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

塑料在我们的日常生活中随处可见。我们将它们用于食品包装、塑料袋和塑料瓶，以及床垫或房屋绝缘材料中的泡沫。塑料是由聚合物制成的，聚合物是由许多构建块（“单体”）组成的长链。为了形成聚合物，单体一个接一个地连接起来，就像一根绳子上的珠子。根据单体的特性，所得聚合物的性质以及因此塑料的性质变化很大。目前，几乎所有用于生产聚合物的单体都来源于原油。这意味着我们依赖化石燃料来制造聚合物，并且与聚合物生产相关的碳排放量相当大。为了应对气候危机，重要的是摆脱原油衍生单体。二氧化碳是一种有吸引力的单体，因为它是无毒的，可再生的，而且价格便宜，因为它在许多工业过程中是作为废物产生的。使用二氧化碳作为单体以两种方式减少聚合物的碳足迹。首先，在含二氧化碳的聚合物中，所使用的单体中只有一半来自原油。这意味着在单体生产过程中需要制造的单体更少，释放到大气中的二氧化碳也更少。第二，作为单体使用的每一个二氧化碳分子本来会排放到大气中，但是通过掺入聚合物中而“节省”了排放。然而，将二氧化碳掺入聚合物中非常困难，因为它不起反应。为了克服这一点，可以使用一种称为催化剂的化学物质。该催化剂加速了二氧化碳向聚合物中的结合反应，而不会在该过程中被耗尽。催化剂还可用于控制二氧化碳和其它单体连接的顺序。这一点很重要，因为不仅所用单体的类型，而且它们排列的顺序也将决定塑料的性能。自20世纪60年代末以来，人们已经开发出将二氧化碳引入聚合物的催化剂。迄今为止开发的催化剂要么含有有毒成分，非常难以制造，要么需要高温或非常纯的二氧化碳。最近发现了一种新型的催化剂，其含有无毒且地球上丰富的金属，如钠、钾或镁。这是使用这些类型的金属的催化剂的第一个例子。到目前为止，对这种类型的催化剂如何帮助二氧化碳掺入聚合物的理解非常有限。然而，更好的理解将使我们能够改进催化剂设计并进一步提高性能。因此，该项目将研究这些催化剂如何将二氧化碳如此好地融入聚合物，以及如何优化它们，使其在较低的二氧化碳压力和较低的温度下发挥作用，以降低其运行成本。该项目福尔斯EPSRC“制造未来”的研究主题。

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.