Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / This thesis reports on an exploratory investigation of proposed sludge guideline limits of heavy metal (cadmium, chromium, copper, nickel, lead and zinc) concentrations for South Africa. The purpose of the study is to determine allowable heavy metal concentrations in sludge for use as fertilizer in agriculture that can be attained and is practically possible without being detrimental to the environment. This determination was done by investigating the potential sources and concentrations of these heavy metals at the Potsdam Wastewater Treatment Works (WWTW) and also the efficiency of the treatment works in removal of these heavy metals. A heavy metal mass balance of both the influent at the Potsdam WWTW and the wastewater through the treatment works was calculated. This study also proposes possible interventions to minimize the levels of these heavy metals. Results for the heavy metal mass balance of the influent showed that a large quantity of some metals were unaccounted for, this implies that either industries discharge illegally after hours or the present monitoring undertaken by the City of Cape Town is inadequate. The large percentage of unaccounted cadmium suggests another source, which should be further investigated. The mass balance of the wastewater through Potsdam WWTW concluded that all these heavy metal limits were attainable, and that in some cases can be lowered even more. The treatment works has a high removal efficiency of these heavy metals, and a substantial reduction of these limits is justified. In the period of this study, the area under investigation gradually expanded, as more industries were established in it. Although the works was performing beyond its capacity it nevertheless was able to attain the rigorous heavy metal limits in sludge that are envisaged. There has also been a reduction in limits of heavy metals for discharge of final effluent into waterbodies; this study shows that these limits are also attainable.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / This study comprises the preparation and characterisation of completely new Fischer-type carbene complexes of chromium and tungsten by deprotonation of (CO)5M=C(NMe2)(Me), (CO)5M=C(OMe)(Me) or (CO)5M=C(NMe2)C≡CH, and subsequent treatment of the formed anion with a variety of reagents, including reactive metal complexes. The deprotonation of the termodynamically stable complexes, (CO)5M=C(NMe2)(Me) (M = Cr or W) followed by reaction with the sulfonium salt, [Me2(MeS)S][BF4], yielded not only the expected products (CO)5M=C(NMe2)CH2SCH3, but also thioether complexes, (CO)5MS(CH3)2, disulfinated complexes (CO)5M=C(NMe2)CH(SCH3)2, S-bridged dinuclear compounds (CO)5M=C(NMe2)CH2S(CH3)M(CO)5, as well as the unique fourmembered- C,S-chelate carbene complexes (CO)4Cr=C(NMe2)CH(SCH3)SCH3 and (CO)4M=C(NMe2)CH2SCH3. Crystal structure determinations of (CO)5W=C(NMe2)CH(SCH3)2, (CO)5Cr=C(NMe2)CH2S(CH3)Cr(CO)5, (CO)4M=C(NMe2)CH2SCH3 (M = Cr, W) and (CO)4Cr=C(NMe2)CH(SCH3)SCH3 were successfully performed. The latter tetracarbonyl complexes have Cr-S bonding distances of 2.4531(9) and 2.4517(5) Å and a W-S distance of 2.577(1) Å. These relatively weak bonds contribute to the short M-C(O)-distances trans to it. The formed four membered chelate rings are essentially planar. The deprotonation of (CO)5Cr=C(NMe2)(Me) and sequential reaction with sulphur and CF3SO3Me does not yield the expected product, (CO)5Cr=C(NMe2)CH2SCH3, but (CO)5CrS=C(NMe2)CH3 resulting from a sulphur insertion was isolated. A single crystal structure determination of the latter complex shows a normal thione carbene complex. The reaction of methyl(methoxy)carbenepentacarbonylchromium(0) and the tungsten analogue with n-BuLi, followed by reaction with [Me2(MeS)S][BF4], afforded unexpected complexes via an unusual addition dissimilar to the above mentioned reactions of dimethylaminocarbene complexes. The formation of the products, (CO)5M=C(OMe)[CH=C(Me)NH(Me)] and (CO)4M=C(OMe)[C(SMe)=C(Me)NH(Me)] (M = Cr, W) can be ascribed to the influence of the heteroatom, oxygen, as well as the presence of acetonitrile in the sulfonium salt reagent [Me2(MeS)S][BF4]. An unusual alkylation by Me+ is also affected. The X-ray crystallographic structure determination of the complexes show hydrogen bonding between the alkoxy oxygen atoms and the protons on the nitrogen atoms. The latter four membered C,S-chelates show bonding distances and angles similar to these of the previously mentioned four membered chelates. Deprotonation of the alkynyl carbene complexes, (CO)5M=C(NMe2)C≡CH (M = Cr, W), with n-BuLi and subsequent reaction with PPh3AuX (X = Cl, NO3), initially afford the β-transmetalated products (CO)5M=C(NMe2)C≡CAuPPh3. In solution (CH2Cl2) the product isomerises through metal migration to Ph3PAuC(NMe2)=C=C=W(CO)5. The conversion was followed by means of 1H-NMR-spectroscopy and it appears that two first order reactions take place consecutively.