Recent developments in metal salen catalysts have enabled the synthesis of structurally and functionally diverse polyesters derived from the ring-opening copolymerization (ROCP) of epoxides and cyclic anhydrides. In contrast to traditional step-growth polymerization, chain-growth ROCP is a low temperature and atom economical alternative for synthesizing aliphatic and semiaromatic polyesters comprising a wide range of tunable thermomechanical properties with controlled molecular weights and low dispersities. In addition, a number of epoxides and cyclic anhydrides derived from biorenewable sources have been employed in polyester synthesis using ROCP. However, current catalyst/cocatalyst systems for ROCP typically require high catalyst loadings (one polymer chain per catalyst) and often fail to prevent deleterious side reactions such as transesterification or polymer backbone epimerization. ROCP of epoxides and cyclic anhydrides typically makes use of a binary catalyst system comprised of a Lewis acid/nucleophilic cocatalyst pair that initiates polymerization, activates epoxide towards ring-opening, and modulates the reactivity of the propagating carboxylate/alkoxide chain-ends. Similar catalyst systems whereby the Lewis acid and nucleophilic cocatalyst are covalently tethered have shown remarkably high activities for the alternating copolymerization of epoxides and CO<sub>2</sub>, whereas little is understood regarding the use of tethered catalysts for the ROCP of epoxides and cyclic anhydrides. In this work we aim to develop high activity catalysts while maintaining control over chain-end reactivity to suppress side reactions such as transesterification and epimerization. Our approach makes use of a modular catalyst synthesis, enabling selective modification of individual ligand components to independently study and optimize catalyst activity.

Design and synthesis of new catalytic systems for the alternating ring-opening copolymerization of epoxides and cyclic anhydrides

256th National Meeting (2018)

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