Hydrolysis-Polycondensation in Binary Phosphorus Alkoxides—TEOS System Studied by GC-MS

It is well known that various phosphorus precursors exhibit different reactivities towards hydrolysis-polycondensation in acidic media. The hydrolysis-condensation in binary P-alkoxides—TEOS system was studied by GC-MS, in relation to the mentioned reactivity. As P-precursors, the following reagents were used: PO(OMe)₃, PO(OEt)₃, PO(OBu)₃, P(OEt)₃ and HOP(OMe)₂. PO(OMe)₃, PO(OEt)₃ and PO(OBu)₃ do not hydrolyze, but change the TEOS hydrolysis-polycondensation ratio. P(OEt)₃ partially hydrolyzes and transforms into a very stable HOP(OEt)₂ form, while HOP(OMe)₂ reacts very fast with nonparental solvent and undergoes transesterification. Si–O–P bonds have not been observed in early stages of hydrolysis-polycondensation. However, the gelling tendency is strongly influenced by the P-precursor.     

Single-site catalyst immobilization using magnesium chloride supports

Immobilization and activation of a broad range of titanium-, chromium-and nickel-based single-site catalysts for ethylene polymerization has been carried out using supports of type MgCl₂/AlR_n(OEt)_{3 − n} , prepared by reaction of AlR₃ with adducts of magnesium chloride and ethanol. The spherical particle morphology of the support is retained and replicated during catalyst immobilization and polymerization, yielding polyethylenes with controlled particle size and morphology. The single-site nature of these catalysts is also retained, giving polymers with narrow molecular weight distribution. Furthermore, very high catalyst activities can be obtained as a result of a stabilizing effect of the support, which prevents the rapid decay in activity often observed in homogeneous polymerization with these catalysts. The text was submitted by the authors in English.     

Influence of monomer structure on chemo- and stereoselectivity of 1,3-diene polymerization

MAO/CpTiCl₃ is an active catalyst for the polymerization of various types of 1,3-dienes. Butadiene, (E) - and (Z) −1,3-pentadiene, (E) −2-methyl-1,3-pentadiene and 2,3-dimethylbutadiene yield, at room temperature, polymers with a cis-1,4 or a mixed cis/1,2 structure. 4-Methyl-1,3-pentadiene and (E,E) −2,4-hexadiene give, respectively, a 1,2 syndiotactic and a trans-1,4/1,2 polymer. MAO/CpTiCl₂·2THF and MAO/(CpTiCl₂)_n are less active than the CpTiCl₃ catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)-1,3-pentadiene: a cis-1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis-η⁴ at +20°C and may be trans-η² at −20°C. Results obtained with catalysts from CpTi(OBu)₃ and Ti(OBu)₄ are reported for comparison. An interpretation is given of the formation of cis-1,4 isotactic poly(2-methylpentadiene) and of 1,2 syndiotactic poly(4-methylpentadiene), as well as of syndiotactic polystyrene.     

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS,PL, and EPR

The electronic structure and photoactivation process in N‐doped TiO₂ is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO₂ catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti³⁺ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO₂, the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N_s^.), oxygen vacancies with one electron (V_o^.), and Ti³⁺ ions are produced with light irradiation and the intensity of N_s^. species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO₂ corresponding to the main absorption band at 410 nm of N‐doped TiO₂, but oxygen vacancies and Ti³⁺ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO₂ is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic N_s^. species but they stabilize the active nitrogen species N_s^?.     

Reaction of Metal Alkoxides with Lysine: Substitution of Alkoxide Ligands vs. Lactam Formation

Summary. Reaction of Ti(OEt)₄ with lysine results in the formation of Ti(OEt)₃(lysinate), as previously reported. Contrary to that, Al(O^sBu)₃ only catalyzes the formation of 3-aminocaprolactam, and no substitution product was observed. The reaction of Zr(OBu)₄ with lysine at room temperature produced both 3-aminocaprolactam and Zr(OBu)₃(lysinate); the lysinate complex was not observed when the reaction was performed at elevated temperatures.Received February 17, 2003; accepted February 21, 2003 Published online June 12, 2003     