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / The synthesis of complex architectures, namely block copolymers with tailored enduse properties, is currently an important research area in academia and industry. The challenge is finding a versatile polymerization technique capable of controlling the molecular properties of the formed copolymers, which in turn determines their macroscopic properties. Reversible addition-fragmentation chain transfer (RAFT)- mediated living polymerization is a robust technique capable of producing controlled polymer products. With the great advances in living polymerization techniques and the environmental awareness of society there is an increasing demand to produce these polymer products via the RAFT living technique in heterogeneous media. Conventional emulsion and miniemulsion polymerization present various problems when used to produce polymers mediated by the RAFT process. There is an inherent need to find cost effective and flexible operating conditions to conduct RAFT polymerization in heterogeneous media with the ability to produce well-defined block copolymers. In this study the use of three novel trithiocarbonate RAFT agents to produce welldefined AB-type, ABA-type and star block copolymers via the RAFT process was investigated. Optimal operating conditions for the production of living block copolymers in homogenous and heterogeneous media were determined. The main focus was on the development of the RAFT process in heterogeneous media to efficiently produce block copolymer latex products. The RAFT-mediated miniemulsion polymerization system stabilized with non-ionic surfactants was thoroughly investigated. The ability of the ab initio and in situ RAFT-mediated emulsion polymerization systems to produce controlled latexes was demonstrated. Controlled block copolymer products were successfully synthesized in homogenous and heterogeneous media via the RAFT process when the optimum reaction conditions were chosen.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / This study concerns the investigation of the isomerization of different metallocene catalysts in solution, and the effects thereof on the microstructure of polypropylenes prepared with these catalysts. Two C2 symmetric ansa metallocenes, ethylene-bis(indenyl) zirconium dichloride (EI) and dimethylsilyl-bis(2-methyl benzoindenyl) zirconium dichloride (MBI) were exposed, in solution, to both sunlight and UV radiation. The rac-meso isomerization of these catalysts were followed by 1H NMR spectroscopy. The reaching of a photostationary state is described, as well as the effect of isomerization of these catalysts in solution on the polymerization of propylene. Results show that metallocene structure has an effect on the isomerization rate and photostationary state. Results also show that the wavelength of light plays a role in the isomerization process. Effects on stereochemistry and molecular weight of the formed polymer as well as the catalyst activity is described and discussed. In addition the effect of activating the catalysts with MAO before exposure to light is discussed.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS) were synthesised. Three different synthetic routes, which allowed control over polymer structure, were chosen to synthesise these block copolymers. The first technique, coupling of functional prepolymers, involved using anionic polymerisation to produce PDMS and PS functional prepolymers of controlled structure. These prepolymers were functionalised with either silane or allyl functionality and then coupled using a hydrosilylation reaction with Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to the incompatibility of the disparate prepolymers. The second technique under study, sequential anionic polymerisation, gave excellent block copolymer formation with good control over the chain architecture. The final technique employed atom transfer radical polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block copolymers of controlled structure. Chromatographic systems that allowed liquid chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography (GEC) of the products were developed. GEC was used successfully in the monitoring of the presence and removal of PDMS homopolymer present in the block copolymer products. LCCC at the critical point of PS allowed successful chromatographic separation of PS homopolymer from the block material, as well as, the molecular weight distribution of the block material according to the segmental length of the PDMS component. LC-CC coupled to FT-IR using a LC-transform device allowed successful characterisation of the block copolymer chemical composition. Corona treatment was used to modify the surface structure of the block copolymer films. Optical microscopy and slow positron beam studies highlighted the formation of a thin silica like layer on the surface of the films after corona. The positron studies enabled determination of the silica like layer’s thickness. Contact angle studies provided the first evidence of hydrophobic loss and recovery for these PDMS containing hybrid polymer materials after corona treatment. A novel offline coupling technique was developed between LC-CC separation and transmission electron microscopy (TEM) analysis. This allowed easy sample preparation without the difficult bulk extraction procedures needed to remove homo-PS contaminants from the block copolymer. This technique also provided morphological information as a function of PDMS segmental length.