Tetrabutoxytitanium adduct formation in esterification reactions

Different mechanisms of the catalytic action of tetrabutoxytitanium in esterification and transesterification reactions are analyzed. New evidence is obtained in favor of the nonionic mechanism of ester formation catalysis by glycol-tetrabutoxytitanium adducts in esterification reactions.     

Ligand effects on dioxygen activation by copper and nickel complexes: reactivity and intermediates

Copper and nickel complexes having various active-oxygen species M n -O 2 ( n = 1 or 2), such as trans-(micro-1,2-peroxo)Cu (II) 2, bis(micro-oxo)M (III) 2, bis(micro-superoxo)Ni (II) 2, and ligand-based alkylperoxo-M (II) n , can be produced by a series of tetradentate tripodal ligands (TMPA analogues) containing sterically demanding 6-methyl substituent(s) on the pyridyl group(s), where TMPA = tris(2-pyridylmethyl)amine. Roles of the methyl substituent(s) for the formation of the active-oxygen species and their oxidation reactivities are reported.     

Structural/textural properties and water reactivity of fluorinated activated carbons

Hydrophobic activated carbons are considered as interesting materials for air or water remediation due to their enhanced affinity for slightly water-soluble organic species. In this context, a commercial activated carbon, in an extruded form, was fluorinated under mild conditions (pure fluorine gas at room temperature) in order to decrease its hydrophilic character and to preserve its microporosity. For comparison, a hydrogenated activated carbon was also prepared by H₂ treatment. The resulting samples were characterised by various techniques in order to determine the evolution of the activated carbon materials in terms of composition (XPS, elemental analysis, TGA and NMR) and porosity (nitrogen physisorption (77 K), mercury intrusion and immersion calorimetry). For the fluorinated carbon, the nature of the CF_x groups and the strength of the C–F bonds were also investigated using ¹³C and ¹⁹F solid state NMR and TGA techniques. A labile character of the C–F bond, so far exclusively observed for fluorine intercalation compounds, is also shown for the first time for a fluorinated activated carbon by water adsorption/desorption isotherms at room temperature. Care should then be taken for its use in presence of water.     

Hydraulic reactivity and cement formation of baghdadite

In this study, the hydraulic reactivity and cement formation of baghdadite (Ca₃ZrSi₂O₉) was investigated. The material was synthesized by sintering a mixture of CaCO₃, SiO₂, and ZrO₂ and then mechanically activated using a planetary mill. This leads to a decrease in particle and crystallite size and a partial amorphization of baghdadite as shown by X-ray powder diffraction (XRD) and laser diffraction measurements. Baghdadite cements were formed by the addition of water at a powder to liquid ratio of 2.0 g/ml. Maximum compressive strengths were found to be ~2 MPa after 3-day setting for a 24-h ground material. Inductively coupled plasma mass spectrometry (ICP-MS) measurements showed an incongruent dissolution profile of set cements with a preferred dissolution of calcium and only marginal release of zirconium ions. Cement formation occurs under alkaline conditions, whereas the unground raw powder leads to a pH of 11.9 during setting, while prolonged grinding increased pH values to approximately 12.3.     

Plasticizer properties of methyl vinyl ketone-methylalpha-eleostearate adduct and derivatives

Summary The Diels-Alder adduct of methyl vinyl ketone and methylalpha-eleostearate was subjected to modification by hydrogenation and epoxidation of its unsaturated centers and by aromatization of its cyclohexene nucleus. These derivatives, as well as the original adduct, were intercompared with DOP as primary plasticizers for vinyl chloride-vinyl acetate copolymer. All of these materials were found to be highly compatible as primary plasticizers and generally more efficient than DOP. The stocks plasticized with the hydrogenated and epoxidized adducts exhibited very good thermal stability on long exposures to heat. The epoxidized adduct not only imparted excellent heat stability to the plastic but also prevented deterioration on exposure to ultraviolet irradiation. One of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Epoxy/montmorillonite nanocomposites: influence of organophilic treatment on reactivity, morphology and fracture properties

Two different alkylammonium modified montmorillonites have been dispersed in epoxy network precursors in order to study the influence of the organophilic treatment on the reactivity and cure behavior of the networks, on the morphology of the final composites and on their elastic and fracture properties. An increase in the interplatelet distance during curing of the network (in addition to the initial swelling by the network precursors) is possible when the competition between cure kinetics, diffusion kinetics and interactions between network precursors and organophilic montmorillonite allows it. Network structure is not modified and a catalytic effect of the organoclays has been demonstrated. Correlation between morphologies and mechanical properties reveals that exfoliated nanocomposites lead to interesting stiffness improvements. However, intercalated nanostructures can lead to very interesting stiffness/toughness balance for glassy epoxy networks without lowering their glass transition temperature. This suggests that stiffness and toughness improvements might not be ruled by the same kind of morphologies.     

