Abstract
Enzymatic oxidative polymerization of phenols with peroxidases and oxidases has been studied to produce phenolic resin without using toxic formaldehyde. We studied enzymatic oxidative polymerization of various phenols by laccase from Trametes sp. Ha1 (Daiwa Kasei) and showed the effects of reaction conditions and substituent groups on phenyl group on the polymerization. The laccase polymerized phenol in McIlvaine buffer (pH 4.5) containing 10-60% acetone although it slightly oxidized phenol in the buffer without organic solvents. The formed polymer was insoluble in both methanol and N,N-dimethylformamide (DMF) and considered to be cross-linked. The polymer yield was also very low (< 10%) in the enzymatic polymerization of alkylphenols ((o-, m-, and p-) cresols, (o- and p-) ethylphenols, and p-t-pentylphenol) in McIlvaine buffer and enhanced by the addition of 20-40% acetone into the buffer. On the other hand, the laccase polymerized methoxyphenols, such as o-methoxyphenol (guaiacol), in McIlvaine buffer without organic solvents. The polymerized methoxyphenols were soluble in DMF. The weight-average molecular weight of the polymers of o-methoxyphenol was 8,000-10,000. Double substituted methoxyphenol, 2,6-dimethoxyphenol, was also polymerized by the laccase in the buffer. The molecular weight of polymerized 2,6-dimethoxyphenol was very high and 80% of the polymer was insoluble in DMF. The reaction rates correlated with the ionization potentials of the methoxyphenols. The mono- and di- methoxyphenols would be suitable for production of phenolic resins by enzymatic oxidative polymerization by laccase without formaldehyde or organic solvent.
