A series of new, well-defined poly(ether ether sulfone), poly(ether ether ketone) and polyimide derivatives containing the diphenylethylene moiety were prepared by step-growth polymerization methods. Poly(ether ether sulfone) derivatives were prepared by two step-growth polymerization methods: (a) The cesium fluoride catalyzed polycondensation reactions of 4,4´-difluorodiphenylsulfone with different mole percentage ratios of silylated bisphenol derivatives, 2,2-bis(4-tbutyldimethylsiloxyphenyl) propane and 1,1-bis(4-t-butyldimethylsiloxyphenyl)ethylene in N-methyl-2-pyrrolidone at 150 °C. (b) The potassium carbonate catalyzed nucleophilic aromatic substitution polycondensation reactions of 4,4´-difluorodiphenylsulfone with different mole percentage ratios of bisphenol A and 1,1-bis(4-hydroxyphenyl)ethylene in N,N-dimethylacetamide and toluene at 165 °C. Poly(ether ether ketone) derivatives were prepared by the cesium fluoride catalyzed polymerization reactions of 4,4´-difluorobenzophenone with different mole percentage ratios of 2,2-bis(4-t-butyldimethylsiloxyphenyl)propane and 1,1-bis[4-(t-butyldimethylsiloxy)- phenyl]ethylene in N-methyl-2-pyrrolidone at 150 °C. Polyimide derivatives were prepared by step-growth polymerization methods by the polycondensation reactions of 4,4´-oxydiphthalic anhydride with different mole percentage ratios of 2,2-bis[4-(4-aminophenoxy)phenyl]propane and 1,1-bis(4-aminophenyl)ethylene. The intermediate polyamic acids were subjected to thermal imidization processes to provide the corresponding polyimide derivatives. Due to the regiospecific introduction of the 1,1-diphenylethylene group along the polymer backbone, the different poly(ether ether sulfone), poly(ether ether ketone) and polyimide derivatives were subjected to post-polymerization sulfonation reactions via the thiol-ene reaction using sodium 3-mercapto-1-propane sulfonate as sulfonating agent and AIBN as initiator in N-methyl-2-pyrrolidone/dimethylsulfoxide at 75 °C for 5 days. The 1,1- diphenylethylene derivatives and the different polymeric compounds were characterized by size exclusion chromatography, dilute solution viscometry, 1H NMR and 13C NMR spectrometry, FTIR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, atomic force microscopy, transmission electron microscopy, elemental analysis, energy dispersive spectroscopy and ion exchange capacity measurements. / Chemistry / M.Sc. (Chemistry)

In the origin of life on the primitive earth a major step must have involved the condensation of amino acids to form the first polypeptides. Several suggestions as to how this might have occurred have been made by other workers. One of the more appealing proposals is that the polymerization was catalyzed by clay minerals. It has been reported, for example, that L-apartic acid polymerizes significantly faster than D-aspartic in the presence of kaolinite in aqueous suspension at 90˚. In this work an attempt was made to repeat this report and extend the pH range to include values presumably present on the prebiotic earth. No evidence for polymerization of L-aspartic acid were found. Polymerization of glycine under dry conditions in the presence of kaolinite and sodium borate was also investigated. Although small amounts of glycylglycine and glycylglycylglycine were detected there was no evidence that the reaction is enhanced by the presence of kaolinite.

A dissertation submitted to the Faculty of Science, School of Chemistry, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2017. / Pyridyl-imine ligands L1-L4 were prepared by condensation of pyridine-2-carboxyaldehyde with an appropriate amine. Characterization by NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis confirmed successful preparation in yields of 64-88%. These ligands were used to prepare Pd(II) complexes C1-C4, from PdCl2(CH3CN)2 and the corresponding pyridyl-imine ligand. 1H-NMR, 13C-NMR, FT-IR, mass spectrometry and elemental analysis confirmed coordination. Attempts to prepare target Fe(II) complexes C5-C8 by reacting the ligands with anhydrous FeCl2 were unsuccessful. Infrared data suggested coordination of ligands to the Fe centre, however mass spectrometry and elemental analysis data revealed that target complexes were not obtained. Pd(II) complexes C1-C4 were evaluated as catalyst precursors for 1-hexene oligomerization and norbornene polymerization using methylaluminoxane (MAO) as co-catalyst. The oligomerization of 1-hexene was investigated in a neat reaction media at various Al:Pd ratios. All investigated complexes were found to be inactive for the oligomerization of 1-hexene. From 1H-NMR spectroscopy and GC-MS analysis it was observed that the product distribution was mainly a mixture of 2-hexene and 3-hexene isomers. Parameters such as temperature and time did not have any significant influence towards the productivity of 1-hexene oligomers. Norbornene polymerization studies were carried out with Pd(II) complex C4 in toluene at room temperature. This complex was found to exhibit good activity for norbornene polymerization, producing a vinyl bicyclic polymer, confirmed with infrared and solid state 13C-NMR spectroscopy. Increasing the amount of co-catalyst (MAO) and temperature did not have any significant influence on the activity and monomer conversion. However, increasing reaction time was observed to have a significant influence on the activity. / MT2017

No description available.

