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Chemistry Faculty Research and Publications

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Full-Text Articles in Chemistry

Electrochemistry And Spectroelectrochemistry Of Iron Porphyrins In The Presence Of Nitrite, Zhongcheng Wei, Michael D. Ryan Jan 2001

Electrochemistry And Spectroelectrochemistry Of Iron Porphyrins In The Presence Of Nitrite, Zhongcheng Wei, Michael D. Ryan

Chemistry Faculty Research and Publications

The reaction of nitrite with ferric and ferrous porphyrins was examined using visible, infrared and NMR spectroscopy. Solutions of either ferric or ferrous porphyrin were stable in the presence of nitrite, with only complexation reactions being observed. Under voltammetric conditions, though, a rapid reaction between nitrite and iron porphyrins was observed to form the nitrosyl complex, Fe(p)(NO), where P = porphyrin. The products of the reduction of ferric porphyrins in the presence of nitrite were confirmed by visible spectroelectrochemistry to be Fe(P)(NO) and [Fe(P)]2O. Visible, NMR and infrared spectroscopy were used to rule out the formation of Fe(P)(NO) by the …

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Xps Characterization Of Friedel-Crafts Cross-Linked Polystyrene, Jiangqi Wang, Jianxin Du, Hongyang Yao, Charles A. Wilkie Jan 2001

Xps Characterization Of Friedel-Crafts Cross-Linked Polystyrene, Jiangqi Wang, Jianxin Du, Hongyang Yao, Charles A. Wilkie

Chemistry Faculty Research and Publications

The combination of a difunctional alkylating agent, either hydroxymethylbenzyl chloride or α,α′-dichloroxylene with polystyrene or high-impact polystyrene together with a Friedel-Crafts catalyst, 2-ethylhexyldiphenylphosphate, and an amine to react with hydrogen chloride has been studied by X-ray photoelectron spectroscopy. The results confirm what had been suggested from previous investigations using thermogravimetric analysis; cross-linking of the polymer occurs as the temperature is raised and the alcohol-containing alkylating agent gives a greater amount of cross-linking than does the dichloro compound.

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The Thermal Stability Of Cross-Linked Polymers: Methyl Methacrylate With Divinylbenzene And Styrene With Dimethacrylates, Fawn Marie Uhl, Galina F. Levchik, Sergei V. Levchik, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie Jan 2001

The Thermal Stability Of Cross-Linked Polymers: Methyl Methacrylate With Divinylbenzene And Styrene With Dimethacrylates, Fawn Marie Uhl, Galina F. Levchik, Sergei V. Levchik, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie

Chemistry Faculty Research and Publications

Cross-linking of polymers is frequently presumed to enhance the thermal stability of polymer systems. Methyl methacrylate has been reacted with divinylbenzene and styrene with various dimethacrylates. These systems have been characterized by gel content, swelling ratio, infrared spectroscopy, thermal analysis, TGA/FT-IR, and solid state NMR. Both systems show enhanced thermal stability and char formation. This is most pronounced in the cases of methyl methacrylate with divinylbenzene and styrene with bisphenol A dimethacrylate.

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Fire Properties Of Polystyrene-Clay Nanocomposites, Jin Zhu, Alexander B. Morgan, Frank K. Lamelas, Charles A. Wilkie Jan 2001

Fire Properties Of Polystyrene-Clay Nanocomposites, Jin Zhu, Alexander B. Morgan, Frank K. Lamelas, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polystyrene−clay nanocomposites have been prepared using a bulk polymerization technique. Three new “onium” salts have been used to prepare the nanocomposites, two are functionalized ammonium salts while the third is a phosphonium salt. By TGA/FTIR, both ammonium and phosphonium treatments have been shown to degrade by a Hofmann elimination mechanism at elevated temperatures. TGA/FTIR showed that the phosphonium treatment is the most thermally stable treatment when compared to the two ammonium salts. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, strength and elongation at break, as a measure of the mechanical properties, thermogravimetric analysis, and cone calorimetry. The …

