摘要:

We have synthesized a series of mono-substituted thiophene derivatives with phenylalkyl and liquid crystalline groups and polymerized them through a chemical oxidative polymerization and a dehalogenative polycondensation, respectively. Poly(phenylalkyl-substituted thiophene)s were found to have highly stereoregular configurations composed of head to tail linkages. The dehalogenative polycondensation of the 2,5-dibrominated thiophene monomer with the liquid crystalline group at the 3-position of thiophene ring showed a monotropic nematic phase with a schlieren and droplet texture in polarizing optical micrograph. All polymers were characterized in terms of chemical and spectroscopic properties as well as electrical conductivities before and after iodine doping.

ISSN:1058-725X    

DOI:10.1080/10587259808045382

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two liquid crystalline (LC) epoxy resins consisting of LC diepoxide and LC hardner were synthesized, diglycidyloxyazoxybenzene (DGA), 4,4′-bis (ω-carboxy decanoxy) azoxybenzene (CAA10) and DGA with 4, 4′-bis (ω-hydroxy undecanoxy) azoxybenzene (HAA11), and their reaction mechanism, mesomorphic phase transition and thermal expansion were investigated by use of DSC, IR, polarized microscopy, X-ray diffractometry and capillary dilatometry. The fully gelated DGA-CAA10 formed a network structure in which one interchain crosslink was made per 5.6 repeating unit, and showed no mesophase. The DGA-HAA11 of linear typed polymer showed a smectic A phase when not fully cured, while a namatic phase when gelated. It was pointed out that the mesogenicity of epoxy resin is governed by the mesogenicity of monomers but is also correlated with the crosslinking density and degree of polymerization. In the fully gelated DGA-CAA10, thermal expansion coefficient (α) was about 2.2 × 10−4°C−1below Tg and 3.4 × 10−4°C−1above Tg, while about 2.3 × 10−4°C−1below Tg and above 6.5 × 10−4°C−1above Tg in the fully gelated DGA-HAA11. It is noted that the α value for DGA-CAA10 is low even above Tg.

ISSN:1058-725X    

DOI:10.1080/10587259808045383

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Alignment and photo polymerization of UV-curable liquid crystals in conjunction with non-polymerizable liquid crystals are discussed.

ISSN:1058-725X    

DOI:10.1080/10587259808045384

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Phase-separation behavior of the composite films composed of polymer of a three dimensional network and low molecular weight liquid crystals (LCs) embedded in the network was studied on the basis of the evolution of optical heterogeneity in a casting solution during a film formation process and the morphology of the polymer networks. The electro-optical properties of the composite films based on electric field controlled light scattering were strongly dependent on the size of LC domains which was controlled by the solvent evaporation rate. When poly(diisopropyl fumarate), which is incompatible with the LC, was used as the matrix polymer, no electro-optical hysteresis was detected, while considerable electro-optical hysteresis was done for the composite film consisting of poly(methyl methacrylate), which is fairly compatible with the LC. However, when poly(methyl methacrylate) with high molecular weight (996k) was used as the matrix polymer, hysteresis decreased due to a decrease of compatibility.

ISSN:1058-725X    

DOI:10.1080/10587259808045385

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The dielectric properties of liquid crystal materials containing ionic impurities are analyzed in terms of space charge polarization. The theoretical expressions of the dielectric constant and the dielectric loss factor are derived by solving a diffusion equation for mobile ions under an AC field. Numerical calculations are performed using the theoretical expressions and the frequency dependent dielectric behaviors are simulated. The calculated curves for the dielectric constant and the dielectric loss factor exhibit a dielectric dispersion and a dielectric absorption respectively in a low frequency region, and successfully trace the observed curves obtained for liquid crystal materials 4-n-pentyl-4′-cyanobiphenyl (5CB) by means of curve fitting with the parameters of the diffusion coefficient and the density of mobile ions.

