Mesolytic Versus Homolytic Cleavage in Photochemical Nitroxide-Mediated Polymerization

Nicholas S. Hill, Melinda J. Fule, Jason Morris, Jean Louis Clément, Yohann Guillaneuf, Didier Gigmes, Michelle L. Coote

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Time-dependent density functional theory calculations have been performed to study the photocleavage reactions of chromophore-functionalized alkoxyamines in nitroxide-mediated photopolymerization. Two case studies were considered: azaphenalene derivatives and benzophenone-based alkoxyamines. For the azaphenalenes, we show that the expected homolysis pathway is actually inaccessible. Instead, these alkoxyamines exhibit low-lying nNπ∗ excited states that exhibit an electronic structure about the nitroxide moiety similar to that of the formally oxidized radical cation. As a result, the cleavage of these alkoxyamines can be described as mesolytic-like rather than homolytic. As with formally oxidized species, mesolytic cleavage can result in the production of either carbon-centered radicals or carbocations, with only the former resulting in radical polymerization. Here, the cleavage products are found to be dependent on the respective radical/cation stabilities of the monomer units of choice (styrene, ethyl propanoate, and ethyl isobutyrate). In contrast to the azaphenalenes, in the benzophenone-based alkoxyamines, conjugation between the nitroxide and chromophore moieties appears to facilitate homolysis because of the ideal alignment of singlet and triplet states of different symmetries.

Original languageEnglish
Pages (from-to)1567-1572
Number of pages6
JournalMacromolecules
Volume53
Issue number5
DOIs
Publication statusPublished - 10 Mar 2020
Externally publishedYes

Keywords

  • Mesolytic
  • Homolytic
  • Photochemical

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