Ryohei Ikeda

A new crosslinkable polyphenol from a renewable resource

Cardanol, a major component obtained by thermal treatment of cashew nut shell liquid, is a phenol derivative mainly having a C15 unsaturated hydrocarbon chain with 1–3 double bonds at the m-position. We polymerized cardanol using an Fe-salen complex as the catalyst to give a soluble polyphenol containing the unsaturated alkyl group in the side chain. The polymer was subjected to hardening by a cobalt naphthenate catalyst or thermal treatment, yielding crosslinked film with high gloss surface.

Enzymatic oxidative polymerization of 4-hydroxybenzoic acid derivatives to poly(phenylene oxide)s

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.

Laccase-catalyzed polymerization of acrylamide

Enzymatic polymerization of acrylamide was carried out in water. Laccase, a copper-containing oxidoreductase derived from Pycnoporus coccineus, induced the polymerization at relatively low temperature (50°C) to give a polymer of high molecular weight. In the presence of 2,4-pentanedione, laccase efficiently mediated the vinyl polymerization at room temperature.

Crosslinkable Polyphenols from Urushiol Analogues

Synthesis and curing behaviors of polyphenol from urushiol analogues have been examined. The analogues were synthesized by lipase-catalyzed esterification of 4-hydroxyphenethyl alcohol with unsaturated fatty acids, in which the primary hydroxy group was regioselectively acylated to give the phenol derivatives having the unsaturated group in the para position. The oxidative polymerization of the analogues was performed using iron-salen or peroxidase as catalyst. Under appropriate reaction conditions, an oily soluble polymer was obtained in high yields. NMR analysis of the product polymer showed that only the phenolic moiety was polymerized and the unsaturated group was not involved in reaction during the polymerization. The polymer was subjected to the hardening by cobalt naphthenate catalyst or thermal treatment, yielding crosslinked film (artificial urushi) with high gloss surface.

Regio‐ and chemo‐selective polymerization of phenols catalyzed by oxidoreductase enzyme and its model complexes

Oxidative polymerizations of phenol derivatives have been performed using an oxidoreductase enzyme and its model complexes as catalyst to produce new functional polymers. Soluble polyphenols were synthesized using peroxidase catalyst in an aqueous methanol. Enzymatic polymerization of syringic acid involved elimination of carbon dioxide and hydrogen from the monomer to give poly(1,4-oxyphenylene) (PPO). Tyrosinase-model complexes catalyzed highly regioselective oxidative polymerization of a 2,6-unsubstituted phenol, 4-phenoxyphenol, to produce unsubstituted PPO showing crystallinity with a melting point. Chemoselective polymerization of phenols having an unsaturated group took place through peroxidase catalysis, yielding crosslinkable polyphenols.

PEROXIDASE-CATALYZED POLYMERIZATION OF FLUORINE-CONTAINING PHENOLS

Peroxidase-catalyzed oxidative polymerization of fluorine-containing phenols has been performed in a mixture of a water-miscible organic solvent and buffer at room temperature under air. The monomers used were 2,6-difluorophenol, 3- and 4-fluorophenols. In the polymerization of 2,6-diflurophenol catalyzed by horseradish peroxidase (HRP), effects of an organic solvent, buffer pH, and their mixed ratio have been systematically investigated with respect to the polymer yield and molecular weight. The resulting polymer was soluble in common polar organic solvents and showed good water repellent property. From NMR and IR data, it was supposed that the polymer was of mainly 2,6-difluoro-1,4-oxyphenylene unit. Elemental analysis showed that the elimination of a small amount of the fluorine atom took place during the polymerization. HRP catalysis induced the polymerization of 3- and 4-fluorophenols, yielding a new class of fluorine-containing polyphenols.