These resins were first synthesized in the late 1950s by American Cyanamid as high-temperature thermosetting polymers. Unlike traditional epoxies and polyesters, cyanate ester resins are based on bisphenol derivatives that react via cycloaddition reactions. The earliest commercial cyanate ester resins were introduced in the 1980s to serve demanding aerospace and electronics applications. Since then, extensive research and development efforts have focused on optimizing the chemistry, curing behavior and mechanical properties of these resins. Today, cyanate ester resins have found widespread use in a variety of high-performance composite and electronic components due to their unique combination of properties.

Chemical Structure and Curing Reaction

Cyanate ester monomers contain reactive cyanate ester groups (–OCN) that lead to thermosetting upon curing. Commonly used cyanate ester monomers are based on bisphenol-A, bisphenol-E and hydrogenated bisphenols. Upon heating, the cyanate ester groups trimerize via cycloaddition reactions to form stable triazine rings. This highly exothermic curing reaction takes place between 150-260°C without requiring any acid catalyst or curing agent. The triazine rings formed are thermally and chemically very stable, providing the cured resin with exceptional performance characteristics even under harsh operating conditions.

Key Properties and Applications

These Cyanate Ester Resins cure to form tough, highly crosslinked thermosets with outstanding properties such as high heat resistance (up to 250°C), low dielectric constant and outstanding dimensional stability. They exhibit very high glass transition temperatures ranging from 210-350°C. These unique properties arise due to the rigid and thermally stable triazine backbone.

Due to their exceptional performance, cyanate ester resins are increasingly replacing traditional thermosets in demanding aerospace and electronics applications. They are commonly used as matrix resins for high-performance composite prepregs and laminates. Notable applications include aircraft components, radomes, satellite and space structures, industrial fasteners and printed circuit boards. They also serve as high-heat adhesives, coatings and matrix resins for carbon-carbon composites used in brake discs.

Processing and Composite Fabrication

Cyanate ester resins share many processing similarities with epoxy resins but require higher curing temperatures. They are processed either as low-viscosity liquids or as solvent-free solids depending on the end-use requirement. Monomer or prepolymer forms are available for bulk molding applications while processed forms such as dispersions and microcapsules are used for coatings.

For composites, uncured cyanate ester resin is impregnated into a fibrous reinforcement like carbon fibers or glass fibers using traditional prepregging techniques. The resin-impregnated composite prepregs or preforms are consolidated in an autoclave or press under programmed time-temperature cycles.