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Bio-derived polymers offer a sustainable alternative to petroleum-derived polymers. One such polymer, polylactide (PLA) is synthesised from the ring-opening polymerisation (ROP) of rac-lactide (rac-LA). The monomer contains two stereocentres which gives a range of tacticities. The isotactic ROP of rac-LA yields the most desirable polymer properties (physical and mechanical properties) and is quantified using a P_i (probability of isotactic enchainment) value. This thesis investigates tri- and tetradentate ligands coordinated to zinc(II), aluminium(III) and indium(III) to understand the ligand effects on both rate and isoselectivity. The first results chapter, Chapter 3, outlines the synthesis of a tetradentate salen ligand, its analogous phosphasalen ligand, where the imine bonds are replaced with iminophosphorane bonds and a hybrid ligand containing a mixture of both imine and iminophosphorane bonds. The salen, phosphasalen and hybrid ligands are coordinated to both aluminium and indium and used as initiators for the ROP. The indium hybrid initiator yields the highest isoselectivity (P_i = 0.71) which is significantly higher than its salen and phosphasalen analogues (P_i = 0.51 - 0.52) Chapter 4 investigates structure-activity relationships of the indium hybrid initiator, by modification of the ligand scaffold. Bulkier ortho-phenolate substituents do not affect rate or isoselectivity. Electron-withdrawing chloride substituents increase rate but decrease isoselectivity (P_i = 0.61). Modification of the phosphorus substituents yields the highest isoselectivity value (P_i = 0.75). It may be hypothesised that isoselectivity depends upon steric hindrance at both ortho-substituents and at phosphorus. Furthermore, the synthesis of a ferrocene containing indium hybrid complex is developed for future use in redox-switch catalysis. Chapter 5 describes the synthesis of two tridentate half-phosphasalen ligands and their coordination chemistry with zinc(II) and indium(III). Zinc initiators are active but display poor polymerisation control and low isoselectivity values (P_i = 0.67). Zinc complexes, with a less sterically encumbered ligand, preferentially form a homoleptic complex, which cannot be used in ROP. Indium initiators are slower than analogous half Schiff base initiators reported in the literature but show an improved isoselectivity value (P_i = 0.72).

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Magister Scientiae - MSc / The objectives of this project was to ameroliate two waste materials, namely Acid Mine Drainage and Fly Ash and recover the solid residues for conversion into an adsorbent to treat brine. The solid residues were then converted into zeolite P through low temperature hydrothermal treatment. The adsorption capacity of the solid residues, zeolite P derived from the solid residues was compared to the commercial zeolite Y and fresh Arnot fly ash. The quality of the resulting water was assessed using different analytical methods before the reaction with adsorbents and after the reaction and a comparison was done based on the removal efficiency of elements Zeolite P from solid residues was successfully synthesized as confirmed by XRD, BET and FTIR. Brine treatment with fly ash, solid residues, zeolite P and commercial zeolite Y adsorbents was done concentration on the following major elements Na, K, Mg, Ca and Si. Zeolite P had higher or similar removal efficiency that the commercial zeolite Y for the following elements K, Ca and Mg. Fly ash is the only adsorbent that managed to reduce the concentration of Na in brine and also had a good removal efficiency of Mg. Si leached out of all the adsorbents which could be ascribed to Si being the major component of these adsorbents which could indicate some dissolution of these adsorbents under the conditions tested. Overall, zeolite P did not completely remove the major elements, especially for Na, but did result in a cleaner waste stream which would improve brine processing. / South Africa

The existence of numerous phosphorus containing functional groups gives phosphorus chemistry its enormous breadth. The range of functional groups stems from phosphorus’ ability to vary its coordination and valance. Phosphorus containing compounds have shown applications in agriculture, biological systems and chemical warfare. High refractive index polymers are used in lenses, fingerprint recognition and optical coatings. However, often these devices rely on to the materials available. Phosphorus rich polymers have shown promise due to the high level of polarisability. A range of poly(phosphate ester)s and polyphosphonates have been synthesised and their thermal and optical properties tested. Some of the samples prepared boast the highest refractive indices for these types of compounds. Polymers synthesised via a polycondensation mechanism usually possess a high dispersity, one way to introduce control is via a ring opening polymerisation (ROP). Novel aromatic phosphonate monomers have been prepared and attempted to polymerise. Monomer, catalyst and copolymerisation scope for aliphatic phosphonate ROP has also been explored. Organocatalysts are becoming increasingly popular in ring opening polymerisation literature, one of the most popular organocatalysts is triazabicyclodecene (TBD). TBD is a dual activating catalyst as it activates both the initiator and monomer via a basic and acidic moiety respectively. Phosphates also have dual activating substituents. A range of aromatic phosphates have been successfully synthesised with varying electron withdrawing/ donating groups. These catalysts were then screened against the polymerisation of β-butyrolactone and their catalytic activity investigated.

The work presented in this thesis falls into four parts. In Chapter 1 results are presented for the detritiation of a number of substituted 2-([3H]-acetyl) thiophenes. These show that when a carboxyl group is present adjacent to the ionising acetyl group intramolecular catalysis makes an important contribution to the overall rate although the effective molarity is no higher than the other base catalysed proton transfers previously reported in the literature. Proton transfer reactions involving the ionisation of carbon acids have usually been studied in aqueous conditions. In Chapter 2 the development of a detritiation procedure for non-aqueous conditions is reported and the method used to establish an order of basicity for a large number of amines in dimethyl sulphoxide. The following chapter extends the investigation carried out in Chapter 2 to a range of other solvents. The results show a marked similarity in relative rates for detritiation of acetophenone as catalysed by a number of amines in these solvents. The ability of enzymes to catalyse many reactions under very mild conditions has prompted chemists to investigate whether they can design molecules that are just as effective. In the last chapter a preliminary investigation has been made to see how amines, when they are part of a macromolecular framework, perform as catalysts.

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