Browsing by Subject "polyethylene"
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Item Evaluation of Quasicrystal Al-Cu-Fe Alloys for Tribological Applications(2013-07-22) Nabelsi, NezarThis research investigated the tribological performance of a composite material, formed from an ultra high molecular weight polyethylene (UHMWPE) matrix and quasicrystalline Al-Cu-Fe alloy powders. An evaluation was conducted for the microstructure, material properties, and tribological performance of quasicrystalline materials formed from Al-Cu-Fe alloys. Arc melting was used as the fabrication technique for these alloys, and some samples were additionally heat treated in an argon environment. Vickers microhardness testing was done to make comparisons to wear rate behavior of the various alloys. Tribological studies were conducted using a linear pinon- desk configuration to evaluate friction and wear. Research indicated the annealed samples of Al-Cu-Fe that formed icosahedral quasicrystalline phases, where the quasicrystalline phase was most dominant of the observed alloys, displayed the greatest wear resistance and hardness. Abrasive wear was observed in each of the samples, as the brittle, hard nature of the quasicrystalline phase would not allow for the ductile adhesion. The addition of small amounts of Al-Cu-Fe quasicrystalline particles, crushed and pulverized from the arc-melted ingots, reduced the coefficient of friction and wear rate of UHMWPE, when added to the polymer.Item Layer-by-layer assembly on polyethylene films via "click" chemistry(2009-05-15) Chance, Brandon ScottLayer-by-layer assembly has received much attention over the last fifteen years. This assembly process can be carried out using different methods including hydrogen-bonding, electrostatic, and to a lesser extent, covalent interactions. However, these assemblies are rarely seen on polyolefin substrates due to the lack of functionality on the surface. ?Click? chemistry has become very popular in recent years as a means to join modular compounds together. This thesis is the first published report to use ?click? chemistry as a means for layer-by-layer assembly on a polymeric substrate. By designing polymers that contain alkyne or azide groups, it is possible to assemble them layer-by-layer on a polyethylene substrate. Polymers based on tert-butyl acrylate were initially designed for use in organic solvents such as tetrahydrofuran. The copper catalyst that facilitated the 1,3-dipolar cycloaddition was air sensitive and expensive. To capture the true essence of ?click? chemistry, a new system was designed based on N-isopropyl acrylamide (NIPAM)-based polymers. These polymers were water soluble and allowed for ?click? chemistry to be performed in water and open to air in benign conditions. With the development of a water soluble polymer system that could be modified to contain either azide groups or alkyne groups, layer-by-layer assembly was carried out in water. A polyethylene film was modified in a series of reactions to have an alkyne-functionalized surface. The poly(N-isopropyl acrylamide)-based polymers were layered in an alternating fashion to form multilayer assemblies. A series of control reactions were also performed, showing that these layers were interconnected via triazole linkages. These assemblies were monitored by attenuated total reflectance spectroscopy. Once the layers were assembled, the polyvalent nature of the polymers allowed for further functionalization. Various surface functionalizations were established using fluorescence microscopy and contact angle analysis. By using spectroscopic and chemical means, layer-by-layer assembly on polyethylene films was proven. Control reactions showed the necessity of components for triazole formation. Therefore, layer-by-layer assembly using ?click? chemistry was achieved.Item Single-site polymerization catalysts: branched polyethylene and syndiotactic poly(alpha-olefins)(2009-05-15) Schwerdtfeger, Eric DeanUtilization of methylaluminoxane (MAO) activated metallocene and constrained geometry (CGC) olefin polymerization catalysts containing fluorenyl or octamethyloctahydrodibenzofluorenyl (Oct) moieties has yielded three series of syndiotactic copolymers of propylene with higher a-olefins. The melting temperatures of these polymers were analyzed, and found to correspond directly with the mole percent incorporation of comonomer, as well as with the frequency