Brominated poly(isobutylene‐co‐para‐methylstyrene) (BIMS)‐clay nanocomposites: Synthesis and characterization

In this work, preparation and properties of different nanoclays modified by organic amines (octadecyl amine, a primary amine, and hexadecyltrimethylammonium bromide, a tertiary amine) and brominated polyisobutylene‐co‐paramethylstyrene (BIMS)‐clay nanocomposites are reported. The clays and the rubber nanocomposites have been characterized with the help of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). The X‐ray diffraction peaks observed in the range of 3 °–10 ° for the modified clays disappear in the rubber nanocomposites. TEM photographs show predominantly exfoliation of the clays in the range of 12 ± 4 nm in the BIMS. In the FTIR spectra of the nanocomposites, there are common peaks of virgin rubber as well as those of the clays. Excellent improvement in mechanical properties like tensile strength, elongation at break, and modulus is observed on incorporation of the nanoclays in the BIMS. Structure‐property correlation in the above nanocomposites is attempted. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4489–4502, 2004     

Studies on crosslinking of EPDM-PE blends by thermoanalytical techniques

The effect of blend ratio and peroxide concentration on crosslinking characteristics of EPDM-PE blends were studied by Differential Scanning Calorimetry, Brabender plasticorder and Rheometer. Crosslinking of EPDM-PE blends follows first order reaction kinetics. The curing exotherm increases but activation energy decreases with increase in EPDM content in the blends. The same however increases with the increase in concentration of DCP upto a certain level, while the activation energy is almost independent of peroxide concentration. The cure rate increases whereas optimum cure time and energy consumption for curing decrease with increase in the EPDM-PE ratio. A method for determination of crosslinking efficiency in the case of blend systems was developed from high temperature modulus to predict the properties and the curing behaviour of the blends.

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Zusammenfassung Mittels DSC, Brabender Plasticorder und Rheometer wurde der Einfluß von Mischungsverhältnis und Peroxidkonzentration auf den Vernetzungsverlauf von EPDM-PE-Gemischen untersucht. Die Vernetzung von EPDM-PE-Gemischen verläuft nach einer Reaktion erster Ordnung. Je höher der Anteil von EPDM im Gemisch, um so exothermer ist die Vernetzung und um so kleiner ist die dazugehörige Aktivierungsenergie. Mit dem Anwachsen der DCP-Konzentration bis zu einem gewissen Niveau wächst der exotherme Charakter, während die Aktivierungsenergie fast unabhängig von der Peroxidkonzentration ist. Mit dem Anstieg des EPDM/PE-Verhältnisses wächst die vernetzungsgeschwindigkeit, während die optimale Vernetzungszeit und der Energieverbrauch für die Vernetzung sinken. Es wurde ein Verfahren zur Bestimmung der Vernetzungseffizienz bei Mischsystemen entwickelt, um Eigenschaften und Vernetzungsverhalten von Gemischen voraussagen zu können.

     

Silver (I)-promoted asymmetric halohydrin reaction of chiral N-enoyl-2-oxazolidinones: scope and limitations

The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br₂/I₂) and water were efficiently carried out in aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diastereoselectivities. The alkenoyl, cinnamoyl and electron-deficient cinnamoyl substrates smoothly underwent bromohydrin reaction in aqueous acetone but no iodohydrin reaction, where as electron-rich cinnamoyl substrates preferred to undergo iodohydrin reaction in aqueous acetone with moderate diastereoselectivity and enhanced diastereoselectivity was observed in aqueous THF.     

Degradation of rocket insulator at high temperature

The degradation of a rocket insulator compound based on ethylene propylene diene rubber (EPDM) containing asbestor, cork and iron oxide (Fe₂O₃) as fillers has been studied at high temperature (up to 600°) by using differential thermal analysis (DTA) and thermogravimetry (TG). The changes in physical properties on high-temperature aging are also reported. EPDM gum vulcanizates involving different types of diene, namely ethylidene norbornene (ENB), dicyclopentadiene (DCPD) and 1,4-hexadiene (HD), were used. In each case, the kinetic parameters for degradation have been evaluated. From these data, the lifetime of the rocket insulator compound has been found.

