Versatile pathways for in situ polyolefin functionalization with heteroatoms: catalytic chain transfer

Chain-transfer processes represent highly effective chemical means to achieve selective, in situ d- and f-block-metal catalyzed functionalization of polyolefins. A diverse variety of electron-poor and electron-rich chain-transfer agents, including silanes, boranes, alanes, phosphines, and amines, effect efficient chain termination with concomitant carbon-heteroelement bond formation during single-site olefin-polymerization processes. High polymerization activities, control of polyolefin molecular weight and microstructure, and selective chain functionalization are all possible, with distinctly different mechanisms operative for the electron-poor and electron-rich reagents. A variety of metal centers (early transition metals, lanthanides, late transition metals) and single-site ancillary ligand arrays (metallocene, half-metallocene, non-metallocene) are able to mediate these selective chain-termination/functionalization processes.     

Studies on selenite adsorption using manganese nodule leached residues

Selenite adsorption on water-washed manganese nodule leached residues (WMNLR) was studied with the aim of detoxifying industrial effluents before their safe disposal into the environment. WMNLR, a solid waste material, was characterized with the help of XRD, FTIR, TG-DTA, pH(pzc), BET surface area, surface oxygen, surface hydroxyl group, and chemical analyses. The adsorption behavior of WMNLR toward selenite was studied as a function of time, pH, temperature, and concentration of adsorbate and adsorbent. Increased adsorption capacity with rise in temperature indicates that the adsorption process was endothermic in nature. Based on the thermodynamic parameters such as the Gibbs free energy change, standard enthalpy change, and standard entropy change, the adsorption process was found to be spontaneous and endothermic in nature. Adsorption followed second-order kinetics. The adsorption capacity of the material was found to be 54.6 mg g(-1) at 60 mg L(-1) of selenite concentration at pH 5 in 3 h contact time.     

Effects of solvent on the reactions of coordination complexes. part 24. kinetics of base hydrolysis of some (aminomonocarboxylato)(tetraethylene‐pentamine)cobalt(III) complexes in methanol+water media: The role of substrate hydrophobicity and solvent structure

The kinetics of base hydrolysis of some (aminomonocarboxylato)(tetraethylenepentamine)cobalt(III) complexes, [(tetren)CoO₂CR]²⁺ (R= NH₂CH₂, pyridine‐2 ,  NH₂CH₂CH₂,  NH₂CH(CH₃) (αβS isomer); R= NH₂CH(CH₃) (αβR isomer)), have been investigated in methanol–water media (0–80 vol % MeOH) at 15.0≤t°C≤40.0 (0.02 mol dm⁻³ NaOH). The second‐order rate constant at zero ionic strength, k₂°, increases nonlinearly with X_MeOH. The transfer free energy of the initial state and the transition state of the amido conjugate base ([Δ_tG (i)]_(s←w)) for the glycinato‐ and pyridine‐2–carboxylato complexes have been calculated using the solubility data of their picrate salts, pK _NH date of their N‐protonated forms, and the k₂° values in mixed solvent media. The kinetic solvent effects have been interpreted in terms of preferential solvation of the initial state, transition state, and the solvent structure. The activation enthalpies and entropies varied nonlinearly with X_MeOH displaying extrema, which is attributable to the solvent structural effects on these thermodynamic parameters. It is also evident that the mutation process, αβR→αβS isomer for the α‐alaninato complex, where this isomerisation refers to the arrangement of the tetren skeleton around the planar secondary NH is sensitive to the nature of the cosolvent molecules and solvent structure. The mutation process is generally more favorable for the five coordinate amido conjugate bases than the initial state. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 55–64, 1999     

Integrated Condition Monitoring of Large Captive Power Plants and Aluminum Smelters

Condition monitoring is implementation of the advanced diagnostic techniques to reduce downtime and to increase the efficiency and reliability. The research is for determining the usage of advanced techniques like Vibration analysis, Oil analysis and Thermography to diagnose ensuing problems of the Plant and Machinery at an early stage and plan to take corrective and preventive actions to eliminate the forthcoming breakdown and enhancing the reliability of the system. Nowadays, the most of the industries have adopted the condition monitoring techniques as a part of support system to the basic maintenance strategies. Major condition monitoring technique they follow is Vibration Spectrum Analysis, which can detect faults at a very early stage. However implementation of other techniques like Oil analysis or Ferrography, Thermography etc. can further enhance the data interpretation as they would detect the source of abnormality at much early stage thus providing us with a longer lead time to plan and take the corrective actions. In Large Captive Power Plants and Aluminium Smelters, Integrated Condition Monitoring techniques play an important role as stoppage of primary system and its auxiliaries (boiler, steam turbine, generator, coal and ash handling plants etc.) results into the stoppage of the entire plant, which in turn leads to loss of productivity. From economical and operational point of view, it is desirable to ensure optimum level of system availability.     

