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2003

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Articles 451 - 463 of 463

Full-Text Articles in Chemistry

A Stibonium-Modified Clay And Its Polystyrene Nanocomposite, Dongyan Wang, Charles A. Wilkie Jan 2003

A Stibonium-Modified Clay And Its Polystyrene Nanocomposite, Dongyan Wang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Triphenylhexadecylstibonium trifluoromethylsulfonate has been prepared and ion-exchanged with sodium montmorillonite to obtain a new organically-modified clay. The clay has higher thermal stability than an ammonium clay; only a portion of the alkyl chain is lost during degradation and all of the antimony is retained. This clay has been used to prepare a polystyrene nanocomposite in which the clay is not uniformly distributed throughout the polymer. Nonetheless the polymer does insert into the clay layers and the d-spacing of the clay expands from 2.0 to 3.0 nm. The enhanced thermal stability of this system may mean that it could be …

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In Situ Reactive Blending To Prepare Polystyrene-Clay And Polypropylene-Clay Nanocomposites, Dongyan Wang, Charles A. Wilkie Jan 2003

In Situ Reactive Blending To Prepare Polystyrene-Clay And Polypropylene-Clay Nanocomposites, Dongyan Wang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites of polystyrene and polypropylene with organically-modified clay may be prepared by melt blending in a Brabender mixer the clay and the polymer. The presence of maleic anhydride increases the likelihood of nanocomposite formation for polystyrene but is less important for polypropylene. The materials that result are immiscible materials, in that the clay is not uniformly distributed throughout the polymer matrix, but there is polymer inserted between the clay layers. The results from cone calorimetry suggest that nanocomposite formation has occurred, since there is a significant reduction in the peak heat release rate.

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Synergy Between Conventional Phosphorus Fire Retardants And Organically-Modified Clays Can Lead To Fire Retardancy Of Styrenics, Grace Chigwada, Charles A. Wilkie Jan 2003

Synergy Between Conventional Phosphorus Fire Retardants And Organically-Modified Clays Can Lead To Fire Retardancy Of Styrenics, Grace Chigwada, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polystyrene–clay nanocomposites combined with phosphorous-containing fire retardants have been prepared and used to explore the thermal stability and mechanical properties of the polymer formed. The amounts of fire retardants and clay used were varied to study the effect of each on thermal stability and mechanical properties of the polymer. The samples were prepared by bulk polymerization and analyzed by X-ray diffraction, thermogravimetric analysis, cone calorimetry, Fourier Transform infrared spectroscopy and the evaluation of mechanical properties. The thermal stability of the polymers is enhanced by the presence of the phosphorus-containing fire retardants.

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Iron-Mediated Preparation Of Vinylcyclopropanes. Scope, Mechanism, And Applications, Young K. Yun, Kamil Godula, Yeyu Cao, William A. Donaldson Jan 2003

Iron-Mediated Preparation Of Vinylcyclopropanes. Scope, Mechanism, And Applications, Young K. Yun, Kamil Godula, Yeyu Cao, William A. Donaldson

Chemistry Faculty Research and Publications

The addition of stabilized carbon nucleophiles to tricarbonyl(1-methoxycarbonylpentadienyl)iron(1+) cation (1a) proceeds via attack at C2 on the face of the ligand opposite the Fe(CO)3 group to generate tricarbonyl(pentenediyl)iron complexes 2. Oxidation of complexes 2 affords vinylcyclopropanecarboxylates in good yield. In general, the relative stereochemistry about the cyclopropane ring reflects reductive elimination with retention of configuration. In cases where the C2 substituent is bulky (i.e., 2b) the major cyclopropane product 9b represents ring closure with inversion at C3. A mechanism involving π−σ−π rearrangement of the initially oxidized (pentenediyl)iron species is proposed to account for these results. …

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Preparation And Flammability Properties Of Polyethylene-Clay Nanocomposites, Jinguo Zhang, Charles A. Wilkie Jan 2003

Preparation And Flammability Properties Of Polyethylene-Clay Nanocomposites, Jinguo Zhang, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polyethylene (PE)–clay nanocomposites have been prepared using melt blending in a Brabrender mixer. X-ray diffraction and transmission electron microscopy were used to characterize the nano-structure of these composites while the thermal stability was evaluated from thermogravimetric analysis and the flammability parameters using cone calorimetry. It is found that the PE–clay nanocomposites have a mixed immiscible-intercalated structure and there is better intercalation when maleic anhydride is combined with the polymer and clay to be melt blended. The reduction in peak heat release rate is 30–40%.

