Poly(α-hydroxy acids) (PAHAs), including polylactide, are widely used in everyday applications ranging from clothing and packaging to agriculture and biomedicine. However, their utility for applications is greatly limited by the lack of side-chain functionality in PAHAs and in their monomers (lactones), which are usually synthesized by multistep methods that are difficult to scale up. Since 2006, O-carboxyanhydrides (OCAs), which can be prepared with a rich variety of side-chain functionalities, have emerged as an alternative class of highly active monomers for polyester polymerization. Unfortunately, current synthetic methods, especially those involving organocatalysts, result in uncontrolled polymerization i. The use of Zn-alkoxide catalyst cannot efficiently produce polymers with a high degree of polymerization. Because of the above-described limitations, the development of a viable catalyst that can mediate controlled polymerization to prepare stereoregular, high-MW PAHAs is crucial. Visible-light photoredox catalysis has recently emerged as a powerful technique for radical polymerization and organic synthesis. Photoredox catalysts and nickel catalysts reportedly can be successfully combined for the decarboxylation of carboxylic acids and anhydrides via a catalytic cycle involving single-electron transfer. Nickel catalysts also mediate the ROP of N-carboxyanhydrides, structural analogues of OCAs. Here we report that a new Ni/photoredox catalyst system—to accomplish OCA decarboxylation—could be merged with a Zn catalyst to mediate ring opening of OCAs in a manner similar to that observed for anhydrides, generating an active Zn-alkoxide chain end for chain propagation, thus enabling controlled synthesis of high-MW polymers (Figure 1).

Photoredox ring-opening polymerization of O-carboxyanhydride

254th National Meeting (2017)

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