Synthesis and properties of hydrolysable polyesters catalysed by hemilabile aluminium pendant arm macrocycle complexes

Hydrolysable polyesters were synthesised via the ring-opening copolymerisation of epoxides and cyclic anhydrides, and the ring-opening polymerisation of ε-caprolactone. These reactions were catalysed by aluminium complexes bearing a phenoxy pendant arm triazacyclononane ligand. The properties of the polymers produced were investigated. Chapter 1 provides an overview into the chemistry of polymers and introduces the environmental issues caused by the use of unsustainable plastics. The ring-opening polymerisation of cyclic monomers is discussed as potential routes to hydrolysable polyesters. The chemistry of complexes based on triazacyclononane ligands is reviewed and the influence of hemilability in homogeneous catalysis is introduced. Chapter 2 provides an introduction to the ring-opening copolymerisation of epoxides and cyclic anhydrides. An aluminium chloride complex bearing a phenoxy pendant arm triazacyclononane ligand was evaluated as catalyst for this copolymerisation under various conditions. The molecular weight, dispersity and ester selectivity of the copolymers produced was measured. The mechanism for this copolymerisation, catalysed by the aluminium pendant arm macrocycle complex, was investigated using density functional calculations and influence of hemilability on the mechanism is described. Efforts to reduce the bimodality of the polymers produced are also presented. Chapter 3 investigates how the thermal and flame retardant properties of the copolymers described in Chapter 2, can be altered and tuned by varying the monomers used in the copolymerisation. The flame retardancy of the copolymers was primarily measured by pyrolysis combustion flow calorimetry. Thermal degradation was investigated by thermogravimetric analysis and glass transition temperatures were obtained by dynamic mechanical analysis. Chapter 4 evaluates the potential to undertake post-polymerisation modification on the copolymers formed from the ring-opening copolymerisation of epoxides and cyclic anhydrides. The thiol-ene click reaction between a copolymer containing pendant vinyl groups and a variety of thiols was investigated. Crosslinking of this copolymer using iii 1,6-hexanedithiol was also explored. The effect on the glass transition temperature of crosslinking or appendage of the thiols to the copolymer was measured. Chapter 5 investigates the efficacy of aluminium pendant arm macrocycle complexes as catalysts for the ring-opening polymerisation of ε-caprolactone. The molecular weight and dispersity of the polymers produced was measured. The mechanism of this polymerisation, catalysed by an aluminium pendant arm macrocycle complex, was investigated using density functional calculations and the influence of hemilabilty on the mechanism is described. Chapter 6 summarises and concludes the thesis. Chapter 7 contains full experimental details and characterising data for the catalysts and polymers described within the thesis