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Studies On The Mechanism By Which The Formation Of Nanocomposites Enhance Thermal Stability, Jin Zhu, Fawn Marie Uhl, Alexander B. Morgan, Charles A. Wilkie Jan 2001

Studies On The Mechanism By Which The Formation Of Nanocomposites Enhance Thermal Stability, Jin Zhu, Fawn Marie Uhl, Alexander B. Morgan, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polystyrene−clay and polystyrene−graphite nanocomposites have been prepared and used to explore the process by which the presence of clay or graphite in a nanocomposite enhances the thermal stability of polymers. This study has been designed to determine if the presence of paramagnetic iron in the matrix can result in radical trapping and thus enhance thermal stability. Nanocomposites were prepared by bulk polymerization using both iron-containing and iron-depleted clays and graphites, and they were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and cone calorimetry. The presence of structural iron, rather than that present as an impurity, significantly increases the …

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How Does Cross-Linking Effect The Thermal Stability Of Polyisoprene, Qiang Yao, Charles A. Wilkie Sep 2000

How Does Cross-Linking Effect The Thermal Stability Of Polyisoprene, Qiang Yao, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polyisoprene can be cross-linked by an initial lithiation followed by reaction with both monochloro compounds and dichloro compounds. The monochloro compounds effect crosslinking through a lithium-chlorine exchange route while the use of dichloro compounds links the PIP chains with the spacer between the two chlorine atoms. A significant amount of char is produced from compounds which have been cross-linked with aromatic dihalides while aliphatic dihalides do not produce significant char.

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Reaction Of Tricarbonyl(Dienal)Iron Complexes With B-Allyldiisopinocampheylborane, Vadapalli Prahlad, Abdel-Aziz S. El-Ahl, William A. Donaldson Aug 2000

Reaction Of Tricarbonyl(Dienal)Iron Complexes With B-Allyldiisopinocampheylborane, Vadapalli Prahlad, Abdel-Aziz S. El-Ahl, William A. Donaldson

Chemistry Faculty Research and Publications

Addition of allyldiisopinocampheylborane to racemic (dienal)iron complexes, followed by oxidation, affords diastereomeric (1,4,6-trien-3-ol)iron complexes with moderate to low enantioselectivity. The high enantioselectivity typically observed for this allylborane reagent is attenuated by steric interaction between the Fe(CO)3 group and the chiral isopinocampheyl groups. Further diminution of the enantioselectivity is observed for dienal complexes in which one rotomer predominates.

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Phorboxazole Synthetic Studies: The C3–C15 Bis-Oxane Segment, Patrick Bernard Greer, William A. Donaldson May 2000

Phorboxazole Synthetic Studies: The C3–C15 Bis-Oxane Segment, Patrick Bernard Greer, William A. Donaldson

Chemistry Faculty Research and Publications

The enantioselective synthesis of the C3–C15 bis-oxane segment of the phorboxazoles has been accomplished from 3-t-butyldiphenylsilyloxypropanal in 9 steps (>90% ee).

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Charge-Transfer Bonding In Metal–Arene Coordination, S. M. Hubig, Sergey V. Lindeman, Jay K. Kochi May 2000

Charge-Transfer Bonding In Metal–Arene Coordination, S. M. Hubig, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

X-ray crystallographic structures of donor–acceptor complexes of aromatic hydrocarbons with transition metals are re-examined with the focus on the arene ligands. Thus, significant structural and electronic changes are revealed in the arene moiety due to coordination to the metal center including: (i) expansion of the aromatic six-carbon ring; (ii) endocyclic π-bond localization; (iii) distortion of the planarity (folding) of the arene ring; and (iv) shortening of the metal-arene bond distances. All structural features are characteristic of metal–arene (π- or σ-) complexes that exhibit various degrees of (metal-to-ligand) charge transfer. The concept of charge-transfer bonding not only explains the structural details …

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Development Of Organoiron Methodology For Preparation Of The Polyene Natural Product Macrolactin A, Heiko Bärmann, Vadapalli Prahlad, Chunlin Tao, Young K. Yun, Zhi Wang, William A. Donaldson Apr 2000

