Novel ‘Open’ heterobimetallic catalyst for carbon dioxide and epoxide copolymerisation at low CO 2 pressures Katharina Eisenhardt , Wouter Lindeboom, Francesca Fiorentini, Charlotte Williams University of Oxford, UK The ring-opening copolymerisation (ROCOP) of propylene oxide (PO) and CO 2 is an attractive strategy to valorise CO 2 waste gas and reduce carbon emissions currently associated with polymer production. 1-2 CO 2- derived polycarbonates are an important, quickly evolving class of materials. Low molecular weight polycarbonates can be used as polyols in the production of polyurethanes, thereby replacing currently used petrochemical based polyether polyols. 3 High molecular weight polycarbonates, used as mid-blocks in block co-polymers with sustainable monomers have shown outstanding thermal and mechanical properties. 4 Polycarbonates have also been demonstrated to be miscible with poly(lactic acid), leading to improved thermo-mechanical properties of the blends. 5 The wide range of properties available to CO 2 -derived polycarbonates illustrates the high potential of this class of materials and underlines the importance of polycarbonates in replacing current petrochemical based polymers. Despite the recent advances in the field, a gap in the understanding of the CO 2 polymerisation mechanism as well as a lack of highly active and selective catalysts remains. Most PO/CO 2 catalysts require high temperatures (T > 50 ℃ ) and high CO 2 pressures (P > 20 bar) to achieve good activity and selectivity. 2, 6 This poster will explore a novel Co(III)K(I) PO/CO 2 ROCOP catalyst. This catalyst is the first catalyst to be active below 5 bar CO 2 pressure in the PO/CO 2 ROCOP. It is also the most active and selective heterobimetallic catalyst at temperatures above 50 ℃ . The here reported, unprecedented combination of high activity and high selectivity at low CO 2 pressures, allowed for the in-depth study of the polymerisation mechanism at low CO 2 pressures, revealing saturation kinetics in the CO 2 -insertion step at pressures below 12 bar. For the first time ever, this enabled the determination of the concentration of the key propagating intermediate in a forward PO/CO 2 ROCOP polymerisation, as well as the determination of the equilibrium constant, describing the CO 2 insertion equilibrium. This poster will present the rate law, equilibrium kinetics and thermodynamic parameters for both the rate- and the selectivity-limiting steps in the catalytic cycle. The gained mechanistic inside is of high relevance for future catalyst design, as shifting the investigated chemical equilibrium towards the forward polymerisation is a key target when designing low pressure PO/CO 2 catalysts. This work also represents an important step towards the future, industrial production of polycarbonate and polycarbonate-containing block polymers on a large scale, as it allows polymerisation under low-pressure conditions similar to those currently used in the industry. References 1. Trott, G.; Saini, P. K.; Williams, C. K., Philos. trans., Math. phys., 2016, 374 (2061), 20150085. 2. Deacy, A. C.; Moreby, E.; Phanopoulos, A.; Williams, C. K., J. Am. Chem. Soc., 2020, 142 (45), 19150-19160. 3. Alagi, P.; Ghorpade, R.; Choi, Y. J.; Patil, U.; Kim, I.; Baik, J. H.; Hong, S. C., ACS Sustain. Chem. Eng., 2017, 5 (5), 3871- 3881. 4. Poon, K. C.; Gregory, G. L.; Sulley, G. S.; Vidal, F.; Williams, C. K., Advanced Materials, 2302825. US Pat., US20160326367A1, 2016. Bhat, G. A.; Darensbourg, D. J., Coord. Chem. Rev., 2023, 492 , 215277.
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