Study on a carbosilane liquid crystalline (LC) dendrimer of the first generation - Containing twelve 4-butoxyazobenzene mesogenic groups in periphery

The divergent synthesis of a new carbosilane liquid-crystalline (LC) dendrimer of the first generation (D1) is described. Twelve 4-butoxyazobenzene groups are used as mesogenic fragments and attached in the periphery of the molecule. Structure and properties of D1 were characterized by element analysis, H-1 NMR, MALDI-TOF-MS, IR, UV-Vis, polarizing optical micrograph, DSC and WAXD. It is argued that mesophase of nematic type is realized. It is shown that the mesophase type of the dendrimer essentially depends on the chemical nature of the mesogenic groups. Phase behavior of D1 is K82N1331132N67K. The melting point of D1 is 30similar to43 degreesC lower than that of M5, its clearing temperature is 9 similar to 11 degreesC higher than that of M5 and its mesophase region is enlarged by 39 similar to 54 degreesC compared to that of M5. Eight extinguished brushes emanating from a stationary point are observed, corresponding to the high-strength disclination of S = + 2 of dendrimer. The clearing enthalpy of D1 is smaller than the value that is commonly found for phase transition n-i in LC and LC polymers. This may be due to the presence of branched dendrimer cores which cannot be easily deformed to fit into the anisotropic LC phase structure.

Liquid crystalline phases, microtwinning in crystals and helical chirality transformations in a main-chain chiral liquid crystalline polyester

A main-chain nonracemic chiral liquid crystalline polymer was synthesized from (R)-(-)4'-{w-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-decyloxyl-4-biphenylcarboxylic acid. This polymer contained 10 methylene units in each chemical repeating unit and was abbreviated PET(R*-10). On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy experiments, chiral smectic C (S-C*) and chiral smectic A (S-A*) phases were identified. Both flat-elongated and helical lamellar crystal morphologies were observed in transmission electron microscopy. Of particular interest was the flat-elongated lamellar crystals were constructed via microtwinning of an orthorhombic cell with dimensions of a = 1.42 nm, b = 1.28 nm, and c = 3.04 nm. On the other hand, the helical lamellar crystals were exclusively left-handed, which was opposite to the right-handed helical crystals grown in PET(R*-9) and PET(R*-11) (having 9 and 11 methylene units, respectively). Note that these three polymers had identical right-handed chiral centers (R*-). Therefore, a single methylene unit difference on the polymer backbones on an atomic length scale substantially changed the chirality of the crystals in the micrometer length scale. Furthermore, aggregates of these helical crystals in PET(R*-10) did not generate banded spherulites in polarized light microscopy. Possible reasons for this change and loss of helical senses (handedness) on different length scales in chirality transferring processes were discussed.

Compatibilization by main-chain thermotropic liquid crystalline ionomer of blends of PBT/PP

The miscibility and mechanical properties of the blends of polybutylene terephthalate (PBT) and polypropylene (PP) with a liquid crystalline ionomer (LCI) containing a sulfonate group on the terminal unit as a compatibilizer were assessed. SEM and optical microscopy (POM) were used to examine the morphology of blends of PBT/PP compatibilized by LCI. DSC and TGA were used to discuss the thermal properties of PBT/PP blends with LCI and without LCI. The experimental results revealed that the LCI component affect, to a great extent, the miscibility and crystallization process and mechanical property of PBT/PP blends, The fact is that increasing LCI did improve miscibility of PBT/PP blends and the addition of 1% LCI to the PBT/PP blends increased the ultimate tensile strength and the ultimate elongation.