Development Of Organoiron Methodology For Preparation Of The Polyene Natural Product Macrolactin A, Heiko Bärmann, Vadapalli Prahlad, Chunlin Tao, Young K. Yun, Zhi Wang, William A. Donaldson

Chemistry Faculty Research and Publications

Methodology for the synthesis of the C7–C13 segment (19) and C14–C24 segment (41) of macrolactin A have been developed. Dicarbonyl(methyl 7-nitro-2E,4Z-heptadienoate)triphenylphosphineiron (19) is prepared by nucleophilic addition to a (1-methoxycarbonylpentadienyl)iron cation. The C23 stereocenter of 41 is established by introduction of a C20 stereocenter, chirality transfer from C20 to C23 followed by (diene)iron mediated selective ionic reduction of the C20 hydroxyl. The C15 stereocenter may be established by nitrile oxide–olefin cyclocondensation.

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Thermal Degradation Of Cross-Linked Polyisoprene And Polychloroprene, David D. Jiang, Galina F. Levchik, Sergei V. Levchik, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie Apr 2000

Thermal Degradation Of Cross-Linked Polyisoprene And Polychloroprene, David D. Jiang, Galina F. Levchik, Sergei V. Levchik, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie

Chemistry Faculty Research and Publications

Polyisoprene and polychloroprene have been cross-linked either in solution or in solid state using free radical initiators. In the comparable experimental conditions higher cross-linking density was observed in the solid state process. Independent of the cross-linking method, polychloroprene tended to give a higher gel content and cross-link density than does polyisoprene. Infrared characterization of the cross-linked materials showed cis-trans isomerization occurred in the polyisoprene initiated by benzoyl peroxide, whereas no isomerization was found in the samples initiated by dicumyl peroxide. Polyisoprene does not cross-link by heating in a thermal analyzer, whereas polychloroprene easily undergoes cross-linking in such conditions. Infrared …

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Polybutadiene Cross-Linked With Various Diols – Effect On Thermal Stability, Fawn Marie Uhl, Michael A. Mckinney, Charles A. Wilkie Jan 2000

Polybutadiene Cross-Linked With Various Diols – Effect On Thermal Stability, Fawn Marie Uhl, Michael A. Mckinney, Charles A. Wilkie

Chemistry Faculty Research and Publications

The relationship between cross-linking and thermal stability as related to polybutadiene is the focus of current research. Cross-linked polybutadienes have been prepared using various diols as the cross-linking agent. Cross-linked polymers have been characterized by gel content, swelling ratios, infrared spectroscopy, and thermal analysis. These polymers are not highly cross-linked, as seen by gel content and swelling ratios, and cross-linking does not have a large effect on the onset temperature of the degradation. Nonetheless, extensive formation of a non-volatile residue occurs.

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Electrophilic Aromatic Nitrosation. Isolation And X-Ray Crystallography Of The Metastable No+ Complex With Nitrosoarene, Sergey V. Lindeman, E. Bosch, Jay K. Kochi Jan 2000

Electrophilic Aromatic Nitrosation. Isolation And X-Ray Crystallography Of The Metastable No+ Complex With Nitrosoarene, Sergey V. Lindeman, E. Bosch, Jay K. Kochi

Chemistry Faculty Research and Publications

Isolation of the unstable 1∶1 complex of 4-nitrosoanisole with NO+PF6− allows its precise X-ray structural characterization. The charge-transfer crystal is formed via strong N⋯N coordination [the distance of 1.938(5) Å corresponding to a σ-bond order of ≈0.2] in the mean plane of the planar 4-nitrosoanisole donor. Thorough analysis of its molecular geometry in terms of valence resonance and MO schemes reveals a strong charge polarization with a local negative charge localized on the nitroso group and a local positive charge distributed over the adjacent p-methoxybenzyl moiety. Such a charge distribution accommodates the well-known passivation of …

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Novel (Heteromolecular) Π-Complexes Of Aromatic Cation Radicals. Isolation And Structural Characterization, P. Le Maguères, Sergey V. Lindeman, Jay K. Kochi Jan 2000

Novel (Heteromolecular) Π-Complexes Of Aromatic Cation Radicals. Isolation And Structural Characterization, P. Le Maguères, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Extensive (electron) delocalization in the novel heteromolecular π-complex of the hindered naphthalene cation radical (OMN+•) with naphthalene (NAP) accompanies the pronounced charge-transfer absorption band at ∼1100 nm in the near-IR. X-ray crystallography establishes the viability of the unusual “club sandwich” structure despite the repulsive electrostatic forces inherent to the dicationic unit.

