Rigid rod molecules as liquid crystal thermosets. II. Rigid rod esters

Nine rigid rod ester monomers endcapped with maleimide, nadimide, and methylnadimide groups were prepared and studied by DSC and hot stage polarized light microscopy. All of the monomers showed thermotropic nematic liquid crystalline phases and could be thermally crosslinked in the nematic phase. The nematic texture was maintained in the crosslinked solid state. The nematic phase range was enlarged by B-staging the monomeric compounds. Heating the monomers for a short period of time in the nematic phase lowered the crystal to nematic transition temperatures and increased the nematic to isotropic transition temperatures. A nonequilibrium phase diagram was proposed to explain the melting behavior of these reactive liquid crystal thermoset materials.     

Effect of stoichiometry on liquid crystalline supramolecular polymers formed with complementary nucleobase pair interactions

We report herein studies on the liquid crystalline behavior of a series of supramolecular materials that contain different ratios of two complementary symmetrically-substituted alkoxy-bis(phenylethynyl)benzene AA- and BB-type monomers. One monomer has thymine units placed at either end of the rigid mesogenic core, while the other has N⁶-(4-methoxybenzoyl)-adenine units placed on the ends. Differential scanning calorimetric and polarized optical microscopy studies have been carried out on these systems. These studies show that the material's behavior is strongly dependent on its thermal history. As a result, the materials can exhibit, on heating, either a liquid crystalline phase, a crystalline phase, or the coexistence of crystalline and liquid crystalline regions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5049–5059, 2006     

Side-chain liquid crystalline polymers with silphenylene-siloxane main chains. II. Preparation and characterization of polymers containing biphenyl mesogens

Side-chain liquid crystalline polymers with poly(silphenylene-siloxane) backbones and 4,4′-biphenyl-containing pendant mesogenic groups have been prepared and characterized. Polymers with spacers having only three methylene groups were not liquid crystalline, LC, but those with spacers having eight methylene groups or more and a long terminal substituent were LC as indicated by an isotropization peak on the shoulder of the melting peak in the DSC thermogram and the appearance of a Schlieren texture on examination by polarized light microscopy. However, the LC behavior could not be confirmed by wide-angle X-ray diffraction, WAXD, because the crystalline pattern apparently remained up to the isotropization temperature, presumably because the melting transition and isotropization are too close. In contrast, polymethylsiloxanes with the same mesogenic side-chains revealed the presence of well-defined smectic phases by WAXD as well as by polarized light microscopy.     

Studies on the thermotropic liquid crystalline polymer. XII. Synthesis and properties of crosslinkable thermotropic liquid crystalline homo- and copoly(ether-ester)s

A series of crosslinkable thermotropic liquid crystalline poly(ether-ester)s and copoly(ether-ester)s was prepared. All of the polymers were crosslinked by thermal treatment or photo-irradiation upon heating. The thermal stability and thermal crosslinking reaction of these polymers were investigated. These polymers also could be crosslinked by copolymerization with vinyl monomers, such as styrene or methyl methacrylate. The crosslinked polymers exhibited thermotropic liquid crystalline behavior after softening by heating. The phase behavior of linear polymers and crosslinked polymers was studied by differential scanning calorimetry (DSC) and an optical polarizing microscope equipped with a heating stage. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of side‐chain liquid‐crystalline polymers and study of their role in the crystallization of high‐density polyethylene

Side‐chain liquid‐crystalline polymers (SCLCPs) as nucleating agents for high‐density polyethylene (HDPE) were investigated. For this purpose, the molecular architectures of four different vinyl monomers with liquid‐crystalline properties were designed and prepared with 1‐butanol, 1‐pentanol, 4‐hydroxybenzoic acid, hydroquinone, and acryloyl chloride as the starting materials through alkylation and acylation reactions. The corresponding polymers were synthesized by homopolymerization in 1,4‐dioxane with benzoyl peroxide as the initiator at 60 °C. Both the monomers and the synthesized polymers were characterized with elemental analysis, Fourier transform infrared, and ¹H NMR measurements. Differential scanning calorimetry, thermogravimetric analysis, and hot stage polarized optical microscopy were employed to study the phase‐transition temperature, mesophase texture, and thermal stability of the liquid‐crystalline polymers. The results showed that all the polymers had thermotropic liquid‐crystalline features. Being used as nucleating agents, SCLCPs effectively increased both the crystallization temperature and rate and, at the same time, raised the crystallinity for HDPE. In comparison with common small‐molecule nucleating agents, such as 1,3:2,4‐dibenzylidenesorbitol, SCLCPs are more efficient and are indeed excellent nucleating agents for HDPE. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3067–3078, 2005     

