Chemistry Commons^™

Polystyrene/Graphite Nanocomposites: Effect On Thermal Stability, Fawn Marie Uhl, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites consisting of polymer and clay have been shown to exhibit a significant reduction in flammability and an increase in mechanical properties. This work examines the effect of thermal stability and mechanical properties of nanocomposites prepared from potassium graphite and styrene. Synthesis of nanocomposites was accomplished by using potassium graphite (KC₈) as the initiator in the polymerization of styrene. A slight increase in thermal stability is observed but mechanical properties are decreased.

An Xps Investigation Of Thermal Degradation And Charring Of Pmma Clay Nanocomposites, Jianxin Du, Jin Zhu, Charles A. Wilkie, Jiangqi Wang

Chemistry Faculty Research and Publications

Poly(methyl methacrylate)–clay nanocomposites have been studied using X-ray photoelectron spectroscopy. It is clear that as the polymer undergoes thermal degradation, the clay accumulates at the surface and the barrier properties which result from this clay accumulation have been described as the reason for the decreased heat release rate for nanocomposites. The surface composition of the clay changes as the nanocomposite is heated and the changes are affected by the organic-modification that were applied to the clay in order to prepare the nanocomposite.

An Xps Study Of The Thermal Degradation Of Polystyrene-Clay Nanocomposites, Jianqi Wang, Jianxin Du, Jin Zhu, Charles A. Wilkie

Chemistry Faculty Research and Publications

X-ray photoelectron spectroscopy, XPS, has been used to examine several polystyrene-clay nanocomposites. The accumulation of oxygen, from the almuniosilicate, on the surface of the polymer was observed, along with the loss of carbon. This confirms that the barrier properties of the clay provide a mechanism by which nanocomposite formation can enhance the fire retardancy of the polymers. No difference is detected depending upon the extent of exfoliation or intercalation of the nanocomposite. #2002 Elsevier Science Ltd. All rights reserved.

Thermal Stability And Flame Retardancy Of Poly(Methyl Methacrylate)-Clay Nanocomposites, Jin Zhu, Paul Start, Kenneth A. Mauritz, Charles A. Wilkie

Chemistry Faculty Research and Publications

Three ammonium salts, hexadecylallyldimethyl ammonium chloride (Allyl16), hexadecylvinylbenzyldimethyl ammonium chloride (VB16) and hexadecylvinylbenzyldimethyl ammonium chloride (Bz16) were synthesized and ion exchanged onto montmorillonite. Poly(methyl methacrylate)–clay nanocomposites of all three clays were prepared by bulk polymerization and the resulting nanocomposites were characterized by X-ray diffraction and transmission electron microscopy. The clays which contain a pendant double bond are more likely to give an exfoliated material while that which contains no double bond is intercalated. The thermal stability and flame retardancy were measured by thermogravimetric analysis (TGA) and Cone Calorimetry respectively.

Structural Evidence That The Methionyl Aminopeptidase From Escherichia Coli Is A Mononuclear Metalloprotease, Nathaniel J. Cosper, Ventris M. D'Souza, Robert A. Scott, Richard C. Holz

Chemistry Faculty Research and Publications

The Co and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectra of the methionyl aminopeptidase from Escherichia coli (EcMetAP) have been recorded in the presence of 1 and 2 equiv of either Co(II) or Fe(II) (i.e., [Co(II)_(EcMetAP)], [Co(II)Co(II)(EcMetAP)], [Fe(II)_(EcMetAP)], and [Fe(II)Fe(II)(EcMetAP)]). The Fourier transformed data of both [Co(II)_(EcMetAP)] and [Co(II)Co(II)(EcMetAP)] are dominated by a peak at ca. 2.05 Å, which can be fit assuming 5 light atom (N,O) scatterers at 2.04 Å. Attempts to include a Co−Co interaction (in the 2.4−4.0 Å range) in the …

Synthesis Of Cyclopropane Containing Natural Products, William A. Donaldson

Chemistry Faculty Research and Publications

The synthesis of select cyclopropane containing natural products is presented.

