Synthesis of Diverse Recyclable Polyesters by Ring Opening Copolymerization using Group 4 complexes

Abstract

The ring-opening copolymerisation (ROCOP) of epoxides and anhydrides affords polyesters which may be (bio)degradable and/or compostable. In addition, some monomers are prepared from renewable resources. This thesis presents Group 4 metal complexes which have been prepared as potential initiators for anhydride/epoxide ROCOP; their catalytic performance is discussed. Chapter 1 discusses the need for such polymers in light of increasing global demand for plastics, rising crude oil prices and environmental stewardship. A brief review of the chemical literature on ROCOP with a particular focus on catalyst development and provides context for the type of the complexes used in this work. Along with some background relating to polymer characterization. Chapter 2 details the synthesis and characterisation of titanium alkoxide Salen-type complexes which contain C2 and C3 backbone (backbone between two imines) which were evaluated as catalysts for this copolymerization of epoxides and anhydrides. Salen complexes are able to perform copolymerisation with high conversions, selectivity, and moderate molecular weight. A range of monomers were employed, thereby diversifying the range of available polymers (and associated properties). The copolymerization reaction was evaluated under various conditions for example: including with and without Lewis base, different types of Lewis base, and the polymers were investigated using 1H NMR spectroscopy, MALDI-ToF-MS, IR spectroscopy, and gel permeation chromatography. Chapter 3 describes the synthesis Salpy complexes bearing pyridyl unit ligands and using them as catalysts for epoxide/anhydride copolymerisation under various conditions. This chapter probes the ring opening copolymerisation with Group 4 metals, different coligands, and phenoxide substituents. Studying the effect of the steric and electronic environment imposed by the Salpy ligand on the polymerization system. Comparisons are iv made between the data obtained for Salen complexes in terms of reactivity, substrate scope, and GPC data. Polymers were evaluated by 1H NMR spectroscopy, IR and by MALDI-ToF-MS. Chapter 4 The commercially available group 4 indenyl complexes were used as catalysts for the ROCOP of epoxides and anhydrides. These complexes have been found to produce polymers with the highest molecular weight values. Chapter 5 contains full experimental details and characterizing data for all ligands and complexes described within the thesis.