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Title: Dinuclear metal catalysts for the synthesis of oxygenated polymers
Author: Saini, Prabhjot Kaur
ISNI:       0000 0004 6347 9944
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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This thesis describes the synthesis of heterodinuclear and homodinuclear catalysts and the in depth investigations carried out when using these catalysts for the ring opening copolymerisation of epoxide/CO2 or epoxide/anhydride to generate polycarbonates or polyesters, respectively. Chapter 2 reports the kinetic and mechanistic studies carried out for cyclohexene oxide/CO2 copolymerisation reactions. Several di-magnesium catalysts bearing a symmetrical N4O2 macrocyclic ligand and different co-ligands (acetate, trifluoroacetate, benzoate, aryl oxide and bromide) were explored. These investigations revealed that both metal centres of the catalyst are involved in the copolymerisation reaction and that the rate determining step is likely to be the carbonate attack on the metal bound epoxide. CO2 insertion is relatively fast. Additionally, there seems to be a co-ligand effect on the rate of copolymerisation, with an optimum activity observed with the acetate co-ligand. These findings support the hypothesis that one co-ligand remains bound to the catalyst during copolymerisation reactions. Chapter 3 describes the synthesis of a Zn-Mg heterodinuclear catalyst, albeit as a mixture with di-zinc and di-magnesium catalysts. However, this mixed catalyst system has an improved activity in cyclohexene oxide or propylene oxide/CO2 copolymerisation reactions, compared to the di-zinc and di-magnesium counterparts alone or in combination. This suggests that the heterodinuclear catalyst promotes the enhanced activity observed with the mixed catalyst system. Furthermore, this mixed catalyst system has enabled the selective formation of α,ω-di-hydroxyl end-capped polycarbonate chains, which can be used in polyurethane synthesis. Additionally, two asymmetrical di-zinc complexes and an asymmetrical Zn-Mg complex have been synthesised and fully characterised. Chapter 4 shows that the di-magnesium and di-zinc catalysts previously reported by our group, for epoxide/CO2 copolymerisations, are also active in cyclohexene oxide/phthalic anhydride copolymerisation reactions. The di-magnesium catalyst is four times faster than the di-zinc derivative. These homodinuclear catalysts were used in terpolymerisation reactions of epoxide/anhydride/CO2, to form block copoly(ester-carbonates), which have significantly higher Tg values ( > 90 °C) compared to polyester and polycarbonate chains (< 85 °C).
Supervisor: Williams, Charlotte K. Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral