Synthesis and characterization of segmented copolymers of aromatic polyether sulfone with liquid crystalline polyesters containing flexible spacers

The synthesis of segmented copolymers of aromatic polyether sulfone and liquid crystalline polyester containing flexible spacers is presented. The segmented copolymers were prepared by solution condensation of hydroxy-terminated polyether sulfone with diacid compounds 1–5 and 4,4′-dihydroxybiphenyl in a mixture of triphenylphosphine, pyridine and hexachloroethane. The obtained polymers show a glass transition at around 160 °C which belongs to the segmental motion of polyether sulfone blocks, and one or two melting transitions which belong to the thermal transitions of LCP blocks. Optical polarized microscopy verifies that the obtained segmented copolymers present a nematic liquid crystalline phase at a temperature higher than their melting transitions.     

Liquid crystalline polyesters with two-dimensional mesogenic units

Summary A series of thermotropic, liquid crystalline (LC) polyesters was prepared in which the mesogenic group contained an unusually large, polarizable pendant group in an attempt to increase intermolecular interactions so as to impart a more isotropic character to the mechanical properties of the solid polymer. The series included repeating units containing main chain, polymethylene flexible spacers of increasing lengths. All of the polymers formed stable nematic LC phases and had relatively low melting temperatures, but recrystallization from the melt was very slow in each case. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

Liquid crystalline and photocrosslinkable poly(4,4′‐stilbeneoxy) alkylarylphosphates

Three series of liquid crystalline and photocrosslinkable poly(4,4′‐stilbeneoxy) alkylarylphosphates were synthesized from various 4,4′‐bis(m‐hydroxyalkyloxy)stilbenes (m = 2, 4, 6, 8, 10) and arylphosphorodichloridates in chloroform by solution polycondensation method. Polarized optical microscope (POM) and differential scanning calorimetry (DSC) observations revealed that polymers containing less than four methylene spacer groups did not exhibit liquid crystalline (LC) texture, possibly due to smaller microdomain and restricted movement of the mesogen. In contrast, polymers containing more than four methylene spacer group established LC texture, which has been attributed to the larger monodomain and free movement of mesogens. Thermogravimetric analysis (TGA) data indicated that thermal stability and char yield decreased with increasing flexible methylene spacer groups, increased significantly for biphenyloxy and 1‐naphthyloxy containing polymers than that of phenyloxy containing polymers ascribed to increasing aromaticity, size, and number of aromatic rings. Photocrosslinking of stilbene containing polymers has been shown to proceed via 2π‐2π cycloaddition reaction by Ultra‐violet (UV) and fluorescence. The rate photocrosslinking has been found to increase with increasing number of methylene group in the main chain. The aromaticity of the side chain also increases the rate of crosslinking. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Liquid crystalline polyesters by staged-addition polycondensation

Summary A series of model liquid crystalline (LC) polyesters have been prepared by low temperature solution polycondensation using staged addition methods. The model thermotropic polyesters were composed of aliphatic spacers and mesogenic groups made from substituted terephthalic acid and methyl hydroquinone. Both the mesogenic groups and the spacers were placed in the main chain. Attractive properties of these polymers include solubility in many organic solvents such as THF and DMSO with softening temperatures below 150°C. Some of these polymers show no melting transitions, and depending on the terephthalate group substituent, either smectic or nematic phases are formed. Results from GPC analysis show good solubility of polymers in THF with M_w lower than 10,000 compared to polystyrene standards. The synthesis and characterization of these LC polyesters are reported here.     

热致液晶性聚合物的序态结构及其相变行为

本文介绍用透射电子显微镜（ＴＥＭ）、光学显微镜（ＯＭ）、热台Ｘ射线衍射（ＨＸＲＤ）等方法研究组成不同全芳香族热致液晶聚合物的序态结构和液晶行为。研究结果表明，它们在序态结构、相变热效应以及衍射强度随温度的变化规律等方面存在明显差异。并证明这种差异不仅取决于材料的组成，而且在一定条件下取决于晶体发育程度和其本身的致密性。     

Liquid crystalline polymers having dimetric moieties as side chains

A new series of liquid crystalline polymers having dimetric moieties as side chains were synthesized. The polymers exhibited nematic and smectic A phases depending on the length and parity of the flexible spacers. As the length of the flexible spacer was varied, the nematic–isotropic transition temperature and the entropy change associated with the transition exhibited a remarkable odd–even effect, in which the even numbers exhibited higher values. The transition properties were compared with those of known liquid crystalline polymers and liquid crystal dimers. The dimetric moieties effectively affected the transition properties of the present polymers, and the odd–even effect was significantly greater than that of the known polymers.     