Liquid crystalline and light emitting polyacetylenes: Synthesis and properties of biphenyl-containing poly(1-alkynes) with different functional bridges and spacer lengths

Biphenyl- (Biph-) containing 1-alkynes (3 and 4) and their polymers (1 and 2) with varying bridge groups and spacer lengths were synthesized and the effects of the structural variation on their properties, especially their mesomorphism and photoluminescence behaviors, were studied. The acetylene monomers 3(3) [HCdropC(CH2)(3)O-Biph-OCO(CH2)(10)CH3] and 4(m) [HCdropC(CH2)(m)OCO-Biph-OCO(CH2)(10)-CH3, m = 3, 4] were prepared by sequential etherization and esterification reactions of 1-alkynes. While 3(3) exhibits enantiotropic crystal E and SmB mesophases, its structural cousin 4(3) displays only a monotropic SmB phase. Enantiotropic SmA and SmB mesophases are, however, developed when the spacer length is increased to 4. Polymerizations of the monomers are effected by Mo-, W-, Rh-, and Fe-based catalysts, with the WCl6-Ph4Sn catalyst giving the best results (isolation yield up to 85% and M-w up to 59000). The polymers were characterized by IR, UV, NMR, TGA, DSC, POM, XRD, and PL analyses. Compared to 1(3), 2(3) shows a red-shifted absorption, a higher T-i, and a better packed interdigitated bilayer SmA(d) structure, while the mesophase of 2(4) involves monolayer-packing arrangements of the mesogens. Upon photoexcitation, 1(3) emits almost no light but 2(m) gives a strong ultraviolet emission (lambda(max) similar to 350 nm), whose intensity increases with the spacer length.

Compatibilization of side-chain, thermotropic, liquid-crystalline ionomers to blends of polyamide-1010 and polypropylene

A novel side-chain, liquid-crystalline ionomer (SLCI) with a poly(methyl hydrosiloxane) main chain and side chains containing sulfonic acid groups was used in blends of polyamide-1010 (PA1010) and polypropylene (PP) as a compatibilizer. The morphological structure, thermal behavior, and liquid-crystalline properties of the blends were investigated by Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. The morphological structure of the interface of the blends containing SLCI was improved with respect to the blend without SLCI. The compatibilization effect of greater than 8 wt % SLCI for the two phases, PA1010 and PP, was better than the effects of other SLCI contents in the blends.

Formation of a metastable phase induced by a liquid crystalline phase in a novel chloropoly(aryl ether ketone)

The phase transition behavior of a thermotropic liquid crystalline poly(aryl ether ketone) synthesized by nucleophilic substitution reactions of 4,4'-biphenol (BP), and chlorohydroquinone (CH) with 1,4-bis(4-fluorobenzoyl)benzene (BF) has been investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The copolymer exhibits multiple first order phase transitions, which are associated with crystal-to-smectic liquid crystal transition and smectic liquid crystal-to-isotropic transition. When the cooling rate is low (<10C/min), only stable crystal from I is formed. With the cooling rate being high (>20 degreesC/min), the metastable crystal form II is formed, which always coexists with form I. The liquid crystalline phase plays an important role in the formation of metastable phase form II.

Crystal form transition during heating of solvent-induced crystalline syndiotactic polystyrene

The phase transition of two kinds of solvent-induced crystalline syndiotactic polystyrene (sPS). gamma-sPS and delta(c)-sPS, has been studied via WAXD and DSC. gamma-sPS transform to a-sPS at 195-225 degrees C before melt during heating, whereas delta(e)-sPS transform to first gamma-sPS and then a-sPS at 100-200 degrees C and 200-215 degrees C, respectively. The transition of delta(e)-gamma and gamma-a occurs for below melting point of sPS indicates they are all solid-solid transition.

The single crystal-like banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group

The banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group have been studied by means of transmission electron microscopy(TEM), electron diffraction(ED) and atomic force microscopy (AFM). The crystallization-induced Landed texture without external shear can be formed when the thin films were annealed at the temperature range(320-330 degrees C) of the liquid crystalline state from the melt, The results show that the banded regions have high orientation of single crystal based on the orthorhombic packing and the growing direction of the Lands is along the b axis of the crystals, This kind of single crystal-like bands is due to the different orientation of the packing molecular chains, The molecular chains of the dark bands in the bright field electron micrograph are perpendicular to the film plane, while the ones of the bright Lands are tilt along the b axis with the tilt angle upto +/-20 degrees.