Effect of SO3 on formation and hydraulic reactivity of belite

SO₃ accelerates the formation of belite between 1100 and 1300°C. Its effeciency rests on the permanent generation of CaO in statu nascendi by the equilibria $\text{CaSO}{}_4\text{?}\text{CaO + SO}{}_3\text{and SO}{}_3\text{?}\text{SO}{}_2\text{+}\text{1}\text{2}\text{O}{}_2$. Via the gaseous phase this CaO is transported to SiO₂ and reacts there to belite. Only 0.5 – 1.5%SO ₃ are dissolved in belite stabilizing its β-modification, but without increasing the hydraulic reactivity markedly.     

Fiber formation and properties of polyester/lignin blends

Thermotropic liquid crystalline polyesters with varied chemical structure are synthesized by melt transesterification polycondensation. They are employed as matrix for blends with lignin materials to obtain melt-spinnable precursors for carbon fibers. The lignin samples are carefully purified by fractionation, enzymatic removal of reducing sugars, and subsequent modification of the terminal OH groups. Effective melt blending is achieved with liquid-crystalline aromatic–aliphatic polyesters having melting ranges that match the softening temperature of the lignin fractions, which is necessary to prevent thermal decomposition of the lignin. Polyester/lignin blends are partially compatibilized, phase-separated materials. The polyester/lignin materials are melt-spun successfully. The fiber properties depend on the lignin purification process. X-ray scattering reveals that orientation in lignin-containing fibers is maintained. First experiments show that the fibers can be converted successfully to carbon fibers by thermal annealing procedures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48257.     

Chemical formation,characterization and properties of polycarbazole

Polycarbazole (PCz) was synthesized by chemical polymerization of carbazole in acetonitrile medium using ammonium persulfate as oxidant. The selection of solvent, concentration of the monomer, composition of the solvent, polymerization time, temperature, and pH were optimized to obtain better quality and yield of the polycarbazole. The synthesized polycarbazole was characterized by various techniques such as UV–Visible, FTIR, ¹H‐NMR, ¹³C‐NMR, COSY, NOESY, and XRD spectroscopy. The solubility of the polycarbazole was tested in various solvents. The thermodynamic stability of the polycarbazole was examined by DSC and TGA‐DTA analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis,miscibility, and properties of rodlike/flexible polymer composites via in-situ rod chain formation

Summary Flexible, soluble poly(amic diethyl ester) precursors of rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and poly(4,4-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), which are more stable than the respective poly(amic acid)s and are not in the equiliration with the constituent anhydride and amine monomers so that chemical exchange reactions are prevented in their solution blending, were synthesized. Homogeneous precursor/precursor solutions with various compositions were obtained in N-methyl-2-pyrrolidinone with appreciably high solid contents. The dried precursor blend films and resultive polyimide composite films thermally imidized were optically transparent, regardless of compositions and film process conditions. The composites showed single T_g behavior. Conclusively, rodlike BPDA-PDA/flexible BPDA-ODA molecular composites were achieved from the blend of the respective flexible poly(amic diethyl ester) precursors through conventional drying and imidization process. In addition, film properties of composites were characterized.     

Mononuclear Cu-O2 complexes: geometries, spectroscopic properties, electronic structures, and reactivity

Using interwoven experimental and theoretical methods, detailed studies of several structurally defined 1:1 Cu-O 2 complexes have provided important fundamental chemical information useful for understanding the nature of intermediates involved in aerobic oxidations in synthetic and enzymatic copper-mediated catalysis. In particular, these studies have shed new light on the factors that influence the mode of O 2 coordination (end-on vs side-on) and the electronic structure, which can vary between Cu(II)-superoxo and Cu(III)-peroxo extremes.     

Chitosan gel formation via the chitosan-epichlorohydrin adduct and its subsequent mineralization with hydroxyapatite

A novel hybrid material of chitosan-hydroxyapatite (HAp) composite gel is proposed. The introduction of epoxy ring onto chitosan via phthaloylchitosan to obtain a precursor from homogeneous DMF solution is demonstrated. The reaction of the precursor with hydrazine in water gives the recovery of amino groups as well as the ring opening reaction of oxirane for gelation. An alternate soaking with calcium and phosphate solution develops HAp mineralization and initiates the gel strength. Cell culture studies reveal 50% cell adhesion, whereas the mineralization with HAp reduces the cell adhesion.     

LaCoO3: Effect of synthesis conditions on properties and reactivity

Two nanostructured bulk LaCoO₃ powders were prepared by co-precipitation and with the citrate gel method and compared with the two nanocomposites obtained depositing, by wet impregnation, cobalt oxide on the La₂O₃ surface. All the prepared samples were characterized by means of X-ray photoelectron (XP) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis.

XRD results suggest that only the citrate gel method allows to obtain a single phase lanthanum cobaltite powder having a rhombohedral perovskite structure. Moreover, SEM images confirm the wide scale homogeneity. In contrast, a lanthanum hydroxide phase (hexagonal) is also evident in the sample obtained by co-precipitation method. In the nanocomposite richer in cobalt, besides the rhombohedral perovskite, the hexagonal lanthanum oxide and hydroxide phases are also detectable. Perovskite phase does not form when the amount of deposited cobalt oxide is too low. Both in the nanostructured sample prepared by citrate gel method and nanocomposite with [Co/La]_nominal = 1.0 XPS, DRIFT and TGA outcomes suggest a lower presence of hydroxyl groups and carbonates species.

