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 curing of new urushiol analogues, which were facilely synthesized by lipase-catalyzed regioselective acylation of catechol derivatives having a primary alcohol 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 gloss surface, which are comparable with those of natural urushi coating. Similar urushiol analogues from 4-hydroxyphenetyl alcohol and unsaturated fatty acids were subjected to an oxidative polymerization by Fe-salen catalyst, yielding soluble polyphenols having the unsaturated group in the side chain. Cardanol, a phenol derivative mainly having a C15 unsaturated hydrocarbon chain with 1-3 double bonds at m-position, is obtained from cashew nut shell liquid. Oxidative polymerization of cardanol by peroxidase or Fe-salen catalyst gave the crosslinkable polyphenol. These prepolymers were subjected to hardening by thermal treatment or cobalt naphthenate catalyst to give a crosslinked film (also, "man-made urushi") with good hardness.