Biobased Aromatic-Aliphatic Polyols from Cardanol by Thermal Thiol-Ene Reaction

Cardanol is a natural phenol which is obtained from high vacuum distillation of cashew nut shell liquid. It contains a hydrocarbon chain of 15 carbon atoms in the meta position, either with one, two or three non-conjugated double bonds. This article describes thermal thiol-ene reaction to synthesize new cardanol-based polyols for polyurethanes with aromatic-aliphatic structure. Phenolic hydroxyl group was blocked by alkoxylation and 2-mercaptoethanol was added to the double bonds of propoxylated cardanol. The resultant product is a mixture of polyols that may contain one, two, three or four hydroxyl groups, as a function of the number of double bonds reacted with 2-mercaptoethanol. Similar polyols, but with much higher functionality, were also synthesized from condensation of cardanol-based novolacs with formaldehyde. These cardanol-based polyols were further utilized to prepare rigid polyurethane foams (PUs) with excellent physical and mechanical properties, useful for various applications in chemical and food industries.