Aliphatic and Aromatic Polyesters in the Quest for Degradable Materials with Improved Physical Properties

Abstract

Chapter 1: Background information on the polymers relevant to the research described herein isprovided. The structure, properties and synthesis of polylactide (PLA), polyhydroxybutyrate(PHB), polymandelic acid (PMA) and other polyesters are discussed. Further to this, in-depthliterature reviews of the copolymerisation of lactide (LA) with β-butyrolactone (BBL) andpolyesters from the ring-opening polymerisation (ROP) of orthocarboxy anhydride monomersare provided. General literature reviews of both metal-based and organic catalysts for the ROPof cyclic esters are included.Chapter 2: This chapter documents a range of group 4 amine tris- and bis(phenolate) complexesand their utility in the ring-opening polymerisation (ROP) of the cyclic esters lactide (LA) andβ-butyrolactone (BBL). The synthesis and characterisation of a range of complexes based onnovel and previously reported amine-phenolate ligands of varying steric bulk is reported. Anumber of zirconium and hafnium complexes were found to be efficient initiators for both LAand BBL. The stereoselective ROP of both LA and BBL under similar conditions was achievedwith a limited number of these initiators. The challenging copolymerisation of LA and BBL wasalso possible, leading to block-like copolymers that were found to be amorphous based onthermal analysis.Chapter 3: The synthesis and ring-opening of mandelic acid orthocarboxy anhydride(manOCA), the activated equivalent of mandelic acid, is discussed. It was found that typicalcombinations organocatalysts and initiators such as 4-dimethylaminopyridine (DMAP) andprimary alcohols gave poorly-controlled polymerisations. Specifically, racemisation of themonomer and transesterification led to low molecular weight atactic polymer. Decreasing thebasicity of the pyridine catalyst was found to improve some aspects of the polymerisation butresults were generally unsatisfactory. It was found that the combination of pyridine and themonomer’s parent acid, mandelic acid, yielded well-controlled reactions with predictablemolecular weights and low polydispersities. Most importantly, a high degree of stereoretentionof the monomer was achieved. For the first time, high molecular weight isotactic polymandelicacid (PMA) has been prepared. The glass transition temperature of these isotactic polymers wasfound to be ~105°C, the highest reported for PMA.Chapter 4: The experimental section gives general details of materials and analytical techniquesas well as detailed preparations and characterisation data for all compounds synthesised.Procedures for the different polymerisation methods are included.

Date of Award	18 Jun 2014
Original language	English
Awarding Institution	University of Bath
Supervisor	Matthew Davidson (Supervisor)