University of Oxford / Chemistry

Modern life relies on polymers, from the materials that are used to make clothing, houses, cars to those with specialist applications in medicine and electronics.

Currently, polymers are overwhelmingly derived from petrochemicals. Since natural resources such as oil are finite, modern society requires a timely sustainable solution. One concept which has drawn a lot of attention is to replace fossil-fuel based starting materials with renewable options to develop biodegradable and recyclable polymers. In light of this idea, polycarbonates synthesized by copolymerisation of CO₂ and epoxides have emerged as promising class of more sustainable polymers. These have been especially attractive as their synthesis consumes the greenhouse gas CO₂ and therefore actively reduces environmental pollution, a complementary strategy to address climate change. Additionally, there is economic benefit in using CO₂ as it is a cheap feedstock that is released as a waste product in industrial synthesis.

Although the field of CO₂ copolymers has great potential, it is immature compared to traditional commodity polymers. Few distinct methodologies are known to catalyse this process. These known systems suffer from distinct challenges which need to be overcome to make commercialisation feasible. Compared to e.g. traditional alkene polymerisation catalysts, current benchmark CO₂/epoxide catalysts suffer from limited monomer scope, low activity and selectivity as well as problematic operating conditions. The latter include the need for a second co-catalytic species which are expensive, toxic, corrosive and require high CO₂ pressures which make them incompatible with current industrial setups. The research proposed herein seeks to solve these problems via catalyst design inspired by recent mechanistic insights into the copolymerisation process to not only obviate the need of co-catalyst but also expand the monomer scope to bio-based epoxides as well as thiiranes, aziridines and other heterocumulenes.