The catalytic chemical recycling of waste oxygenated plastics Thom McGuire, Antoine Buchard, Charlotte Williams University of Oxford, UK The chemical recycling of polymers to monomers is important to realizing a truly circular, plastic economy. 1 Oxygenated polymers derived from biomass, like poly( L -lactic acid) and CO 2 -based polycarbonates, are attracting attention in applications ranging from elastomers to toughened plastics. 2 However, investigations of their chemical recycling to monomer (CRM) are needed to develop highly efficient catalysts showing high selectivity for true monomer. Here, a range of catalysts and processes, operated in neat polymer films, are presented for the CRM of various polyesters and polycarbonates, including commercial materials. 3,4,5 These depolymerization catalysts deploy earth-abundant metals (e.g. Mg(II)) and operate at accessible reaction temperatures (100-160 °C). The depolymerizations show very high rates and excellent monomer selectivity (>99%), with catalytic activity reaching up to 26000 h -1 (5 kg polymer/ g of catalyst/h). Depolymerization kinetics are investigated suggesting that chain-end unzipping processes occur, with extrusion of monomer. The best methods to apply the chemical recycling are discussed, including with a focus on optimizing the scalability and recovery of the monomers. The depolymerization catalysts can, themselves, be reused over four cycles without any compromise in turnover number or monomer purity. This research shows that bio- and carbon dioxide-derived polyesters and polycarbonates can be fully chemically recycled to their true monomers, i.e. epoxides and carbon dioxide or lactide/lactones. The reactions are efficient, high yielding and very selective offering potential benefits for sectors such as packaging, consumer goods and the automotive industry. References 1. G. W. Coates, Y. D. Y. L. Getzler, Nat. Rev. Mat. 2020, 5, 501–516. 2. A. C. Deacy, G. Gregory, G. S. Sulley, T. T. D. Chen, C. K. Williams J. Am. Chem. Soc. 2021, 143, 27, 10021–10040. 3. F. N. Singer, A. C. Deacy, T. M. McGuire, C. K. Williams, A. Buchard, Angew. Chem. Int. Ed. 2022, 61, e202201785; 4. T. M. McGuire, A. Deacy, F. N. Singer, A. Buchard, C. K. Williams, J. Am. Chem. Soc. 2022, 144, 40, 18444–18449T. 5. M. McGuire, A. Buchard, C. K. Williams, J. Am. Chem. Soc. 2023, accepted.
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