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Polymers 2018, 10(6), 638; https://doi.org/10.3390/polym10060638

Ring-Expansion/Contraction Radical Crossover Reactions of Cyclic Alkoxyamines: A Mechanism for Ring Expansion-Controlled Radical Polymerization

1
Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, Jonan 4-3-16, Yonezawa 992-8510, Japan
2
Chair of Macromolecular Chemistry, Faculty of Natural Science II (Chemistry, Physics and Mathematics), Martin-Luther University Halle-Wittenberg, Von-Danckelmann-Platz 4, D-06120 Halle (Saale), Germany
3
Department of Chemistry and Chemical Engineering, Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa 992-8510, Japan
4
Department of Polymeric and Organic Materials Engineering, Faculty of Engineering, Yamagata University, Jonan 4-3-16, Yonezawa 992-8510, Japan
*
Author to whom correspondence should be addressed.
Received: 29 May 2018 / Revised: 5 June 2018 / Accepted: 7 June 2018 / Published: 8 June 2018
(This article belongs to the Special Issue Cyclic Polymers)
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Abstract

Macrocyclic polymers present an important class of macromolecules, displaying the reduced radius of gyration or impossibility to entangle. A rare approach for their synthesis is the ring expansion-controlled radical “vinyl” polymerization, starting from a cyclic alkoxyamine. We here describe ring-expansion radical crossover reactions of cyclic alkoxyamines which run in parallel to chain-propagation reactions in the polymerization system. The radical crossover reactions extensively occurred at 105–125 °C, eventually producing high molecular weight polymers with multiple inherent dynamic covalent bonds (NOC bonds). A subsequent ring-contraction radical crossover reaction and the second ring-expansion radical crossover reaction are also described. The major products for the respective three stages were shown to possess cyclic morphologies by the molecular weight profiles and the residual ratios for the NOC bonds (φ in %). In particular, the high φ values ranging from ca. 80% to 98% were achieved for this cyclic alkoxyamine system. This result verifies the high availability of this system as a tool demonstrating the ring-expansion “vinyl” polymerization that allows them to produce macrocyclic polymers via a one-step vinyl polymerization. View Full-Text
Keywords: cyclic alkoxyamine; radical crossover reaction; ring-expansion reaction; ring-contraction reaction; ring-expansion vinyl polymerization; living radical polymerization; nitroxide-mediated controlled radical polymerization (NMP); macrocyclic polymer; cyclic topology cyclic alkoxyamine; radical crossover reaction; ring-expansion reaction; ring-contraction reaction; ring-expansion vinyl polymerization; living radical polymerization; nitroxide-mediated controlled radical polymerization (NMP); macrocyclic polymer; cyclic topology
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Narumi, A.; Kobayashi, T.; Yamada, M.; Binder, W.H.; Matsuda, K.; Shaykoon, M.S.A.; Enomoto, K.; Kikuchi, M.; Kawaguchi, S. Ring-Expansion/Contraction Radical Crossover Reactions of Cyclic Alkoxyamines: A Mechanism for Ring Expansion-Controlled Radical Polymerization. Polymers 2018, 10, 638.

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