Synthesis,Characterization, and Properties of Aligned Polyacetylene Films

Highly aligned polyacetylene films are synthesized by three different methods in which nematic liquid crystals are used as an ordered matrix solvent: Method 1, polymerization of acetylene is carried out in a quiescent nematic solution in which a Ti(OBu)₄-AlEt₃ Ziegler-Natta catalyst is dissolved homogeneously; Method 2, macroscopic alignment is attained by gravity flow of the nematic liquid crystal-catalyst system; and Method 3, the nematic liquid crystal-catalyst solution is aligned under a magnetic field. Characterization of these films is carried out through SEM observation and measurements of polarized visible and infrared absorption spectra. Results indicate that as-prepared films have highly aligned fibrils. Upon doping by I₂ and AsF₅, these films exhibit high electrical condactivity of the order of 10₄ S/cm.     

Single-chain nanoparticle catalyzed polymerization toward composite nanoparticles

Single-chain nanoparticles (SCNPs) as a confined space are promising to synthesize structured nanoparticles. We report a facile synthesis of SCNP colloidal initiators by loading reducing agents during the formation of the SCNPs and the application in redox free radical polymerization to achieve composite nanoparticles with tunable compositions and microstructures. The SCNP initiators could be large-scale achieved by electrostatic-mediated intramolecular crosslinking polymers by metallic complexation with protonated PVP at ambient temperature. The catalytic polymerization occurs inwardly under facile conditions to large scale fabricate composite nanoparticles with tunable microstructures from core-shell to tadpole-shapes. The facile approach could be extended to derive functional composite nanoparticles by loading desired materials such as paramagnetic Fe₃O₄, catalytic Pt, and enzymes.     

Synthesis and spectral properties of new N-substituted naphthalimide luminophores for structural coloration of polymethylmethacrylate and polystyrene

Two new unsaturated acryloxide derivatives of 4-amino-substituted-1,8-naphthalimide luminophores were synthesized. Their absorption and fluorescent properties were determined in both CHCl₃ and C₂H₅OH. The luminophores display a broad absorption band in the visible spectral region (halfband-width up to 4433 cm⁻¹) and a fluorescence in the yellow-green region (526–530 nm). The compounds are yellow colored, with a high brightness (from 2.92 up to 6.75) and a purity of color. The possibility of including naphthalimide luminophores in copolymerization process with ST and MMA resulting in the formation of colored polymers was investigated. It was found that no changes in the chemical structure of the chromophore group occurred during copolymerization. More than 92% of the initial luminophores were bound to the polymer chain. The influence of the luminophores on the kinetics of polymerization was studied, and the average viscosimetric molecular weight, M_v, of the obtained colored polymers estimated. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1069–1076, 1997     

Identification and dosimetric features of γ-irradiated cefadroxil by electron spin resonance

In the present work, electron spin resonance (ESR) identification of γ-irradiated cefadroxil monohydrate (CM), duricef capsule (DC) and duricef suspension (DS) and their potential use as normal and/or accidental dosimetric materials were investigated in the dose range of 1–25 kGy. Although unirradiated samples did not exhibit any ESR signals, irradiated samples were observed to present ESR spectra with many resonance lines originating from radiation induced radical or radicals. Dose-response curves associated with the resonance peak heights of CM (I₁, I₂) and DS (I₃, I₄, I₅, I₆) were found to follow linear and power functions of applied radiation dose, respectively. Simulation calculations were performed to determine the structure and spectral parameters of the radiation-induced radicalic species involved in the formation of experimental ESR spectrum of CM using, as input, the room temperature signal intensity data obtained for a sample irradiated at dose of 10 kGy. Kinetic behaviors and activation energies of the radicalic species were also calculated using the data obtained from annealing studies performed at five different temperatures. The presence of detectable signal intensities even after a storage period of 100 days was considered as providing an opportunity in the discrimination of irradiated CM and DS from unirradiated ones. Basing on room temperature signal intensity decay and dose–response data, it was concluded that CM and DS present the features of a good dosimetric material.     