Phase behavior and polymerization of lyotropic phases. II. A series of polymerizable amphiphiles with systematically varied critical packing parameters

A group of polymerizable amphiphiles, with their critical packing parameters systematically varied, were studied with respect to the phase behavior and immobilization of their lyotropic liquid‐crystalline phase structures. Small‐angle X‐ray scattering and polarized light microscopy were used to study their liquid‐crystalline phases before and after photopolymerization. The liquid crystallinity of the amphiphiles depended on the contents of both oil and water in the ternary systems. Through photopolymerization, hexagonal phases could generally be immobilized, with the structural order reduced to various degrees. However, the cubic phases evolved with polymerization into another structural pattern, which was possibly related to the lamellar structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5887–5897, 2006     

Physicochemical Characterization and Rheological Behavior Evaluation of the Liquid Crystalline Mesophases Developed with Different Silicones

This article presented physicochemical characterization and rheological behavior evaluation of the liquid crystalline mesophases developed with different silicones. There were prepared 5 ternary systems, which were carried out the determination of the relative density, the electric conductivity and polarized light microscopy analysis, being selected two systems to promote the Preliminary Stability Tests. The results showed that System 1 obtained the major liquid crystal formation and a higher stability. The temperature influences in the systems stability and phases structure. In hot oven, observed oneself the mixture of lamellar and hexagonal phase, for both systems.     

Bireactive calamitic liquid crystals derived from fluorene ester linkage

New thermotropic liquid crystalline monomer esters, containing fluorene in their mesogenic core with luminescent properties, were synthesized and characterized. The monomers studied exhibited a broad mesomorphic range and a nematic phase was identified by differential scanning calorimetry and polarized optical microscopy. Absorption and photoluminescence spectra studied in solution indicated that these compounds possess good optical stability. Linearly polarized light emission was observed in oriented thin films prepared by an in‐situ photopolymerization technique. The preparation of oriented thin films shows a preferential emission direction necessary for application in linearly polarized blue light‐emitting diodes.     

光致取向调控偶氮苯侧链液晶聚合物的阻隔特性研究

研究了液晶分子的排列方式对聚合物膜阻隔特性的影响,采用473 nm线偏振光照无定形偶氮液晶聚合物,使其介晶基元发生从无序到有序的取向排列.用膜透射率变化和锥光干涉图表征了分子的取向,其锥光干涉图为粗黑十字,说明在线偏振光下作用下液晶分子取向形成了单相畴沿面内排列的有序态.用金属表面氧化法进一步研究了取向态聚合物膜的阻隔...     

New liquid‐crystalline poly(ester amide)s: The role of nitro groups in the phase behavior

New hydrogen‐bonded liquid‐crystalline poly(ester amide)s (PEA)s were obtained from 1,4‐terephthaloyl[bis‐(3‐nitro‐N‐anthranilic acid)] (5) or 1,4‐terephthaloyl[bis‐(N‐anthranilic acid)] (6), with or without nitro groups, respectively, through the separate condensation of each with hydroquinone or dihydroxynaphthalene. The dicarboxylic monomers were synthesized from 2‐aminobenzoic acid. The phase behavior of the monomers and polymers were studied with differential scanning calorimetry, polarized light microscopy, and wide‐angle X‐ray diffraction methods. Monomer 5, containing nitro groups, exhibited a smectic liquid‐crystalline phase, whereas the texture of monomer 6 without nitro groups appeared to be nematic. The PEAs containing nitro groups exhibited polymorphism (smectic and nematic), whereas those without nitro groups exhibited only one phase transition (a nematic threaded texture). The changes occurring in the phase behavior of the polymers were explained by the introduction of nitro groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1289–1298, 2004     