Synthesis and thermotropic liquid crystalline behaviour of novel poly(aryl ether ketone)s with a lateral methoxy group

Novel poly(aryl ether ketone)s containing a lateral methoxy group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and methoxyhydroquinone with 1,4-bis(4-fluorobenzoyl)benzene in a sulfolane solvent in the presence of anhydrous potassium carbonate. Their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques, e.g. differential scanning calorimetry (DSC), polarized light microscopy and temperature-dependent FTIR. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 30-80 mol-% mexthoxyhydroquinone. Both melting (T-m) and isotropization (T-i) transitions appeared in the DSC curves. The polarized light microscopy study of the liquid crystalline copolymers suggested their ordered smectic structures. As expected, the copolymers had lower melting transitions than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer methoxyhydroquinone.

Shear-induced spiral-like morphology of a main-chain liquid crystalline poly(aryl ether ketone)

The shear-induced spiral-like morphology of a main-chain thermotropic liquid crystalline poly(aryl ether ketone) is observed and characterized by means of polarizing light microscopy, atomic force microscopy, transmission electron microscopy and electron diffraction techniques. The spiral-like texture is formed during shearing in the temperature range of liquid crystalline to isotropic transition (335-340 degreesC), and dispersed discontinuously in the mosaic matrix. Electron diffraction results indicate that the spiral exhibits orthorhombic lateral packing of the crystals and homeotropic alignment of the molecules. The spiral formation process and possible affecting factors are discussed.

Homoepitaxial crystallization in films of a thermotropic liquid crystalline chloro-poly(aryl ether ketone)

The homoepitaxial crystallization in the films of a thermotropic liquid crystalline chloro-ply(aryl ether ketone) is studied by transmission electron microscopy (TEM) and electron diffraction (ED). The homoepitaxy takes place in the temperature range 330-320 degreesC, in which a highly-ordered smectic crystalline phase of the copolymer with a single-crystal-like banded structure is formed during the cooling process from the isotropic melt. The homoepitaxial crystallizations with angles of 32 degrees and 122 degrees between the two b axes are the major populations observed, and possess epitaxial contact planes of (100)(I)-(210)(II) and (010)(I)-(210)(II); respectively.

Effect of branch content on the transition of crystalline structure and morphology of metallocene-catalyzed branched polyethylene

Transition of crystalline structure and morphology of metallocene-catalyzed butyl branched polyethylene with branch content has been studied. It was found that the long periods of the branched polyethylene were controlled by crystallization conditions for the lower branch content samples and by branch contents for the higher branch content samples. When the branch content increased to a critical value the branched polyethylene had no long period because the crystalline morphology was changed from folded chain crystal to a bundled crystal. The TEM observations supported the results. The transition of the crystalline morphology resulted from the reduction of lamellar thickness with increasing of branch content since the branches were rejected from the lattice. The reduction of lamellar thickness with increasing of branch content also resulted in lattice expansion and decrease of melt temperature of the branched polyethylene. (C) 2001 Kluwer Academic Publishers.

Study on a series of main-chain liquid-crystalline ionomers containing sulfonate groups

A series of main-chain Liquid-crystalline ionomers containing sulfonate groups pendant on the polymer backbone were synthesized by an interfacial condensation reaction of 4,4'-dihydroxy-alpha,alpha'-dimethyl benzalazine, a mesogenic monomer, with brilliant yellow (BY), a sulfonate-containing monomer, and a 1/9 mixture of terephthaloyl and sebacoyl dichloride. The structures of the polymers were characterized by LR and UV spectroscopies. DSC and thermogravimetric analysis were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by a polarized optical microscope, DSC, and wide-angle X-ray diffraction. The ionomers were thermally stable to about 310 degreesC. They were thermotropic liquid-crystalline polymers (LCPs) with high mesomorphic-phase transition temperatures and exhibited broad nematic mesogenic regions of 160-170 degreesC, and they were lyotropic LCPs with willowy leaf-shaped textures in sulfuric acid. However, the thermotropic liquid-crystalline properties were somewhat weakened because the concentration of BY was more than 8%. The inherent viscosity in N-methyl-2-pyrrolidone suggested that intramolecular associations of sulfonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration. (C) 2001 John Wiley & Sons, Inc.