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Cross-Linking Of Polystyrene By Friedel-Crafts Chemistry: Multi-Functional Additives, Hongyang Yao, Jin Zhu, Michael A. Mckinney, Charles A. Wilkie Jan 2000

Cross-Linking Of Polystyrene By Friedel-Crafts Chemistry: Multi-Functional Additives, Hongyang Yao, Jin Zhu, Michael A. Mckinney, Charles A. Wilkie

Chemistry Faculty Research and Publications

Various multifunctional aromatic compounds were synthesized and tested to ascertain if they were able to cross-link polystyrene. Catalysis and inhibition at high temperature were studied to achieve control over the cross-linking temperature, in order to develop suitable formulations which may function as flame retardants.

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On The Stabilizing Action Of Protein Denaturants: Acetonitrile Effect On Stability Of Lysozyme In Aqueous Solutions, Evgenii L. Kovrigin, Sergey A. Potekhin Jan 2000

On The Stabilizing Action Of Protein Denaturants: Acetonitrile Effect On Stability Of Lysozyme In Aqueous Solutions, Evgenii L. Kovrigin, Sergey A. Potekhin

Chemistry Faculty Research and Publications

Stability of hen lysozyme in the presence of acetonitrile (MeCN) at different pH values of the medium was studied by scanning microcalorimetry with a special emphasis on determination of reliable values of the denaturational heat capacity change. It was found that the temperature of denaturation decreases on addition of MeCN. However, the free energy extrapolation showed that below room temperature the thermodynamic stability increases at low concentrations of MeCN in spite of the general destabilizing effect at higher concentrations and temperatures. Charge-induced contribution to this stabilization was shown to be negligible (no pH-dependence was found); therefore, the most probable cause …

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Silver(I) Complexation Of (Poly)Aromatic Ligands. Structural Criteria For Depth Penetration Into Cis-Stilbenoid Cavities, Sergey V. Lindeman, Rajendra Rathore, Jay K. Kochi Jan 2000

Silver(I) Complexation Of (Poly)Aromatic Ligands. Structural Criteria For Depth Penetration Into Cis-Stilbenoid Cavities, Sergey V. Lindeman, Rajendra Rathore, Jay K. Kochi

Chemistry Faculty Research and Publications

Silver(I) complexes with aromatic donors are thoroughly analyzed (with aid of the Cambridge Crystallographic Database) to identify the basic structural factors inherent to the bonding of an arene ligand. Most strikingly, the distance parameter d (which simply measures the normal separation of Ag from the mean aromatic plane) is singularly invariant at d = 2.41 ± 0.05 Å for all silver/arene complexes, independent of the hapticity (η1 or η2), hybridization, or multiple coordination. As such, a systematic series of stilbenoid ligands has been successfully designed to precisely modulate the penetration of silver(I) into the ligand cleft, and …

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Synthesis And Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Model Studies For The Preparation Of The 8E,10Z,16E,18E-Tetraene Segment Of Macrolactin A, Abdel-Aziz S. El-Ahl, Young Yun, William A. Donaldson Dec 1999

Synthesis And Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations: Model Studies For The Preparation Of The 8E,10Z,16E,18E-Tetraene Segment Of Macrolactin A, Abdel-Aziz S. El-Ahl, Young Yun, William A. Donaldson

Chemistry Faculty Research and Publications

The dicarbonyl(1,2-dimethylpentadienyl)triphenylphosphineiron(1+) cation (11) has been prepared from methyl 4-methyl-2E,4E-hexadienoate in four steps. The cation (11) reacts with hydride and carbon nucleophiles in a regiospecific fashion to afford (3-methyl-2E,4Z-diene)iron complexes. Dicarbonyl(3-methyl-7-nitro-2E,4Z-heptadiene)triphenylphosphineiron (15), the product from the reaction of 11 with nitromethane anion, has been utilized as a precursor for nitrile oxide–olefin cyclocondensations.

