Radical-controlled oxidative polymerization of phenols. Substituent effect of phenol monomers on the reaction rate

A "radical-controlled" oxidative polymerization of phenols catalyzed by a tyrosinase model complex, (1,4,7-triisopropyl-1,4,7-triazacyclononane)cop dichloride, has been achieved. The polymerization of 4-phenoxyphenol regioselectively proceeded to give poly(1,4-phenylene oxide) showing heat-reversible crystallinity with a melting point. For this polymerization, as the steric hindrance of substituent of the catalyst ligands increased the selectivity for coupling at the p-position became higher. In this work, the substituent effect of phenol monomers on the reaction rate in the "radical-controlled" oxidative polymerization was examined. If was found that the steric factors of the phenol substituents, especially those at the o-positions, influenced the reaction rates more greatly than the electronic ones. These data strongly support the reaction mechanism of "radical-controlled" oxidative polymerization, in which the coupling of phenoxy radical species takes place from phenoxo-copper(II) complex and/or phenoxy radical-copper(I) complex. Copyright (C) 2000 John Wiley & Sons, Ltd.