Shear-Induced orientation in liquid crystalline polymers

The orientation development characteristics in shear flow of wholly aromatic thermotropic liquid crystalline polymers were studied. Based on the analysis of shear flow in a capillary followed by elongational flow, an experimental setup has been proposed to determine the shear-induced orientation. Experimental results have indicated that shear-induced orientation depends on total shear strain. However, orientation enhancement due to shear flow is much less effective compared with orientation buildup in the case of elongational flow. Thermotropic liquid crystalline polymers that exhibited higher orientability in elongational flow exhibited also higher orientability in shear flow. Finally, to obtain high, shear orientation in processing of thermotropics, special care should be exercised in the design of dies and molds and in optimizing processing conditions, so that high shear rates and/or long shearing times should prevail.     

Synthesis and characterization of high molecular weight side chain liquid crystalline/photoactive polymers

Various liquid crystalline and photoactive azobenzene monomers were synthesized and attached to copoly(methyl methacrylate‐glycidyl methacrylate) [copoly (MMA‐GMA)] to get high molecular weight side chain liquid crystalline (LC)/photoactive copolymers. Further, spacers are generated in situ and reactive groups are obtained after the modification. All monomers and polymers were thoroughly characterized by FTIR, ¹H and ¹³C NMR, UV‐VIS spectrophotometry, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy. All side chain LC polymers showed higher thermal stability than that of copoly(MMA‐GMA). Three LC and one azo monomer exhibited characteristic nematic mesophase where as one LC monomer has shown nematic and sanded smectic‐A texture. The rate of trans‐cis isomerization of polymer was lower than that of the monomer and both monomers and polymers showed slow back isomerization. Present approach offers convenient way to synthesize high/desired molecular weight photoactive LC polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermotropic liquid‐crystalline polyphosphate esters containing phenolphthalein moiety

A new series of thermotropic liquid‐crystalline (LC) polyphosphate esters containing phenolphthalein as a part of their mesogen has been synthesized by a solution polycondensation method. The even‐numbered methylene spacers were varied from 2–10, and ethyl phosphate was used as a phosphorus heterogeneity. Thermal analysis showed that these polymers are stable up to 275–342°C with high char yield. All of the polymers exhibited liquid‐crystalline properties except for Polymers I and VI. Differential scanning calorimetry (DSC) confirmed the mesophase formation of the polymers. The glass transition temperature (T_g) and melting temperature (T_m) of the polymers were considerably low. A polymer containing phenolphthalein alone as a rigid segment with decamethylene spacers was also synthesized, but it did not show birefringent melt properties. These results reveal that phenolphthalein alone cannot act as a mesogen, whereas phenolphthalein phenylester can. Molecular modeling studies and conformational analysis confirmed that the steric hindrance of phenylester and the conjugation effect could explain the promotion of mesogenic behavior by phenolphthalein phenylester. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 194–200, 2004     

Selective Conversion of Polycyclic Hydrocarbons to Specialty Chemicals over Zeolite Catalysts

Recent studies demonstrate that high-value chemicals can be obtained by selective conversion of polycyclic hydrocarbons such as naphthalene,biphenyl,and phenanthrene, over some zeolite catalysts. This article gives examples of shape-selective alkylation of naphthalene into 2,6-dialkylnaphthalene,ring-shift isomerization of sym-octahydrophenanthrene into sym-octahydroanthracene,shape-selective alkylation of biphenyl into 4,4'-dialkylbiphenyl,conformational isomerization of cis-decalin into trans-decalin,selective hydrogenation of naphthalene into either cis-or trans-decalin, and regio-selective hydrogenation of heteroatom-containing aromatic compounds such as 1-naphthol.The products of such selective reactions are specialty chemicals, monomers of advanced polymer materials such as high-performance polyesters, advanced engineering plastics,and liquid crystalline polymers,or components of advanced thermally stable aviation jet fuels for high-Mach aircraft.     