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Zusammenfassung Die Zersetzung einer Raketenisolator-Verbindung auf Äthylen-Propylen-Dien-Gummibasis (EPDM) mit Asbest, Kork und Eisenoxid (Fe₂O₃) als Füllstoffe wurden bei hohen Temperaturen (bis 600°) mittels Differentialthermalanalyse (DTA) und Thermogravimetrie (TG) untersucht. Die bei Hochtemperaturen eintretenden Veränderungen der physikalischen Eigenschaften sind ebenfalls angegeben. Verschiedene Typen von Dienen, nämlich Äthyliden-norbornen (ENB), Dicyclopentadien (DCPD) und 1,4-Hexadien (HD) enthaltenden EPDM-Gummivulkanisate waren Gegenstand der Untersuchung. In allen Fällen wurden die kinetischen Parameter der Zersetzung ermittelt. Aus diesen Daten wurde die Lebensdauer der Raketenisolator-Verbindung bestimmt.

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600° (), , . , . , , 1,4- . . .

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The authors are grateful to the Indian Space Research Organization for funding, and acknowledge the help and suggestions from Mr. T. S. Ram and Mr. Baby John, R.P.P., V.S.S.C., Trivandrum. The authors are also grateful to Prof. S. K. De, Rubber Technology Centre, and Prof. R. Ghosh, Chemistry Department, I.I.T., Kharagpur.

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The authors thank Mr. Asutosh Ghosh, Indian Association for the Cultivation of Science, for experimental assistance.     

Magnetic nanoparticle‐tethered Schiff base–palladium(II): Highly active and reusable heterogeneous catalyst for Suzuki–Miyaura cross‐coupling and reduction of nitroarenes in aqueous medium at room temperature

As a continuation of our efforts to develop new heterogeneous nanomagnetic catalysts for greener reactions, we identified a Schiff base–palladium(II) complex anchored on magnetic nanoparticles (SB‐Pd@MNPs) as a highly active nanomagnetic catalyst for Suzuki–Miyaura cross‐coupling reactions between phenylboronic acid and aryl halides and for the reduction of nitroarenes using sodium borohydride in an aqueous medium at room temperature. The SB‐Pd@MNPs nanomagnetic catalyst shows notable advantages such as simplicity of operation, excellent yields, short reaction times, heterogeneous nature, easy magnetic work up and recyclability. Characterization of the synthesized SB‐Pd@MNPs nanomagnetic catalyst was performed with various physicochemical methods such as attenuated total reflectance infrared spectroscopy, UV–visible spectroscopy, inductively coupled plasma atomic emission spectroscopy, energy‐dispersive X‐ray spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy, powder X‐ray powder diffraction, thermogravimetric analysis and Brunauer–Emmett–Teller surface area analysis.     

Four‐Center Oxidation State Combinations and Near‐Infrared Absorption in [Ru(pap)(Q)2]n (Q=3,5‐Di‐tert‐butyl‐N‐aryl‐1,2‐benzoquinonemonoimine,pap=2‐Phenylazopyridine)