<p> The work in this thesis focuses on the search for a system that would allow for the controlled anionic polymerization of N,N-dimethylacrylamide. The resulting polymer would serve as a macromonomer equipped with a chain end functional group originated from diallylamine.</p> <p> Poly(dimethylacrylamide) macromonomers were produced on a laboratory scale by reacting diallylamine with sec-butyllithium initiator, followed by the monomer addition. The synthesis was terminated, the polymer product precipitated in hexane, and dried in a vacuum oven at 45°C. The reactions were performed at 0°C and -77°C in tetrahydrofuran solvent.</p> <p> The polymerization control was achieved as a means of controlling the molecular weight and stereoregularity of the macromonomer, which in turn dictated solubility of the final product in the reaction solvent. The addition of triethylborane coordinating agent allowed for the polymerization of soluble product. The produced macromonomers characterized with atactic and syndiotactic structure were completely soluble in tetrahydrofuran.</p> <p> The molecular weights of macromonomers were evaluated by a gel permeation chromatography, GPC. The best results were obtained by using dimethylformamide as a mobile phase and poly(methylmethacrylate) standards</p> <p> The macromonomer yield was evaluated by 1H NMR and the stereoregularity by 13C NMR. Although the molecular weight of the macromonomer was under good control, the NMR measurements did not show the best yield control.</p> <p> The study of the triethylborane coordinating power showed that varying concentration of this ligand affected the solubility of the polymer in the reaction solvent. The soluble macromonomer was synthesized when triethylborane was in 1.5 molar excess over the initiator concentration. The 13C NMR measurements indicated that 23% of isotactic and atactic structure was required as a borderline for the solubility.</p> <p> The kinetic measurements performed in a batch reactor proved the livingness of the polymerization system with the propagation rate constant kobs equal to 1.9 · 10^-3 [1/s].</p> / Thesis / Master of Engineering (MEngr)

No description available.

No description available.

No description available.

Substituent effects in eta5-cyclopentadienyl (Cp) transition metal complexes have been intensely studied since the discovery of the first such complex, ferrocene. Modifications of the Cp ligand framework effect changes in the physical properties and chemical reactivity of the coordinated transition metal. This concept is useful when applied to catalysis mediated by Cp complexes, because the performance of the catalyst can be markedly improved using well-chosen ligand substituents. Studies of electronic substituent effects ideally employ a wide range of electron-donating and electron-withdrawing groups. Unfortunately, most of the available electron-withdrawing groups suffer from problems with Cp ligand synthesis, Cp anion stability, and electron-withdrawing group stability under catalytic conditions. This dissertation shows that the pentafluorophenyl (C6F5) substituent is highly electron-withdrawing but avoids all of these problems. Several new C6F5-substituted cyclopentadienes are prepared by the reaction of sodium cyclopentadienide and hexafluorobenzene (C6F6) under varying conditions. Corresponding C6F5-substituted cyclopentadienyl ligands (sodium salts) are obtained upon deprotonating the dienes with NaH. Complexes of Mn(I), Re(I), Fe(II), Co(II), Zr(IV) are synthesized by reacting these ligands with transition metal halides. The acidities of several C6F5- and C5F4N-substituted cyclopentadienes and indenes are measured using 19F NMR spectroscopy. The electron-withdrawing fluorinated aryl groups have a substantial acidifying effect. The identity and number of substituents (C6F5, C5F4N, CH3, and t-Bu), the position of the substituents on the cyclopentadiene, and the intramolecular (vicinal) steric effects also influence acidity. The electron-withdrawing ability of the C6F5 group is also characterized by infrared spectroscopic analysis of substituted CpM(CO)3 (M = Mn(I) and Re(I)) and electrochemical analysis of substituted ferrocenes. X-ray crystal structures of several C6F5-substituted Cp complexes reveal interesting structural motifs, including pi-stacking of the C6F5 substituents, Cp-M bond elongation, and CO-C6F5 interactions. In addition, dynamic Cp-C6F5 and Cp-M rotational barriers are measured by variable temperature NMR spectroscopy. Finally, ethylene polymerizations and ethylene/1-hexene copolymerizations are conducted using C6F5- and C6H5-substituted zirconocene dichlorides as catalysts. Contrary to findings published elsewhere, this study shows that substituent electronic effects induce substantial changes in comonomer incorporation. / Ph. D.

