Cyanate esters are chemical substance

Chemical substance

In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...

s generally based on a bisphenol

Bisphenol

The bisphenols are a group of chemical compounds with two hydroxyphenyl functionalities. Most of them based on diphenylmethane. The exceptions are Bisphenol S, P, and M ....

 or novolac derivative, in which the hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atom of the phenolic OH group is substituted by a cyanide

Cyanide

A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

 group. The resulting product with an -OCN group is named a cyanate

Cyanate

The cyanate ion is an anion with the chemical formula written as [OCN]− or [NCO]−. In aqueous solution it acts as a base, forming isocyanic acid, HNCO. The cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron-pair...

 ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

.

Cyanate esters can be cured

Curing (chemistry)

Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...

 and postcured by heating, either alone at elevated temperatures or at lower temperatures in presence of a suitable catalyst. The most common catalysts are transition metal complexes of cobalt, copper, manganese and zinc. The result is a thermoset material with a very high glass-transition temperature (Tg) of up to 400 °C, and a very low dielectric constant

Dielectric constant

The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...

, providing excellent long term thermal stability at elevated end use temperatures, very good fire, smoke and toxicity performance and specific suitability for printed circuit board

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

s installed in critical electrical devices.

The chemistry of the cure reaction is a trimerization of three CN groups to a triazine

Triazine

A triazine is one of three organic chemicals, isomeric with each other, whose molecular formula is 333 and whose empirical formula is CHN.- Structure :...

 ring. Because the starting material is a product with two cyanate groups the resulting structure is a 3D polymer network. Product properties can be finetuned by the choice of substituent

Substituent

In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...

s in the bisphenolic compound. Bisphenol-A and novolac based cyanate esters are the major products, bisphenol-F and bisphenol-E are also used. The aromatic ring of the bisphenol can be substituted with an allyl

Allyl

An allyl group is a substituent with the structural formula H2C=CH-CH2R, where R is the connection to the rest of the molecule. It is made up of a methylene , attached to a vinyl group . The name is derived from the Latin word for garlic, Allium sativum. Theodor Wertheim isolated an allyl...

ic group for improved toughness of the material. Cyanate esters can also be mixed with bismaleimides to form BT-resins

BT-Epoxy

BT-Epoxy belongs to the group of thermoset resins used in printed circuit boards . It is a mixture of epoxy resin, a common raw material for PCBs and BT resins. BT stands for Bismaleimide-Triazine resin. This is in turn a mixture of Bismaleimide, which as such is also used as a raw material for...

or with epoxy resins to optimize the end use properties.