Ethylene-propylene copolymerization with bis(beta-enaminoketonato) titanium complexes activated with modified methylaluminoxane

Ethylene-propylene copolymerization, using [(Ph)NC(R-2)CHC(R-1)O](2)TiCl2 (R-1 = CF3, Ph, or t-Bu; R-2 = CH3 or CF3) titanium complexes activated with modified methylaluminoxane as a cocatalyst, was investigated. High-molecular-weight ethylene-propylene copolymers with relatively narrow molecular weight distributions and a broad range of chemical compositions were obtained. Substituents R-1 and R-2 influenced the copolymerization behavior, including the copolymerization activity, methylene sequence distribution, molecular weight, and polydispersity. With small steric hindrance at R-1 and R-2, one complex (R-1 = CF3; R-2 = CH3) displayed high catalytic activity and produced copolymers with high propylene incorporation but low molecular weight. The microstructures of the copolymers were analyzed with C-13 NMR to determine the methylene sequence distribution and number-average sequence lengths of uninterrupted methylene carbons.

Preparation of TiO2 nanocrystallites by hydrolyzing with gaseous water and their photocatalytic activity

TiO2 nanocrystallites were prepared front precursors tetra-n-butyl titanate (Ti(OC4H9)(4)) and titanium tetrachloride (TiCl4). The precursors were hydrolyzed by gaseous water in autoclave, and then calcined at predetermined testing temperatures. The samples were characterized by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR), and UV-vis diffuse reflectance spectra (DRS). The photocatalytic activities of the samples were evaluated by the photobleaching of methylene blue (MB) in aqueous solution and the photocatalytic oxidation of propylene in gas phase at ambient temperature. The results showed that the anatase phase nanocrystalline TiO2 could be obtained at relatively low temperatures (for precursor Ti(OC4H9)4 at I I VC and for TiCl4 at 140 degrees C, respectively), and that the as prepared samples exhibited high photocatalytic activities to photobleach MB in aqueous solution. As the calcination temperatures increasing. the decolor ratio of MB increased and reached the maximum value of nearly 100% at 600 degrees C, and then decreased. The photobleaching of MB by all samples followed the pseudo-first-order kinetics with respect to MB concentration.

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.

Interactions of thiamine monophosphate (TMP) with one- and two-dimensional polymeric halogenomercurate anions. Crystal structures of (TMP)(Hg2Br5)center dot 0.5H(2)O and (TMP)(2)(Hg3I8)

An investigation into the interactions between thiamine monophosphate (TMP) and anions has resulted in the preparation and X-ray characterization of the compounds (TMP)(Hg2Br5).0.5H(2)O (1) and (TMP)(2)(Hg3I8) (2). In each compound the TMP molecule exists as a monovalent cation in the usual F conformation. The halogenomercurate anions occur in two-dimensional (2-D) network in 1 or one-dimensional (1-D) chain in 2. In both 1 and 2, the structures consist of alternating cationic sheets of the hydrogen-bonded TMP molecules and anionic sheets of the polymeric halogenomercurate anions. The TMP molecule binds to the polymeric anions through the characteristic 'anion bridge I', C(2)-H..X...pyrimidinium (X = Br in 1 and 1 in 2), and electrostatic interactions between electropositive S(1) and halogen atoms. The 'anion bridge II' of the type N(4'1)-H...X...thiazolium (X = phosphate group) plays a role in stabilizing the molecular conformation. The biological implication of the host-guest-like complexation between TMP and polymeric anions is discussed.

Synthesis and crystallization of a novel poly(ether ketone ether ketone ketone) containing meta-phenylene linkage: PEKEKK(T/I)

Poly(ether ketone ether ketone ketone) containing meta-phenylene linkage (PEKEKK(T/I)) was synthesized by electrophilic Friedel-Crafts acylation condensation of 1, 4-diphenoxybenzophenone with terephthaloyl chloride (T) and isophthaloyl chloride (I) with a T/I ratio of 1 and characterized by LR,DSC,TGA and WAXD. PEKEKK(T/I) has two different crystal structures: a conventional Farm I structure, the same as that observed in PEEK and PEK, wich is usually developed from melt crystallization, and a new Form II structure which can be developed from cold crystallization or solvent induced crystallization (by exposing the glassy sample to methylene chloride).

