Epoxy Resin

Pierre Castan, a Swiss chemist at the dental firm De Trey Frères, was looking for a resin for dentures. He reacted a phenol carrying two hydroxy groups with epichlorohydrin, then hardened the product with an acid anhydride, and got a hard, clear, unusually adherent solid. Ciba licensed it and sold it as Araldite; in the US Sylvan Greenlee developed epoxies independently. **US 2,324,483**, "Process of preparing synthetic resins", Castan, granted 20. July 1943, claims condensing "a polybasic carboxylic acid anhydride" with the product of "a phenol having at least two phenolic hydroxy groups and of an epichlorhydrine". It does not single out bisphenol A, the phenol most epoxies use today. **Epichlorohydrin is a carcinogen; you start from a two-part kit.** You glue pine lap joints at the right ratio and four wrong ones, then test hardness and break the joints.