Catalyst development for the ring-opening copolymerisation of epoxides and anhydrides

This thesis describes the development of a range of catalysts for polyester synthesis via the ring-opening copolymerisation (ROCOP) of epoxides and anhydrides. Chapter 1 provides an introduction to the ROCOP of epoxides and anhydrides, with a particular focus on catalyst development and mechanism. It also introduces the concept of switchable catalysis and describes its application to the synthesis of block polyesters. Chapter 2 details the synthesis and characterisation of a series of monometallic M(III) complexes (M = Al, Cr, Mn, Fe, Co). Their application as catalysts for the ROCOP of cyclohexene oxide (CHO) and phthalic anhydride (PA), and the ROP of decalactone (DL), is explored. The complexes featuring Al(III) and Co(III) are found to be the most active catalysts for these polymerisations. Chapter 3 details the application of the Al(III) and Co(III) complexes synthesised in Chapter 2 to the one-pot switchable catalysis reaction of CHO, PA and DL. Triblock copolymers with molar masses up to 57 kg mol-1 are synthesised. The catalytic activity of these complexes is shown to be significantly higher than previously used commercial salen catalyst systems. Chapter 4 details the synthesis and characterisation of a series of heterodinuclear Al(III)/M(I) (M(I) = Group 1 metal) complexes. All are shown to be excellent catalysts for the ROCOP of CHO and PA, with the Al(III)/K(I) and Al(III)/Rb(I) congeners being the most active. Subsequent kinetic investigations, combined with DFT calculations, result in the proposal of a mechanism where the epoxide is bound and activated by the Al(III) centre and the M(I) ion binds the carboxylate chain end. The scope of the catalysis is established for a wide range of epoxides with anhydrides and CO2. Chapter 5 details the development of an Al(III)/K(I) complex bearing organometallic coligands. It is demonstrated that use of this complex, in conjunction with bifunctional protic chain transfer agents, can yield monodisperse high molar mass polyesters via the ROCOP of vinyl-cyclohexene oxide (vCHO) and PA. The mechanical and thermal properties of the polyesters are investigated to establish the impact of increasing polymer molar mass. Chapter 6 outlines the key developments of this thesis and suggests future avenues for research that build on the work described. Chapter 7 provides experimental details for Chapters 2 – 5. An Appendix is provided that contains supplementary figures and data that support the discussion throughout Chapter 2 – 5.