Syntheses and properties of polyimides derived from diamines containing 2,5-disubstituted pyridine group

A Series of novel homo- and copolyimides containing pyridine units were prepared from the heteroaromatic diamines, 2,5-bis (4-aminophenyl) pyridine and 2-(4aminophenyl)-5-aminopyridine, with pyromelltic dianhydride (PMDA), and 3,3',4,4'-biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two-step thermal imidizaton method. The poly(amic acid) precursors have inherent viscosities of 1.60-9.64 dL/g (c = 0.5 g/dL in DMAC, 30 degrees C) and all of them can be cast and thermally converted into flexible and tough polyimide films. All of the polyimides show excellent thermal stability and mechanical properties. The polyimides have 10% weight loss temperature in the range of 548-598 degrees C in air. The glass transition temperatures of the PMDA-based samples are in the range of 395-438 degrees C, while the BPDA-based polyimides show two glass transition temperatures (T(g)1 and T(g)2), ranging from 268 to 353 degrees C and from 395 to 418 degrees C, respectively. The flexible films possess tensile modulus in the range of 3.42-6.39 GPa, strength in the range of 112-363 MPa and an elongation at break in the range of 1.2-69%. The strong reflection peaks in the wide-angle X-ray diffraction patterns indicate that the polyimides have a high packing density and crystallinity.

Morphology and structures of self-assembled symmetric poly(di-n-alkylsilanes)

The self-assembly of poly(di-n-butylsilane) (PDBS) and poly(di-n-hexylsilane) (PDHS) on the surfaces of amorphous carbon and highly oriented pyrolytic graphite (HOPG) have been investigated, respectively. The morphology and structures of these self-assembled thin films were studied by using atomic force microscopy, transmission electronic microscopy, and wide-angle X-ray diffraction. In the case of weak van der Waals interactions between absorbed molecules and substrate, i.e., on amorphous carbon, the self-assembly process was driven by absorbate-absorbate intermolecular interactions. For PDBS with weak absorbate-absorbate intermolecular interactions, the thin film showed organization lacking any measurable preferred orientation on the surface of amorphous carbon. While for PDHS with rigid backbone and strong intermolecular interactions, flat-on lamellae with silicon backbones perpendicular to the surface of amorphous carbon were formed. However, in the case of strong van der Waals interactions between absorbed molecules and substrate, i.e., on HOPG, the self-assembly process was tailored by the balance of absorbate-absorbate intermolecular interactions and molecule-substrate interactions. Both PDHS and PDBS thin films grew into edge-on lamellae on the surface of HOPG, which aligned according to a Mold symmetry.

Effect of alkyl group length on the conductivity in the 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins and redox properties of the metallooctakis(hexyl-thio)tetraazaporphyrins

A series of 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins (H(2)OATTAP) with different alkyl chain lengths have been synthesized. Cyclic voltammetry and differential pulse voltammetry have been used to investigate the effect of the controlled lengths of the eight peripheral thioether tails on the redox behavior of the molecules. The electrochemical reduction of octakis(hexyl-thio)tetraazaporphyrins, MOHTTAP (where M = Cu, Ni), was studied in 1,2-dichloroethane at a platinum electrode. The Cu derivative was oxidized in one single-electron-transfer step to yield a pi-cation radical and reduced in three single-electron-transfer steps to yield a pi-anion radical, dianion and trianion, respectively. For the Ni derivative, electron transfer reactions involving both the central metal atom and the macrocyclic ring were observed. Electron transfer pathways are proposed based upon voltammetric and in situ spectroelectrochemical results.

Hydrothermal synthesis and structural characterization of a novel P-V-O layered compound [H(2)en](2)[H3O](6)[Co(H2O)(2)(VO)(8)(OH)(4)(PO4)8]

A new compound [H(2)en](2)[H3O](6)[Co(H2O)(2)(VO)(8)(OH)(4)(PO4)(8)] has been hydrothermally synthesized. Single crystal X-ray analysis indicates that this compound crystallizes in a monoclinic system, space group P2(1)/n with a=1.438 5(3) nm, b=1.012 2(2) nm, c=1.832 5(4) nm, beta=90.21degrees, V=2.668 2 (9) nm(3), Z = 2, D-c = 2.112 g/cm(3), R = 0.055, wR = 0.149 7, S = 1.037. The structure of [H(2)en](2)[H3O](6)[Co(H2O)(2)(VO)(8)(OH)(4)(PO4)(8)] is characterized by P-V-O layers constructed by [(VO)4 (OH)(2)(PO4)(4)](6-) non-symmetric units. The P-V-O layers are pillared by [Co(H2O)(2)](2+) group, resulting in the channels within which the protonated diaminoethane and H3O+ are located.

The study on automorphism group of ESESOC

It is necessary to generate the automorphism group of a chemical graph in computer-aided structure elucidation. In this paper, an algorithm was developed by the all-paths topological symmetry algorithm to build the automorphism group of a chemical graph. A comparison of several topological symmetry algorithms reveals that the all-paths algorithm (APA) could yield the correct class of a chemical graph. It lays a foundation for the ESESOC system in computer-aided structure elucidation.

Aggregation behavior of amphiphilic D-pi-A molecules bearing recognition group

Aggregation behavior of two amphiphilic D-pi -A molecules bearing barbituric acid as both recogniton group and electron-drawing substituent, 5-(4-dodecyl oxybenzylidene)-(1H, 3H)-2,4,6-pyrimidine trione (PB12) and 5-(4-N,N-didodecyl aminobenzylidene)-(1H,3H)-2,4,6-pyrimidine trione (AB(12)) was studied by UV-visible, fluorescence, and surface voltaic spectroscopies (SPS). The experimental results indicate that PB12 tends to form J-aggregate and AB(12) tends to form H-aggregate under increasing concentration. An intramolecular twisted charge transfer (TICT) emission around 500 nm is observed when J-aggregate is formed between PB12 molecules, and an excimer emission around 600 nm is observed when H-aggregate is formed between AB(12) molecules.