This research is focused on the polymerization of 2-alkyl-2-oxazoline homopolymers and 2-alkyl-2-oxazoline containing copolymers with well-defined structures. In addition, the potential of selected materials as polymer blend compatibilizers was briefly evaluated. The polymerization of 2-alkyl-2-oxazoline was investigated with regard to the effects of initiator structures on molecular weight control and molecular weight distribution, living characteristics, and mechanisms and kinetics. The structure of initiators was shown to greatly affect the molecular weight control and molecular weight distribution of poly (2-ethyl-2-oxazoline). The living nature of poly (2-ethyl-2-oxazoline) in chlorobenzene initiated by benzyl iodide, benzyl chloride/NaI, or chloroethyl ethyl ether/NaI has been established by Mn-conversion plots and sequential monomer addition experiments. However, the molecular weight distributions of these polymers were not as narrow as Poisson distributions, Mechanistic and kinetic studies of 2-ethyl-2-oxazoline polymerizations suggested that, at very early stages of polymerization, the active species is covalent. After that very early Stage of polymerization, ionic species are present and the overall propagation rates increases. The rate determining step was found to be the initial propagation step(s) using benzyl iodide as the initiator, and initiation and/or the initial propagation step(s) in the case of iodobutane as an initiator. A kinetic study of 2-methyl-2-oxazoline polymerization in CD₃CN also indicated slower initiation than propagation rates using both butyl mesylate and butyl iodide as initiators. Based on the knowledge of 2-alkyl-2-oxazoline homopolymerizations, poly(2-alkyl-2-oxazoline) containing copolymers were prepared using macroinitiator methods, with poly(2-alkyl-2-oxazoline) being either the macroinitiator or the second component synthesized. Narrow distribution poly(dimethylsiloxane) oligomers terminated with benzyl chloride endgroups were prepared by living anionic ring-opening polymerization of hexamethylcyclotrisiloxane followed by termination with a benzyl chloride containing chlorosilane reagent. Cationic ring-opening polymerization of 2-ethyl-2-oxazoline using these macroinitiators in combination with NaI generated a series of well defined block copolymers. Poly(butyl vinyl ether) and poly(methyl vinyl ether) oligomers with Poisson distributions and precisely terminated on one end with a chloroethyl ether functional group were prepared by living cationic polymerization of alkyl vinyl ethers using a chloroethyl vinyl ether/HI initiating system with ZnI₂ as catalyst and terminated by lithium borohydride. The chloroethyl ether functional groups were used in conjunction with sodium iodide to polymerize 2-ethyl-2-oxazoline blocks. In order to insure effective initiation and to narrow the copolymer molecular weight and composition distributions, the chloride to iodide conversion was made prior to the addition of monomer. A series of these diblock materials was prepared wherein the molecular weight distributions ranged from 1.3 to 1.4. The bulk, solution and surface properties of these copolymers were investigated by NMR, DSC, XPS and surface tension measurements. Both types of materials described above are currently being utilized for studying the parameters important for steric stabilization of inorganic particles in polar media. A less defined series of materials was also prepared. Using poly(butyl vinyl ether-co-chloroethyl vinyl ether) random copolymers as: macroinitiators, 2-methyl-2-oxazoline was polymerized, resulting in poly(butyl vinyl ether-2-methyl-2- oxazoline) graft copolymers. Poly(2-methyl-2-oxazoline-ε-caprolactone) block copolymers were prepared using hydroxyterminated poly(2-methyl-2-oxazoline) as miacroinitiators. Poly(butyl vinyl ether-g-2-methyl-2-oxazoline) (PBVE-g-PMOX) or poly(2-methyl-2-oxazoline-b-ε-caprolactone) (PMOX-b-PCL) were screened as potential blend compatibilizers for poly(ε-caprolactam) (Nylon 6) and isotactic poly(propylene). Analysis of these blends by SEM indicated that PBVE-g-PMOX might function as a blend compatibilizer for Nylon 6/poly(propylene) blend while PMOX-b-PCL would not. / Ph. D.