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Photocatalyst-Independent Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides: Stereocontrol and Mechanism

preprint
submitted on 06.10.2020 and posted on 06.10.2020 by Yongliang Zhong, quanyou feng, xiaoqian wang, Lei Yang, Rong Tong
Photoredox ring-opening polymerization of O-carboxyanhydrides allows for the synthesis of polyesters with precisely controlled molecular weights, molecular weight distributions, and tacticities. While powerful, obviating the use of precious metal-based photocatalysts would be attractive from the perspective of simplifying the protocol and enabling unexpected reactivity. Herein, we report the Co and Zn catalysts that are activated by external light to mediate efficient ring-opening polymerization of O-carboxyanhydrides, without the use of exogenous precious metal-based photocatalysts. Our methods allow for the synthesis of isotactic polyesters with high molecular weights (>200 kDa) and narrow molecular weight distributions (Mw/Mn < 1.1). Mechanistic studies indicate that light activates the oxidative status of CoIII intermediate that is generated from the regioselective ring-opening of the O-carboxyanhydride. We also demonstrate that the use of Zn or Hf complexes together with Co can allow for stereoselective photoredox ring-opening polymerizations of multiple racemic O-carboxyanhydrides to synthesize syndiotactic and stereoblock copolymers, which vary widely in their glass transition temperatures.

Funding

National Science Foundation CHE-1807911

ACS-Petroleum Research Foundation 57926-DNI-7

History

Email Address of Submitting Author

rtong@vt.edu

Institution

Virginia Tech

Country

United States

ORCID For Submitting Author

0000-0002-2034-9272

Declaration of Conflict of Interest

Provisional patents (U.S. Patent Application No: 62/414,016 and VTIP No. 19-112) have been filed pertaining to the results presented in this paper.

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