Realizing high hydrogen evolution activity under visible light using narrow band gap organic photocatalysts

The design and synthesis of conjugated semiconducting polymers for photocatalytic hydrogen evolution have engendered intense recent interest. However, most reported organic polymer photocatalysts show a relatively broad band gap with weak light absorption ability in the visible light region, which commonly leads to a low photocatalytic activity under visible light. Herein, we synthesize three novel dithieno[3,2-b:2′,3′-d]thiophene-S,S-dioxide (DTDO) containing conjugated polymer photocatalysts by a facile C–H arylation coupling polymerization reaction. The resulting polymers show a broad visible light absorption range up to 700 nm and a narrow band gap down to 1.81 eV due to the introduction of the DTDO unit. Benefiting from the donor–acceptor polymer structure and the high content of the DTDO unit, the three-dimensional polymer PyDTDO-3 without the addition of a Pt co-catalyst shows an attractive photocatalytic hydrogen evolution rate of 16.32 mmol h⁻¹ g⁻¹ under visible light irradiation, which is much higher than that of most reported organic polymer photocatalysts under visible light.

Narrow band gap conjugated polymer photocatalysts containing dithieno[3,2-b:2′,3′-d]thiophene-S,S-dioxide show an attractive photocatalytic hydrogen evolution rate of 16.32 mmol h⁻¹ g⁻¹ under visible light irradiation.     

Effects of nano graphene oxide as support on the product properties and performance of Ziegler–Natta catalyst in production of UHMWPE

The synthesis of mono‐ and bi‐supported Ziegler–Natta catalysts using magnesium etoxide Mg(OEt)₂ and graphene oxide (GO) as catalyst support for production of Ultra High Molecular Weight Polyethylene (UHMWPE) is reported in this investigation. Nano‐graphene oxide was prepared by the modified Hummer's method and its structure was analyzed by XRD and FTIR indicating the presence of hydroxyl groups on graphene oxide and the formation of an exfoliated structure. The activity of TiCl₄/Mg(OEt)₂, TiCl₄/Mg(OEt)₂‐GO, and TiCl₄/GO catalysts in terms of grams of PE produced per mmol of Ti per hour was experimentally obtained for catalysts with different ratios of co‐catalyst (triisobutylaluminium) to TiCl₄. For all three series of catalysts, the activity curve showed an optimum point at a specific Al/Ti molar ratio. Catalyst activity was highest for TiCl₄/Mg(OEt)₂ and lowest for TiCl₄/GO. The characterization of UHMWPE products indicated that the viscosity average molecular weight (Mv) was highest for the polymer produced by TiCl₄/Mg(OEt)₂ and lowest for the polymer produced by TiCl₄/GO. Furthermore, thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA), and mechanical tensile testing were conducted on the prepared polymers indicating that the polymer produced by TiCl₄/GO had the highest thermal and mechanical properties, while these properties were at their minimum for polymers produced by TiCl₄/Mg(OEt)₂. Copyright © 2015 John Wiley & Sons, Ltd.     

Radiolysis of Aqueous Solutions of Poly(ethylene oxide) at 77 K

Low-temperature (77 K) γ-radiolysis of aqueous solutions of poly(ethylene oxide) was studied by ESR spectroscopy. Trapped electrons, hydroxyl radicals, and -CH₂-ĊH-O- radicals were identified as principal paramagnetic products of radiolysis. It was shown that an increase in the polymer concentration in solution led to a growth in number of trapped electrons and -CH₂-ĊH-O- macroradicals. The decay of hydroxyl radicals occurring at 110–115 K was accompanied by the formation of -CH₂-ĊH-O- macroradicals and partial recombination of hydroxyl radicals. Action of visible light resulted in virtually quantitative transformation of trapped electrons into -CH₂-ĊH-O- macroradicals. The radiation-chemical yields of the species trapped at 77 K were estimated and the scheme of radiation-induced chemical processes was suggested.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 243–249.Original Russian Text Copyright © 2005 by Zakurdaeva, Nesterov, Feldman.     