Growth of oriented crystalline Ag nanoislands on air-exposed Si(0 0 1) surfaces

Growth of Ag islands under ultrahigh vacuum condition on air-exposed Si(0 0 1)-(2 × 1) surfaces has been investigated by in-situ reflection high energy electron diffraction (RHEED). A thin oxide is formed on Si via exposure of the clean Si(0 0 1)-(2 × 1) surface to air. Deposition of Ag on this oxidized surface was carried out at different substrate temperatures. Deposition at room temperature leads to the growth of randomly oriented Ag islands while well-oriented Ag islands, with (0 0 1)_Ag||(0 0 1)_Si, [1 1 0]_Ag||[1 1 0]_Si, have been found to grow at substrate temperatures of ≥350 °C in spite of the presence of the oxide layer between Ag islands and Si. The RHEED patterns show similarities with the case of Ag deposition on H-passivated Si(0 0 1) surfaces.     

Nano-graphitic clustering and break down of phonon selection rule in diamond-like carbon films

Diamond-like carbon films are deposited on silicon substrates at different substrate bias using ECR-CVD technique. Raman spectroscopic studies show the presence of broad G and D peaks. In contrast to the position of D peak, the G peak shows a systematic red-shift with increase in the bias voltage. From the analysis it is found that an increase in bias voltage decreases the sp² cluster diameter. Furthermore, two additional Raman peaks at around 690 and 880 cm^?1 are also observed. These peaks, forbidden in the first order Raman scattering, arise due to the breakdown of phonon selection rule in graphitic nanoclusters.     

Alkenylsilane effects on organotitanium-catalyzed ethylene polymerization. Toward simultaneous polyolefin branch and functional group introduction

The comonomer 5-hexenylsilane is introduced into organotitanium-mediated ethylene polymerizations to produce silane-terminated ethylene/5-hexenylsilane copolymers. The resulting polymers were characterized by 1H and 13C NMR, GPC, and DSC. High activities (up to 107 g polymer/(mol Ti.atm ethylene.h)) and narrow polydispersities are observed in the polymerization/chain transfer process. Ethylene/5-hexenylsilane copolymer molecular weights are found to be inversely proportional to 5-hexenylsilane concentration, supporting a silanolytic chain transfer mechanism. Control experiments indicate that chain transfer mechanism by 5-hexenylsilane is significantly more efficient than that of n-hexylsilane for organotitanium-mediated ethylene polymerization. The present study represents the first case in which a functionalized comonomer is efficiently used to effect both propagation and chain transfer chemistry during olefin polymerization.     

Adsorption of organic molecules on silica surface

The adsorption behaviour of various organic adsorbates on silica surface is reviewed. Most of the structural information on silica is obtained from IR spectral data and from the characteristics of water present at the silica surface. Silica surface is generally embedded with hydroxy groups and ethereal linkages, and hence considered to have a negative charged surface prone to adsorption of electron deficient species. Adsorption isotherms of the adsorbates delineate the nature of binding of the adsorbate with silica. Aromatic compounds are found to involve the pi-cloud in hydrogen bonding with silanol OH group during adsorption. Cationic and nonionic surfactants adsorb on silica surface involving hydrogen bonding. Sometimes, a polar part of the surfactants also contributes to the adsorption process. Styryl pyridinium dyes are found to anchor on silica surface in flat-on position. On modification of the silica by treating with alkali, the adsorption behaviour of cationic surfactant or polyethylene glycol changes due to change in the characteristics of silica or modified silica surface. In case of PEG-modified silica, adsolubilization of the adsorbate is observed. By using a modified adsorption equation, hemimicellization is proposed for these dyes. Adsorptions of some natural macromolecules like proteins and nucleic acids are investigated to study the hydrophobic and hydrophilic binding sites of silica. Artificial macromolecules like synthetic polymers are found to be adsorbed on silica surface due to the interaction of the multifunctional groups of the polymers with silanols. Preferential adsorption of polar adsorbates is observed in case of adsorbate mixtures. When surfactant mixtures are considered to study competitive adsorption on silica surface, critical micelle concentration of individual surfactant also contributes to the adsorption isotherm. The structural study of adsorbed surface and the thermodynamics of adsorption are given some importance in this review.     

Determination of indium in high purity antimony by electrothermal atomic absorption spectrometry (ETAAS) using boric acid as a modifier

The use of boric acid as a modifier for the determination of trace amount of indium in high purity antimony by electrothermal atomic absorption is described. It was found that the negative influence of the hydrofluoric acid, used for the digestion could not be eliminated by using stabilized temperature platform furnace (STPF) alone. Due to the high dissociation energy (D₀ = 506 kJ mol⁻¹) of indium fluoride, it is difficult to dissociate in the gas phase and hence is lost. In presence of HF (used for the dissolution of antimony), the universal Pd-Mg modifier does not work satisfactorily. Additionally, rising corrosion and reduced tube lifetime were observed when the acid digested (HF-HNO₃) antimony solution was injected in to the platform. Improvement in platform life and elimination of interferences were achieved by the addition of boric acid as a chemical modifier together with ruthenium coating of the platform. Corrosive changes of the transversely heated graphite atomizer (THGA) platform surface were examined by scanning electron microscopy. The standard addition method was applied. A characteristic mass of 36 pg was obtained. The detection limit of the proposed method is around 0.04 μg g⁻¹. The developed method was applied to the determination of indium in real samples. The data obtained by this method were in good agreement with those obtained by ICP-MS.