Synthesis of polymeric materials derived from abundant natural feedstocks using non-toxic heavy metals

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Synthetic polymers are ubiquitous materials in the modern world. The vast majority are derived from petrochemical feedstocks and are unable to degrade in natural environments. It is estimated that by the end of 2015, 78% of all ever produced plastic waste was discarded in landfills or natural environment, whereas only 9% was recycled. The persistence of commodity polymers has resulted in severe land and marine pollution. A viable strategy to address this issue involves replacing petroleum based polymers with sustainable polymers derived from abundant natural feedstocks. Catalysis is key to enabling the transformation of natural resources into polymeric materials capable of competing with existing synthetic polymers in terms of both performance and cost. Suitable catalyst systems can improve the efficiency of synthetic processes and can tune polymer properties for target applications. This project falls within the EPSRC Manufacturing the Future theme. The project aims to develop novel catalysts featuring non toxic heavy metals (such as bismuth, indium and lanthanides) for the synthesis of sustainable polymers. The initial focus of this project is on bismuth, as one of the most environmentally-benign heavy metals. The developed systems will be tested as catalysts in a series of synthetic methods to produce sustainable polymers using natural feedstocks. One of these is the ring opening polymerisation of lactide monomers derived from starch-rich biomass. This produces poly(lactic acid), a biodegradable and biocompatible polymer that has already found applications in medicine, packaging and fibre technology. Currently, poly(lactic acid) is industrially produced in harsh conditions using a catalyst containing a toxic tin metal. The use of more environmentally benign catalyst systems is of great interest as a means of preventing toxic residues in final polymer products. Although catalysts containing heavy metals have been studied scarcely compared to lighter elements, they have shown potential for unique reaction pathways and enhanced activity. The developed catalyst systems will also be investigated for the conversion of carbon dioxide, a major environmental pollutant, into polycarbonate polymers. While a traditional synthesis of polycarbonates relies on hazardous petrochemical raw materials, carbon dioxide could be used to replace up to 50% of a polymer's mass, thereby offering an opportunity to both reduce the carbon footprint and turn an industrial waste into high value chemicals. The optimisation of new heavy metal based catalyst systems could broaden the scope of viable catalytic strategies used to produce sustainable polymers and afford new insights into rational polymerisation catalyst design.