Reactivity Of Acyclic (Pentadienyl)Iron(1+) Cations With Weak Carbon Nucleophiles, M. Azad Hossain, Myung-Jong Jin, William A. Donaldson

Chemistry Faculty Research and Publications

The reaction of acyclic tricarbonyl(pentadienyl)iron(1+) cations with allyl trimethylsilane or with excess furan leads to (E,E-diene)iron complexes. Attack of these weak nucleophiles on the transoid form of the pentadienyl cation is presumably faster than attack on the more stable cisoid form.

Cross-Linking Of Polystyrene By Friedel-Crafts Chemistry: Reaction Of P-Hydroxymethylbenzyl Chloride With Polystyrene, Hongyang Yao, Michael A. Mckinney, Caroline Dick, John J. Liggat, C.E. Snape, Charles A. Wilkie

Chemistry Faculty Research and Publications

p-Hydroxymethylbenzyl chloride was found to be an effective cross-linking agent for polystyrene. The reaction was found to occur by Friedel–Crafts alkylation between the benzyl alcohol/chloride functional groups in the additive and phenyl ring in polystyrene. The reaction was studied by TGA–IR to monitor the evolution of hydrogen chloride and water, and the structure of the resultant gel was analyzed by solid state NMR and elemental analysis. The potential application in flame-retardancy was evaluated using Cone calorimetry.

An Efficient And Simple Synthesis Of Optically Pure Tricarbonyl(Methyl 6-Oxo-2,4-Hexadienoate)Iron, Kamil Godula, Heiko Bärmann, William A. Donaldson

Chemistry Faculty Research and Publications

No abstract provided.

Synthesis And Reactivity Of Tricarbonyl(1-Ethoxy-Carbonyl-2-Methylpentadienyl)Iron(1+) Cation, Young K. Yun, Heiko Bärmann, William A. Donaldson

Chemistry Faculty Research and Publications

The title cation was prepared in two steps from the known (ethyl 3-methyl-6-oxo-2,4-hexadienoate)Fe(CO)3. Reation of the cation with NaBH3CN, methyl cuprate, phthalimide, water, PPh3, or malonate anions gave predominantly the products from nucleophilic attack at the C5 pentadienyl carbon.

Intramolecular (Electron) Delocalization Between Aromatic Donors And Their Tethered Cation–Radicals. Application Of Electrochemical And Structural Probes, Duoli Sun, Sergey V. Lindeman, Rajendra Rathore, Jay K. Kochi

Chemistry Faculty Research and Publications

To study the mechanism of electronic transduction along (poly)phenylene chains, a series of aromatic donors with general formula D–B–D has been synthesized [where D = 2,5-dimethoxy-4-methylphenyl donor and B = (poly)phenylene bridge]; and the corresponding cation–radical salts D–B–D⁺˙ SbCl₆⁻ have been isolated for X-ray crystallographic analyses. The magnitude of the electronic interaction between the D and D⁺˙ moieties through the various B bridges has been measured (i) as the difference between the first and the second oxidation potentials of D–B–D donors and (ii) as the structural changes induced in neutral D by the presence …

Thermal Degradation Of Pvc In The Presence Of Polystyrene, Qiang Yao, Charles A. Wilkie

Chemistry Faculty Research and Publications

The thermal degradation of poly(vinyl chloride) (PVC) and blends of PVC with polystyrene has been studied using thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. The degradation of PVC commences at weak links by an ionic pathway, but there is evidence to suggest the presence of a radical pathway at high temperatures. While there is some chemical interaction between PVC and polystyrene, the principal mode of stabilization is a physical process.

