Water is an environmentally friendly medium for conducting reversible deactivation radical polymerizations. In this paper, we report the investigation of iodine-mediated photocontrolled atom transfer radical polymerization (photoATRP) in aqueous media. The iodine-based initiator was generated by an in situ halogen exchange from a commercially available bromine-based initiator, ethyl α-bromophenylacetate, using different iodide salts. Fast and well-controlled polymerization of a water-soluble methacrylate monomer was achieved in water under visible light irradiation, including blue, green and yellow lights. The nature of the reaction medium greatly affected the kinetics and control over the growth of polymers. Polymerizations in water resulted in a well-controlled reaction that provided high monomer conversion and polymers with low dispersities, whereas control over the polymerization was poor in bulk or in an organic solvent, N , N -dimethylformamide. Polymerizations were performed over a wide range of visible light in the absence of any photocatalyst. The selection of water as a reaction medium enabled use of iodide salts without the need for solubilizing agents. Moreover, iodine-mediated photoATRP was successfully performed in the presence of residual oxygen, signifying the potential of this polymerization system to tolerate oxygen without performing deoxygenation processes.
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Photocontrolled cationic degenerate chain transfer polymerizations via thioacetal initiators
Recent developments in photocontrolled polymerizations have facilitated the development of previously inaccessible materials. While photocontrolled radical polymerizations have been extensively studied, related processes involving cationic polymerizations are underexplored and limited to RAFT processes. In this study, we disclose a visible light, temporally controlled cationic polymerization of vinyl ethers utilizing thioacetals and a photoredox catalyst. We demonstrate a broad scope of thioacetal initiators that achieve a well-controlled polymerization by recapping propagating chains via photocatalyst turnover in combination with a degenerate chain transfer process through sulfonium intermediates. Furthermore, we show that a photocatalyst with a more reducing ground state reduction potential allows for enhanced control and excellent temporal regulation of polymerization.
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- Award ID(s):
- 1752140
- NSF-PAR ID:
- 10286941
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 11
- Issue:
- 40
- ISSN:
- 1759-9954
- Page Range / eLocation ID:
- 6499 to 6504
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Gaining temporal control over chain growth is a key challenge in the enhancement of controlled living polymerizations. Though research on photocontrolled polymerizations is still in its infancy, it has already proven useful in the development of previously inaccessible materials. Photocontrol has now been extended to cationic polymerizations using 2,4,6‐triarylpyrylium salts as photocatalysts. Despite the ability to stop polymerization for a short time, monomer conversion was observed over long dark periods. Improved catalyst systems based on Ir complexes give optimal temporal control over chain growth. The excellent stability of these complexes and the ability to tune the excited and ground state redox potentials to regulate the number of monomer additions per cation formed allows polymerization to be halted for more than 20 hours. The excellent stability of these iridium catalysts in the presence of more nucleophilic species enables chain‐end functionalization of these polymers.
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Abstract Gaining temporal control over chain growth is a key challenge in the enhancement of controlled living polymerizations. Though research on photocontrolled polymerizations is still in its infancy, it has already proven useful in the development of previously inaccessible materials. Photocontrol has now been extended to cationic polymerizations using 2,4,6‐triarylpyrylium salts as photocatalysts. Despite the ability to stop polymerization for a short time, monomer conversion was observed over long dark periods. Improved catalyst systems based on Ir complexes give optimal temporal control over chain growth. The excellent stability of these complexes and the ability to tune the excited and ground state redox potentials to regulate the number of monomer additions per cation formed allows polymerization to be halted for more than 20 hours. The excellent stability of these iridium catalysts in the presence of more nucleophilic species enables chain‐end functionalization of these polymers.
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Cationic reversible addition–fragmentation chain transfer (RAFT) polymerizations have permitted the controlled polymerization of vinyl ethers and select styrenics with predictable molar masses and easily modified thiocarbonylthio chain ends. However, most cationic RAFT systems require inert reaction conditions with highly purified reagents and low temperatures. Our groups recently developed a living cationic polymerization that does not require these rigorous conditions by utilizing a strong organic acid (pentacarbomethoxycyclopentadiene (PCCP)) and a hydrogen bond donor. By combining our PCCP acid promoted polymerization with a chain transfer agent, we have designed a tolerant cationic RAFT system that can be performed neat, open to the air, and at room temperature. Additionally, this system allows us to utilize catalytic amounts of the PCCP acid to furnish polymers with chain end functionality that can be easily isolated and further manipulated to make functional materials.more » « less
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Cationic polymerization is a powerful strategy for the production of well-defined polymers and advanced materials. In particular, the emergence of living cationic polymerization has enabled pathways to complex polymer architectures inaccessible before. The use of light and electricity as external stimuli to regulate cationic polymerization represents another advance with increasing applications in surface fabrication and patterning, additive manufacturing, and other advanced material engineering. The past decade also witnessed vigorous progress in stereoselective cationic polymerizations, allowing for the dual control of both the tacticity and the molecular weight of vinyl polymers towards precision polymers. In addition, in addressing the plastics pollution crisis and achieving a circular materials economy, cationic polymerization offers unique advantages for generating chemically recyclable polymers, such as polyacetals, polysaccharides, polyvinyl ethers, and polyethers. In this review, we provide an overview of recent developments in regulating cationic polymerization, including emerging control systems, spatiotemporally controlled polymerization (light and electricity), stereoselective polymerization, and chemically recyclable/degradable polymers. Hopefully, these discussions will help to stimulate new ideas for the further development of cationic polymerization for researchers in the field of polymer science and beyond.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0PY01100B