The reactivity of the powders with respect to carbon monoxide was studied (at atmospheric pressure, between RT and 573 K) by means of the diffuse reflectance infrared Fourier transform spectroscopy. A significant signal around 2058 cm⁻¹ testifies about the interaction of CO with the Lewis acidic sites distributed on the surface of all the samples. The two nanostructured bulk LaCoO₃ show a high reactivity toward CO oxidation since 423 K. A similar oxidation capability is observed also for the nanocomposite richer in cobalt. In contrast, a rather low reactivity is displayed from the nanocomposite with lower Co/La nominal atomic ratio and La₂O₃.     

Waterborne polyurethane/poly(n-butyl acrylate-styrene) hybrid emulsions: Particle formation,film properties,and application

In this work, a hybrid synthesis technology has been used to fabricate waterborne polyurethane (WPU)/poly(n-butyl acrylate-styrene) (PBS) emulsions with dimethylol-propionic acid (DMPA) as chain extender. The influences of the PBS, styrene, and DMPA contents on the physical properties of the resultant emulsions and cast films have been investigated in detail using various characterization methods. The experimental results show that with an increase in the PBS or styrene content, the particle size in emulsions increases but the viscosity of the emulsions decreases and that the opposite applies for the DMPA content. For cast films, with an increase in the styrene or DMPA content, the tensile strength increases whereas the elongation decreases. The water absorption capacity of the film decreases with an increase in the styrene content or a decrease in the DMPA content. Furthermore, the emulsions synthesized have been used for paper sizing applications. The treated papers exhibit greatly improved water resistance, and the Cobb values at 30 and 60 s are only 10.23 and 11.89%, respectively, of those of unsized papers. The other paper properties, such as gloss, smoothness, folding resistance, and burst strength, are also considerably improved.     

Spectroscopic EPR and IR studies of monomeric and dimeric species formed upon adsorption of nitric oxide on Ce0.75Zr0.25O2 and their reactivity with dioxygen

The interaction of nitric oxide with Ce_0.75Zr_0.25O₂ solid solution were investigated by means of EPR and IR spectroscopies. The influence of adsorption parameters such as adsorption temperature and pressure, presence of the O₂ co-reactant on the nature and relative surface abundance of the resultant mono- and dimeric NO species was elucidated. The thermal stability of the surface nitrosyl complexes and their reactivity toward dioxygen were also examined.     

Polymers from renewable resources,part 7. Synthesis and properties of polyamideimide from rosin-maleic anhydride adduct

A polyamideimide was synthesized from a rosin-maleic anhydride adduct in three different ways. The rosin maleic anhydride adduct was condensed with hexamethylenediamine to obtain an amino acid. This amino acid was polymerized either by melt condensation technique or by reacting with thionyl chloride at ambient temperatures to produce a polyamideimide. Polyamideimide from rosin may also be prepared by reacting acid chloride of rosin-maleic anhydride with hexamethylenediamine. The polymer was characterized by IR and elemental analysis. The polymer was found to be soluble only in highly polar solvents such as dimethyl formamide, dimethyl sulfoxide, m-cresol etc. The thermal stability of the polymer has been studied.     

Studies on the reactivity of epoxy/polyol/isocyanate blend resins and the properties of epoxy/polyurethane composites

Epoxy resin (ER) is one of the most widely used synthetic resins, and the improvement of its toughness is an important issue. In this study, Epon 828 is used as ER resin, polytetramethylene ether glycol (PTMG) and liquefied wood (LW) are used as polyol, and IPDI, H₁₂-MDI, Desmodur N, and Desmodur L are used as isocyanate. The influence of polyurethane resin (PU) composition on the reactivity of ER/polyol/isocyanate blended resin and the properties of ER/PU composite are investigated. The results show that the mixture of ER/PTMG/IPDI has greater reactivity, followed by ER/PTMG/Desmodur N, while ER/PTMG/Desmodur L has lower reactivity. In the structure of ER/PU blended resin composites, ER and PU resins not only form a physical interpenetrating structure, but also undergo a copolymerization crosslinking reaction. The modulus of elasticity of ER/PU composites prepared with trifunctional Desmodur L and Desmodur N is greater than that of bifunctional IPDI and H₁₂-MDI, while those with LW as polyol is greater than that of PTMG as the raw material.     

FCC catalysts with different zeolite crystallite sizes: acidity, structural properties and reactivity

Two FCC catalysts with a 60 μm average size, prepared with different crystallite sizes (0.4 and 0.9 μm), are studied in terms of total acidity, energy of ammonia desorption, specific surface area, relative amount of Brönsted and Lewis acid sites, crystallite and particle size, and micropore size distribution.

Characterization of these catalysts is relevant in view of their application to test the extent of intracrystallite diffusive transport influence on the overall catalytic cracking rates as developed, in separate studies [Ind. Eng. Chem. Res. 42 (2003) 4162] in a novel CREC Riser Simulator.