Enzymatic oxidative polymerization of 4-hydroxybenzoic acid derivatives using oxidoreductases has been carried out in an aqueous organic solvent at room temperature under air. The monomers used in this study were 4-hydroxybenzoic acid, 3,5-dimethoxy-4-hydroxybenzoic acid (syringic acid) and 3,5-dimethyl-4-hydroxybenzoic acid. The latter two monomers were subjected to oxidative polymerization using horseradish peroxidase (HRP), which involved elimination of carbon dioxide and hydrogen from the monomer to produce poly(1,4-oxyphenylene). Oxidoreductases, soybean and Coprinus cinerius peroxidases, Pycnoporus coccineus and Myceliophthore laccases, were active for the polymerization and the enzyme type and its origin greatly affected the polymerization behaviour. The effects of solvent composition have been systematically investigated with respect to polymer yield and molecular weight. In the case of HRP-catalysed polymerization of syringic acid, the highest molecular weight (1·5×104) was achieved in acetone/phosphate buffer (pH 7) (40: 60vol%). NMR, IR and matrix-assisted laser desorption/ionization–time of flight mass spectroscopic analyses of the polymer showed that the present polymer consisted made exclusively of 1,4-oxyphenylene unit and that the terminal structure was a carboxylic acid group at one end and a phenolic hydroxyl group at the other.
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Ikeda et al. (1998) studied this question.