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Thermal Degradation Of Blends Of Polystyrene And Poly(Sodium 4-Styrenesulfonate) And The Copolymer, Poly(Styrene-Co-Sodium 4-Styrenesulfonate), Qiang Yao, Charles Wilkie Dec 1999

Thermal Degradation Of Blends Of Polystyrene And Poly(Sodium 4-Styrenesulfonate) And The Copolymer, Poly(Styrene-Co-Sodium 4-Styrenesulfonate), Qiang Yao, Charles Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of blends and copolymers of styrene with styrenesulfonic acid has been studied using thermogravimetric analysis, TGA/FTIR, and cone calorimetry. The blends have enhanced thermal stability relative to virgin polystyrene but there is no enhancement in thermal stability for the copolymers. Apparently, it is necessary to have adjacent sulfonic acid groups in order to permit the formation of a graphite-like char which can provide thermal protection to the polymer. It is necessary to have a good match in degradation temperatures of the two components if one is to have significantly enhanced thermal stability.

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Further Studies On Fire Retardant Polystyrene By Friedel–Crafts Chemistry, Zhitao Wang, David D. Jiang, Charles Wilkie, Jeffery W. Gilman Dec 1999

Further Studies On Fire Retardant Polystyrene By Friedel–Crafts Chemistry, Zhitao Wang, David D. Jiang, Charles Wilkie, Jeffery W. Gilman

Chemistry Faculty Research and Publications

The combination of a copolymer of 4-vinylbenzyl alcohol and styrene with 2-ethylhexyldiphenylphosphate (DPP) and with metal chlorides has been studied by TGA, radiative gasification, Cone Calorimetry, and oxygen index measurements. Evidence is presented in support of a cross-linking reaction with the additives and the copolymer, which proceeds through a Friedel–Crafts mechanism. This approach reduces the peak heat release rate (HRR) by 60% as measured in the Cone Calorimeter. There is a significant reduction in the mass loss rate during the thermal degradation, and evidence of char formation is observed in the radiative gasification experiments.

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Tga/Ftir: An Extremely Useful Technique For Studying Polymer Degradation, Charles A. Wilkie Dec 1999

Tga/Ftir: An Extremely Useful Technique For Studying Polymer Degradation, Charles A. Wilkie

Chemistry Faculty Research and Publications

Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy, TGA/FTIR, has been used to probe the degradation of several polymeric systems. These include poly(methyl methacrylate) in the presence of various additives, graft copolymers of acrylonitrile-butadiene-styrene and styrene-butadiene with sodium methacrylate and styrene with acrylonitrile, blends of styrene-butadiene block copolymers with poly(vinylphosphonic acid) and poly(vinylsulfonic acid), and cross-linked polystyrenes. Additives may interact with poly(methyl methacrylate) by coordination to the carbonyl oxygen to a Lewis acid and the subsequent transfer of an electron from the polymer chain to the metal atom or by the formation of a radical which can trap the degrading …

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Stabilization Of Polystyrene By Friedel-Crafts Chemistry: Effect Of Position Of Alcohol And The Catalyst, Jin Zhu, Michael A. Mckinney, Charles Wilkie Nov 1999

Stabilization Of Polystyrene By Friedel-Crafts Chemistry: Effect Of Position Of Alcohol And The Catalyst, Jin Zhu, Michael A. Mckinney, Charles Wilkie

Chemistry Faculty Research and Publications

Polystyrene has been copolymerized with 4-vinylbenzyl alcohol, 4-(2-hydroxyethyl)styrene, and 4-(3-hydroxypropyl)styrene and it has been shown that thermal cross-linking of these copolymers is dependent upon the alcohol content. When the alcohol content is low, no thermal cross-linking is observed. When various phosphate esters are present as catalysts with these low alcohol content copolymers, cross-linking is observed at temperatures of about 250°C but not at lower temperatures. Cross-linking enhances the thermal stability of the copolymers. Studies of the thermal stability of the copolymers and their blends with the catalysts have been performed using thermogravimetric analysis and thermogravimetric analysis coupled to Fourier transform …

