The effect of chemical constitution of mesogenic monomer unit on liquid crystalline properties of polymers

Glass transition temperatures and thermodynamic parameters of mesophase melting of polymers with mesogenic side-groups of the phenyl benzoate class depend on the length of the alkoxy substitutent, the mobility of the mesogenic groups and the nature of the main chain. Polymers with mesogenic groups connected directly to the main chain, obtained by precipitation from solution, have equilibrium liquid crystalline structures in which the macromolecules exist in a compact coil conformation with an ordered arrangement of the mesogenic groups. The nature of the main chain of these polymers affects the liquid crystalline structure. Mesophase melting parameters of the polymers with mesogenic groups, connected by flexible spacer groups to the main chain, are almost independent of the thermal history of the samples. These polymers in the isotropic melts are assumed to contain aggregates of the mesogenic groups.     

STUDY OF CHIRAL SIDE CHAIN LIQUID CRYSTALLINE POLYMERS

Five kinds of side chain liquid crystalline polymers with a chiral component in the pendant group were synthesized and characterized by GPC, polarizing microscopy, DSC, X-ray diffraction ano Dielectric Relaxation Spectroscopy. The liquid crystalline behaviour of the polymers is affected by the length of flexible spacer, which links the mesogenic side chain to the polymer backbone and mesogenic moiety. The characteristic of smectic phase is observed for all the polymers.     

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...     

刚性侧链型液晶高分子与含二维液晶基元的液晶高分子

提出了“刚性侧链型液晶高分子”与“含二维液晶基元的液晶高分子”两个新概念。     

SYNTHESIS AND PROPERTIES OF NEW MESOGEN-JACKETED LIQUID CRYSTALLINE POLYMERS*

Some new mesogen-jacketed liquid crystalline polymers (MJLCP) with polymer backbones, spacers, andmesogenic units of different structures were synthesized by radical polymerization. The mesomorphic behavior of thesepolymers was examined using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Theirliquid crystallinity is influenced by the variation of polymer backbone, spacer, mesogenic unit and its terminal groups. Theresults show that 1) a more flexible polymer main-chain is more favorable to the formation of a liquid crystal phase, while 2)a flexible spacer will decrease the "Jacket Effect" and the liquid crystallinity and 3) a subtle modification of the terminalgroups on the mesogenic unit may also have a significant influence on properties of the polymers.     

Synthesis and properties of two new series of isomeric liquid crystalline polyesters with conjugated double bonds

Two homologous series of flexible main chain liquid crystalline polyesters with isomeric mesogenic groups containing conjugated double bonds, were synthesized and studied by differential scanning calorimetry and optical microscopy. One series (S1) has the p-phenylene-diacryloyloxydibenzoyl moiety as a mesogenic unit. The other (S2) has the terephtaloyl dioxydicinnamoyl moiety as a mesogenic unit. The reactivity of the conjugated double bonds of the p-phenylenediacryloxy unit, at the temperature of mesophase formation, impedes the stability of liquid crystalline mesophases of polymers of series (S1). Two low molecular weight analogues of polymers were also prepared and their properties compared with those of polymers of similar structure. The two model compounds form stable smectic mesophases over a wide range of temperatures, which shows the high mesomorphogenic ability of both mesogenic units.     

A series of azo-type side-chain liquid crystalline polysiloxane–palladium complexes

A series of azo-type side-chain liquid crystalline polysiloxanes (AZLCPs) were synthesized, starting from organic polysiloxane and azo-type mesogenic compounds having an end allyl group. The AZLCPs were further used to coordinate with palladium dichloride and potassium chloride, by which a series of palladium complexes of AZLCPs (Pd–AZLCPs) were prepared. The mesogenic properties of all of the liquid crystalline polymers were characterized by using differential scanning calorimetry, polarized microscope and wide-angle X-ray diffraction. It was found that all of the polymer ligands and their palladium complexes showed thermotropic liquid crystallinity and that the incorporation of the palladium ions gave positive effects to the mesogenic properties of their polymer ligand counterpart. Compared with the corresponding AZLCPs, the Pd–AZLCPs have higher isotropization temperatures and a broader mesophase temperature range. The mesogenic properties of the liquid crystalline polymer ligands and their palladium complexes were also varied gradually by changing the length of the alkoxy groups on the side chain. The polymers that have a color emissive group and a highly flexible polysiloxane main chain may potentially be used as nonlinear optical materials.     

Liquid crystal polymers—VI.: Synthesis and properties of main chain thermotropic polyesters with disiloxane spacers

New thermotropic, liquid crystalline polymers were synthesized, and their thermal properties and the characteristics of their mesophases were studied by differential scanning calorimetry, by use of a hot stage on a polarizing microscope, and by small-angle light scattering. The polymers had an aromatic ester triad mesogenic group and a flexible siloxane spacer in the main chain. Equimolar copolymers containing both siloxane and decamethylene spacers were also prepared and characterized. All the polymers formed nematic phases, and the thermodynamic characteristics of their nematic-to-isotropic phase transitions could be explained on the basis of their structural features.     

