The development and improvement of biodegradable plastics from renewable resources is a hot topic in chemical research. One example is the ring-opening polymerisation (ROP) of the cyclic ester rac-lactide to give polylactide (PLA). Current industrial metal initiators are non-stereoselective and this thesis investigates a range of catalytic initiators for the ROP of lactide and its copolymerisation with ε-caprolactone. Chapter 1 presents an introduction to the polymerisation of lactide to yield PLA with insights into polymer tacticity and associated polymer analytical techniques. A current review of the literature, with respect to the controlled polymerisation of lactide using metal initiators, is followed by a discussion of lactide copolymerisation and a review of kinetic studies. Chapter 2 consists of a series of imine bis(phenolate) ligands, with variation in phenol substituents, that have been coordinated to aluminium (III) and titanium (IV) metal centres. For the aluminium-based initiators ligand steric bulk was found to influence the coordination motif; whilst with the larger titanium metal centre the experimental methodology was also influential. Trialling as initiators for the ROP of lactide found the initiators to be non-stereoselective but with rate constants an order of magnitude higher than similar aluminium initiators in the literature. Chapter 3 describes the development of a synthetic route to tripodal unsymmetrical amine tris(phenolate) ligands. Complexes with zirconium (IV) and hafnium (IV) were characterised and a monomer-dimer equilibrium is proposed. An in-depth study for the ROP of lactide suggested that dimer dissociation into an active species, and aggregation during propagation, is influential in determining rate and molecular weight control. The unsymmetrical nature resulted in a step-reduction in stereoselectivity providing more evidence of the enhanced chain-end control previously reported for a C3-symmetric zirconium amine tris(phenolate) initiator. Chapter 4 looks to apply the aforementioned group IV initiators in the one-pot copolymerisation of lactide and ε-caprolactone. Microstructure is analysed and quantified by different methods, with tapered block copolymers being produced similar to that previously reported for aluminium isopropoxide. Few examples of zirconium-based initiators for the copolymerisation of lactide are present in the literature. Chapter 5 compiles the procedures followed for the synthesis of ligands, complexes and polymers. Conditions for the polymerisation kinetics experiments and reactivity ratios are also provided, along with details of all analytical techniques used.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:619244 |
| Date | January 2014 |
| Creators | Forder, Thomas R. |
| Contributors | Jones, Matthew |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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