Catalysis and Materials Chemistry
My research interests include the study of metal complexes for use as homogeneous catalysts to make polymers, fuels and materials. I am motivated to discover how to use and recycle renewable resources, such as plants or carbon dioxide, to make useful products such as polymers. In the area of inorganic chemistry, research in my group includes the preparation of new metal complexes, their use in homogeneous catalysis, uses of in situ spectroscopy for catalyst characterization and analysis of the reaction kinetics. Recently discovered catalysts include complexes of transition metals, lanthanides and main group elements. Furthermore, we have recently investigated a series of colloidal nanoparticles, comprising Cu/ZnO and other metals, as catalysts for the production of methanol and other liquid fuels. Some common themes of all catalysis research in my group are to apply earth-abundant and cost-effective metals; to develop efficient processes and to maximise selectivity and control so as to produce valuable products. Polymer chemistry research in my group involves polymer preparation, exploration of materials’ properties and assessments of future applications. We are particularly interested in new oxygenated polymers, such as polyesters/carbonates, and in developing methods to prepare, re-use and recycle polymers as products from bio-refining, industrial wastes and biomass so as to improve sustainability. In collaboration with other research groups worldwide, the new polymers have been evaluated for applications including as rigid plastics, elastomers, coatings, fibre-reinforced composites, matrices for tissue engineering, antimicrobial surfaces and as self-assembled nanostructures in controlled release.
The Williams Research Team
Our group is diverse, international and multi-disciplinary and we collaborate with other experts worldwide across a range of fields. The Williams team have expertise in areas including inorganic chemistry, organic chemistry, catalysis, polymer chemistry, materials science and chemical engineering. The team are based in new laboratories in the Department of Chemistry at University of Oxford (located in the CRL for synthesis and the ICL for catalysis/analysis). A few researchers are also co-located at Imperial College London (Dept. Chemistry). Candidates interested to apply for future positions/studentships in the Williams research team are advised to contact Charlotte (please include a CV and covering letter) and/or to apply for advertised posts.
Williams Research Group, Oxford, October 2016
Research Group Website
Catalysis to Deliver Polymers from Carbon Dioxide
My research group have discovered a series of dinuclear catalysts which show good activity, control and high selectivity in the alternating copolymerization of carbon dioxide and epoxides to produce polycarbonates. The ring opening copolymerization (ROCOP) of CO2 and epoxides provides a useful method to make aliphatic polycarbonates and allows 30-50% reduction in petrochemical raw materials by substitution with carbon dioxide. Our team synthesize dinuclear metal complexes, typically featuring Zn(II), Mg(II) and transition metals, which are highly efficient catalysts even using low pressures of carbon dioxide. The catalysts are even active at 1 bar pressure of CO2 and show a high tolerance to common contaminants, such as water. We have recently demonstrated that these catalysts can even copolymerize carbon dioxide captured from a UK power station to deliver polycarbonate polyols suitable for polyurethane production. In 2015, our group reported a heterodinuclear catalyst, featuring both Zn(II) and Mg(II) coordinated by a symmetrical macrocycle; it shows better activity than either homodinuclear analogues or combinations of them.
Switchable Catalysis Allowing Selective Polymerizations From Monomer Mixtures
Discovering how to selectively polymerize monomer mixtures to give well-controlled copolymers is still a fundamental challenge in polymer synthesis but remains important as an efficient means to deliver reproducible repeat unit sequence and tailored properties. Although such selective polymerization catalysis is still under-explored, it could have the potential to mimic Natural selectivity observed in biopolymer synthesis and to deliver more complex and sophisticated polymer structures. Our research group are investigating means to control block copolymer selectivity using monomer mixtures. Recently, we discovered how to switch single catalysts between distinct polymerization reactions – such switchable catalysis offers an attractive and rapid means to control block sequence. It enables a single catalyst to be used together with mixtures of monomers to deliver specific block copolymer sequences and patterns. The selectivity is controlled by the nature of the chemical bond between the growing polymer chain and the metallic active site. By controlling and switching the type of metal chain end group chemistry it is possible to direct the enchainment of particular monomers even from mixtures.
Lactone Ring-Opening Polymerization Catalysts
The ring-opening polymerization of lactones allows the controlled production of aliphatic polyesters, such as polylactide (PLA) or polycaprolactone (PCL), which are applied as commodity plastics or in medicine. An on-going research interest for our team is to discover high activity and selectivity ring-opening polymerization catalysts, particularly focussing on the production of polylactide. PLA is a bio-renewable polymer; the monomer lactide is harvested from high starch content biomass and PLA is degradable or recyclable after use. Our research into catalyst development focusses on improving activity and control of stereochemistry so as to modulate the thermal-mechanical performance of PLA. Recent research has focussed on phosphasalen ligands and lanthanide complexes, which can be targeted to deliver both high isoselectivity and activity and forming stereoblock PLA.
Bio-renewable Monomers and Polymers
Making monomers from waste renewable resources, such as plants or carbon dioxide, may enable the replacement of petrochemical feedstocks in the production of new materials. Our research interests in this area include the recycling of waste CO2emissions into useful polymers and the preparation of monomers, such as epoxides or lactones, from waste biomass. We have developed an efficient and scalable synthesis of carbohydrate lactones, starting from abundant D-glucose, which are (co)polymerized to deliver hydrophilic and degradable polyesters. In collaboration with Molly Stevens (Imperial College London), the carbohydrate copolyesters are applied as matrices in tissue regeneration. In collaboration with Alexander Bismarck (Vienna), we have developed fully renewable composites comprising cellulose fibres and bio-renewable polymer matrices.
Exploiting Organometallic Chemistry to Make Colloidal Metal and Metal Oxide Nanoparticles
In collaboration with Milo Shaffer (Materials, Imperial College London), we investigate the preparation and uses of metal (Cu) and metal oxide (ZnO) nanoparticles. The nanoparticles are prepared from well-defined organometallic reagents, using low-temperature conditions and are produced as colloidal solutions/inks, in common organic solvents. By controlling the hydrolysis of organo-zinc reagents, a useful method to prepare small (3-4 nm), highly crystalline ZnO nanoparticles was developed. Well-dispersed nanoparticles as colloids are produced by carrying out the hydrolysis in the presence of sub-stoichiometric quantities of zinc carboxylate or phosphinate complexes. As part of an on-going investigation into how molecular compounds are transformed into metal oxide nanoparticles, we have recently discovered the structures of a series of zinc cluster complexes relevant to formation of zinc oxide. In particular, by using phosphinate ligands it has been possible to use 31P NMR spectroscopy, in combination with single crystal X-ray diffraction experiments, to identify clusters comprising 4, 6, 9, 11 zinc centres. The low-pressure hydrogenation/oxidation of organo-copper reagents allows the preparation of narrow dispersity, small Cu or Cu2O colloidal nanoparticles which are well-dispersed in common organic solvents
Catalysts Allowing Liquid Fuel Production
New catalysts, including Cu/ZnO colloidal nanoparticles, have been developed to show high activities and selectivity in the transformation of carbon dioxide to methanol. The use of CO2/H2 or syn-gas to make methanol, and other liquid transport fuels, is attracting attention as a means to deliver more sustainable liquid transport fuels and for efficient chemical energy storage. In collaboration with teams in engineering, we continue to discover new catalysts, investigate the optimum processes for fuel production and to characterize, under operando conditions, the structures present during catalysis.
Organometallic Light Emitting Complexes for Electronics Applications
In collaboration with teams in Physics, we have developed organometallic complexes for applications as emitters in light emitting devices. These include phosphorescent Ir(III) complexes and first-row transition metal complexes as fluorescent emitters.
Milo Shaffer (Imperial College London), Nick Long (Imperial College London), Henry Rzepa (Imperial College London), Molly Stevens (Materials, Imperial College London), Geoff Kelsall (Chemical Engineering, Imperial College London), Klaus Hellgardt (Imperial College London), Nilay Shah (Chemical Engineering, Imperial College London), Donal Bradley (Physics, Oxford), Ji Seoun Kim (Physics, Imperial College London), Mark Bown (CSIRO), Andrew Holmes (CSIRO), Marc Hillmyer (University of Minnesota), Beppe Battaglia (UCL), James Clarke (York), Mike North (York), Adam Harvey (Newcastle), Robert Mathers (Penn State, USA), Michael Meier (KIT), Stefan Mecking (Konstanz), Alexander Bismarck (Vienna), Robert Raja (Southhampton), Cor Koning (Eindhoven), Sally Brooker (Otago).