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Flame Retardancy Of Polystyrene Nanocomposites Based On An Oligomeric Organically-Modified Clay Containing Phosphate, Xiaoxia Zheng, Charles A. Wilkie Jan 2003

Flame Retardancy Of Polystyrene Nanocomposites Based On An Oligomeric Organically-Modified Clay Containing Phosphate, Xiaoxia Zheng, Charles A. Wilkie

Chemistry Faculty Research and Publications

Novel modified clays, which may enable the formation of flame retarded polystyrene nanocomposites by melt or solution blending, have been prepared using an ammonium salt which contains an oligomeric material consisting of vinylbenzyl chloride, styrene and vinyl phosphate reacting with dimethylhexadecylamine. These nanocomposites have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the evaluation of mechanical properties. Melt blending is an effective, economical way to produce intercalated nanocomposites with greatly reduced peak heat release rate and a decreased total heat release; the polymer does not all undergo thermal degradation.

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Exfoliated Poly(Methyl Methacrylate) And Polystyrene/ Nanocomposites Occur When The Clay Cation Contains A Vinyl Monomer, Shengpei Su, Charles A. Wilkie Jan 2003

Exfoliated Poly(Methyl Methacrylate) And Polystyrene/ Nanocomposites Occur When The Clay Cation Contains A Vinyl Monomer, Shengpei Su, Charles A. Wilkie

Chemistry Faculty Research and Publications

The bulk polymerization of methyl methacrylate and styrene in the presence of an organically modified clay containing a vinyl group that can be involved in the polymerization produces exfoliated nanocomposites. These nanocomposites have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, mechanical properties, and cone calorimetry. The onset temperature of thermal degradation increases with the mechanical properties. The peak heat release rate is significantly reduced for nanocomposites containing 3 or 5% clay. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1124–1135, 2003

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Characterization Of Native And Bypass Human Coronary Artery Plaque Deposits From The Same Heart: Investigation Of The Chemical Form Of Calcium In Human Coronary Artery Plaque Deposits, Serigne Thiam Jan 2003

Characterization Of Native And Bypass Human Coronary Artery Plaque Deposits From The Same Heart: Investigation Of The Chemical Form Of Calcium In Human Coronary Artery Plaque Deposits, Serigne Thiam

LSU Doctoral Dissertations

Gradual deposits of lipids, proteins, and calcium on the coronary arterial walls cause atherosclerosis, leading to blockage of the blood flow and possible heart attack. Despite many studies, the mechanism underlying these processes remains unclear. In this research, differences between native and bypass plaque deposits from the same heart were examined. In addition, the crystalline and the amorphous plaques within these native and bypass vessels were characterized. The techniques used to characterize the deposits included inductively coupled plasma mass spectrometry (ICPMS), solid-state nuclear magnetic resonance (NMR), high performance liquid chromatography (HPLC), etc. The results from the ICPMS technique showed that …

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Synthesis Of Montiporynes A And B, Traci Jenelle Speed Jan 2003

Synthesis Of Montiporynes A And B, Traci Jenelle Speed

Honors Theses

This thesis reports the first complete synthesis of monriporynes A and B. isomeric diacetylenes that bear α, β unsaturated ketone functionalities. Recently isolated from the stony coral Montipora sp. these compounds are reported to possess in vitro cytotoxic activity against several human solid tumor cells. We have synthesized both isomers in three simple steps. In the first step, l-iodononyne was prepared by reacting 1-nonyne with N-iodosuccinimide and a catalytic amount of silver nitrate. This iodoalkyne was then coupled with propargyl alcohol using copper iodide as the catalyst to give 2,4dodecadiynyl alcohol. Finally, the diacetylenic alcohol was subjected to the Swern …

