Grafting of m-isopropenyl-alpha, alpha-dimethylbenzyl-isocyanate (m-TMI) onto isotactic polypropylene: Synthesis and characterization

A novel vinyl monomer with an isocyanate functional group, m-isopropenyl-alpha,alpha-dimethylbenzyl-isocyanate (m-TMI), was grafted onto isotactic polypropylene (i-PP) using dicumyl peroxide (DCP) as the initiator. This would open up the possibility of using the grafted polymer with the reactive isocyanate group as compatibilizer for blending carbohydrates such as cellulose with. polypropylene. The grafting was carried out in a Brabender Plasticoder at 180degreesC. The effects of monomer and initiator concentrations on the yield of grafting were investigated by performing statistical analysis. While the grafting yield increased with the concentration of DCP at any given concentration of m-TMI, the variation of the grafting yield with m-TMI concentration, for a given concentration of DCP, went through a maximum, the optimum yield of 7.8% (w/w) being obtained at 10 wt.% concentration of both DCP and m-TMI. The grafting reaction is. accompanied by considerable chain scission of I-PP, resulting in a decrease in the molecular weight of the grafted polymer. While the molecular weight drops sharply even at a low concentration of DCP, there occurs no further significant change in the molecular weight even at much higher concentrations of the initiator.

Covalent Grafting of Polydimethylsiloxane over Surface-Modified Alumina Nanoparticles

The synthesis of ``smart structured'' conducting polymers and the fabrication of devices using them are important areas of research. However, conducting polymeric materials that are used in devices are susceptible to degradation due to oxygen and moisture. Thus, protection of such devices to ensure long-term stability is always desirable. Polymer nanocomposites are promising materials for the encapsulation of such devices. Therefore, it is important to develop suitable polymer nanocomposites as encapsulation materials to protect such devices. This work presents a technique based on grafting between surface-decorated gamma-alumina nanoparticles and polymer to make nanocomposites that can be used for the encapsulation of devices. Alumina was functionalized with allyltrimethoxysilane and used to conjugate polymer molecules (hydride-terminated polydimethylsiloxane) through a platinum-catalyzed hydrosilylation reaction. Fourier transform infrared spectroscopy, X-ray-photoelectron spectroscopy, and Raman spectroscopy were used to characterize the surface chemistry of the nanoparticles after surface modification. The grafting density of alkene groups on the surface of the modified nanoparticles was calculated using CHN and thermogravimetric analyses. The thermal stability of the composites was also evaluated using thermogravimetric analysis. The nanoindentation technique was used to analyze the mechanical characteristics of the composites. The densities of the composites were evaluated using a density gradient column, and the morphology of the composites was evaluated by scanning electron microscopy. All of our studies reveal that the composites have good thermal stability and mechanical flexibility and, thus, can potentially be used for the encapsulation of organic photovoltaic devices.

A New Tetrahydrofurannulation Via Tandem Radical Cyclization Reaction-Reductive Deoxygenation Sequence

Treatment of bromoketals 2, derived from allyl alcohols 1, with tributyltin chloride, sodium cyanoborohydride and AIBN furnishes the tetrahydrofurannulated products 3 via a 5-exo-trig radical cyclisation reaction followed by reductive cleavage of ketal 4.

Vanadium Catalysis in Bromoperoxidation Reaction

Peroxidative bromination of phenol red to its tetrabromo derivative, bromophenol blue, required vanadate in addition to H2O2 when carried out in the pH range of 5-7. Excess H2O2, with ratio of H2O2:vanadate of 2:1 and above, prevented the reaction. Diperoxovanadate, known to be formed in such reaction mixtures, was ineffective by itself and needed uncomplexed vanadate (V-v) or vanadyl (V-iv) to support bromination. Bromide-assisted reduction of the excess vanadate to vanadyl appeared to be an essential secondary reaction. In the absence of phenol red oxygen was released, and concomitantly bromide was oxidized to a form competent to brominate phenol red added after termination of oxygen release. These findings indicated participation of reactions leading to an intermediate derived from vanadyl and diperoxovanadate, previously described from this laboratory (Arch. Biochem. Biophys. 316, 319-326, 1995). Continuous bromination of phenol red occurred when glucose oxidase-glucose system was used as a source of continuous flow of H2O2. A scheme of reactions involving peroxovanadates (mono-, di-, mu-, and bromo-) is proposed for the formation and utilization of an active brominating species and for the recycling of the product, mono-peroxovanadate, by H2O2, which explains the catalytic role of vanadium in the bromoperoxidation reaction.

