含硝基偶氮苯侧基的丙烯酸酯液晶聚合物的合成、结构与性质研究(Ⅲ)——分子结构对结晶的影响

以含硝基偶氮苯侧基的丙烯酸酯液晶聚合物为研究对象,利用DSC、WAXD、偏光显微镜等手段研究了分子结构对侧链液晶聚合物结晶行为的影响.结果表明:丙烯酸酯类液晶聚合物的晶区是由介晶基团的规整排列形成的,大分子主链和柔性间隔基不参与结晶.随着柔性间隔基长度的增加,晶区分子排列有序性提高,结晶度增大;非晶共聚组分MA含量的增加,限制了介晶基团的有序排列,当MA含量超过83％后,只得到非晶共聚物.     

含1,3,4-噁二唑甲壳型液晶聚合物的合成与表征

甲壳型液晶聚合物（mesogen-jacketed liquid crystal polymer,MJLCP）是1987年由周其凤教授[1]首先提出的概念.从化学结构看,甲壳型液晶聚合物属于侧链型,由烯类单体经链式聚合制得,容易得到高分子量的产物,具有一般柔性侧链型液晶聚合物的一些优点.但是与柔性侧链型液晶聚合物不同的是,MJLCP分子中的刚性液晶基元是通过腰部或重心位置与主链相联结的,在主链与刚性液晶基元的侧基之间只有很短或者没有柔性间隔基.由于在这类液晶聚合物的分子主链周围空间内刚性液晶基元的密度很高,分子主链被由液晶基元形成的外壳所包裹并被迫采取相对伸直的刚性链构象.因此,这类液晶聚合物又和主链型刚性链液晶聚合物相似,具有较明显的链刚性.近年来,周其凤课题组围绕甲壳型液晶聚合物深入开展了分子设计与合成、分子结构与性能等多方面的研究.其中,设计合成具有特定功能的甲壳型液晶聚合物是在以往研究工作和学科交叉融合的基础上发展起来的一项新的研究工作.将一些有特殊功能的基团引入到甲壳型液晶聚合物中会使其具有崭新的特性.     

含硝基偶氮苯侧基的丙烯酸酯液晶聚合物的合成,结构与性…

以含硝基偶氮苯侧基的丙烯酸酯液晶聚合物为研究对象，利用ＤＳＣ、ＷＡＸＤ、偏光显微镜等手段研究了分子结构对侧链液晶聚合物结晶行为的影响。结果表明：丙烯酸酯类液晶聚合物的晶区是由介晶基团的规整排列形成的，大分子主链和柔性间隔基不参与结晶。随着柔性间隔基长度的增加，晶区分子排列有序性提高，结果度增大；非晶共聚组分ＭＡ含量的增加，限制了介晶基团的有序排列，当ＭＡ含量超过８３％后，只得到非晶共聚物。     

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.     

含有联苯和肉桂酸酯基团的侧链液晶共聚物的合成与表征

合成了两种含有联苯刚性基元的甲基丙烯酸酯单体M1和M2,其中M1为含有可光交联的肉桂酸酯端基的单体.通过溶液自由基聚合,得到一系列含不同比例M1和M2单体单元的聚丙烯酸酯类侧链液晶共聚物.采用1H-NMR、FT-IR等方法对单体和聚合物的结构进行了详细表征.用示差扫描量热法、偏光显微镜以及广角和小角X-射线衍射对单体和聚合物的液晶性进行了研究.结果表明,末端为肉桂酸酯基团的单体M1无液晶性,其均聚物P1有微弱的液晶性,而端基为正丁基的单体M2及其均聚物P9则表现出近晶相液晶行为.共聚物P2~P5均为向列型液晶,P6~P9则为近晶型液晶.随在聚合物中M2单体含量的增加,共聚物的玻璃化转变温度、熔点及清亮点温度均呈现增加趋势.     

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。     

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。     

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.     

含偶氮基团的聚丙烯酸酯型功能侧链液晶高分子的性能及其应用前景

综述了基于具光致双折射和光存储性质的偶氮功能基团的新型功能性侧链液晶聚丙烯酸酯的液晶性质、光电性质及应用前景.指出该类聚合物是一类非常重要的非线性光学材料 ,一般显示热致性向列型或近晶型液晶相, 液晶相转变温度和液晶态温度范围随链结构的不同发生显著变化,具有较短的电场及光场响应时间.此类材料在不断开发研究下可望用作长久的高对比度的光学信息储存材料.     

基团转移聚合制备侧链型联苯液晶高分子的研究

<正> 由具有刚性介晶结构同时又具有双键的单体进行加聚反应,是制备侧链型液晶高分子最方便的方法。大多采用甲基丙烯酸酯或丙烯酸酯类,聚合后形成乙烯型柔性主链,同时侧链上又带有刚性介晶相结构单元。以联苯类作为介晶相的液晶,由于具有稳定性好的优点,是目前应用得最广泛的一种液晶材料。Maganini用自由基聚合的方法进行了侧链型联苯液晶高分子的合成和研究。基团转移聚合作为一种新的加聚方式,为丙     

Polymer nanostructure development of fluorinated and aliphatic monoacrylates in smectic liquid crystals via photopolymerization

To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase.     

Polymer nanostructure development of fluorinated and aliphatic monoacrylates in smectic liquid crystals via photopolymerization

To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase.     

Synthesis and characterization of side chain liquid crystalline polymers exhibiting cholesteric and blue phases

A series of cyclosiloxane-based cholesteric liquid crystalline (LC) polymers were synthesized from a cholesteric LC monomer cholest-5-en-3-yl(3β) 4-(2-propenyloxy)benzoate and a nematic LC monomer butyl 4-[4-(2-propenyloxy)benzoxy]benzoate. All the polymers exhibit thermotropic LC properties and show cholesteric phases. Most of the polymers display four types of phase transition behaviour corresponding to glass transition, melting point, cholesteric phase-blue phase transition and clearing point. The mesophase temperature range of the blue phases are as broad as 20°C. The blue phase was confirmed by the apperance of planar textures and cubic packings. With an increase of non-chiral component in the polymers, the clearing point decreases slightly, while the glass transition and melting temperatures change little. In the reflection spectra of the polymer series the reflected wavelength broadens and shifts to longer wavelength with increase of the non-chiral component in the polymer systems, suggesting that the helical pitch P lengthens.     

Morphological studies of a hydrogen-bonded LC polymer obtained by photopolymerization in LC solvents

Anisotropic morphologies and the phase behaviour of a hydrogen-bonded LC polymer obtained by photopolymerization in two kinds of LC solvent are discussed. The hydrogen-bonded LC monomer, 4-(6-acryloyloxyhexyloxy) benzoic acid (A6OBA), was photopolymerized in 4-cyano-4′-hexyloxybiphenyl (6OCB) and in 4-cyano-4′-undecyloxybiphenyl (11OCB), which show a nematic phase and a smectic A phase, respectively. After photo-polymerization, the LC media were removed by extraction and the pure polymer was observed by scanning electron microscopy. SEM images showed that the polymer possessed fibrous morphology with a fibre diameter of a few micrometers, based on polymerization-induced phase separation. The overall geometries reflected typical LC characteristics such as schlieren and focal-conic fan textures. It was found that the hydrogen bond between benzoic acid groups in the monomer was rigid enough to fix the anisotropic phase-separated structure forming during the early stage of phase separation; however, it could not permanently maintain the fibre structure due to dissociation at elevated temperature. X-ray measurements revealed that a well developed layer structure of the hydrogen-bonded mesogen existed in the polymer obtained from the smectic phase of 11OCB, whereas a polymer layer structure could develop only partially from the nematic phase of 6OCB.     

Morphological studies of a hydrogen-bonded LC polymer obtained by photopolymerization in LC solvents

Anisotropic morphologies and the phase behaviour of a hydrogen-bonded LC polymer obtained by photopolymerization in two kinds of LC solvent are discussed. The hydrogen-bonded LC monomer, 4-(6-acryloyloxyhexyloxy) benzoic acid (A6OBA), was photopolymerized in 4-cyano-4'-hexyloxybiphenyl (6OCB) and in 4-cyano-4'-undecyloxybiphenyl (11OCB), which show a nematic phase and a smectic A phase, respectively. After photo-polymerization, the LC media were removed by extraction and the pure polymer was observed by scanning electron microscopy. SEM images showed that the polymer possessed fibrous morphology with a fibre diameter of a few micrometers, based on polymerization-induced phase separation. The overall geometries reflected typical LC characteristics such as schlieren and focal-conic fan textures. It was found that the hydrogen bond between benzoic acid groups in the monomer was rigid enough to fix the anisotropic phase-separated structure forming during the early stage of phase separation; however, it could not permanently maintain the fibre structure due to dissociation at elevated temperature. X-ray measurements revealed that a well developed layer structure of the hydrogen-bonded mesogen existed in the polymer obtained from the smectic phase of 11OCB, whereas a polymer layer structure could develop only partially from the nematic phase of 6OCB.     

Phase behaviour and electro-optic characteristics of a polymer stabilized ferroelectric liquid crystal

The effects of adding a diacrylate monomer or its polymerized network to a ferroelectric liquid crystal have been characterized. The monomer lowers the temperatures of transition to the more ordered phases, whereas the polymer network phase separates into polymer rich and LC rich phases and has little effect on the LC phase behaviour. Ferroelectric polarization decreases comparably in both monomer and networked systems. As the network concentration increases, the size of LC domains decreases considerably. With low concentrations of polymer and, thus large LC domains, optical response and tilt angle remain fairly independent of polymer concentration, but as the polymer concentration increases, switching speed and tilt angle decrease dramatically. Polymerization rate maxima increase with monomer concentration until saturation of monomer in the liquid crystal is reached. The rate maxima then decrease as monomer must diffuse from monomer rich droplets. Double bond conversion during the polymerization is comparable for all monomer concentrations below 50 per cent.     

Size control of phase‐separated liquid crystal droplets in a polymer matrix based on the phase diagram

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Effect of external electrical field on phase behavior and morphology development of polymer dispersed liquid crystal

Phase diagrams for mixtures of liquid crystal (LC)/monomer with and without an external electrical field applied have been established using polarized light microscope (PLM).The (isotropic + nematic) coexistent phase region and (isotropic + isotropic) phase boundary of LC/monomer mixtures were observed to shift upward to higher temperatures when the external electrical field exists. It was found that the electrical field applied during the cross-linking polymerization has a significant influence on the phase diagrams for the LC/polymer mixtures by rendering the coexistent phase regions shift upward to higher temperatures. The influence of the external electrical field on the processes of the isotropic-isotropic phase separation and liquid crystal ordering in PDLC formation has also been investigated. The results revealed that both the processes could be highly accelerated by the electrical field.     

Effect of chiral isosorbide groups on mesomorphic properties of side-chain liquid-crystalline polysiloxanes

Chiral side-chain liquid-crystalline (LC) polysiloxanes containing isosorbide groups were graft copolymerised with poly(methylhydrogeno)siloxane, a chiral LC monomer 6-(4-methoxy-benzoyloxy)-hexahydro-furo[3,2-b]furan-3-yl 4'-(4-undec-10-enoyloxy-benzoyloxy)-biphenyl-4-yl adipate and a nematic LC monomer 4'-(4-methoxy-benzoyloxy)-biphenyl-4-yl 4-(2-undec-10-enoyloxy-ethoxy)-benzoate. The chemical structures and LC properties of the monomers and polymers were characterised by use of various experimental techniques including Fourier transform infrared spectroscopy (FTIR), ¹H-nuclear magnetic resonance (NMR), element analyses (EA), differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD). All the chiral LC polymers showed LC properties with very wide mesophase temperature ranges and the chiral component in the LC polymer systems lead to the appearance of a cholesteric phase. The polymers bearing most chiral LC monomer component showed smectic phases by reason of regular structures in the polymer systems. With the increase of another nematic LC monomer in the polymers, the regular polymer structures were destroyed because of different chemical structures between the two kinds of LC monomers, leading to the disappearance of the smectic arrangement.     

Contribution of monomer functionality and additives to polymerization kinetics and liquid crystal phase separation in acrylate-based polymer-dispersed liquid crystals (PDLCs)

Fundamental control of the polymerization behaviour of polymer-dispersed liquid crystals (PDLCs) is critical to the formation of high-performance devices by polymer-induced phase separation (PIPS). Previous PDLC research has shown that monomer functionality and additives such as surfactants or reactive diluents can impart significant changes to the electro-optical behaviour of a system, especially in acrylate-based materials. The influence of monomer functionality and additives on the polymerization kinetics and LC phase separation were examined in the formation of acrylate-based PDLCs. Real-time infrared (RTIR) spectroscopy was utilized to simultaneously monitor polymerization rate, double bond conversion and LC phase separation. In the formation of PDLCs by PIPS, increasing acrylate monomer functionality reduces the polymerization rate, overall double bond conversion and the extent of LC phase separation. Interestingly, the additives octanoic acid and N-vinylpyrrolidone (NVP) increase the polymerization rate but suppress LC phase separation. During PDLC formation, both octanoic acid and NVP enhance the solubility of the LC in the growing polymer matrix, reducing the rate of liquid-gel demixing and decreasing nematic fraction in PDLCs. As a non-reactive component, octanoic acid increases the polymerization rate by plasticizing the crosslinked polymerization. NVP, a reactive diluent added to decrease viscosity, increases polymerization rate through favourable copolymerization with acrylate monomer.