Novel luminescent liquid crystalline polyazomethines. Synthesis and study of thermotropic and photoluminescent properties

Novel semiflexible polyazomethines containing chromophoric units into azomethine mesogenic core have been synthesised by condensation of a flexible dialdehyde with mesogenic diamines containing fluorene, antraquinone, pyrimidine, azobenzene and benzophenone. The thermotropic behaviour of the resulting polyazomethines was assessed by differential scanning calorimetry, polarised light microscopy and investigations of the miscibility relations. While the pure polyazomethines showed a birefringent viscous texture difficult to be ascribed, by mixing with a liquid crystal dimer, clear Schlieren or marbled textures were observed, indicating a nematic mesophase. The polymers exhibited violet, blue or yellow light emission.     

Chiral liquid-crystalline copolyacrylates with biphenyl and phenyl benzoate side groups

The phase behavior and structure of liquid-crystalline phases of three series of copolymers with mesogenic units belonging to the families of biphenyls and phenyl benzoates have been studied, with the former mesogenic units containing a chiral center in a flexible spacer. A variation in the isotropization temperature as a function of composition is well described by the additivity rule, whereas the tilt angle of mesogenic groups in smectic layers changes nonlinearly. This angle decreases beginning from homopolymers and attains the minimum value for the copolymers of the equimolar composition, which show the highest ferroelectric activity among the polymer systems under study.     

一类新的刚性链侧链型液晶高分子的合成

以自由基聚合方法，合成了一系列含有三个苯环通过酯键相联的液晶性单体及其聚合物．在这类新的液晶高分子中，刚性液晶基元不通过柔性间隔基而直接竖挂在聚甲基丙烯酸酯大分子主链上．这些高分子有很高的玻璃化转变温度，表明其分子链刚性较大，因而代表了一类新的刚性链侧链型液晶高分子．它们的液晶行为用ＤＳＣ、偏光显微镜和Ｘ－光衍射进行了表征．发现所有单体和聚合物均为向列型热致性液晶．     

Alternative synthetic strategies for Schiff base derived liquid crystal polymers: A comparative study

Semiflexible liquid crystalline polymers based on Schiff bases as mesogenic cores have been synthesized through different synthetic strategies. The mesogenic cores are derived from 1,5-naphthalenediamine linked to a polymethylenic spacer by means of ether or ester groups. The synthetic strategies differ in the disconnection of the molecules to design the synthesis of the repeating units. Polymers were synthesized either as polyazomethines, where imine bonds are formed in the polymer synthesis, or as polyethers or polyesters, where the ether or ester groups are formed at the polymer-forming stage. The influence of the synthetic method and the linking groups between mesogenic core and flexible spacer on the thermal and mesogenic properties has been analyzed by DSC, thermogravimetry, and optical microscopy. The possibility of obtaining hydroxy-functionalized polymers by different synthetic strategies has been studied as well as the influence of these groups on the thermal and mesogenic properties. © 1996 John Wiley & Sons, Inc.     

The synthesis of mesogenic polymers provoked by molecular mobility. polysiloxanarylenes

An approach to the synthesis of potentially thermotropic liquid crystalline polymers based on parallel investigation of their molecular mobility was realized. The initial idea was provoked by the observation that there exists some correspondence of molecular mobility data and the ability of a polymer to form a liquid crystalline phase. Previously this phenomenon was demonstrated on the example of a series of thermotropic main chain polymers with flexible dimethylsiloxane spacers of variable length. The relation between the structure of the main chain and local molecular mobility of different fragments was investigated in a series of regular polysiloxane-silarylenes containing rigid aromatic sequences. Molecular mobility was studied by dielectric spectroscopy in solution and in solid state. The structure of the main chain has been changed by variation of the repeated fragments' length, substituents and joint groups. The data of molecular mobility and their conformity with the chain structure were used for directed synthetic search of desired mesogenic polymers.     

Polysiloxanes substituted with forked mesogens

Mesomorphic properties including structural aspects are investigated in a homologous series of forked side chain polymers: the mesogenic units, which are conventionally attached to a polysiloxane backbone via a flexible spacer, possess two long aliphatic tails at their extremities as in forked polycatenar molecules. Several polymers with different proportions, x, of such mesogenic units have been studied. The influence of this parameter is especially interesting on the structure of the mesophases: the layer spacings of the fluid smectics observed at high temperature vary irregularly as a function of x. Microsegregation into sublayers is observed for low values of x while ordered phases with lamellar or/and columnar features appear at low temperatures.     

