New Initiators for the Controlled Production of Copolymers
: (Alternative Format Thesis)

  • Sarah Kirk

Student thesis: Doctoral ThesisPhD


The topic of the production and characterisation of biopolymers, with a specific focus on polylactide is introduced in Chapter 1. Previously reported initiators for the production of polylactide and other biopolymers and copolymers are discussed, with a focus on zinc, group 2, aluminium and group 4 initiators. This chapter puts into context the research carried out for this thesis.Chapter 2 investigates the effect of dinuclear vs mononuclear aluminium salen complexes featuring a naphthalene backbone. All the initiators synthesised in this chapter were found to yield atactic PLA during the ROP of rac-lactide, however the dinuclear complex was found to achieve high conversions of polylactide within 2 hours. A kinetic investigation was performed in order to understand this effect. It was found that at the same concentration of initiating metal centres, the kapp values were comparable between mononuclear and dinuclear species, thus ruling out the possibility of cooperative effects between the metal centres in the dinuclear complex accelerating the polymerisation rate. Investigation into the copolymerisation of lactide and caprolactone using these initiators found that lactide was selectively consumed in the first instance, however the final copolymer product was found to be random in nature due to transesterification reactions. This work has been published in Dalton Transactions, 2016.Chapter 3 reports the synthesis of a range of aluminium and zinc complexes using Schiff base ligands featuring an NHBoc moiety and {ONN} ligands with both an amine and imine group. For the aluminium NHBoc complexes, it was found that either 2:1 or 1:1 ligand to metal complexes would form, depending on the steric bulk of the substituent groups on the phenolate ring. These aluminium initiators were all found to produce atactic PLA. Zinc complexes were also formed using these NHBoc ligands, in 2:1 ligand to metal centre ratio. These initiators produced high molecular weight PLA in an uncontrolled manner when no coinitiator was employed. It is proposed that these zinc complexes undergo the activated monomer mechanism when benzyl alcohol is utilised as a coinitiator. For the tridentate zinc complexes Zn(10)Me and Zn(12)Me, two stereoisomers were observed in the solution-state NMR spectrum. These initiators were found to produce mildly heterotactic PLA, in high conversions after one hour at ambient temperature.Chapter 4 discusses the relationship between salen and salalen ligands featuring a phenylene backbone and their complexes with aluminium, zirconium and hafnium. It was found that the salen ligand formed dinuclear metal complexes, with the exception of zirconium tert-butoxide. The dinuclear salen complexes were found to have high activity but little selectivity, producing atactic PLA. The aluminium salalen complex was found to be slightly isoselective, and the zirconium isopropoxide salalen complex even more so. At a reduced temperature of 50 °C, the latter yielded PLA with a Pr value of 0.15. This complex was taken forward for copolymerisation studies of lactide and caprolactone, it was found to produce a copolymer that is ‘blocky’ in character. This work has been published in Organometallics, 2016.Chapter 5 details the synthetic procedures for all ligands, complexes and polymers reported in this thesis, along with details of general experimental methods and techniques utilised.
Date of Award13 Mar 2017
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorMatthew Jones (Supervisor)


  • Catalysis
  • polymerisation
  • Polylactide
  • Copolymers

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