Synthesis of a main-chain liquid crystalline azo-polymer via “click” chemistry

A main-chain liquid crystalline azo-polymer (BPHCHA) was prepared through the copper-catalyzed “click” reaction between the alkyne group on 4,4′-bis((6-(propargyloxy)hexyl)oxy) biphenyl (BPH) and the azide group on 4-(6-azidohexyloxy)carbonyl-4′-(6′-azidohexyloxy) azobenzene (AHCHA). The “click” reaction was confirmed by FT-IR, ¹H NMR, and GPC studies. The phase transition behavior of BPH, AHCHA, and the resulting azo-polymer BPHCHA was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). AHCHA and BPHCHA exhibited mesomorphic behavior, while BPH is a crystalline compound. A liquid crystalline phase from 39 to 69 °C for AHCHA upon heating was observed under POM. Schlieren texture was observed at 130 °C for BPHCHA on cooling from 150 °C and annealed at 130 °C for 15 min. Moreover, DSC and POM studies showed that BPHCHA exhibited monotropic mesomorphic behavior.     

Novel study on the liquid crystalline behavior of poly(methacrylate)s with biphenyl side groups

We report the synthesis and characterization of a series of liquid crystalline polymers substituted with the 4′-methoxybiphenyl-4-yloxy group. The spacer length is varied from 4–8 methylene units. The materials are characterized by polarized light microscopy, differential scanning calorimetry, and X-ray analysis. All homologues show highly ordered phases. Additionally, the butylene polymer shows a broad nematic mesophase. For the first time, the narrow nematic phase of the hexylene homologue could be confirmed experimentally. X-ray analysis of the polymers made exact assignments of the low temperature phases possible, thus giving access to the analysis of the arrangement of the mesogenes within the layers. The pentylene homologue shows a distinct deviation from the behavior of the other polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2669–2679, 1998     

一类含萘环结构的聚酯酰亚胺液晶聚合物的结构与性能研究

利用Higashi芳香聚酯直接缩聚法的原理,采用分步投料的方法,以N,N′-1,6-亚己基-双苯偏三酸酰亚胺二酸(IA6)、6-羟基-乙-萘甲酸(HNA)和4,4′-二羟基二苯酮(DHBP)为单体原料,合成了一系列聚酯酰亚胺共聚物.用核磁共振(NMR)、差热分析(DSC)、偏光显微镜(PLM)、广角X射线衍射(WAXD)、热重分析(TGA)等手段对所合成的聚酯酰亚胺的液晶行为、结构以及热性能进行了表征.研究结果表明,当HNA投料量占单体总投料量高于33mol%时,所得聚合物均呈明显的向列型热致液晶特性.但是,此类液晶聚合物仅在升温过程中出现液晶的相转变,而在降温过程中并未观察到液晶的相转变行为.由DSC结果分析可知,此类聚合物具有较高的玻璃化转变温度(Tg)和较低的熔融温度(Tm),有望成为一类既具有较低加工温度又有较高使用温度的液晶聚合物材料.     

Synthesis and characterization of novel epoxy monomers and liquid crystal thermosets

Four new epoxy monomers have been synthesized and characterized as part of a program to prepare novel liquid crystal thermoset (LCT) materials. Three of the new epoxy monomers contained a biphenyl mesogen and were not liquid crystalline (LC). The remaining epoxy monomer, which contained a 1,4-dibenzoyloxybenzene mesogen, was synthesized in an overall yield of 30% and displayed a broad (83°C) nematic liquid crystalline phase. The new liquid crystalline epoxy monomer was cured at 120°C and postcured at 175°C with a stoichiometric amount of 1,4-phenylenediamine. The thermal transitions of the resulting LCT were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM), thermomechanical analysis (TMA), and wide angle x-ray diffraction (WAXD) as a function of cure time and temperature. A process characterization diagram was constructed which shows that LCTs based on this new LC monomer can be processed in the liquid crystalline phase over a broad range of times and temperatures. Qualitative agreement with previous epoxy LCT results was found, as LCT's with smectic phases and without clearing temperatures were observed at long cure times (high crosslink densities), whereas nematic phases with clearing temperatures predominated in networks at short cure times (low crosslink densities). © 1993 John Wiley & Sons, Inc.     

