Synthesis and curing behaviors of a crosslinkable polymer from cashew nut shell liquid

In the present study, we have oxidatively polymerized cashew nut shell liquid (CNSL), whose main component is cardanol, a phenol derivative having a meta substituent of a C15 unsaturated hydrocarbon chain with one to three double bonds as the major, and examined the curing behaviors of the resulting polymer. Fe–salen efficiently catalyzed the polymerization in bulk at room temperature to give a soluble crosslinkable polymer in a good yield. Various metal complexes also catalyzed the polymerization at 80 °C, although their catalytic activity was lower than that of Fe–salen. The curing by cobalt naphthenate catalyst or thermal treatment took place to give the crosslinked film (artificial urushi) with high hardness and gloss surface. In the curing of polyCNSL by the thermal treatment, the crosslinking behaviors and properties of the resulting film were similar to those of a commercially available CNSL–formaldehyde resin.