Synthesis of polyesters by ring opening polymerization and copolymerization using aluminium and titanium complexes

Bahili, Mohammed 2017. Synthesis of polyesters by ring opening polymerization and copolymerization using aluminium and titanium complexes. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

A series of new aluminium(III) and titanium(IV) complexes bearing a series of salen ligands have been prepared; the ligands have not been previously used to support Al or Ti. The complexes have been tested as initiators for polymerization reactions, including both ring-opening polymerization of cyclic esters, and the ring-opening copolymerization of cyclic anhydrides and epoxides. This thesis has been divided into six chapters: Chapter 1 provides an overview of the use of Al and Ti complexes in the ringopening polymerization of cyclic esters, and the use of Al complexes in the ringopening copolymerization of cyclic anhydrides and epoxides. An introduction to these catalytic reactions is discussed, along with some background relating to polymer characterization. Chapter 2 provides details of the ligand synthesis, and the preparation of the monometallic metal complexes used in the rest of the thesis. A relatively new class of salen-type ligands bearing a hemi-labile pyridyl donor have been prepared and fully characterized. The challenges that accompanied the preparation of some derivatives of the ligand have been discussed, and the identity of the ligands has been supplemented by solid state analysis. Complexes based upon Al and Ti, derived from these ligands, have been reported in this thesis. Their synthesis and characterization in both solution and solid state are reported. Three types of Al complex have been synthesized: alkyl, alkoxide/aryloxide, and chloride. These complexes have been characterized using NMR spectroscopy, which includes a discussion of the hemi-labile nature of the pyridyl; this was confirmed using variable temperature NMR spectroscopy and equilibrium analysis. The synthesis and characterization of Ti(IV) isopropoxide complexes is described. NMR spectroscopy, including two dimensional experiments such as COSY, HSQC and HMBC, were instrumental in determining the stuructures of these complexes. Chapter 3 describes how to exploit the complexes described in Chapter 2 as catalysts for the ring-opening polymerization of cyclic esters such as rac-lactide and ε-caprolactone. Both aluminium and titanium showed good to moderate activity in this type of polymerization. Various conditions were investigated in order to obtain the optimum conditions to afford polyester with acceptable molecular weights and polydispersity indices. Chapter 4 describes how to exploit the aluminium chloride complexes described in Chapter 2 in the ring-opening copolymerization of cyclic anhydrides and epoxides, thereby diversifying the range of available polymers (and associated properties) by incorporating various monomers. The copolymerization reaction was investigated under various conditions, including with and without cocatalyst, and the polymers were evaluated using 1H NMR spectroscopy and gel permeation chromatography. Chapter 5 describes the synthesis and characterization of bimetallic aluminium complexes using the Salpy ligand framework. Three bimetallic aluminium complexes were obtained and were characterized in both solution and in the solid state. The complexes were used as initiators in the ring-opening polymerization of ε-caprolactone. The polymerization performance was evaluated and the polymers characterised using gel permeation chromatography. Chapter 6 contains full experimental details and characterizing data for all ligands and complexes described within the thesis.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
Date of First Compliant Deposit:	14 December 2017
Last Modified:	18 May 2021 13:54
URI:	https://orca.cardiff.ac.uk/id/eprint/107587

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