Liquid crystalline poly(enamine ketone)s formed through hydrogen bonding

A series of poly(enamine ketone)s (PEAKs) which exhibit liquid crystalline phases has been synthesized. The enamine ketone groups are able to exist in the cis and trans conformations. Molecular modelling results show that the cis conformation is energetically more favorable due to intramolecular hydrogen bonding. Model compound studies indicate that the formation of the mesogen requires the cis conformation in the enamine ketones to stabilize the liquid crystalline phase. This liquid crystalline phase is nematic for the model compound and the polymers. The heats of liquid crystal transition in the model compound and in PEAKs are very close (4.7 kJ/mol in model compound and 4.0 kJ/mol of repeating units in polymers). This is not only an indication of a similar percentage of the cis conformation in both cases, but also an example that the flexible ethyleneoxy spacers in the polymers do not contribute to the orientational order of this liquid crystalline phase. PEAKs can crystallize through either quenching from the isotropic melt or from the liquid crystalline phase. Crystallization kinetics exhibit the effect of pre-ordering when these two different kinetics are compared.     

Synthesis and properties of liquid crystalline polymers with low Tm and broad mesophase temperature ranges

Novel thermotropic liquid crystalline polymers (TLCP) with improved processability and lower cost than Vectra^® were synthesized by esterification and melt polycondensation. Aromatic compounds, 6-hydroxyl-2-naphthoic acid, 2,6-naphthlenedicarboxylic acid, 4-hydroxybenzoic acid or terephthalic acid, were used as polycyclic stiff rod-like mesogenic groups. Aliphatic diol, ethylene glycol or 1,4-butanediol was used as flexible spacers to form semi-flexible main chain TLCP. The LCP products were characterized by FT-IR and ¹H NMR to identify their chemical structures. The analytical results showed the polymers had inherent viscosities of 0.35-0.54 dL/g. The crank shaft structure of the naphthalene decreased the melting temperature (T_m) of LCP (181-272 °C) to facilitate extrusion or injection molding, and maintained relatively high heat deflection temperature for high performance engineering plastics applications. The 5% weight loss decomposition temperatures were above 400 °C. LCPs have good solvent resistance and low hygroscopicity. The SEM morphology showed strong orientation on the surface in the flow direction and many micro-fibers structure in a sectional drawing. The optical textures of polymers observed by POM revealed a strong birefringence in the melts and indicated that they form nematic mesophase. All polymers have broad mesophase temperature (ΔT_meso) ranges.     

Thermotropic Liquid Crystalline Polyesters with Rigid or Flexible Spacer Groups

Several different series of rigid and flexible polyesters with main chain liquid crystalline units were prepared and their properties were examined in relation to their structures. The first group of polymers were rigid aromatic copolyesters with mesogenic groups based on either chloro or methyl hydroquinone terephthalate units combined with varying amounts of different types of bisphenol terephthalate units The bisphenol comonomers used contained the structure: in which X was none, ? C(CH₃)₂? , ? CH₂? , ? O? , ? S? , and ? So₂? . It was observed that the bisphenols with the bulkier X group were more efficient in destroying thermotropic liquid crystallinity of the resulting copolymers. The second group of polymers studied were flexible polyesters consisting of various types of mesogenic units which were connected together by different lengths of polymethylene flexible spacers. The liquid crystalline behaviours of these polymers, particularly their transition temperatures, were correlated with their structures. A brief review of previous studies on the synthesis of thermotropic liquid crystalline polyesters is included.     

Blends of thermotropic liquid crystalline polyesters and poly(butylene terephthalate): Thermal,mechanical, and morphological properties

