Ring-expansion/contraction radical crossover reactions of cyclic alkoxyamines: A mechanism for ring expansion-controlled radical polymerization

Atsushi Narumi*, Tetsuya Kobayashi, Masatsugu Yamada, Wolfgang H. Binder, Keigo Matsuda, Montaser Shaykoon Ahmed Shaykoon, Kazushi Enomoto, Moriya Kikuchi, Seigou Kawaguchi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


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.

Original languageEnglish
Article number638
Issue number6
Publication statusPublished - 2018 Jun 8
Externally publishedYes


  • Cyclic alkoxyamine
  • Cyclic topology
  • Living radical polymerization
  • Macrocyclic polymer
  • Nitroxide-mediated controlled radical polymerization (NMP)
  • Radical crossover reaction
  • Ring-contraction reaction
  • Ring-expansion reaction
  • Ring-expansion vinyl polymerization

ASJC Scopus subject areas

  • Chemistry(all)
  • Polymers and Plastics


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