jo302830r_si_001.pdf (1.46 MB)
Trialkyl Phosphites and Diaryliodonium Salts as Co-initiators in a System for Radical-Promoted Visible-Light-Induced Cationic Polymerization
journal contribution
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. KlankowskiTrialkyl 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).