Tuning the aggregation of polyimide thin films by modification of their molecular interactions

Thin films of an organo-soluble polyimide based on 1,4-(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA) have been studied. A prism coupler was used to measure the refractive indices. The average refractive indices of thin films prepared by annealing at different temperatures and times were chosen to characterize the condensation states of thin films. Thin films annealed at 200 degrees C show irreversible changes in physical properties, eg solubility. FTIR spectroscopy showed that the chain structures of the above thin films remained unchanged. It is proposed that specific molecular interactions induce the irreversible changes revealed by fluorescence spectroscopy. (C) 2000 Society of Chemical Industry.

Study on a novel polyimide precursor prepared by a modified polymerization of monomeric reactants (MPMR) procedure

A novel polyimide precursor based on the dimethyl ester of 3,3',4,4'-biphenyltetracarboxylic acid, 4,4'-methylene dianiline and the monomethyl ester of 5-norbornene-2,3-dicarboxylic acid (BPDE/MDA/NE) was prepared by a modified polymerization of monomeric reactants (PMR) approach (MPMR). The composition of the precursor was quantitatively characterized by means of FTIR, HPLC and GC. The fractions of imide, amic ester and amic acid units in the precursor, typically prepared by refluxing in 1,4-dioxane for 2 h, were 33.7, 30.8 and 1.1 mol-%, respectively. The portion of free MDA was 3.34 wt.-% as determined by HPLC.

Synthesis and crystallization behavior of poly(ether ether ketone ether ketone) (PEEKEK)

In this paper, the synthesis and crystallization behavior of poly(ether ether ketone ether ketone) (PEEKEK) are reported. PEEKEK was prepared from 4,4'-bis(p-fluorobenzoyl) diphenyl ether (4,4'-FBDE) and hydroquinone along the nucleophilic substitution route. The thermal properties were investigated by using DSC and TGA. The crystallization behavior of PEEKEK under several conditions, i.e., crystallization from the molten state (melt crystallization), crystallization from a quenched sample (cold crystallization) and crystallization induced by exposing glassy sample to methylene chloride (solvent-induced crystallization) has also been investigated. The results show that crystallization of PEEKEK could be induced by the above methods, and no polymorphism was found. The differences in the crystallization of PEEKEK induced by the above methods are seen in their degree of crystallinity.

Spectrometric investigation on the thermooxidative degradation of ethylene oxide and tetra-hydrofuran co-polyether

The thermooxidative degradtion of ethylene oxide and tetra-hydrofuran (EO-THF) co-polyether has been studied by electron spin resonance (ESR), Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The initial degradation site was found to be at the a-carbon of the ether bond. Two free radicals which derived from dehydrogenation and oxygen addition were successfully detected by spin-trapping technique which used alpha -phenyl-N-tert-butyl nitrone(PBN) as spin trap. Both FT-IR and NMR have been used to follow structural changes of the copolyether during degradation. Nearly 20 product fragments including formate, carbonate, methyl, alcohol, methylene-dioxy, hydroperoxide and semiformal have been characterized by D-1 and D-2 NMR. The thermooxidtion of co-polyether preferred to occur on the THF units especially at the alternating linkage of EO and THF. Antioxidant (BHT) not only retarded the thermooxidation but also modified the degradation products with less ester and methylene-dioxy groups hut more hydroxyl and methyl groups.

Electrostatic-field-induced chain alignment of liquid crystalline copolyether TPP thin films

A liquid crystalline (LC) copolyether has been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane with 1,7-dibromoheptane and 1,11-dibromoundecane with a 50/50 (both in %) equal composition of the 7- and 11-methylene monomers [coTPP-7/11(5/5)]. A mono-domain with a homeotropic alignment can be induced by a thin film surface in the LC phase. When an electrostatic field is applied to the surface-induced mono-domains parallel to the thin film surface normal, the molecular alignment undergoes a change from the homeotropic to uniaxial homogeneous arrangement. However, when the field is applied to a direction perpendicular to the thin film surface normal. the molecular alignment is about 10 degrees -tilt with respect to the homeotropic alignment toward the a*-axis. This is because the permanent dipole moment of the copolyether is not right vertical to the molecular direction. The calculation of molecular dipoles indicates that the permanent dipole moment of this copolyether is about 70 degrees away from the molecular axis, which leads to a negative dielectric anisotropy. It is speculated that the 10 degrees- rather than 20 degrees -tilt is due to a balance between the alignment induced by the electrostatic field and the surface. In the electrostatic field, molecules are subjected to a torque tau, which is determined by the permanent dipole moment P and the electrostatic field E: tau = P x E. The molecular realignment in both parallel and perpendicular directions to the thin film surface normal is determined by satisfying the condition of tau = P x E = 0. (C) 2001 Elsevier Science Ltd. All rights reserved.