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / This study involved (a) the development and testing of a solution turbidity fractionation analyser (TFA) and (b) the investigation of possible molecular weight effects on solution crystallisation. To investigate the latter highly isotactic polypropylene was polymerised with a C2 symmetric metallocene catalyst. Blends were made of these homopolymers. The homopolymers as well as the blends were fractionated by means of temperature rising elution fractionation (TREF). The fractionated and unfractionated homopolymers as well as the fractionated blends were characterised by 13C NMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The TFA was successfully developed and helped in explaining the shifting of solution crystallisation temperature that was seen when blending of the homopolymers occurred. This was done performing analyses on the machine of blends of the homopolymers. Fractions, of the homopolymers and blends, obtained from TREF were also done. Subsequent runs of blends made from the fractions obtained from TREF were also done. In the end it was shown that the shift of the solution crystallisation temperature is either due to the tacticity or the molecular weight depending on the sample.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Graft and block copolymers were synthesized using multifunctional and monofunctional macroinitiators to produce the copolymers. The process involved hydroboration of commercially available unsaturated rubbers and chain-end unsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). The resulting secondary alkyl 9-BBN moieties in the starting materials were subsequently exposed to oxygen in the presence of free radical polymerizable monomers to facilitate the formation of graft and block copolymers. This research was initiated by first studying the hydroboration of a model compound, 2-hexene, in order to determine the optimal conditions for the graft reactions. The model compound was subsequently used as a macroinitiator to initiate the polymerization of methylmethacrylate (MMA). The same borane chemistry was extended to the synthesis of polystyrene (PS) block copolymers. Chain-end unsaturated PS macromonomers, synthesized by anionic polymerization, were effectively hydroborated and then polymerized to produce PS-b-PMMA block copolymers. The synthesis of polyolefin graft copolymers was subsequently achieved by hydroboration. Several commercial rubbers with different levels of unsaturated segments were efficiently grafted with vinyl monomers MMA and styrene (St) following the “graft from” approach. The grafted reactions were carried out under various reaction conditions to determine the effect of the following factors: concentration of oxygen, amount of borane and monomer concentration. By controlling these factors, different graft densities were achieved with high graft efficiencies. All reactions produced mixed products including unreacted (non-functional) macroinitiator, homopolymer, graft copolymer and in case of the highly unsaturated polymer a crosslinked gel. Finally, the chemical compositions as well as the molar mass distribution of the graft copolymers were fully characterized by different chromatographic techniques. 1H-NMR and FTIR were also used to confirm the structure of these copolymers. Gradient HPLC was developed and extensively used to characterize the graft copolymers.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Synthesis of two surfmers (cationic and anionic) was carried out and the surfmers were used to stabilize particles in miniemulsion polymerization. Surfmers were used to eliminate adverse effects associated with free surfactant in the final product e.g. films and coatings. The Reversible Addition Fragmentation chain Transfer (RAFT) polymerization process was used in miniemulsion polymerization reactions to control the molecular weight distribution. RAFT offers a number of advantages that include its compatibility with a wide range of monomers and solvents. Moreover block copolymer synthesis is possible via chain extension. A comparative study between classical surfactants and surfmers was conducted in regard to reaction rates and molar mass distribution. The rates of reactions of surfmer stabilized RAFT miniemulsion polymerization of Styrene and MMA were similar (in most cases) to classical surfactant stabilized RAFT miniemulsion polymerization reactions. The final particle sizes were also similar for polystyrene latexes stabilized by surfmers and classical surfactants. However PMMA latexes stabilized by surfmers had larger particle sizes compared to latexes stabilized by classical surfactants. The surfmers were also oligomerized in homogeneous media using the RAFT process and their Mn values were estimated using UV-VIS spectroscopy. The oligosurfmers were then used as emulsifiers in RAFT miniemulsion polymerization. The rates of reaction were slower than rates obtain when the surfmers (monomer or oligosurfmers) were used directly as emulsifiers in RAFT miniemulsion polymerization of styrene and MMA. The final latex particle sizes obtained with oligosurfmers were also larger than that of latex stabilized by their parent monomers. The RAFT process was successfully applied in miniemulsion polymerization in both classical surfactant and surfmer stabilized miniemulsions. The molecular weight increased with conversion showing that the molecular weights of the polymers were controlled.