Electron Redistribution Of Aromatic Ligands In (Arene)Cr(Co)3 Complexes. Structural (Bond-Length) Changes As Quantitative Measures, P. Le Maguères, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Arene ligands experience significant ring expansion upon coordination with chromium tricarbonyl, as established by precise X-ray crystallographic analyses of various (η⁶-arene)Cr(CO)₃ complexes. Such changes in ligand structures result from the charge (electron) redistribution, Ar⁺−Cr^-, upon arene coordination, since they are closely related to those found in the intermolecular 1:1 complexes of the corresponding series of arenes with nitrosonium cation (NO⁺). The latter are prototypical examples of charge-transfer complexes as described by Mulliken. As such, they show enhanced degrees of charge (electron) transfer that approach unity, which is confirmed by quantitative comparison …

Noncovalent Binding Of The Halogens To Aromatic Donors. Discrete Structures Of Labile Br2 Complexes With Benzene And Toluene, Alexandr V. Vasilyev, Sergey V. Lindeman, Jay K. Kochi

Chemistry Faculty Research and Publications

Precise molecular structures resulting from the noncovalent interaction of Br₂ with benzene (and toluene) reveal the unusual localized bonding to specific (one or two) carbon centers in prereactive complexes leading directly to the transition states for electrophilic aromatic brominations.

Photooxidation Of Polymeric-Inorganic Nanocomposites: Chemical, Thermal Stability And Fire Retardancy Investigations, Adams Tidjani, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites of polypropylene-graft-maleic anhydride/clay and polypropylene/clay were prepared by melt blending using two different approaches. X-Ray diffraction results showed an intercalated structure. Samples of nanocomposites were exposed to UV light under atmospheric oxygen and their photo-oxidative stability was studied using FTIR and UV spectroscopy. The consequences of this photo-oxidation on the thermal stability and fire retardant performance of the nanocomposites were also addressed from thermogravimetry analysis and Cone calorimetry.

An Xps Investigation Of Thermal Degradation And Charring Of Cross-Linked Polyisoprene And Polychloroprene, Jianwei Hao, Charles A. Wilkie, Jiangqi Wang

Chemistry Faculty Research and Publications

Our interest in butadiene-containing polymers had led to an investigation of the thermal degradation of polyisoprene, PIP, and polychloroprene, PCP. The connection between cross-linking and thermal stability through an examination of PIP and PCP has been reported. Like the course of thermogravimetric analysis (TGA) the cross-linking and charring of polymers subjected to heat can also be experimentally observed as function of temperatures by the pseudo-in-situ XPS (X-ray Photoelectron Spectroscopy). Data acquisition of C1s spectra as function of temperature permits us to explore: (1) the extent of cross-linking and/or carbon accumulation of systems of PCP and PIP with/without initiators, BPO and …

Synthesis Of Cyclopropanes Via Organoiron Methodology: Preparation Of 2-(2′-Carboxy-3′-Ethylcyclopropyl)Glycine, Kamil Godula, William A. Donaldson

Chemistry Faculty Research and Publications

A route to 1,2,3-trisubstituted cyclopropanes has been developed. The relative stereochemistry at the three cyclopropane centers is established by nucleophilic attack on the pentadienyl ligand on the face opposite to iron and subsequent oxidatively induced reductive elimination with retention of configuration. This methodology was applied to the synthesis of 2-(2′-carboxy-3′-ethylcyclopropyl)glycines. The diastereomeric glycine dimethyl esters are separable as their diphenylmethylene imines.

The conformationally restricted glutamate analogs (2S,1′S,2′S,3′R)- and (2R,1′S,2′S,3′R)-ECCG's 5a and5b were prepared in five steps (17 and 15% yield, respectively) from (pentadienyl)Fe(CO) …

Fire Retardancy In 2001, Gordon L. Wilson, Charles A. Wilkie

Chemistry Faculty Research and Publications

Fire is a world-wide problem which claims lives and causes significant loss of property. Some of the problems are discussed and the solution delineated. This peer-reviewed volume is designed to be as the state-of-the-art. This chapter provides a perspective for current work.

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 …

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.

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.

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 …

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 …

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.

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.

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).

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 …

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.

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 …

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.