Polymerisation Catalysts enabling Carbon Dioxide Utilization

The project will focus on the discovery, development and characterisation of new catalysts enabling carbon dioxide copolymerisation processes, in order to reduce the reliance on fossil fuel for plastic production. It will involve close collaboration with the industry co-sponsor, Econic Technologies, managed through regular meetings and by a student secondment to the company in year 2/3 of the research. The project falls within the EPSRC Physical science research area, specifically looking at the Chemical sciences and engineering grand challenge of utilising carbon dioxide in synthesis and transforming the chemical industry.
The research focuses on the synthesis of asymmetric macrocycles which enable the preparation of heterodinuclear complexes, which have here to been only marginally explored for carbon dioxide copolymerisation. In the first stages, research will address ligand preparation, coordination chemistry and characterisation of heterodinuclear complex formation. Heterodinuclear complexes are targeted to take advantage of a mechanistic hypothesis proposed by the Williams team (chain shuttling); it relies on different roles for the two metals in the catalytic cycle. To test the hypothesis a series of complexes using a main group element from Group 1, 2 or 13 will be combined with a transition metal element selected from Cr(III), Fe(II/III), Co(II/III) Ni(II) and Zn(II). Some of the new heterodinclear complexes feature paramagnetic metal centres and thus characterization experiments will include standard spectroscopic measures as well as specialist techniques like cyclic voltammetry, SQUID, epr and XPS. The new catalysts will be tested in the alternating copolymerisation of epoxides/CO2. The measures of success include activity, selectivity and control and will be assessed using protocols and equipment developed in the Williams group. The best performing catalysts will be selected for further development and understanding, thus focusses on determining the polymerisation kinetics using in situ spectroscopies. After determination of the rate laws, the mechanistic hypothesis will be re-evaluated and fine-tuned. We will also conduct experiments to identify catalytic intermediates and off-cycle processes (side-reactions/degradation products). The testing of the catalyst will also occur at Econic Technologies, under industry relevant conditions. A period of secondment in year 2/3 will enable testing of leading complexes in reactors and, if sufficiently promising, at the customer development site. In parallel with testing the catalyst for CO2/epoxide copolymerisation, the complexes will also be tested as catalysts for switchable polymerisation processes using anhydrides and lactones. The polymerisation activity and selectivity will be evaluated using methods developed by the Williams laboratory. The goal of this work are to evaluate the catalysts for switchable processes and to compare them to current leading catalyst. Further, to develop catalysts which challenge the Al-salen complexes when using propene oxide as a monomer.