New initiators for the ring-opening polymerisation of lactones
File(s)
Author(s)
Myers, Dominic William
Type
Thesis
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.
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.
Version
Open Access
Date Issued
2017-05
Date Awarded
2017-08
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Williams, Charlotte
Bown, Mark
Sponsor
Engineering and Physical Sciences Research Council
Commonwealth Scientific and Industrial Research Organization (Australia)
Grant Number
EP/L017393/1; EP/H046380/1
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)