、相变和热力学性质的影响,观测到聚合物的ＴＮＩ随间隔基的长度变化表现出的奇偶效应．     

含X-型和棒型两种液晶基元的主链型系列芳族共聚酯的研究

采用含X-型和棒型液晶基元的两种不同单体,通过改变X-型液晶基元单体的结构和柔性链段长度,经高温溶液缩聚,合成了一系列主链型共聚液晶高分子.研究发现,所有样品都具有很好的热致液晶性及宽广的液晶态温度范围.随单体结构改变,共聚物的相转变温度大致呈规律性变化.     

Mesogenic behaviour of p-nitrophenyl group linked with biphenyl mesogens via flexible spacers

Three series of nematogens with a terminal p-nitrophenyl group linked with biphenyl groups via flexible spacers were synthesised and their transitional properties were studied by means of differential scanning calorimetry (DSC) and polarising microscopy (POM). The nematic–isotropic transition temperature and the associated entropy change showed an odd–even effect as the length of the spacers was varied, in which the even members exhibited higher values. Such an odd–even effect was in consistency with the feature of liquid crystal dimers and trimers. On the basis of these data, it seemed reasonable to assume that the terminal p-nitrophenyl group played a role of mesogen in the nematic liquid crystal. The p-nitrophenyl group may work as a mesogen as a result of the interaction with the biphenyl mesogens. The mesogenic behaviour of the terminal p-nitrophenyl group is explained on the basis of neighbouring group effect.     

主链具有X-型液晶基元的液晶高分子系列的合成与研究

以低温溶液缩聚方法,合成了一系列主链上具有X-型液晶基元的液晶高分子。所有聚合物样品均具有明显的热致液晶性。不同柔性链段长度和取代基对聚合物的液晶性呈规律性的影响。并用IR、H-NMR、WAXD和热台偏光显微镜等方法对聚合物进行了表征。     

To be or not to be – nematic liquid crystals from shape-persistent V-shaped nematogens with the ‘magic angle’

The tetrahedral bending angle in V-shaped nematogens was claimed to be the optimum for finding a biaxial nematic liquid crystal phase. The benzo[1,2-b:4,3-b’]dithiophene core, recently successfully applied as a tetrahedral bending unit in mesogens with lateral flexible chains, is here embedded in a scaffold with only terminal chains, which conventionally promotes the formation of nematic phases at low temperature. A series of new mesogens has been successfully prepared, realising hockey-stick, hockey-stick dimer and V-shaped molecular topologies. Only the hockey-stick mesogens assemble in uniaxial nematic phases over a broad temperature range. Single crystal structure analysis of a hockey-stick and V-shaped compound reveal remarkable similarities with the benzodithiophene core wrapped by aliphatic chains. A model explaining the absence of nematic mesophases in the family of V-shaped, shape-persistent mesogens with terminal aliphatic chains is presented and results in the proposal of a new design for biaxial nematogens.     

MOLECULAR FIELD THEORY FOR NEMATIC LIQUID CRYSTAL POLYMER COMPRISING FLEXIBLE SPACER

Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes account of orientational correlation among all mesogens in a polymer chain and the relationship between the intramolecular orientation and spatial orientation of the mesogens. The free energy, temperature and entropy of the nematic-isotropic transition were determined with the theory and compared with experiments in current work. It was found that many unique transition properties of the MC-LCPs comprising flexible spacer are correctly predicted by the theory and the agreement of the theory with the experiments is impressive.     

含X-型和棒型两种液晶基元的主链型系列芳族共聚酯的研究

 采用含X-型和棒型液晶基元的两种不同单体,通过改变X-型液晶基元单体的结构和柔性链段长度,经高温溶液缩聚,合成了一系列主链型共聚液晶高分子.研究发现,所有样品都具有很好的热致液晶性及宽广的液晶态温度范围.随单体结构改变,共聚物的相转变温度大致呈规律性变化.     

Shear-Induced Order in Nematic Polymers

Several nematic side-chain polysiloxanes with the same backbone and the same mesogens but containing various ratios of two spacers having different lengths were prepared. Within this series of homo- and copolymers, the phase behavior changes continuously from purely nematic for the homopolymer containing only the shorter of the two spacers to nematic plus smectic for the homopolymer containing only the longer spacer. The flow behavior determined by in situ deuterium NMR spectroscopy under shear and the anisotropy of the coil conformation measured by small angle neutron scattering exhibit a continuous change as well.     

Symmetrical and asymmetrical liquid crystal dimers: synthesis,characterisation and mesomorphic behaviour

ABSTRACT

A series of new asymmetrical liquid crystal dimers, R_nO–S2O–OR_n (n = 2–10), linked by an ethylene spacer having carbothiol – COS – and carboxyl – COO – linkages to the core centre of the molecule and bearing different lengths of terminal alkoxy chains were synthesised in order to study the effects of the length of the terminal alkoxy chains on mesomorphic properties. As well as, five symmetrical and asymmetrical dimers linked by butylene spacers bearing different linkages to the core and various terminal chains were also synthesized in order to study the effect of the nature of the spacer and terminal groups. The structures of the synthesised dimers were confirmed by physico-chemical techniques, i.e. FTIR, NMR and mass spectra. Differential scanning calorimetry and polarising optical microscopy verified the liquid crystal behaviour transition temperatures. The isotropic transition temperatures of the dimers R_nO–S2O–OR_n (n = 2–10) decreased with increasing length of alkoxy chain. Structural effects on the mesomorphic and physical properties were investigated in terms of alteration of carboxylate and thioester groups linking the spacer. The mesomorphic investigation reveals that all the dimers formed an enantiotropic Nematic phase except for dimer HO2SH which is not a liquid crystal.     

Effect of the dimeric H-bonded mesogens of chiral acids on the mesogenic and optical properties

A serial of chiral aromatic acid derivatives was systematically prepared to study the effect of dimeric H-bonded mesogens on liquid crystal (LC) and optical behaviours. The lateral fluoro-substituent and the chiral terminal chains were also studied for comparison. When the H-bonded mesogens changed from biphenyl or phenyl benzoate to naphthalene ring or benzene ring, the molecular length?width ratio reduced greatly, which thus led the temperature range of mesophases reduced and the phase transition decreased. The lateral fluoro-substituent, a shorter or meta-substituted terminal chain, could make the mesophase range narrowed or disappeared. Besides the chiral nematic (N*) phase, twist grain boundary C (TGBC*) phase was found in the double aromatic-ring acids with a chiral para-substituted octan-2-yloxyl group. Interestingly, the TGBC* phase could scatter away most incident light in any surface anchoring condition, and the light scattering performance exceeded any other phases of low-molecular-weight LCs known. The unusual H-boned material could be used for preparing reversible optical switches without using any polariser and any surface alignment treatment.