A game of tug-of-war: balancing enhanced activity and control in multimetallic complexes for block copolymer synthesis Maisarah Abdul Rahman. Thomas J. Neal, Jennifer A. Garden The University of Edinburgh, School of Chemistry, UK The ring-opening polymerisation (ROP) of cyclic esters is an efficient route for producing biodegradable polyesters. Poly(ε-caprolactone) (PCL) and poly(lacticacid)(PLA) are among the most utilised aliphatic polyesters, with various commodity applications owing to their desirable properties, biocompatibility and biodegradability. Accessing a well-defined block copolymer of PCL and PLA (PCL- block -PLA) through controlled polymerisation offers tuneable polymer structures and properties, thus further broadening the range of applications available. 1 Recently, heterometallic Mg/Zn and Ca/Zn ProPhenol complexes were reported that displayed enhanced activity in the homopolymerisation of ε-caprolactone or rac‑ lactide and outperformed their homometallic analogues (Mg 2 , Ca 2 and Zn 2 ). 2,3 These activity improvements were attributed to the electronic modulation of each metal via a M‑O‑M’ framework. Monomer coordination and nucleophilic attack/insertion are both key steps in ROP; here, the Lewis acidic metals (M = Mg, Ca) can enhance monomer coordination, while simultaneously increasing the nucleophilicity of the M’-R bond (where M’ = Zn). Despite the emerging interest in cooperative heterometallic catalysts for cyclic ester ROP, the use of heterometallic catalysts to prepare PCL- block- PLA copolymers is, to the best of our knowledge, unreported. This presentation describes the first use of heterometallic catalysts for the synthesis of PCL‑ block -PLA, benchmarking the catalyst performance of Mg/Zn and Ca/Zn ProPhenol complexes against their homobimetallic analogue (Zn 2 ). Here, we demonstrate the powerful potential of heterometallic cooperativity in PCL‑ block -PLA copolymer synthesis, highlight the trade-offs that exist between activity and control, and reveal how the careful choice of a second metal is essential to generate well-defined block copolymer microstructures. References 1. I. Fortelny, A. Ujcic, L. Fambri and M. Slouf, Front. Mater. , 2019, 6 , 1-13.
2. W. Gruszka, H. Sha, A. Buchard and J. A. Garden, Catal. Sci. Technol. , 2022, 12 , 1070–1079. 3. W. Gruszka, L. C. Walker, M. P. Shaver and J. A. Garden, Macromolecules , 2020, 53 , 4294‑4302.
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