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Linear poly(α‐hydroxy acids) are important degradable polymers, and they can be efficiently prepared by ring‐opening polymerization of O‐carboxyanhydrides with pendant functional groups. However, attempts to prepare cyclic poly(α‐hydroxy acids) have been plagued by side reactions, including epimerization and uncontrolled intramolecular chain transfers or termination, that prevent the synthesis of high‐molecular‐weight stereoregular cyclic polyesters. Herein, we report a scalable method for the synthesis of high‐molecular‐weight (>100 kDa) stereoregular functionalized cyclic poly(α‐hydroxy acids) by means of controlled polymerization of O‐carboxyanhydrides using a catalytic system consisting of a lanthanum complex with a sterically bulky ligand and a manganese silylamide. Additionally, using this system, we could readily prepare cyclic block poly(α‐hydroxy acids) by means of sequential addition of O‐carboxyanhydrides. The obtained cyclic polyesters and their cyclic block copolyesters exhibit distinctive physicochemical properties—including elevated phase transition temperature, improved toughness, and reduced viscosity—compared to their linear counterparts.
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Resilient Poly(α-hydroxy acids) with Improved Strength and Ductility via Scalable Stereosequence-Controlled Polymerization
Despite the degradability and biocompatibility of poly(α-hydroxy acids), their utility remains limited because their thermal and mechanical properties are inferior to those of commodity polyolefins, which can be attributed to the lack of side-chain functionality on the polyester backbone. Attempts to synthesize high-molecular-weight functionalized poly(α-hydroxy acids) from O-carboxyanhydrides have been hampered by scalability problems arising from the need for an external energy source such as light or electricity. Herein, we report an operationally simple, scalable method for the synthesis of stereoregular, high-molecular-weight (>200 kDa) functionalized poly(α-hydroxy acids) by means of controlled ring-opening polymerization of O-carboxyanhydrides mediated by a highly redox reactive manganese complex and a zinc-alkoxide. Mechanistic studies indicated that the ring-opening process likely proceeded via the Mn-mediated decarboxylation with alkoxy radical formation. Gradient copolymers produced directly by this method from mixtures of two O-carboxyanhydrides exhibited better ductility and toughness than their corresponding homopolymers and block copolymers, therefore highlighting the potential feasibility of functionalized poly(α-hydroxy acids) as ductile and resilient polymeric materials.
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- Award ID(s):
- 1807911
- PAR ID:
- 10296630
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- ISSN:
- 0002-7863
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/jacs.1c08802