ISSN:1058-725X    

DOI:10.1080/10587259808045386

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Binary mixtures of nematic 4-pentyl-4′-cyanobiphenyl (5CB) with some kinds of non-nematic solutes were found to show the increase in nematic-isotropic transition temperature, contrary to usually observed decrease. All these ‘unusual’ solutes found in this work have active hydrogen atoms which can act as hydrogen bond donor. ‘Unusual’ increase in the clearing temperature was attributed to the hydrogen bonding interaction between 5CB and solutes. The effect of hydrogen bonding interaction between 5CB and various non-nematic solutes on thermal and spectroscopic properties were studied in detail.

ISSN:1058-725X    

DOI:10.1080/10587259808045387

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Some solid and crystalline materials derived from the reactions of diorganotin(IV) with salicylaldehyde- and 3-methoxysalicylaldehyde- substituted aliphatic and aromatic Schiff's bases have been synthesized at room temperature. The 1:1 and 1:2 molecular adducts thus obtained have been characterized by elemental analyses, differential scanning calorimetry and NMR spectroscopic techniques which indicated that the coordination to tin occurs through the hydroxyl oxygen. The single crystals of 1:1 and 1:2 (tin:Schiff's base) diphenyltin(IV) and dibutyltin(IV) adducts with 6-methoxy-l-[(4-cyanophenylimino)methyl]phenol and (2- (phenylethylimino)methyl) phenol have been carried out using the charged-coupled device (CCD) area detector and four-circle diffractometers, respectively. The geometries about the Sn atom in both 1:1 and 1:2 materials are trigonal bipyramidal and octahedral. The DSC spectra of the adducts possessing the long alkoxylated group at the lateral position appear to suggest the existence of liquid crystal/isotropic liquid biphasic region.

ISSN:1058-725X    

DOI:10.1080/10587259808045388

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new series of cyclotriphosphazenes bearing Schiff bases with different carbon number alkoxy end groups(HAICP) in the side chains were synthesized and their phase transitions and liquid crystallinity were studied using DSC measurements and polarizing microscope observations. We found a monotropic Sml phase for n = 3 and an enantiotropic Sml phase for n = 4 −5, enantiotropic Sml, SmC and SmA phases for n = 6 – 7, enantiotropic SmC and SmA phases for n = 8 – 10, and enantiotropic Sm2, SmC and SmA phases for n=11 and 12 in the HAICP series. The Sml phase is a low-order uniaxial smectic phase and Sm2 phase is a low-order biaxial smectic phase. The melting point decreased with an increase in the end alkoxy carbon number, n, of the cyclotriphosphazenes, but the clearing point decreased with an increase in n. As a result, the mesomophic region expands with an increase in n. The melting and clearing points do not show clear odd-even effects, which is caused by the peculiar shape of the cyclotriphosphazenes.

ISSN:1058-725X    

DOI:10.1080/10587259808045389

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Structures and tensile properties were investigated for magnetically oriented commercial thermotropic liquid crystalline copolyesters, Xydar and Rodrun. The orientation dependence and the magnitude of the tensile properties were similar between these two copolyesters. Comparison was made with the results obtained for the mechanically oriented samples of these copolyesters. It was found that the ultimate tensile strength and the elongation at break obtained for the magnetically oriented samples were different from those obtained for the mechanically oriented samples. Structure analyses conducted by means of polarizing microscope and X-ray diffraction showed that the two different orientation methods provide different structures on macroscopic as well as microscopic levels. The difference in the tensile properties could be attributed to the difference in structures.

ISSN:1058-725X    

DOI:10.1080/10587259808045390

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In order to investigate the effect of hydrogen bonding formed between carboxylic acid groups on thermal properties of the side chain type liquid crystalline polymers, we synthesized the side chain type copolymers composed of a mesogenic monomer and a non-mesogenic monomer with carboxylic acid group. Hydrogen bonding was examined by thermally controlled FT-IR measurements. A mesophase was exhibited for the copolymers containing the mesogenic monomer above 40∼65 mol%. The mesomorphic temperature range(MR) of the copolymers increased in the order of the copolymer with methacrylic acid monomer, with benzoic acid monomer containing a flexible spacer and with benzoic acid monomer. This difference in the MR of the copolymers was demonstrated by FT-IR quantitative analysis of the area of the peak assigned to the dimer structure of the carboxylic acid group.

ISSN:1058-725X    

DOI:10.1080/10587259808045391

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor