Peroxidase-catalyzed oxidative polymerization of m-substituted phenol derivatives

Peroxidase-catalyzed oxidative, polymerization of m-substituted phenols has been performed in a mixture of a water-miscible organic solvent and buffer at room temperature under air to give a new class of polyphenols. The catalysts used were horseradish and soybean peroxidases (HRP and SEP, respectively). In the polymerization of m-cresol using HRP as the catalyst, effects of an organic solvent, buffer pH, and their mixed ratio have been systematically investigated with respect to the polymer yield, solubility, and molecular weight. The HRP-catalyzed polymerization of m-cresol in an equivolume mixture of methanol and phosphate buffer (pH 7) produces the polymer in a high yield, which is readily soluble in polar solvents such as methanol, acetone, N,N-dimethylformamide, and dimethyl sulfoxide. The polymer was estimated to consist of a mixture of phenylene and oxyphenylene units from NMR and IR analyses as well as titration of the residual phenolic moiety of the polymer. The polymerization behavior of the m-substituted monomers greatly depends on the enzyme type. In using SEP as a catalyst, the polymer yield increases as a function of the bulkiness of the substituent, whereas the opposite tendency was observed in case of HRP catalysis. The relationships between the monomer substituent and the polymerization behavior are discussed in terms of the HOMO level of the monomer and the substituent volume.