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / A method for the detection of adulteration of South African Sauvignon blanc wines, by enrichment with foreign sources of 3-alkyl-2-methoxypyrazenes, is described. The levels of three 3-alkyl-2-methoxypyrazenes (3-isobutyl-, 3- isopropyl- and 3-sec-butyl-2-methoxypyrazine) in South African Sauvignon blanc wines were measured with liquid chromatography-mass spectrometry. Sample preparation involved clean-up and pre-concentration by distillation followed by solvent extraction of the distillate with dichloromethane. Extracts were acidified and concentrated by evaporation and finally reconstituted to a fixed volume to affect quantitative pre-concentration of the samples. Sample extracts were separated with reversed phase liquid chromatography utilizing a phenyl-hexyl separation column. Residues were measured with liquid chromatography-mass spectrometry utilizing a tandem quadrupole mass spectrometric detector operated in multiple reaction monitoring mode for optimal trace level quantitation. Atmospheric pressure chemical ionization was utilized as electrospray ionization was found to suffer from quenching effects attributed to the sample matrix. Qualitative information was obtained from the relevant molecular ions as well as two secondary ion transitions (and one ion ratio) in each case. Recoveries obtained by the extraction procedure were better than 90% with coefficient of variance of better than 10% at concentrations from 1 to 100 ng/L. The limit of detection of the method was 0.03 ng/L and the limit of quantification 0.10 ng/L for the three analytes measured. The described LC-MS method is more sensitive for the determination of 3-alkyl-2-methoxypyrazines in wine than GC methods reported for the same purpose. From the experimental data, a set of parameters were established to discriminate adulterated South African Sauvignon blanc wines. It was demonstrated that the 3-isobutyl-2-methoxypyrazine concentration, despite showing considerable variance, was confined to a relatively narrow range spanning approximately two orders of magnitude (0.20 to 22 ng/L). A clear indication of possible maximum values for this compound in South African Sauvignon blanc wines was obtained from the analysis of a large number of samples (577), spanning most relevant wine producing regions and representing vintages 2003 to 2006. It was also demonstrated that South African Sauvignon blanc wines contain the major 3- alkyl-2-methoxypyrazenes in reasonably distinct relative amounts and that the said ratios of abundance may be used to elucidate authenticity. The expected effect of adulteration with green pepper extracts or some synthetic preparations on the 3-isobutyl-2-methoxypyrazine concentration as well as the relative abundances were also determined by characterizing the corresponding profiles in green peppers and some synthetic flavor preparations. Two adulterated samples in the dataset were identified by both outlined criteria. A limited number of wines of other cultivars were also analyzed. The results represent the most complete and accurate data on the 3-alkyl-2-methoxypyrazine content of South African Sauvignon blanc wines to date. A publication covering the work presented in this thesis is currently in preparation.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Two series of poly(methyl methacrylate)-graft-poly(dimethylsiloxane) copolymers were synthesized via conventional free radical copolymerization of methylmethacrylate and monomethacryloxypropyl terminated PDMS macromonomers of different lengths. It is shown how these copolymers can be electrospun to produce the copolymer nanofibers. The affects of copolymer compositions, the electrospinning tip-to-collector (TCD) distance and the concentration of the polymer solution on the fiber morphology are discussed. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to establish the surface topography as well as the fiber morphology of the electrospun copolymer nanofibers. It is also shown that these nanofibers produce superhydrophobic surfaces where the preferential surface segregation of the PDMS component is combined with the roughness of the nanofiber surface. It is shown that after exposure of these nanofiber surfaces to corona discharge, the initial superhydrophobic surfaces become easily wettable. The samples show the phenomena of hydrophobicity recovery after corona exposure. The rate and extent of this recovery depends on the PDMS content of the nanofibers as well as the time of corona treatment. The hybrid copolymer nanofibers were evaluated as potential reinforcing fillers for cross linked polydimethylsiloxane compounds. The fibers show a remarkably good distribution in the PDMS matrix and show a dramatic improvement in the mechanical properties of the composites.