Abstract/Summary

Oxidation processes have a detrimental effect on hydrocarbon based materials such as fuels, lubricants, polymers and foodstuffs. Antioxidants are known to interrupt oxidation processes by predominantly reacting with radical species. The development of such stabilisers is discussed in Chapter 1. The use of dendritic architectures in antioxidant development is a relatively 'young’ area of research. This unique class of macromolecule consists of a well-defined, branched structure which can potentially bear a high loading of antioxidant under an excellent degree of structural control. Dendritic architectures are the focus of this thesis and Chapter 2 discusses the synthesis of a series of antioxidant functionalised polyester dendrons via the growth of the AB2 monomer bis(MPA). The intention was to provide a high degree of sterically hindered phenolic end groups for enhanced oxidative stabilisation properties in addition to good solubility within a hydrocarbon matrix and good thermal stability with a resistance to volatilisation at high temperatures. It was revealed that these new branched antioxidants provided superior thermal and oxidative stability properties in comparison to the small molecule antioxidants currently used in the industry. Alternative functional core monomers were also investigated in Chapter 3. The functionalisation of glycerol and triethanolamine (TREN) with antioxidant moieties plus solubilising alkyl chains to yield a series of first generation polyester antioxidants is discussed. Once again, superior thermal and oxidative properties were revealed in comparison to the current industry antioxidants Irganox L135 and Irganox L57. The incorporation of a diphenylamine derivative into the same branching unit as the hindered phenol was investigated in Chapter 4 with the aim of targeting synergistic antioxidant properties. Excellent oxidative stabilities were observed, when compared to a 1:1 blend of Irganox L135 and Irganox L57, whereby an impressive 52% increase in oxidation induction time was observed. The enhanced stabilities were attributed to interesting structure-activity relationships from which it was concluded that the close contact of both amine and phenol functionalities was key in accessing improved antioxidant capabilities. A radical scavenging assay was investigated in Chapter 5 with the aim to understand structure-activity relationships of new sterically hindered phenolic antioxidants. It was revealed that complex mechanistic pathways, in addition to solvent effects, limited the use of this assay. Therefore, further refinement of this potentially time-saving spectroscopic assay is required in order to render it usable in fuel and lubricant development.