Investigation of amine bis(phenol) transition metal complexes to unravel the controlled ring-opening polymerisation of cyclic esters Thomas Malcomson 2 and Ruaraidh McIntosh 1 1 Heriot-Watt University, UK, 2 University of Manchester, UK Presenting an alternative pathway in the production of sustainable polyesters, ring-opening polymerisation of cyclic esters such as ε-caprolactone can produce significantly increased physical properties with respect to biodegradability. With a very low degree of biotoxicity, mechanical modifications achieved through alterations to chain length, crystallinity, and branching extend, as well as the natural occurrence of the major degradation product, 6-hydrohexanoic acid, results in poly(ε-caprolactone) presenting a promising, environmental alternative to conventional polyesters. Here we present a combined experimental and theoretical investigation into the ring- opening polymerisation of ε-caprolactone by a series of systematically modifiable amine bis(phenol) transition metal complexes. Commonly assumed to progress through a coordination-insertion mechanism in mono-metallic complexes, density functional theory is utilised to investigate the relative energetics of the mechanistic steps followed by each complex, providing insight into relative protonation and oxidation states at each stage, in addition to the role of the local solvent environment as an external initiator for the overall reaction. Experimental synthesis and characterisation of each complex was carried out, with kinetic and mechanistic findings presented here showing the comparative activity, solvent dependency, in addition to the role of both water and external initiators as the apply to both the molecular weight of polymer observed and reaction time. Overall, the stability and activity of the complexes presented here show a strong start in the construction of a series of robust polymerisation catalysts, active in a range of non-dry conditions, providig promising results with respect to potential larger scale applications in the future.
P62
© The Author(s), 2022
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