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Mesolytic Versus Homolytic Cleavage in Photochemical Nitroxide-Mediated Polymerization

Date

2020

Authors

Hill, Nicholas
Fule, Melinda
Morris, Jason
Clement, Jean-Louis
Guillaneuf, Yohann
Gigmes, Didier
Coote, Michelle

Journal Title

Journal ISSN

Volume Title

Publisher

American Chemical Society

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.

Description

Keywords

Citation

Source

Macromolecules

Type

Journal article

Book Title

Entity type

Access Statement

Open Access

License Rights

DOI

10.1021/acs.macromol.0c00134

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