Design of initiators for the production of bio-based polymers

• Main Author: McKeown, Paul
• Other Authors: Davidson, Matthew ; Jones, Matthew
• Published: University of Bath 2017
• Subjects: 660; Sustainable Polymers
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715295

The current plastic production and use is unsustainable, relying on non-renewable sources. The pollution caused by petro-chemical based plastics is also becoming a problem due to non-biodegradation of these materials. The research into alternative bio-based plastics represents an important challenge in both academia and industry. At the forefront of such research is poly(lactic acid) (PLA), a biodegradeable polyester that also boasts biocompatibility. Chapter 1 discusses properties and synthesis routes for PLA as well initiators for the stereoselective polymerisation of rac-lactide. In Chapter 2, the synthesis of ligands based on 2-(aminomethyl)piperidine (2-AMP) is discussed. In the first instance, a study exploring the ring-chain tautomerism of 2-AMP condensation products is discussed. This is followed by the realisation of a range a ligands including monophenols, bicyclic phenols, salalen and salan structures. These ligands were fully characterised by NMR spectroscopy and mass spectrometry. In Chapter 3, the complexation of the 2-AMP based ligands is discussed. The choice of metals was dependent on the possible coordination modes of the ligand set. Mg(II) and Zn(II) complexes were realised for monophenolate based ligands, and Al(III) and group IV metals were applied to both monophenolate and bisphenolate motifs. Metal complexes were characterised in solution and in the solid-state by NMR spectroscopy and X-ray crystallography respectively. Due to the application of a racemic ligand, diastereomeric forms were commonly observed in solution for some complexes. In Chapter 4, the catalytic activity of these complexes is assessed with respect to the ring opening polymerisation (ROP) of lactide. Both the solution and solvent-free ROP were trialled. Best results were achieved with Al(III) salan complexes which demonstrated high activity under both solution and solvent-free conditions. A strong degree of isotacticity was also realised within this series of initiators.