Automorphism group algorithm in computer-aided structure elucidation

It is necessary to generate automorphism group of chemical graph in computer-aided structure eluciation. In this paper, an algorithm is developed by all-path topological symmetry algorithm to build automorphism group of chemical graph. A comparison of several topological symmetry algorithm reveals that all-path algorthm can yield correct of class of chemical graph. It lays a foundation for ESESOC system for computer-aided structure elucidation.

Synthesis and properties of three novel series of monomers containing para-methoxyazobenzene as the mesogenic group

Three novel series of monomers, namely n-1-bromo-[4-(4-methoxyphenylazo)phenyloxy]-alkanes (Bn, n = 3, 6, 10), n-[4-(4-methoxyphenylazo) phenyloxy]alkyloxy-4-methoxybenzene (Cn, n = 3, 6, 10) and n-[4-(4-methoxyphenylazo)phenyloxyl]alkyloxy-[4-methoxy-2,5-bis-(chloromethyl)] benzene (Dn, n = 3, 6, 10) were synthesized and characterized with FTIR, H-1 NMR, UV-visible and fluorescence spectroscopy. Their thermal behaviour was studied by different scanning calorimetry and polarizing optical microscopy. The results show that B3, B6 and C6 exhibit monotropic nematic liquid crystalline behaviour.

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.

Synthesis and characterization of side chain liquid crystal M5MPP/MMEANB copolymers containing NLO active group

A new series of side chain liquid crystal polymers based on the backbone of polymethacrylate containing 4-nitroazobenzene and 4-methoxybiphenyl group as side chain mesogen were prepared and characterized, FTIR, H-1 NMR, POM and WAXD were used to study the structure, phase behavior and mesophase texture of this series of SCLC copolymers. The researches show that polymer PM5MPP and copolymer M5MPP/MMEANB are enantiotropic liquid crystalline polymers, but polymer PMMEANB has no liquid crystalline properties. DSC results showed that the thermal stability of the mesophase of this series of copolymers was enhanced by the existence of intermolecular electron donor-acceptor interaction. It was found that the temperature range of the mesophase of the copolymers was broadened with increasing 4-nitroazobenzene units. The focal-conic texture observed by POM indicated that this series of the copolymers possessed the characteristics of smectic liquid crystal.

Synthesis of the first mono(cyclopentadienyl)lanthanide Schiff base complex bearing C-2-symmetric tetradentate ligand: crystal structure of [(eta(5)-C5H5)Yb(mu-OC20H20N2O)](2)(mu-THF)(THF)

Reaction of YbCl3 with 3 equimolar CpNa (Cp = cyclopentadienide) in THF, followed by treatment with trans-(+/-)-N,N'-bis(salicylidene)-1,2-cyclohexanediamine led to the isolation of first mono(cyclopentadienyl) lanthanide Schiff base complex, [(eta(5)-C5H5)Yb(mu-OC20H20N2O)](2) (mu-THF)(THF) (1). The molecular structure of 1 shows that it is a dimer in which the two [(eta(5)-C5H5)Yb(mu-OC20H20N2O)] units connecting via a bridging THF oxygen and two bridging oxygen atoms from Schiff base ligands. (C) 1998 Elsevier Science S.A.

Synthesis and X-ray crystal structure of [(eta(5)-C5H5)Sm(mu-OC20H20N2O)](2)(mu-THF)(THF)(2): Mono(cyclopentadienyl)lanthanide complex bearing a C-2-symmetric tetradentate Schiff-base ligand

Cp2SmCl(THF) reacts with 0.5 equivalent disodium salts of trans-(+/-)-N,N'-bis(salicylidene)-1,2-cyclohexanediamine give the title complex [(eta(5)-C5H5)Sm(mu-OC20H20N2O)](2)(mu-THF)(THF)(2) (1). X-ray crystal determination shows that the molecule is a dimer, in which two (eta(5)C(5)H(5))Sm(mu-OC20H20N2O) units are connected via a THF oxygen and two bridging oxygen atoms of Schiff base ligands. The average Sm-C distance is 2.78(7) Angstrom, while those of Sm-O (bridging THF oxygen) and Schiff base oxygens are 2.79(3) and 2.43(4) Angstrom; respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.

The synthesis and thermotropic liquid crystalline behaviour of novel main chain poly(aryl ether ketone)s containing a lateral phenyl group

Novel main chain poly(aryl ether ketone)s containing a lateral phenyl group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and phenylhydroquinone with either 4,4'-difluorobenzophenone or 1,4-bis(4-fluorobenzoyl)benzene and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 50 and 70mol% biphenol. Melting (T-m) and isotropization (T-i) transitions both appeared on the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline nematic state. As expected, each of the copolymers had a relatively lower melting transition than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer phenylhydroquinone.

Synthesis and investigation of monoesters of polymaleic acids with azo-group

A series of amphiphilic polymers, monoesters of polymaleic acid containing ate-side groups (PMAN-A(n)Me) was synthesized by the reaction of alcohol(A,Me) with polymaleic anhydride (PMAN) for Langmuir-Blodgett assembly. The effects of the length of flexible spacer in the side chain on the pi-A isotherms and LB films were investigated. The UV-Vis and infrared linear dichroism spectra showed that the ate-side groups were highly oriented in PMAN-A(6)Me LB film deposited on silica or CaF2 substrate.