Synthesis and characterization of new mesogenic esters derived from 1,2,4-oxadiazole and study the effect of alkoxy chain length in their liquid crystalline properties

In this study, a new series of non-symmetrically 3,5-disubstituted of 1,2,4-oxadiazole derivatives, 4-[5-(4-methylphenyl)-1,2,4-oxadiazol-3-yl]-phenyl-4-alkoxybenzoate (G₁–G₁₁), which containing ether and ester linkages in the same molecule, is synthesized using different synthetic procedures and their structures are confirmed by several spectroscopic techniques (FT-IR and ¹H nuclear magnetic resonance). The mesomorphic properties of these compounds are studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM); all these derivatives exhibited as mesogens and displayed an enantiotropic liquid crystal with nematic texture, the nematogenic phase of these materials was appeared in wide temperature ranges on heating and cooling cycles that were observed by POM and DSC. The influence of 1,2,4-oxadiazole ring and the elongation of alkyl chain in the mesomorphic properties of this series were investigated. The mesogenic behaviour of this series was compared with the compounds possessing a somewhat similar structure.     

硬段含介晶的多嵌段共聚物的合成和研究

通过对-乙酰氧基苯甲酸或对-乙酰胺基苯甲酸和聚酯-聚醚多嵌段共聚物的硬段PET进行酸解反应,和随后的乙酰氧基或乙酰胺基,和羧基间的缩聚反应,分别合成了硬段含介晶的共聚酯-聚醚多嵌段共聚物和聚酯酰胺-聚醚多嵌段共聚物,研究了它们的热致液晶行为。     

β-环糊精的低临界溶解温度现象及其在有序纳米孔道片晶制备中的应用

将β-环糊精(β-CD)溶解于N,N-二甲基甲酰胺(DMF)中, 加热至140 ℃后有大量白色晶体析出. 扫描电子显微镜观察发现析出物为β-CD片状结晶. 红外光谱(IR)和核磁共振波谱(NMR)结果证明了片状结晶的化学结构与β-CD原料相同. 热重分析(TGA)和差示扫描量热(DSC)分析结果证明片状结晶的理化性质与β-CD原料相同. X射线衍射分析(XRD)测试结果表明, β-CD片晶的结晶结构与β-CD原料不同. 利用Diamond软件模拟了具有开通管道结晶结构的β-CD晶体的XRD谱图, 发现其与实测的β-CD片晶谱图基本相符, 说明β-CD片晶具有有序纳米开通管道结晶结构. 比表面积测试和酚酞吸附实验进一步证实β-CD片晶具有比β-CD原料更大的比表面积和更好的吸附性能.     

发光液晶高分子:分子构筑、结构与性能及其应用

发光液晶高分子结合了液晶高分子的有序性、稳定性、力学性能和发光分子的发光特性,有着广阔的应用前景。为了获得高效的发光液晶高分子,不同结构的发光液晶高分子被成功地设计与合成,包括主链型、侧链型、“甲壳”型发光液晶高分子、发光液晶高分子网络等。同时,分子结构、液晶相结构与光物理性质的关系也得到了相应的深入研究。本文总结了发光液晶高分子的最新研究进展,详细介绍了不同类型发光液晶高分子的分子结构设计合成、结构与性能、相关应用,并对其发展前景进行了展望。     

聚劳酯液晶硬核的构象与键级的理论研究

液晶已有一百年的历史了。液晶化学,液晶物理,液晶材料方面的科学都有了相当丰富的积累与长足的发展。十三年前Chandrase khar发现了碟形液晶,它具有特征的二维有序的柱状液晶相。从学术上讲,该发现对液晶科学的一些概念有一定的冲击,传统的有关液晶的分类(向列型、胆甾型、近晶型)正在被更加合理的从液晶分子聚集结构的几何特性而进行的分类(向列相、层状相、柱状相)所取代。这些进展鞭策着人们去追本求     

Polymeric dopant effects of bent‐core covalent‐bonded and hydrogen‐bonded structures on banana‐shaped liquid crystalline complexes

Two series of banana‐shaped liquid crystalline (LC) H‐bonded complexes HP_m / CB_n (i.e., bent‐core H‐bonded side‐chain homopolymer HP mixed with bent‐core covalent‐bonded small molecule CB ) and CP_m / HB_n (i.e., bent‐core covalent‐bonded side‐chain homopolymer CP mixed with bent‐core H‐bonded small molecular complex HB ) with various m/n molar ratios were developed. The bent‐core covalent‐ and H‐bonded structural moieties were homopolymerized in the banana‐shaped LC H‐bonded complexes HP_m / CB_n and CP_m / HB_n , respectively. The influences of m/n molar ratios (polymeric moieties vs. small molecular moieties) on the mesomorphic and electro‐optical properties of both banana‐shaped LC H‐bonded complexes HP_m / CB_n and CP_m / HB_n were investigated. The polar smectic phases could be achieved and stabilized by smaller contents of polymeric dopants in banana‐shaped LC H‐bonded complexes, such as HP1/CB10 , HP1/CB15 , CP1/HB10 , and CP1/HB15 , which possessed tunable spontaneous polarization (Ps) values according to the molar ratios of m/n , that is, lower Ps values obtained in H‐bonded complexes HP_m /CB_n and CP_m / HB_n with higher ratios of H‐bonded moieties (larger m/n molar ratios), respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 764–774, 2010     