Side-chain liquid crystal copolymers containing nonmesogenic units: Dependence of the thermal behavior upon composition

The reactivity ratios have been determined for a mesogenic/nonmesogenic comonomer system, namely 5-[4-(4′-methoxyphenyl)phenoxy]pentyl methacrylate/methyl methacrylate. The reactivity ratios were found to be equal and approximately unity. The copolymerization is, therefore, azeotropic and the resulting copolymers possess a random distribution sequence of the two monomers. The thermal properties of the copolymers were evaluated using differential scanning calorimetry and polarized light microscopy. Copolymers containing 0.56 or greater mol fraction of the mesogenic side-chain exhibited liquid crystallinity, specifically smectic behavior. The glass transition temperatures exhibited a negative deviation from linear behavior on varying the composition. By contrast, the clearing temperatures decrease in essentially a linear fashion as the mol fraction of the nonmesogenic unit is increased. The behavior of these copolymers is compared with a range of materials from the literature, revealing that on increasing backbone flexibility a greater mol fraction of nonmesogenic units can be incorporated into the copolymer structure while retaining liquid crystallinity. This behavior is rationalized in terms of a microphase separated smectic phase. © 1996 John Wiley & Sons, Inc.     

Bireactive calamitic liquid crystals derived from fluorene ester linkage

New thermotropic liquid crystalline monomer esters, containing fluorene in their mesogenic core with luminescent properties, were synthesized and characterized. The monomers studied exhibited a broad mesomorphic range and a nematic phase was identified by differential scanning calorimetry and polarized optical microscopy. Absorption and photoluminescence spectra studied in solution indicated that these compounds possess good optical stability. Linearly polarized light emission was observed in oriented thin films prepared by an in-situ photopolymerization technique. The preparation of oriented thin films shows a preferential emission direction necessary for application in linearly polarized blue light-emitting diodes.     

光致变色液晶高分子的研究(Ⅰ)─含胆甾介晶基无侧链聚硅氧烷及其单体的液晶行为

用POM、DSC和WAXD研究了十一烯酸胆甾酯及含胆甾介晶基元侧链聚硅氧烷的液晶行为。单体呈现明甾相的油条及螺旋织构,单致变近晶相的扇形织构和固-固相变。均聚物显示S_A相的扇形织构。     

刚性链侧链型液晶高分子合成与研究

以自由基聚合方法，合成了一系列含有３个苯环通过酯键相联的液晶性单体及其聚合物，这类刚性液晶基元不通过柔性间隔基而直接竖挂在聚丙烯酸酯大分子主链上，具有很高的Ｔｇ·ＤＳＣ及偏光显微镜结果表明，所有的单体和聚合物均为向列型热致性液晶。     

Synthesis and thermal properties of side-chain liquid crystalline polyethers with racemic and chiral backbone

Racemic and chiral [(4-cyano-4′-biphenyl)oxy] and [(4-methoxy-4′-biphenyl)oxy]methyloxiranes were prepared from racemic epichlorohydrin or racemic and chiral glycidols and polymerized in dimethylsulfoxide (DMSO) with Bu^tOK as the initiator system. Initial phase identifications were made by differential scanning calorimetry (DSC) and optical microscopy techniques and confirmed by X-ray diffraction measurements. Upon heating, all the monomers show only a crystal–isotropic phase transition. The racemic and chiral [(4-cyano-4′-biphenyl)oxy]methyloxiranes exhibit a nematic and a cholesteric monotropic phase, respectively. Methoxybiphenyl substituted polyethers are crystalline and insoluble in virtually all common solvents. Cyanobiphenyl substituted polyethers are soluble under the same experimental conditions and show enantiotropic liquid crystalline properties. The racemic polymer exhibits a nematic phase, while the optically active polymer forms a cholesteric phase.     

High strength disclinations in a rigid rod nematic polytolane

Transient disclinations of strength ± 3/2 were observed in the nematic phase of a single-component, thermotropic, rigid rod polytolane. These disclinations were characterized by 6 extinction brushes in textures observed by hot stage transmitted polarized light microscopy. The small number and short lifetime of these disclinations is discussed in terms of their energy per unit line length, and in terms of the force that causes them to be attracted to and annihilated at other disclinations.