Heterobimetallic Catalysts for Carbon Dioxide and Propene Oxide Copolymerization: Exploiting and Understanding Synergy

Plastics are found everywhere in our daily lives. We use them in everything from food packaging, plastic bags, and plastic bottles to foams in mattresses or house insulation. Plastics are made of polymers, which are long chains made up of many building blocks ("monomers"). To form a polymer the monomers are linked up one after the other, like beads on a string.

Depending on the identity of the monomer, the properties of the resulting polymer, and therefore the plastic, vary drastically. Currently, nearly all of the monomers that are used in the production of polymers are derived from crude oil. This means that we are reliant on fossil fuels to make polymers and that there are considerable carbon emissions associated with polymer production. In order to address the climate crisis, it is important to move away from the crude oil derived monomers. One approach to do this is to replace half of the monomers used to form a polymer with carbon dioxide.

Carbon dioxide is an attractive monomer because it is non-toxic, renewable, and inexpensive, as it is produced as a waste product in many industrial processes. Using carbon dioxide as monomer reduces the carbon footprint of polymers in two ways. Firstly, in carbon dioxide containing polymers, only half of the monomers used are derived from crude oil. This means that less monomers need to be made and less carbon dioxide is released into the atmosphere during monomer production. Secondly, each molecule of carbon dioxide used as a monomer would otherwise be emitted into the atmosphere, but is "saved" from being emitted by incorporation into the polymer.

It is, however, very difficult to incorporate carbon dioxide into polymers, because it is unreactive. To overcome this, a chemical, known as a catalyst can be used. The catalyst speeds up the incorporation reaction of carbon dioxide into the polymer, without being used up in the process. The catalyst can also be used to control the order in which the carbon dioxide and the other monomer are linked up. This is important as not only the type of monomer used, but also the order in which they are lined up, will determine the properties of the plastic.
Catalysts for the incorporation of carbon dioxide into polymers have been developed since the late 1960s. The catalysts developed so far either contain toxic components, are very difficult to make, or need high temperatures or very pure carbon dioxide. This makes them expensive and inconvenient to use at a large industrial scale.

Recently a new type of catalyst, that contains non-toxic and earth abundant metals, such as sodium, potassium or magnesium, was discovered. This is the first example of a catalyst that uses these types of metals. So far, the understanding of how exactly this type of catalyst helps with the carbon dioxide incorporation into the polymer is very limited. However, a better understanding would allow us to improve catalyst design and enhance the performance even further. This project will therefore investigate how these catalysts incorporate carbon dioxide so well into polymers and how they can be optimized to function under lower carbon dioxide pressure and lower temperatures in order to lower their running costs.

This project falls within the EPSRC "manufacturing the future" research theme.

The primary impact of the OxICFM CDT will be the highly-trained world-class scientists that it delivers. This impact will encompass both the short term (during their doctoral studies), the medium term (subsequent employment) and ultimately the longer timescale defined by their future careers and consequent impact on science, engineering and policy in the UK.

The impact of OxICFM students during their doctoral studies will be measured by the culture change in graduate training that the Centre brings about - in working at the interface between inorganic synthesis and manufacturing, and fostering cross-sector industry/academia working practices. By embedding not only from larger companies, but also SMEs, we have developed a training regime that has broader relevance across the sector, and the potential for building bridges by fostering new collaborations spanning enormous diversity in scientific focus and scale. Moreover, at a broader level, OxICFM offers to play a unique role as a major focus (and advocate) for manufacturing engagement with academic inorganic synthetic science in the UK.

From a scientific perspective, OxICFM will be uniquely able to offer a broad training programme incorporating innovative and challenging collaborative projects spanning all aspects of fundamental and applied inorganic synthesis, both molecular and materials based (40+ faculty). These will address key challenges in areas such as energy provision/storage, catalysis, and resource provision/renewal necessary to enhance the capability and durability of UK plc in the medium term. To give some idea of perspective, the output from previous CDTs in Oxford's MPLS Division include two start-up companies and in excess of 30 patents.

It is not only in the industrial and scientific realms that students will have impact during their timeframe of their doctorate. Part of the training programme will be in public engagement: team-based challenges in resource development/training and outreach exercises/implementation will form part of the annual summer school. These in turn will constitute a key part of the impact derived from the CDT by its engagement with the public - both face-to-face and through electronic/web-based media. As the centre matures, our aspiration is that our students - from diverse backgrounds - will act as ambassadors for the programme and promote even higher levels of inclusion from all parts of society.

For our partners, and businesses both large and small in the manufacturing sector, it will be our students who are considered the ultimate output of the OxICFM CDT. Our programme has been shaped by the need of such companies (frequently expressed in preliminary discussions) to recruit doctoral graduates who can apply themselves to a broad spectrum of multi-disciplinary challenges in manufacturing-related synthesis. OxICFM's cohort-based training programme integrates significant industry-led training components and has been designed to deliver a much broader skill set than standard PhD schemes. The current lack of CDT training at the interface of inorganic chemistry and manufacturing (and the relevance of inorganic molecules/materials to numerous industrial sectors) heightens the need for - and the potential impact of - the OxICFM CDT. Our students will represent a tangible and valuable asset to meet the long-term skills demand for scientists to develop new materials and nanotechnology identified in the UK Government's 2013 Foresight report.

In the longer term, the broad and relevant training delivered by OxICFM, and the uniquely wide perspective of the manufacturing sector it will deliver, will allow our graduates to obtain (and thrive in) positions of significant responsibility in industry and in research facilities/institutes. Ultimately we believe that many will go on to be future research leaders, driving innovation and changing research culture, and thereby making a lasting contribution to the UK economy.