B. N. Avasthi’s research while affiliated with Indian Institute of Technology Kharagpur and other places

The contact angles and surface energies have been determined for silicone rubber functionalized with amide group and EPDM rubber modified with sulfonic acid and maleic anhydride. The functionalization of the polymers decreases the equilibrium contact angles of water and formamide with an increase in the surface energy. The changes in the surface properties are due to the changes in the concentration of the polar groups as measured by IR spectroscopy. The lap shear measurement on joints of silicone and EPDM rubber indicates an increased strength on modification. © 1996 John Wiley & Sons, Inc.

Oxidative degradation of ethylene propylene diene (EPDM) rubber containing varying amounts of ethylene units has been carried out using phase-transferred permanganate as oxidant. The oxidised products have been characterised by IR spectroscopy. The degradation behaviour of EPDM rubbers has been studied by thermogravimetry in air. A comparison of the IR spectra of EPDM and oxidised EPDM confirms the appearance of new peaks near 1735 cm−1 due to the stretching vibration, which may arise from carboxyl, ester or ketone groups. Nonaqueous acid-base titration confirms the presence of carboxyl groups in oxidised EPDM. The onset temperature of oxidative degradation as determined by differential scanning calorimetry shows that Tonset values decrease significantly on oxidation. The measurement of glass transition temperature (Tg) suggests an increase in Tg due to oxidation. Scanning electron microscopy (SEM) observations indicate surface roughening due to oxidation.

Expoxidized natural rubber has been selectively hydrogenated in the presence of a homogeneous palladium acetate catalyst. The hydrogenated product has been characterized by infra-red and nuclear magnetic resonance spectroscopies. No change is noted in the epoxy content of the polymer after the reaction. The catalyst is highly selective in reducing carbon-carbon double bonds in the presence of epoxy groups. Natural rubber has also been hydrogenated for a comparative study. The rate constant of hydrogenation is decreased with increase in epoxy content of the polymer.

Homogeneous catalytic hydrogenation of styrene-isoprene-styrene triblock copolymer (SIS) has been carried out selectively at the carbon-carbon double bond in the presence of palladium acetate catalyst under mild conditions. Degree of hydrogenation has been calculated with the help of infrared and nuclear magnetic resonance spectroscopic techniques. Almost 90 mol % complete hydrogenation has been achieved at 60°C under 1.4 MPa hydrogen pressure, 40 mg catalyst (for 2 g of polymer) in chloroform-acetone solution for 1 h. © 1993 John Wiley & Sons, Inc.

Molybdenum disulphide has been prepared by atmospheric-pressure hydrogen reduction of molybdenum trisulphide in the temperature range 400–750 C for 4 h and characterized. Chemical analysis of the product confirmed the S to Mo ratio 2.00 as desired for MoS2, consistent with its thermogravimetric analysis data in an air atmosphere. MoS2 prepared under these reducing conditions possessed a hexagonal structure with n-type diamagnetic semiconducting behaviour and a lower surface area. The catalytic activity of the MoS2 was studied for liquid-phase hydrogenation of nitrobenzene. X-ray studies on MoS3 when reduced at 750 C for 48 h indicated that MoS2 so formed is unstable, resulting in the formation of its over-reduced products Mo2S3 and Mo.

New uncatalysed chemical oscillations have been found in the Rhodamine B base−BrO −3 −H2SO4 and Rhodamine B−BrO −3 −H2SO4 systems in a batch reactor. A non-oscillating absorption band due to an intermediate species was isolated, which is anticipated to have close relationship with the one-electron redox couple of these dye oscillators.

In recent years, the transition metal trichalcogenides (TX3) of Group IVB, VB and VIB have received much more attention because of the considerable diversity in their physical properties. The most striking feature of these compounds is that the structure here may be classified into three types depending on the number of different TX3 chains present in the unit cell. Thus ZrSe3, TaSe3 and NbSe3 are the representative compounds having one, two and three types of chain based on the different bond lengths for the (X2)2– pairs in the base of the TX3 trigonal prismatic framework. A similar model is also applicable in the case of NbS3, with the addition of a 2b-superstructure associated with the formation of niobium pairs. The chain structure also facilitates the process of intercalation which has been most effectively used in secondary batteries. These compounds exhibit the superconductivity phenomena and charge density wave, etc. and also find application in photoelectrochemical cells. An attempt has been made here to review the up-to-date chemistry of transition metal trichalcogenides related with their preparation, structure and properties such as physical and chemical, thermodynamic, electrical, magnetic and optical properties, intercalation and use in the photoelectrochemical cells. 93

Homogeneous catalytic hydrogenation of olefinic bonds in liquid carboxylated nitrile rubber (L-XNBR) has been carried out selectively in the presence of nitrile and carboxyl functionality using a six-membered cyclopalladate complex of 2-benzoyl pyridine as catalyst. The degree of hydrogenation has been calculated from IR and NMR spectroscopic studies. For example, 68% hydrogenation has been obtained for a sample (containing 0.057 carboxyl equivalent/100 g and 26.1% acrylonitrile) under 2.7 MPa hydrogenation pressure, 0.18 mmol/L catalyst, at 333 K for 1 h in acetone solution. The overall extent of hydrogenation depends on the catalyst-to-double-bond ratio. The kinetics of hydrogenation of L-XNBR has been investigated. The reaction exhibits a pseudo-first order dependence on the concentration of the substrate. The rate constant of the reaction is reduced by the increase in carboxyl and nitrile content of the polymer. The effect of temperature on reaction kinetics has also been studied and the activation energy of hydrogenation of L-XNBR is 20.2 kJ/mol. Intrinsic viscosity of the polymer remains unchanged during the reaction. A significant lowering of the glass transition temperature and improvement of thermal stability have been observed on hydrogenation. © 1992 John Wiley & Sons, Inc.

Selective homogeneous catalytic hydroformylation of nitrile rubber (NBR) has been carried out in presence of trans-chlorocarbonylbis(triphenylphosphine)rhodium(I) [trans-RhCl(CO)(PPh3)2] and hydridocarbonyltris(triphenylphosphine)rhodium(I) [RhH (CO)(PPh3)3] as catalysts. At 363 K, under 5.6 MPa pressure (CO: H2 = 1 : 1) in presence of 0.43 mmol/l catalyst, the amount of hydroformylation is 25% in the case of trans-RhCl (CO)(PPh3)2 and 30% in the case of RhH (CO)(PPh3)3 for NBR with 40 mol-% acrylonitrile. Reaction kinetics suggest that both the reactions are pseudo-first order with respect to olefinic substrate and catalyst concentration. The rate of the reaction is higher in the case of RhH(CO)(PPh3)3. The characterization of the products by IR and NMR spectroscopy shows the formation of internal aldehyde groups from 1,4-units and terminal branched aldehyde groups from 1,2-units of the copolymer. Measurements on intrinsic viscosity [eta] and glass transition temperature (T(g)) suggest a decrease in [eta] and an increase in T(g) with the degree of formyl functionalization. Gel formation has been observed at higher degree of hydroformylation.

Hydrogenation of liquid carboxylated nitrile rubber (L-XNBR) was carried out using homogeneous palladium and rhodium catalysts. It was observed that the six-membered cyclic palladate complex of 2-benzoylpyridine, 1, reduces the carbon-carbon double bonds without affecting the nitrile and carboxyl functionality. The intrinsic viscosity of the polymers remains unchanged during hydrogenation. The glass transition temperature is marginally lowered for the hydrogenated products. A great extent of decarboxylation was obtained for samples hydrogenated in presence of the rhodium complex, 2.