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

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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.