Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.784266
Title: New initiators for the ring-opening polymerisation of lactones
Author: Myers, Dominic William
ISNI:       0000 0004 7969 8201
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Abstract:
This thesis describes the preparation of new yttrium and indium phosphasalen catalysts for the stereocontrolled ring-opening polymerisation of rac-lactide. Systematic ligand modification was performed by changing the size of the phosphine substituents, the identity of the central donor of the diimine bridge, and through increasing the steric bulk at the ortho and para phenolate positions. The coordination chemistry of the final complexes was then explored with full characterisation by multinuclear NMR spectroscopy, elemental analysis or high-resolution mass spectrometry, and in most cases, single crystal X-ray diffraction. Yttrium phosphasalen compounds were found to be active initiators for the ring-opening polymerisation of rac-lactide, affording moderately isotactic polymers. The level of stereocontrol was shown to be influenced by the nature of the phosphine substituents, the diimine bridge, and to a limited extent, the size of the ortho phenolate substituents. The stereocontrol was observed to change when the diimine bridge donor atom was changed, with an NH substituent yielding isotactic enchainment (Pi = 0.72) and an O donor yielding moderately heterotactic (Ps = 0.73) enchainment. Indium phosphasalen compounds were similarly active for ROP, affording isotactic polymers, with one exception, which afforded atactic PLA. The level of stereocontrol was found to correlate with the flexibility of the diimine bridge and largely by the size of the ortho phenolate substituents. In the best cases, highly isotactic polylactide was afforded (Pi = 0.87 at 298 K) concurrent with fast rates, showcasing one of the best performing initiators in the stereocontrolled ring-opening polymerisation of raclactide. Finally, an yttrium phosphasalen complex was applied for the ring-opening polymerisation of three large macrolactones: ω-pentadecalactone (C15), ω-nonadecalactone (C19) and ω- tricosalactone (C23). A comparison is made between yttrium phosphasalen and aluminium salen complexes as initiators for these monomers, showing that with the former, higher rates (minute vs. hour timescales) are observed. The polymerisations of macrolactones are generally more challenging as they are entropically driven, hence the thermodynamic parameters are also uncovered, showing that high conversions (near-quantitative) remain feasible, with molecular weights up to 32 kg mol-1, even using ring sizes up to C23.
Supervisor: Williams, Charlotte ; Bown, Mark Sponsor: Engineering and Physical Sciences Research Council ; Commonwealth Scientific and Industrial Research Organization (Australia)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.784266  DOI:
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