Nanoporous Pt with High Surface Area by Reaction-Limited Aggregation of Nanoparticles

Nanoporous structures with high active surface areas are critical for a variety of applications. Here, we present a general templateless strategy to produce such porous structures by controlled aggregation of nanostructured subunits and apply the principles for synthesizing nanoporous Pt for electrocatalytic oxidation of methanol. The nature of the aggregate produced is controlled by tuning the electrostatic interaction between surfactant-free nanoparticles in the solution phase. When the repulsive force between the particles is very large, the particles are stabilized in the solution while instantaneous aggregation leading to fractal-like structures results when the repulsive force is very low. Controlling the repulsive interaction to an optimum, intermediate value results in the formation of compact structures with very large surface areas. In the case of Pt, nanoporous clusters with an extremely high specific surface area (39 m(2)/g) and high activity for methanol oxidation have been produced. Preliminary investigations indicate that the method is general and can be easily extended to produce nanoporous structures of many inorganic materials.

Enantiospecific approach to the tricyclic core structure of tricycloillicinone, ialibinones, and takaneones via ring-closing metathesis reaction

Enantiospecific synthesis of the tricyclic core structure present in the biologically active natural products tricycloillicinone, ialibinones, and takaneones, starting from the readily available campholenaldehyde employing a transannular RCM reaction as the key step, has been accomplished.

Acid-catalysed cyclisations: structures of novel products isolated in the reaction of 2-[3-(2,6-dimethoxyphenyl)but-2-enyl]-2-methylcyclopentane-1,3-dione with MeOH-HCl

Reaction of the title compound (1a) with anhydrous MeOH-HCl gave 2-endo-(2,6-dimethoxyphenyl)-2-exo-methyl-5-methylbicyclo[3.2.1]octane-6,8-dione (3a), 1,5,14-timethoxy-5,8-seco-6,7-dinorestra-1,3,5(10),9(11)-tetraen-17-one (4), 1,5-dimethoxy-5,8-seco-6,7-dinorestra-1,3,5(10),8,14-pentaen-17-one (5), and 3,4,5,6-tetrahydro-2,7-dimethoxy-3,6-dimethyl-3,2,6-(13-oxopropan[1]yI[3]ylidene)-2H-1-benzoxocin (6). Structures assigned to compounds (3a), (4), and (6) are based on spectral data. The exo-tricyclic acetal structure (6) was further confirmed by the analysis of the 1H n.m.r. spectra of the isomeric alcohols (11) and (12), obtained by sodium borohydride reduction of (6).

Vilsmeier reaction on some 6- and 7-methoxy-1- and 2-tetralones.

Vilsmeier reaction on a few representative 6- and 7-methoxy-1- and 2-tetralones has been investigated. While 1-tetralones give the corresponding 1-chloro-2-formyl3, 4-dihydronaphthalenes, the 2-tetralones afford 1,3-bisformyl-2-chloronaphthalenes. Spectral characteristics of all the products obtained are given and a mechanistic proposal has been made to explain the observed chlorobisformylation.

A reply to a discussion by D.J. Cook of the paper a reaction product of lime and silica from rice husk asha star, open

Abstract is not available.

Graphene-nanocrystalline metal sulphide composites produced by a one-pot reaction starting from graphite oxide

Graphene-nanocrystalline metal sulphide composites were prepared by a one-pot reaction. A dispersion of graphite oxide layers in an aqueous solution of metal ions (Cd2+/Zn2+) was reacted with H2S gas, which acts as a sulphide source as well as a reducing agent, resulting in the formation of metal sulphide nanoparticles and simultaneous reduction of graphite oxide sheets to graphene sheets. The surface defect related emissions shown by free metal sulphide particles are quenched in the composites due to the interaction of the surface of the nanoparticles with graphene sheets.

Reactivity in the spinel formation reaction in CuO/Al2O3, Fe2O3, Cr2O3 systems

Abstract is not available.

Influence of Solvent on Photoinduced Electron-Transfer Reaction: Time-Resolved Resonance Raman Study

Time-resolved resonance Raman spectroscopy (TR3) has been used to study the effect of solvent polarity on the mechanism and nature of intermediates formed in photoinduced electron-transfer reaction between triplet flouranil ((FL)-F-3) and tetramethylbenzene (TMB). Comparison of the TR3 spectra in polar, nonpolar, and medium polar media suggests that formation of radical anion due to electron-transfer reaction between (FL)-F-3 and TMB is favored in more polar solvents, whereas ketyl radical formation is more favored in less polar media. Compared to ketyl radical, the extent of radical anion formation is negligible in nonpolar solvents. Therefore, it is inferred that in nonpolar media ketyl radical is mainly generated by hydrogen-transfer reaction in the encounter complex between (FL)-F-3 and TMB. In solvents of medium polarity, the ion-pair decay leads to the formation of both ketyl radical and ketyl radical formed from the encounter between triplet state and the donor. Thus, competition between the formation of ketyl radical and ion pair is influenced by the solvent polarity. The nature of the ion pair in different solvent polarity has been investigated from the changes observed in the vibrational frequency of (fluoranil) FL part of the complex.