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Title: Unsymmetrical group 4 permethylindenyl ansa-metallocenes as polymerisation catalysts
Author: Lamb, Jessica Victoria
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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The primary aims of the thesis were to: (i) discover catalyst systems that maintained high α-olefin polymerisation activities in the presence of hydrogen while producing polymers with low molecular weights (Mw <10 kg mol−1) and (ii) find new single-site initiators for the ring-opening polymerisation (ROP) of lactide monomers. The thesis begins by offering a brief introduction to α-olefin and lactide polymerisation, including discussions on known polymerisation catalysts. The synthesis and characterisation of a series of well-defined group 4 ansa-bridged permethylindenyl complexes based on the Me2SB(CpR,I*)ZrX(Y) ({(η5-C9Me6)Me2Si(η5-C5H3R)}ZrX(Y) where R = H, Me and nBu) motif is then discussed. The application of these complexes as α-olefin polymerisation catalysts, both in solution-phase and when immobilised on a range of inorganic solid supports (MAO modified silica, MAO modified layered double hydroxide and solid MAO) is then detailed. It was found that solid MAO supported catalytic systems exhibited some of the highest slurry-phase polymerisation activities reported in the literature. The systems produced HDPE with minimal branching, uniform polymer morphology and low polymer molecular weights (Mw <100 kg mol-1 at 80 °C). A variety of polymerisation conditions were studied, including the effects of temperature, scale, pressure, scavenger, catalyst loading and time. The slurry-phase ethylene/1-hexene copolymerisation ability of the catalysts is then demonstrated. The effects of hydrogen on ethylene polymerisation activity and polymer properties are also discussed. The overall effect of 1-hexene was found to depend on the identity of the catalyst and the amount of co-monomer in the system. All catalysts demonstrated remarkable stability in the presence of hydrogen, which was accompanied by a significant decrease in polymer molecular weights to produce commercially viable polyethylene waxes. Finally, four unsymmetrical permethylindenyl zirconocenes are presented as initiators for the ROP of L-, D- and rac-lactide. The kinetics of polymerisation, overall rate equations and the effects of temperature, initiator concentration, scale and co-initiator concentration are discussed. A variety of techniques were used to characterise the polymers in order to deduce tacticity, molecular weights and chain end groups.
Supervisor: O'Hare, Dermot Sponsor: SCG Chemicals Co. ; Ltd (Thailand)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry, Inorganic