Cyanate ester

Cyanate esters are chemical substances generally based on a bisphenol derivative, in which the hydrogen atom of the phenolic OH group is substituted by a cyanide group. The resulting -OCN group is named a cyanate ester.

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Cyanate esters can be cured by heating in presence of a strong tertiary amine catalyst like DABCO (diazabicyclooctane) or DMAP (4-dimethylaminopyridine), at temperatures of 150 - 250 °C. The result is a thermoset material with a very high glass-transition temperature (Tg) of up to 250 °C, and a very low dielectric constant. This is the reason for their use in printed circuit boards.

The chemistry of the cure reaction is a trimerization of three CN groups to a triazine ring. Because the starting material is a product with two cyanate groups the resulting structure is a 3D polymer network. Product properties can be fine-tuned by the choice of substituents in the bisphenolic compound. Bisphenol-A is the major product, bisphenol-F and bisphenol-E are also used. The aromatic ring of the bisphenol can be substituted with and allylic group for improved toughness of the material. Cyanate esters can also be mixed with bismaleimides to form BT-resins.