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Trialkyl Phosphites and Diaryliodonium Salts as Co-initiators in a System for Radical-Promoted Visible-Light-Induced Cationic Polymerization

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posted on 2013-04-19, 00:00 authored by Thomas W. Nalli, Lee G. Stanek, Rebekka H. Molenaar, Krysia L. Weidell, Justin P. Meyer, Brandon R. Johnson, Timothy T. Steckler, Jay Wm. Wackerly, Missy Jo Studler, Kevin L. Vickerman, Stephen A. Klankowski
Trialkyl phosphites ((RO)3P) can act as co-initiators for the diaryliodonium-induced cationic polymerization of cyclohexene oxide (CHO) or THF. A radical initiation step is also required, consistent with the essential role of a radical chain reaction of the phosphite with the iodonium salt to form polymerization-starting aryltrialkoxyphosphonium salts (ArP+(OR)3). We used the visible photolysis of phenylazoisobutyronitrile (PAIBN) as the radical initiation step. The presence of multiple fluorine substituents on the phosphite, as in tris­(2,2,2-trifluoroethyl) phosphite (TFP), allows polymerization to proceed with a minimal amount of chain transfer from nucleophilic attack by the phosphite. In a typical experiment, a CHO solution of bis­(4-tert-butylphenyl)­iodonium hexafluorophosphate (0.05 M), TFP (0.1 M), and PAIBN (0.02 M) was illuminated with a 65-W compact fluorescent bulb for 1 h, resulting in a 78% conversion to poly­(cyclohexene oxide) with an average molecular weight (MW) of 25000. We also used competition experiments to determine approximate rate constants for reactions of phenyl radicals with CHO (k = 2 × 106 M–1 s–1) and with TFP (k = 2 × 108 M–1 s–1).

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    The Journal of Organic Chemistry

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