The complex series [Ru(pap)(Q)₂]ⁿ ([ 1 ]ⁿ–[ 4 ]ⁿ; n=+2, +1, 0, ?1, ?2) contains four redox non‐innocent entities: one ruthenium ion, 2‐phenylazopyridine (pap), and two o‐iminoquinone moieties, Q=3,5‐di‐tert‐butyl‐N‐aryl‐1,2‐benzoquinonemonoimine (aryl=C₆H₅ ( 1⁺ ); m‐(Cl)₂C₆H₃ ( 2⁺ ); m‐(OCH₃)₂C₆H₃ ( 3⁺ ); m‐(tBu)₂C₆H₃ ( 4 ⁺)). A crystal structure determination of the representative compound, [ 1 ]ClO₄, established the crystallization of the ctt‐isomeric form, that is, cis and trans with respect to the mutual orientations of O and N donors of two Q ligands, and the coordinating azo N atom trans to the O donor of Q. The sensitive C? O (average: 1.299(3) Å), C? N (average: 1.346(4) Å) and intra‐ring C? C (meta; average: 1.373(4) Å) bond lengths of the coordinated iminoquinone moieties in corroboration with the N?N length (1.292(3) Å) of pap in 1 ⁺ establish [Ru^III(pap⁰)(Q^.?)₂]⁺ as the most appropriate electronic structural form. The coupling of three spins from one low‐spin ruthenium(III) (t_2g⁵) and two Q^.? radicals in 1 ⁺– 4 ⁺ gives a ground state with one unpaired electron on Q^.?, as evident from g=1.995 radical‐type EPR signals for 1 ⁺– 4 ⁺. Accordingly, the DFT‐calculated Mulliken spin densities of 1 ⁺ (1.152 for two Q, Ru: ?0.179, pap: 0.031) confirm Q‐based spin. Complex ions 1 ⁺– 4 ⁺ exhibit two near‐IR absorption bands at about λ=2000 and 920 nm in addition to intense multiple transitions covering the visible to UV regions; compounds [ 1 ]ClO₄–[ 4 ]ClO₄ undergo one oxidation and three separate reduction processes within ±2.0 V versus SCE. The crystal structure of the neutral (one‐electron reduced) state ( 2 ) was determined to show metal‐based reduction and an EPR signal at g=1.996. The electronic transitions of the complexes 1 ⁿ– 4 ⁿ (n=+2, +1, 0, ?1, ?2) in the UV, visible, and NIR regions, as determined by using spectroelectrochemistry, have been analyzed by TD‐DFT calculations and reveal significant low‐energy absorbance (λ_max>1000 nm) for cations, anions, and neutral forms. The experimental studies in combination with DFT calculations suggest the dominant valence configurations of 1 ⁿ– 4 ⁿ in the accessible redox states to be [Ru^III(pap⁰)(Q^.?)(Q⁰)]²⁺ ( 1 ²⁺– 4 ²⁺)→[Ru^III(pap⁰)(Q^.?)₂]⁺ ( 1 ⁺– 4 ⁺)→[Ru^II(pap⁰)(Q^.?)₂] ( 1 – 4 )→[Ru^II(pap^.?)(Q^.?)₂]^? ( 1 ^?– 4 ^?)→[Ru^III(pap^.?)(Q^2?)₂]^2? ( 1 ^2?– 4 ^2?).     

A review on sources,toxicity and remediation technologies for removing arsenic from drinking water

Arsenic is a natural element found in the environment in organic and inorganic forms. The inorganic form is much more toxic and is found in ground water, surface water and many foods. This form is responsible for many adverse health effects like cancer (skin, lung, liver, kidney and bladder mainly), and cardiovascular and neurological effects. The estimated number of people in Bangladesh in 1998 exposed to arsenic concentrations above 0.05 mg/l is 28–35 million, and the number of those exposed to more than 0.01 mg/l is 46–57 million. The estimated number of people in West Bengal, India (the border province to Bangladesh), in 1997 actually using arsenic-rich water is more than 1 million for concentrations above 0.05 mg/l and is 1.3 million for concentrations above 0.01 mg/l. The United States Environmental Protection Agency (USEPA) has estimated that 13 million of the US population are exposed to arsenic in drinking water at 0.01 mg/l. The situation has prevailed for more than 10 years and is more severe now. The USEPA lowered the maximum contaminant level (MCL) for drinking water arsenic from 50 to 10 μg/l in 2001 based on international data analysis and research. This recommendation is now on hold. The level of 10 ppb become standard in the European Union (EU) in 2001. Arsenic may be found in water flowing through arsenic-rich rocks. The source is diverse. These include the earth's crust, introduced into water through the dissociation of minerals and ores, industrial effluents to water, combustion of fossil fuels and seafoods. Arsenic-removal methods are coagulation (ferric sulfate, ferrous sulfate, ferric chloride, aluminum sulfate, copper sulfate, and calcium hydroxide as coagulants), adsorption (activated carbon, activated alumina, activated bauxite) ion exchange, bio-sorption, etc.