Man-made urushi - Preparation of crosslinked polymeric films from renewable resources via air-oxidation processes

"Man-made (artificial) urushi" has been prepared by laccase-catalyzed curin g of new urushiol analogues, which were facilely synthesized by lipase-cata lyzed regioselective acylation of catechol derivatives having a primary alc ohol with unsaturated fatty acids derived from plant oils, one of the most important renewable resources. The curing of the catechol derivative having two or three unsaturated group proceeded under mild reaction conditions to produce the crosslinked film ("man-made urushi") with high hardness and gl oss surface, which are comparable with those of natural urushi coating. Sim ilar urushiol analogues from 4-hydroxyphenetyl alcohol and unsaturated fatt y acids were subjected to an oxidative polymerization by Fe-salen catalyst, yielding soluble polyphenols having the unsaturated group in the side chai n. Cardanol, a phenol derivative mainly having a C15 unsaturated hydrocarbo n chain with 1-3 double bonds at m-position, is obtained from cashew nut sh ell liquid. Oxidative polymerization of cardanol by peroxidase or Fe-salen catalyst gave the crosslinkable polyphenol. These prepolymers were subjecte d to hardening by thermal treatment or cobalt naphthenate catalyst to give a crosslinked film (also, "man-made urushi") with good hardness.