Selective Photoactivation: From a Single Unit Monomer Insertion Reaction to Controlled Polymer Architectures
2016
Xu, Jiangtao | Shanmugam, Sivaprakash | Fu, Changkui | Aguey-Zinsou, Kondo-Francois | Boyer, Cyrille
Here, we exploit the selectivity of photoactivation of thiocarbonylthio compounds to implement two distinct organic and polymer synthetic methodologies: (1) a single unit monomer insertion (SUMI) reaction and (2) selective, controlled radical polymerization via a visible-light-mediated photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) process. In the first method, precise single unit monomer insertion into a dithiobenzoate with a high reaction yield (>97%) is reported using an organic photoredox catalyst, pheophorbide a (PheoA), under red light irradiation (λₘₐₓ = 635 nm, 0.4 mW/cm²). The exceptional selectivity of PheoA toward dithiobenzoate was utilized in combination with another catalyst, zinc tetraphenylporphine (ZnTPP), for the preparation of a complex macromolecular architecture. PheoA was first employed to selectively activate a dithiobenzoate, 4-cyanopentanoic acid dithiobenzoate, for the polymerization of a methacrylate backbone under red light irradiation. Subsequently, metalloporphyrin ZnTPP was utilized to selectively activate pendant trithiocarbonate moieties for the polymerization of acrylates under green light (λₘₐₓ = 530 nm, 0.6 mW/cm²) to yield well-defined graft co-polymers.
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