Blends of poly(butylene terephthalate) (PBT) with three different thermotropic liquid crystalline polyesters (TLCPs) were prepared. The first TLCP (HBH-6) consists of diad aromaticester type mesogenic units and the hexamethylene spacers along the main chain, and the second (TB-S6) is a wholly aromatic polyester TLCP having alkoxy side groups on the terephthaloyl moiety. The last (TR-4,6) is an LC copolymer comsisting of triad aromatic ester type mesogenic units and two differents spacers; tetramethylene and hexamethylene units. Blends of TLCP with PBT were melt spum at different LCP contents and differnt draw ratios to produce monofilaments. For the HBH-6/PBT and TB-S6/PBT blends, the ultimate tensile strength showed a maximum value at the 5 wt% level of LCP in the blends, and then it decreased when the LCP content was increased up to 20%. On the other hand, the initial modulus monotonically increased with increasing LCP content in all cases. The blends with TB-S6 showed the highest tensile properties of the three blends systems. This can be ascribed to the highest rigidity of the polymer chain, which still carries relatively long alkoxy substituents that promote sufficient adhesion between the LCP and PBT matrix. When compared with the PBT fiber itself, the fibers obtained from the 5% TB-S6/PBT blends exhibited an improvement in tensile strength by > 25% and in tensile modulus by ～ 200%.     

Side chain polysiloxane liquid crystals and their behaviour in electric fields

Optical and electro-optical properties of side chain liquid crystalline polymers are described. The polymers studied were homopolysiloxanes with mesogenic side groups separated from the polymer backbone by flexible polymethylene spacers of varying length. The effect of the flexible spacer on the phase properties and electric field effects will be discussed. Low frequency a.c. fields induced a turbulent scattering texture, whilst at higher frequencies (> 1 kHz) a homeotropic alignment was obtained. The latter effect leads to high contrast displays which are durably stored at temperatures well above the glass transition. Various parameters affecting the response of the polymers to applied fields will also be discussed. These include temperature, frequency and magnitude of the electric field, film thickness and the length of the flexible spacer.     

热致性液晶全芳共聚酯的设计合成及其性能研究

通过熔融酯交换法,合成了一系列五元全芳共聚酯。利用热台偏光显微镜(PLM)、示差扫描量热法(DSC)等测试分析手段对所合成的产物进行了表征。研究发现,二羟基二苯酮在二酚单体中相对含量较高的情况时聚合产物具有较好的液晶性和成纤性能,表明该单体有利于合成高成纤性、高强度和低熔融加工温度的全芳液晶共聚酯。     

新型萘环衍生物类液晶的研究进展

新型的萘环衍生物类液晶化合物具有优越的物理性能,是近年来显示用液晶材料研究的热点领域。综述了萘环衍生物类液晶对混合液晶物理性能的影响。大量文献数据表明其可加宽混合液晶的向列相温度范围;增大介电各向异性;降低阈值电压以及调节适宜的双折射率,适用于超扭曲向列型(STN型),薄膜晶体管型(TFT型)等高性能液晶材料。     

液晶聚合物——新型的涂料树脂

液晶聚合物是一种新型的涂料树脂 ,具有独特的性质和潜在的应用。介绍液晶改性醇酸树脂和可除去性涂料树脂的研究概况。这种侧链型的液晶聚合物在用于高固体涂料和特种涂料方面有进一步开发的价值     

Anisotropic properties of aromatic polyamides containing non-rigid rodlike units

Summary Three kinds of aromatic polyamides were synthesized by Higashi reaction: aromatic polyamides with even, odd number of methylenes and a meta phenylene as a joint in the main chain. Each polymer consisted of 7 p-phenylene-amide elements as a rigid segment. The polymer with even number of methylenes showed a lyotropic liquid crystalline behavior and a broader biphasic region than the fully para aromatic polyamide such as poly(p-phenylene terephthalamide). Most polymers with odd number of methylenes did not form a liquid crystalline phase and showed a crystallo-solvate. Exceptionally, the polymer with glutaryl unit was observed to have the swollen gel of colored pattern by the polarized microscope. The zigzag polymer, characterized by the highly kinetic rigidity, revealed an anisotropic gel phase in a solution.     

Preparation and thermal characterisation of some new liquid crystalline copolymers involving a spacer unit based on vinylacetic acid

Summary Three series of new liquid crystalline (LC) copolymers having a polysiloxane backbone and two different mesogenic pendant groups, one involving a vinylacetic acid moiety in the spacer, have been synthesised. Thermal characterisation of these polymeers has allowed comparison of behaviour between a number of different copolymer systems. It was found that increasing amounts of the vinylacetic acid moiety lowered the clearing points (T_i) of the copolymers in an almost linear fashion whilst also inhibiting crystallinity in these polymers.