Laterally attached liquid crystalline polymers as stationary phases in reversed-phase high-performance liquid chromatography. II. Optimization of the molecular parameter of the polymer

Stationary phases obtained by coating side-chain liquid crystalline polymers (LCPs) with the mesogenic rod like units laterally attached to a polysiloxane backbone via a flexible spacer have been already reported. These phases show excellent planarity and shape recognition for polynuclear aromatic hydrocarbon (PAH) solutes in reversed-phase liquid chromatography. Optimization of these stationary phases in terms of molecular parameters of the polymer is here described. Fifteen stationary phases have been prepared varying different parameters such as the spacer length, the aliphatic tail length, and the proportion of laterally attached mesogenic units along the polymer chain. The results show that the combination of a long spacer and long terminal chains, which generates a smectic phase in the polymer bulk, leads to the best chromatographic performances towards planarity and shape recognition for PAH solutes.     

High hole mobility for a side-chain liquid-crystalline smectic polysiloxane exhibiting a nanosegregated structure with a terthiophene moiety

Side-chain liquid-crystalline siloxane polymers bearing terthiophene moieties as mesogenic pendant groups have been synthesized. An alkenylterthiophene derivative was treated with poly(hydrogenmethylsiloxane) and poly(dimethylsiloxane-co-hydrogenmethylsiloxane)s in Me(2)SiO/MeHSiO ratios of 1:1 and 7:3, respectively, in the presence of the Karstedt catalyst, to produce pale yellow polymers. The degrees of introduction of the mesogenic unit were 100, 50, and 30%, respectively. The polymers exhibit ordered smectic phases at room temperature. The copolymers with dimethylsiloxane units form smectic phases as a consequence of nanosegregation between the mesogenic units and siloxane backbones with the alkylene spacers. Time-of-flight measurement reveals that the hole mobility exceeds 1×10(-2) cm(2) V(-1) s(-1) in the ordered smectic phase of the copolymer with a degree introduction of the mesogenic units of 50%. This value is comparable to that of the highly ordered mesophases of low-molecular-weight derivatives of phenylnaphthalene and terthiophene. Because of the segregation behavior induced by the flexible backbone, a closer molecular packing structure favorable for fast carrier transport may be formed in the smectic phase of the copolymer in spite of the low density of the mesogenic groups.     

Side-chain liquid crystalline polyesters derived from diethylmalonate and/or 1,3-propanediol

A series of azo monomers for polycondensation have been synthesized and characterized. These monomers, which contain electron-donor or acceptor substituents, have been condensed with aliphatic monomers to obtain two different series of aliphatic main-chain polyesters with pendant mesogenic groups. The polymers display nematic or smectic phases depending on the structural modifications of pendant mesogenic groups and the length of the flexible main-chain. In addition to these series, two polyesters with a high concentration of side pro-mesogenic groups have been synthesized. © 1996 John Wiley & Sons, Inc.     

Study on new chiral liquid crystalline monomers and polymers containing menthyl groups

A series of new chiral monomers (M1–M4) and the corresponding siloxane polymers (P1–P4) containing menthyl groups were synthesised to establish the relationship between their structure and liquid crystalline properties. The effect of the mesogenic core rigidity and the spacer length on the phase behaviour of the monomers and polymers obtained in this study was discussed. The selective reflection of light for the chiral monomers was studied with UV-Vis spectrometer. Polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis were used to characterise the phase behaviour and thermal stabilities. It was found that these chiral monomers and polymers were beneficial for the formation of the mesophases when a flexible spacer was inserted between the mesogenic core and terminal menthyl groups. M1–M3 showed enantiotropic chiral smectic C phase and cholesteric phase, and monotropic cubic blue phase on cooling cycle. M4 only showed cholesteric phase. P1–P4 showed a smectic A phase. With increasing the mesogenic core rigidity or decreasing the spacer length, the corresponding melting temperatures, glass transition temperatures and isotropic temperatures all increased.     

A NEW STRATEGY FOR THE DESIGN OF LIQUID CRYSTALLINE POLYMERS WITH FLEXIBLE AND APOLAR BUILDING BLOCKS

The synthesis and characterization of a new series of liquid crystalline polymers, poly(dicycloalkylvinylterephthalate)s, are reported. The basic building blocks of these polymers are not mesogenic by themselves. However,very stable mesophases can be generated by self-assembly of the polymer molecules. This approach suggests a novel designstrategy of liquid crystalline polymers with flexible and apolar building blocks.     

刚性链侧链型液晶高分子（甲壳型液晶高分子）研究进展

普通的侧链型液晶高分子属柔性链高分子,而“甲壳型液晶高分子”虽从化学结构着属于侧链型液晶高分子,其性质却和典型的眩链型液晶高分子相似,具有很大的分子链刚性。本文介绍了“甲型液晶高分子”这一科学概念及其研究进展,并对尚待解决的问题进行了探讨。