'Green' approaches for chemical synthesis

Synthetic polymers and polymeric materials have become ubiquitous with our daily lives. However, their production often relies on non-environmentally friendly chemical processes, based upon fossil fuel derived energy and toxic organic solvents. With the growing concern for the environmental impact of polymeric material, a transition towards more sustainable and ‘green’ polymer synthesis approaches are necessary. Reversible-deactivation radical polymerisations (RDRPs) processes, particularly atom transfer radical polymerisation (ATRP), pave the way towards more sustainable and practically less demanding polymerisation methods. Atom transfer radical polymerisation (ATRP) is a ‘controlled/living’ technique which enables the synthesise of polymers with well-defined macromolecular characteristics and complex architectures. Advances in this method have enabled polymerisation to proceed with low concentrations of transition metals and often in ‘green’ aqueous conditions. One such advancement is Activators Regenerated by Electron Transfer (ARGET) ATRP. However, conventional ARGET ATRP typically requires a continuous supply of a reducing agents. This study seeks to overcome these challenges by either reducing sugars coupling electrogenic bacteria with ARGET ATRP. Such an approach enables the synthesis of biocompatible polymers in aqueous media, while also investigating correlations between the electrochemical activity of the bacteria and the resulting polymer quality. To investigate this hypothesis, ARGET ATRP was carried out with both gram-negative and gram-positive microorganisms to polymerise the hydrophilic monomer, oligo(ethylene glycol) methyl ether methacrylate (OEGMA500). The gram-negative bacteria, Shewanella loihica (S. loihica) and Pseudomonas aeruginosa (P. aeruginosa), and gram-positive bacteria L. monocytogenes demonstrated the ability to facilitate polymerisation with high monomer conversions of 100, 81, and 88% respectively. ARGET ATRP was also performed using ascorbic acid (AA) as the reducing agent to allow direct comparison with state-of-the-art systems. A substantial and sustained negative redox potential ( Eh > −400 mV for 16 h) was measured for both S. loihica and L. monocytogenes, demonstrating the promising potential of these bacteria to effectively modulate the equilibrium of the ATRP reactions for controlled polymer synthesis. In addition, the capacity of reducing sugars to drive controlled ATRP reactions was also evaluated. Reducing sugars, such as glucose, cellobiose and lactose, are often employed as carbon sources to grow electrogenic bacteria. Complete monomer conversion was observed for glucose- and cellobiose-mediated ARGET ATRP. Future work will focus on further optimising these reactions with electrogenic bacteria under aerobic conditions, and using reducing sugars from food waste as alternative/sustainable carbon sources.