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An Xps Study Of The Radiation-Induced Effect On The Thermal Degradation And Charring Of Butadiene And Its Copolymers, Jianwei Hao, Shaoli Wu, Charles Wilkie, Jianqi Wang Oct 1999

An Xps Study Of The Radiation-Induced Effect On The Thermal Degradation And Charring Of Butadiene And Its Copolymers, Jianwei Hao, Shaoli Wu, Charles Wilkie, Jianqi Wang

Chemistry Faculty Research and Publications

A pseudo-in-situ XPS approach shows that cross-linking induced by irradiation may lead to char formation even though it shows only a small or no effect on the onset temperature of degradation.

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Thermal Decomposition Of Cross-Linked Polybutadiene And Its Copolymers, David D. Jiang, Galina F. Levchik, Sergei V. Levchik, Charles Wilkie Sep 1999

Thermal Decomposition Of Cross-Linked Polybutadiene And Its Copolymers, David D. Jiang, Galina F. Levchik, Sergei V. Levchik, Charles Wilkie

Chemistry Faculty Research and Publications

Polybutadiene and two copolymers containing butadiene and styrene have been cross-linked by thermal processes, by the use of initiators in solution, and by intimately mixing an initiator with the polymer and then heating this blend. The most efficient cross-linking process is the use of an intimate blend of the initiator and polymer. Most cross-linking processes lower the onset temperature of degradation, presumably because chain scission reactions occur simultaneously with cross-linking, while also increasing the fraction of non-volatile residue which is produced. It is believed that the density of cross-links is responsible for the increased yield of non-volatile residue.

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1H Nmr Studies On The Cua Center Of Nitrous Oxide Reductase From Pseudomonas Stutzeri, Richard C. Holz, Marcela L. Alvarez, Walter G. Zumft, David M. Dooley Aug 1999

1H Nmr Studies On The Cua Center Of Nitrous Oxide Reductase From Pseudomonas Stutzeri, Richard C. Holz, Marcela L. Alvarez, Walter G. Zumft, David M. Dooley

Chemistry Faculty Research and Publications

1H NMR spectra of the CuA center of N2OR from Pseudomonas stutzeri, and a mutant enzyme that contains only CuA, were recorded in both H2O- and D2O-buffered solution at pH 7.5. Several sharp, well-resolved hyperfine-shifted 1H NMR signals were observed in the 60 to −10 ppm chemical shift range. Comparison of the native and mutant N2OR spectra recorded in H2O-buffered solutions indicated that several additional signals are present in the native protein spectrum. These signals are attributed to a dinuclear copper(II) center. At least …

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The Methionyl Aminopeptidase From Escherichia Coli Can Function As An Iron(Ii) Enzyme, Ventris M. D'Souza, Richard C. Holz Aug 1999

The Methionyl Aminopeptidase From Escherichia Coli Can Function As An Iron(Ii) Enzyme, Ventris M. D'Souza, Richard C. Holz

Chemistry Faculty Research and Publications

The identity of the physiologically relevant metal ions for the methionyl aminopeptidase (MetAP) from Escherichia coli was investigated and is suggested to be Fe(II). The metal content of whole cells in the absence and presence of expression of the type I MetAP from E. coli was determined by inductively coupled plasma (ICP) emission analysis. The observed change in whole cell concentrations of cobalt, cadmium, copper, nickel, strontium, titanium, and vanadium upon expression of MetAP was negligible. On the other hand, significant increases in the cellular metal ion concentrations of chromium, zinc, manganese, and iron were observed with the increase in …

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Cross-Linking Of Polystyrene By Friedel–Crafts Chemistry To Improve Thermal Stability, Zhitao Wang, David D. Jiang, Michael A. Mckinney, Charles Wilkie Jun 1999

Cross-Linking Of Polystyrene By Friedel–Crafts Chemistry To Improve Thermal Stability, Zhitao Wang, David D. Jiang, Michael A. Mckinney, Charles Wilkie

Chemistry Faculty Research and Publications

Copolymers which contain either alcohol or chloride functionalized polystyrene units have been prepared and they participate in Friedel–Crafts chemistry to give cross-linked polymers by the evolution of either hydrogen chloride or water. Proof of cross-linking comes from the identification of the evolved gas, the insolubility of the product, and the thermal resistance of the newly formed polymer. The onset temperature for the degradation is raised by about 100°C relative to that of polystyrene and the fraction which is not volatile at 800°C ranges from 10% for the alcohol copolymers to 20% for the chloride copolymers.