Syntheses of novel macrocyclic polyarylate oligomers based on phenolphthalein and m-phthaloyl-dichloride

Novel macrocyclic oligomers were synthesized through the condensation of phenolphthalein and m-phthaloyl-dichloride with triethylamine as catalyst in the mixed solution of methylene chloride and THF via pseudo-high-dilution technique. The oligomers were characterized by IR, H-1 NMR, MS, WAXD, TGA and DSC. It was found that the 3 : 3 adduct (molar ratio of phenolphthalein to m-phthaloyl-dichloride) and the 4 : 4 adduct were the main products and there was a small amount of crystalline in the macrocyclic mixtures. When the mixtures were heated to 360 degrees C, the crystalline disappeared.

Oxidation of NADH by dopamine incorporated in lipid film cast onto a glassy carbon electrode

Stable lipid film was made by casting lipid in chloroform onto a glassy carbon electrode. This model of a biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by dopamine. After this electrode had been immersed in dopamine solution for 10 h, it was found that some dopamine had been incorporated in the film. The cyclic voltammogram was obtained for the oxidation of 2.0 X 10(-3) mol 1(-1) NADH with dopamine incorporated in the films. All electrochemical experiments were performed in 0.005 mol 1(-1) phosphate buffer (pH 7.0) containing 0.1 mol 1(-1) NaCl without oxygen. The oxidation current increased gradually with successive sweeps and reached steady state. It was a different phenomenon from previous results. The anodic overpotential was reduced by about 130 mV compared with that obtained at a bare glassy carbon electrode. The diffusion coefficient for 2.0 X 10(-3) mol 1(-1) NADH was 6.7 X 10(-6) cm(2) s(-1). (C) 1999 Elsevier Science S.A. All rights reserved.

Sol-gel thin-film immobilized soybean peroxidase biosensor for the amperometric determination of hydrogen peroxide in acid medium

An acid-stable soybean-peroxidase biosensor was devel oped by immobilizing the enzyme in a sol-gel thin film. Methylene blue was used as a mediator because of its high electron-transfer efficiency. The sol-gel thin film and enzyme membrane were characterized by FT-IR, and the effects of pH, operating potential, and temperature were explored for optimum analytical performance by using the amperometric method. The H2O2 sensor exhibited a fast response (5 s), high sensitivity (27.5 mu A/mM), as well as good thermostability and long-term stability. In addition, the performance of the biosensor was investigated using flow-injection analysis (FIA).

Specific mass spectrometric fragmentations from the dissociation of intermediate ion-neutral complexes

It is reported that two kinds of specific mass spectrometric fragmentations are generated from dissociations of the intermediates of both the ion-neutral complex and the proton-bound complex. Collision-induced dissociation, isotopic labelling, and semi-empirical AM1 calculations were used to investigate the formation mechanism of the ion of m/z 139 from ionized tetrahydroimidazole-substituted methylene beta-diketones and the unimolecular fragmentations pathway of 3-phenyl-1-butyn-3-ol upon electron impact.

Chain conformation of a high-performance polyimide in organic solution

An organo-soluble polyimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2'dimethyl-4,4'-methylene dianiline (DMMDA), was synthesized via two-step polycondensation accompanied by chemical imidization. Five fractions were prepared by fractionation. The dilute solutions of the fractions were studied by LLS (Laser Light Scattering) and the intrinsic viscosities of the fractions were measured. The unperturbed dimension was determined by the intrinsic viscosity with the Stockmayer-Fox equation. The results indicate that the polyimide in this study has a flexible chain conformation in chloroform and N,N-dimethyl acetamide (DMAc). However, the degree of chain expansion differs in different solvents. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.