of stereoerrors in the polymers. Further analysis indicated that rmrr stereoerrors, a result of site epimerization, occur in close proximity to the incorporated comonomers. The MAO-activated fluorenyl/Oct-containing metallocene and CGC catalysts were further utilized to produce syndiotactic samples of poly(1-butene) (s-PB) and poly(1- pentene) (s-PPe). The syndiotacticity of the samples was quantified by 13C NMR and the melting temperatures determined by DSC. The samples of s-PB and s-PPe produced by Me2Si( h1-C29H36)( h1-N-tBu)ZrCl2?OEt2 (Oct-CGC) were found to melt at higher temperatures (55.9 and 43.1 ?C, respectively) than any previously reported samples. The MAO-activated Oct-CGC was also used to produce polyethylene samples at a variety of polymerization temperatures and pressures. All of the samples were found to contain an unprecedented degree of branching (13-65 total branches per 1000 carbon atoms) for an early transition metal single-site catalyst. The branches were found to be almost exclusively of two or greater than five carbon atoms in length, and the levels of the longer branches could be controlled by varying the polymerization conditions. The number of ethyl branches was roughly 5 per 1000 carbon atoms for all samples. Finally, a binary catalyst system comprising the Oct-CGC and a chromium-based ethylene trimerization catalyst, ((tBuSCH2CH2)2NH)CrCl3, was developed. This MAOactivated catalyst system could be tuned to produce polyethylene samples with 17-49 total branches per 1000 carbon atoms. Between 4 and 16 of these branches were found to arise from incorporation of 1-hexene produced by the chromium oligomerization catalyst. Adjusting the ratios of oligomerization catalyst, polymerization catalyst, and activator was found to allow rational control over the branch content of the polymers. The branching levels could also be varied by altering the time between injection of the oligomerization and polymerization catalysts into the system.Item Studies of Soluble Polymer-supported Organocatalysts(2012-10-19) Yang, Yun-ChinPolymer-supported reagents and catalysts have been extensively studied in the past few decades as they not only facilitate separation and isolation of products after reactions but also enable reuse of reagents/catalysts. In particular, chemistry using polymer-supported organocatalysts has the advantage of avoiding the use of sometimes toxic transition metals. Since organocatalysts are often used at high mol% loading in catalytic reactions, immobilizing organocatalysts on polymers for recycling and reusing makes chemistry using organocatalysts attractive in larger scale syntheses. Chapter II of this dissertation focuses on using variable temperature 31P NMR spectroscopy to study and compare the dynamic behavior of silver complexes prepared from soluble polymer-supported phosphines and electronically similar low molecular weight phosphine ligands. The phosphine-silver complexes supported on terminally functionalized polyisobutylene (PIB) and poly(ethylene glycol) show similar kinetic behavior compared to their low molecular weight counterparts. However, the dynamic behavior of phosphine-silver complexes supported as pendent groups on a linear polystyrene is difficult to study because of significant line-broadening on 31P NMR spectra. Chapter III of this dissertation aims at examining the recyclability and reusability of PIB-supported phosphines as organocatalysts and reagents. PIB-supported alkyldiphenyl- and aryldiphenylphosphines were prepared and used as recyclable organocatalysts in addition and allylic amination reactions. The PIB-bound phosphines were useful reagents in aza-Wittig and Mitsunobu reactions. The PIB-bound phosphine oxides formed either from adventitious oxidation or during the course of reactions can be reduce to PIB-phosphines for reuse. Chapter IV of this dissertation describes preliminary studies on soluble polymer-supported N-heterocyclic carbene (NHC) organocatalysts. PIB- and polyethylene oligomer (PE_Olig)-supported NHC adducts were synthesized and the corresponding polymer-supported NHC catalysts were generated in situ in lactide polymerization and phenyl isocyanate trimerization reactions. The PIB-bound NHC catalyst generated in situ was not recyclable in a lactide polymerization. However, PIB- and PEOlig-bound NHC precatalysts showed modest recyclability in lactide polymerization and phenyl isocyanate trimerizations.