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Quantitative Analysis Of Diepoxybutane Damage Within The Chicken Β-Globin Domain, André M. Pilon Jan 2003

Quantitative Analysis Of Diepoxybutane Damage Within The Chicken Β-Globin Domain, André M. Pilon

Honors Theses

In industrial polymer and synthetic rubber production facilities, workers are exposed to 1,3-butadiene. This compound is converted in vivo to 1,2,3,4-diepoxybutane (DEB) and has been linked to increased incidences of cancer in these individuals. Carcinogenesis has been attributed to formation of DEB induced DNA interstrand cross-links. Previous studies have demonstrated that DEB cross-links deoxyguanosine residues within 5'-GNC sequences in synthetic DNA, in restriction fragments, and in defined sequence nucleosomes. The current study utilized the polymerase chain reaction (PCR) to examine DEB damage frequencies within nuclear genes, found within "open" regions of chromatin, as compared to regions of unexpressed sequence that …

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Sedimentological And Plant Taphonomic Evaluation Of The Early Middle Devonian Trout Valley Formation, Jonathan Allen Jan 2003

Sedimentological And Plant Taphonomic Evaluation Of The Early Middle Devonian Trout Valley Formation, Jonathan Allen

Honors Theses

The Trout Valley Formation of Emsian-Eifelian age, outcropped in Baxter State Park, Maine, consists offluvial and coastal deposits preserving early land plants. Massive, crudely bedded conglomerate represents deposits of proximal braided channels on an alluvial fan complex. Lithic sandstone bodies in channel-form geometries represent deposits of river channels draining the Acadian highlands whereas associated siltstones represent overbank deposits, intertidal flats, and tidal channels. Localized lenticular quartz arenites represent nearshore shelf bar deposits that were storm influenced. The majority of plant assemblages preserved mainly in siltstone lithologies are allochthonous and parautochthonous, with only one autochthonous assemblage identified in the sequence. Plant …

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Double Stranded Dna-Binding Studies Of Potential Rhodium(Ll) Antitumor Complexes, Amity Elizabeth Burr Jan 2003

Double Stranded Dna-Binding Studies Of Potential Rhodium(Ll) Antitumor Complexes, Amity Elizabeth Burr

Honors Theses

In 1952, Dwyer and coworkers began testing a series of metal complexes for potential inhibition of cancer cell proliferation in animals.[l] The complexes tested were unsuitable for such studies due to their high toxicity. Therefore, no further work was done on the project. However, in 1965, Rosenberg and coworkers revisited the possibility of potential metal-based drugs. Serendipitously, they discovered that cis-diamminedichloroplatinum(lI) (cisplatin) inhibits cell division in E. coli.[2] Further studies of this and other platinum compounds revealed inhibition of tumor cell lines sarcoma 180 and leukemia LI2l0 in mice.[l] Cisplatin was approved by the Food and Drug Administration in 1970 …

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Application Of The Chan-Evans Diaryl Ether Synthesis To The Formation Of Bis(Bibenzyls), Eric Rosenthal Jan 2003

Application Of The Chan-Evans Diaryl Ether Synthesis To The Formation Of Bis(Bibenzyls), Eric Rosenthal

Honors Theses

Alkene (6) was produced in three steps from 3-hydroxybenzaldehyde (8), and 3-bromobenzyl bromide (10). A variety of strategies were employed to synthesize the desired boronic acid (13), but as of this time none have been successful. The synthesis of this boronic acid is necessary to study the feasibility of applying the Chan-Evans copper mediated formation of diaryl ethers to a bis(bibenzyl) synthesis. In seeking to exploit the advantages of the Chan-Evans ether synthesis over the Ullman ether synthesis, we have encountered some of the associated difficulties. The utilization of an arylboronic acid to produce a diaryl ether first requires the …

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