Lewis Pair Radical Polymerization “On-Water”
Kazumasa Mori, Atsushi Shimizu, Mayo Horibe, Momoko Takei, Naoki Awano, Shin‐ichi Matsuoka, Masato Suzuki
Abstract
An unprecedented radical polymerization of various (meth)acrylates, diethyl acrylamide, and 4-vinylpyridine initiated by Lewis pair (LP) catalysts, specifically PPh3/Cu(OTf)2 or PPh3/Sn(OTf)2, is reported herein. The reaction occurred at the interface between monomer and water phases, namely, “on-water”, at room temperature. The polymerization of (meth)acrylates “on-water” was significantly more efficient than the reaction in organic solvents or in bulk. It was determined that the propagation occurs via a single electron transfer, which was evidenced by the inhibition of the reaction by the addition of trace amounts of phenols or phenothiazine. Additionally, MALDI-TOF-MS analysis revealed the occurrence of disproportionation termination. Initiation at the interface was supported by various polymerization studies. Specifically, a higher rate of polymerization of methacrylates was observed for hydrophilic monomers. Moreover, the polymerizations in a mixed solvent of water and MeOH indicated that the heterogeneous system is critical. The generation of a PPh3 radical cation following a single electron transfer from LP was not plausible. Instead, we propose a mechanism involving a Michael addition of PPh3 to monomers activated by Lewis acids “on-water” to generate Cu(II) or Sn(II) enolates and/or free radical as propagating species.