Preparation and photocatalytic activity of magnetic samarium-doped mesoporous titanium dioxide at the decomposition of methylene blue under visible light

Preparation of samarium-doped mesoporous titanium dioxide (Sm/MTiO₂) coated magnetite (Fe₃O₄) photocatalysts (Sm/MTiO₂/Fe₃O₄) and their activities under visible light were reported. The catalysts with Sm/MTiO₂ shell and a Fe₃O₄ core were prepared by coating photoactive Sm/MTiO₂ onto a magnetic Fe₃O₄ core through the hydrolysis of tetrabutyltitanate (Ti(OBu)₄, TBT) with precursors of Sm(NO₃)₃ and TBT in the presence of Fe₃O₄ nanoparticles. The morphological, structural and optical properties of the prepared samples were characterized by BET surface area, transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The effect of Sm ion content on the photocatalytic activity was studied. The photocatalytic activities of obtained photocatalysts under visible light were estimated by measuring the decomposition rate of methylene blue (MB, 50 mg/L) in an aqueous solution. The results showed that the prepared photocatalyst was activated by visible light and used as effective catalyst in photooxidation reactions. In addition, the possibility of cyclic usage of the prepared photocatalyst was also confirmed. Moreover, Sm/MTiO₂ was tightly bound to Fe₃O₄ and could be easily recovered from the medium by a simple magnetic process. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

Soluble magnesium–titanium catalysts for ethylene polymerization. I

A study has been made of a catalyst system comprising the heptane-soluble magnesium and titanium compounds in combination with an organoaluminum compound for ethylene polymerization at a high temperature. The productivity for ethylene polymerization of the catalyst system, n-butylethyl magnesium (BEM)-2-ethyl hexanol (C₈H₁₇OH)-tetra-n-butoxytitanium[Ti(OBu)₄]/diethyl aluminum chloride (DEAC) is higher than for MgCl₂-Cl₂-C₈H₁₇ OHTi(OBu)₄/DEAC and much higher than MgCl₂-Ti(OBu)₄/DEAC. The nature of the three different catalyst systems have been discussed in comparison with experimental data on polymerization behavior and the data of the elemental and x-ray diffraction analysis of the solid products obtained from the reactions between the catalyst components.     

Facile ion-exchange synthesis of Gd-doped K2Ta2O6 photocatalysts with enhanced visible light activity

One of the well-known ways of increasing the visible light absorption capability of semiconducting materials is cation doping. This study aims to use Gd doping to tailor the bandgap energy of K₂Ta₂O₆ (KTO) for photocatalytic degradation of organic pollutants under visible light irradiation. Accordingly, the parent KTO and Gd-doped KTO with different Gd concentrations (K_2-3xGd_xTa₂O₆; x = 0.025, 0.05, 0.075 and 0.1 mol%) were synthesized by hydrothermal and facile ion-exchange methods, respectively. The powder XRD, FT-IR, SEM-EDS, TEM-SAED, N₂ adsorption-desorption, XPS, UV–Vis DRS, PL and ESR techniques were used to investigate the effect of Gd dopant concentration on the structural and photocatalytic properties of KTO. The photocatalytic activity of these samples was investigated for the photocatalytic degradation of methylene blue (MB) dye in an aqueous solution at room temperature under visible light irradiation. The experimental results show that all Gd-doped KTO samples exhibit enhanced photocatalytic activity compared with parent KTO toward MB degradation. In particular, Gd-KTO obtained by doping of 0.075 mol% shows the highest photocatalytic activity among the Gd-doped samples and the degradation efficiency of MB was 79% after 180 min of visible light irradiation, which is approximately 1.5 times as high as that by parent KTO (53%). In addition, trapping experiments and electron spin resonance (ESR) analysis demonstrated that the hydroxyl radicals (^?OH) have played a crucial role in the photocatalytic degradation of MB. The reusability and stability of Gd doped-KTO with a Gd content of 0.075 mol% against MB degradation were examined for five cycles. Based on the present study results, a visible light induced photocatalytic mechanism has been proposed for Gd0075-KTO sample.     

A novel N-doped TiO2 with high visible light photocatalytic activity

A novel N-doped TiO₂ with high visible light photocatalytic activity was obtained by treating nanotube titanic acid (NTA) in NH₃ flow and investigated by means of XRD, TEM, ESR and XPS. The ESR results revealed that the visible light photocatalytic activity is originated from N-doping into TiO₂ with the forming of triplet paramagnetic species, the higher triplet paramagnetic species concentration, the better visible light photocatalytic behavior.     

