The advantageous material properties that arise from combining non-polar olefin monomers with activated vinyl monomers have led to considerable progress in the development of viable copolymerization strategies. However, unfavorable reactivity ratios during radical copolymerization of the two result in low levels of olefin incorporation, and an abundance of deleterious side reactions arise when attempting to incorporate many polar vinyl monomers via the coordination–insertion pathway typically applied to olefins. We reasoned that design of an activated monomer that is not only well-suited for radical copolymerization with polar vinyl monomers ( e.g. , acrylates) but is also capable of undergoing post-polymerization modification to unveil an olefin repeat unit would allow for the preparation of statistical olefin-acrylate copolymers. Herein, we report monomers fitting these criteria and introduce a post-polymerization modification strategy based on single-electron transfer (SET)-induced decarboxylative radical generation directly on the polymer backbone. Specifically, SET from an organic photocatalyst (eosin Y) to a polymer containing redox-active phthalimide ester units under green light leads to the generation of reactive carbon-centered radicals on the polymer backbone. We utilized this approach to generate statistical olefin-acrylate copolymers by performing the decarboxylation in the presence of a hydrogen atom donor such that the backbone radical is capped by a hydrogen atom to yield an ethylene or propylene repeat unit. This method allows for the preparation of copolymers with previously inaccessible comonomer distributions and demonstrates the promise of applying SET-based transformations to address long-standing challenges in polymer chemistry.
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Self-catalyzing photoredox polymerization for recyclable polymer catalysts
We describe a self-catalyzing photoredox polymerization system for the modular generation of macromolecular photocatalysts. Specifically, we designed a photoactive eosin Y-derived monomer that can induce photoelectron/energy transfer, while simultaneously partaking in reversible addition–fragmentation chain transfer polymerization as a monomer, affording polymer catalysts with tunable eosin Y incorporations.
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- Award ID(s):
- 1904631
- NSF-PAR ID:
- 10233893
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 12
- Issue:
- 15
- ISSN:
- 1759-9954
- Page Range / eLocation ID:
- 2205 to 2209
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X–Cu II /L). The role of PC was to trigger and drive the polymerization, while X–Cu II /L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X–Cu II /L, generating Cu I /L activator and PC˙ + . The ATRP ligand (L) used in excess then reduced the PC˙ + , closing the photocatalytic cycle. The continuous reduction of X–Cu II /L back to Cu I /L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X–Cu II /L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1py00208b