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Thermal Decomposition And Combustion Of Γ-Irradiated Polyamide 6 Containing Phosphorus Oxynitride Or Phospham, A. I. Balabanovich, Sergei V. Levchik, Galina F. Levchik, W. Schnabel, Charles Wilkie May 1999

Thermal Decomposition And Combustion Of Γ-Irradiated Polyamide 6 Containing Phosphorus Oxynitride Or Phospham, A. I. Balabanovich, Sergei V. Levchik, Galina F. Levchik, W. Schnabel, Charles Wilkie

Chemistry Faculty Research and Publications

Polyamide 6 (PA-6) containing the fire retardants phosphorus oxynitride ((PON)m) or phospham ((PN2H)n) was exposed to 60Co-γ-rays (absorbed dose: 1.0–4.0 MGy). The irradiation led to crosslinking of the polymer which caused an increase in the char yield and a decrease in the flammability of the polymer. The combustion behavior was strongly affected by irradiation: dripping was totally prevented in the case of system PA-6/(PN2H)n and strongly retarded in the case of system PA-6/(PON)m. The thermal stability of the system PA-6/(PN2H)n decreased with increasing absorbed dose …

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Thermal Degradation Of Polystyrene, Poly(1,4-Butadiene) And Copolymers Of Styrene And 1,4-Butadiene Irradiated Under Air Or Argon With 60co-Γ-Rays, W. Schnabel, Galina F. Levchik, Charles Wilkie, David D. Jiang, Sergei V. Levchik May 1999

Thermal Degradation Of Polystyrene, Poly(1,4-Butadiene) And Copolymers Of Styrene And 1,4-Butadiene Irradiated Under Air Or Argon With 60co-Γ-Rays, W. Schnabel, Galina F. Levchik, Charles Wilkie, David D. Jiang, Sergei V. Levchik

Chemistry Faculty Research and Publications

60Co-γ-irradiated samples of polystyrene (PSt), poly(1,4-butadiene), (PBD), and two poly(styrene-co-butadiene)s containing 25 and 75% BD were subjected to thermogravimetric analysis (TGA), in the presence and absence of O2. In the case of PSt the irradiation caused a significant shift in Tonset, the onset temperature for mass loss, to higher temperatures, whereas in the cases of the BD-containing polymers irradiation caused a decrease in Tonset (oxic irradiation) or had little or no effect on Tonset (anoxic irradiation). The amount of non-volatile residue formed in the cases of BD-containing polymers was augmented by …

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Use Of Evolutionary Factor Analysis In The Spectroelectrochemistry Of Escherichia Coli Sulfite Reductase Hemoprotein And A Mo/Fe/S Cluster, Robert L. Keesey, Michael D. Ryan May 1999

Use Of Evolutionary Factor Analysis In The Spectroelectrochemistry Of Escherichia Coli Sulfite Reductase Hemoprotein And A Mo/Fe/S Cluster, Robert L. Keesey, Michael D. Ryan

Chemistry Faculty Research and Publications

The deconvolution of spectroelectrochemical data is often quite difficult if the spectra of intermediates are not known. Factor analysis, however, has been shown to be a powerful technique which can make it possible to deconvolute overlapping spectra. In this work, evolving factor analysis will be used to determine the number of intermediates and the spectra of those species for two typical spectroelectrochemical experiments:  linear scan voltammetry and chronoabsorptometry in a thin-layer cell. The first system was the reduction of E. coli sulfite reductase hemoprotein (SiR-HP). Principal factor analysis indicated that three species were present. By using evolving factor analysis, …

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