Studies on polymers containing functional groups. II. Polymerization behavior of o-hydroxystyrene

The polymerization behavior of o-hydroxystyrene with free-radical and cationic initiators and without an initiator was examined. The structures thus obtained were estimated. Although polymerization behavior of o-hydroxystyrene was rather complicated, according to the results, it appeared that each polymerization more or less might simultaneously follow the two types of mechanisms: normal vinyl polymerization and polymerization through the addition to benzene nuclei. The proportion of addition to benzene nuclei was considered to be highest in the polymerization with BF₃·(OEt)₂ and lowest in that with azobisisobutyronitrile. Degrees of polymerization of these polymers were low in all cases (42–82). Some brief experiments on copolymerization of o-hydroxystyrene were carried out.     

Simultaneous Tuning Band Gaps of Cu2O and TiO2 to Form S-Scheme Hetero-Photocatalyst

Photocatalytic Z or S scheme merits higher redox potentials and faster charge separation. However, heterostructure photocatalysts with band gaps of bulk materials often have a type I band structure leading to poor photocatalytic activity. In view of this, we report simultaneous tuning of band gaps of Cu₂O and TiO₂, where quantum dot Cu₂O nanoparticles were formed on doped TiO₂ with Ti³⁺. The reduced size of Cu₂O made its conduction band more negative, whereas the introduction of Ti³⁺ made the absorption edge red shift to the visible light region. The as-formed heterostructure enabled an S-Scheme mechanism with remarkable activity and stability for visible light photodegradation of 4-chlorophenol (4-CP). The as-obtained photocatalysts’ activity demonstrated ca. 510-fold increase as compared to individual ones and a mechanical blend. The as-obtained photocatalysts maintained over 80 % for 5 cycles and 2 months exposure to O₂ did not decrease the degradation rate. ESR characterization and scavenger experiments proved the S-Scheme mechanism.     

Photoinitiation by radical-cationic mechanism in the polymerization of isobutylene with lewis acids

ESR spectra of Lewis acids (VCl₄, TiCl₄, TiBr₄, SnCl₄, and AlBr₃) and their mixtures with isobutylene were investigated in a n-heptane solution in the dark and under irradiation at 400–480 nm at ?80 to ?150°C. A signal was observed only upon irradiating mixtures of VCl₄, TiCl₄, or TiBr₄ and isobutylene. The signal was identified as an isobutylene radical-cation by comparison with a simulated spectrum. A signal indicating the presence of peroxy radicals were recorded in measurements carried out in the presence of oxygen; these radicals originated from reaction of the isobutylene radical-cation with oxygen. Radical-cation initiation by visible light is indicated by the polymerization of isobutylene by VCl₄, TiCl₄, and TiBr₄ and by ESR spectra. The inhibiting effect of oxygen in photochemically initiated polymerization of isobutylene was also elucidated.     

POLYCYCLOTRIMERIZATION OF DIYNES,A NEW APPROACH TO HYPERBRANCHED POLYPHENYLENES*

Polycyclotrimerization of diynes was explored as a new route to hyperbranched polymers in thisinvestigation. Polymerization of terminal diynes of 1,8-nonadiyne and 1,9-decadiyne was studied usingTaCl_5, NbCl_5, Mo(CO)_4(nbd) and [Mo(CO)_3cp]_2 as catalysts (where nbd = 2,5-norbornadiene, cp = cyclo-pentadiene). A soluble polymer was obtained when the polymerization of 1.9-decadiyne was initiated byTaCl_5 at low temperature (0℃). The polymer, however, became partially soluble after purification, possiblydue to the postpolymerization-induced crosslinking. NbCl_5-catalyzed polymerization of 1,9-bis(trimethylsilyl)-1,8-nonadiyne gave a completely soluble polymer. Soluble polymers were also obtainedfrom the polymerization of 3,9-dodecadiyne initiated by NbCl_5, Mo(CO)_4(nbd), [Mo(CO)_3cp]_2, PdCl_2-ClSiMe_3 and Pd/C-ClSiMe_3. IR, UV, and NMR spectroscopic analysis revealed that different catalysts gavepolymers with different structures, ranging from linear polyenes to hyperbranched polyphenylenes. Thepolymers absorb UV light at around 250 nm and emit fluorescence at 340 nm when they are excited at 248nm.