Infrared linear dichroism as a tool to evaluate volatile guest partition between amorphous and nanoporous‐crystalline polymer phases

Desorption kinetics of ethene, propene, and butadiene from films exhibiting axially oriented nanoporous‐crystalline δ phases of syndiotactic polystyrene (s‐PS) have been followed by gravimetric and infrared linear dichroism measurements. The reported data can be rationalized by assuming that, after the initial desorption mainly involving molecules absorbed in the amorphous phase, most gaseous molecules are included as guest in the nanoporous‐crystalline phase. This allows establishing a simple method to evaluate guest partition between nanoporous‐crystalline and amorphous polymeric phases, which possibly can be applied for most volatile guest molecules. The described method also allows establishing the presence of one guest molecule (ethene, propene, or butadiene) per cavity of the nanoporous δ form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Ordered nanostructures at two different length scales mediated by temperature: A triphenylene‐containing mesogen‐jacketed liquid crystalline polymer with a long spacer

A mesogen‐jacketed liquid crystalline polymer (MJLCP) containing triphenylene (Tp) moieties in the side chains with 12 methylene units as spacers (denoted as PP12V) was synthesized. Its liquid crystalline (LC) phase behavior was studied with a combination of solution ¹H NMR, solid‐state NMR, gel permeation chromatography, thermogravimetric analysis, polarized light microscopy, differential scanning calorimetry, and one‐ and two‐dimensional wide‐angle X‐ray diffraction. By simply varying the temperature, two ordered nanostructures at sub‐10‐nm length scales originating from two LC building blocks were obtained in one polymer. The low‐temperature phase of the polymer is a hexagonal columnar phase (Φ_H, a = 2.06 nm) self‐organized by Tp discotic mesogens. The high‐temperature phase is a nematic columnar phase with a larger dimension (a′ = 4.07 nm) developed by the rod‐like supramolecular mesogen—the MJLCP chain as a whole. A re‐entrant isotropic phase is found in the medium temperature range. Partially homeotropic alignment of the polymer can be achieved when treated with an electric field, with the polymer in the Φ_H phase developed by the Tp moieties. The incorporation of Tp moieties through relatively long spacers (12 methylene units) disrupts the ordered packing of the MJLCP at low temperatures, which is the first case for main‐chain/side‐chain combined LC polymers with MJLCPs as the main‐chain LC building block to the best of our knowledge. The relationship of the molecular structure and the novel phase behavior of PP12V has implications in the design of LC polymers containing nanobuilding blocks toward constructing ordered nanostructures at different length scales. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 295–304     

Crystalline Stereocomplexed Polycarbonates: Hydrogen‐Bond‐Driven Interlocked Orderly Assembly of the Opposite Enantiomers

Four novel crystalline stereocomplexed polymers are formed by mixing isotactic (R)‐ and (S)‐polycarbonates in 1:1 mass ratio. They show the enhanced thermal stability and new crystalline behavior, significantly distinct from the component enantiomer. Two stereocomplexed CO₂‐based polycarbonates from meso‐3,4‐epoxytetrahydrofuran and 4,4‐dimethyl‐3,5,8‐trioxabicyclo[5.1.0]octane have high melting temperatures of up to 300 °C, about 30 °C higher than the individual enantiomers. Isotactic (R)‐ or (S)‐poly(cyclopentene carbonate) and poly(cis‐2,3‐butene carbonate) are typical amorphous polymeric materials, however, upon mixing both enantiomers together, a strong interlocked interaction between polymer chains of opposite configuration occurs, affording the crystalline stereocomplexes with melting temperatures of about 200 °C and 180 °C, respectively. A DFT study suggests that the driving force forming the stereocomplex is the hydrogen‐bonding between carbonate units of the opposite enantiomers.     

Extensively Reversible Thermal Transformations of a Bistable,Fluorescence‐Switchable Molecular Solid: Entry into Functional Molecular Phase‐Change Materials

Functional phase‐change materials (PCMs) are conspicuously absent among molecular materials in which the various attributes of inorganic solids have been realized. While organic PCMs are primarily limited to thermal storage systems, the amorphous–crystalline transformation of materials like Ge‐Sb‐Te find use in advanced applications such as information storage. Reversible amorphous–crystalline transformations in molecular solids require a subtle balance between robust supramolecular assembly and flexible structural elements. We report novel diaminodicyanoquinodimethanes that achieve this transformation by interlinked helical assemblies coupled with conformationally flexible alkoxyalkyl chains. They exhibit highly reversible thermal transformations between bistable (crystalline/amorphous) forms, along with a prominent switching of the fluorescence emission energy and intensity.