Cyanate ester thermoset

The global thermoset resins market is expected to reach as high as 95 million metric tons by 2016 (Axis Research Mind report 2012). Excluding the alkyd resins, which are used primarily in the coatings, commercially important major types of thermoset resins, altuig with their relative % market share, estimated from literature (Fosdyke and Starr 2002), can be categorized as follows Polyurethanes (31 %), PhenoUcs (18 %), Amino resins (18 %), Unsaturated polyesters (12 %), Epoxies and other specialty/high performance thermosets (12 %), such as silicones, polyimides, bismaleimides (BMl), cyanate ester thermosets, etc. 

Thus, several properties of the common bisphenol A-diglycidyl ether-based epoxy thermosets can be improved by cocuring with a commercial bisphenol A-dicyanate ester, and the blend is more cost-effective than the cyanate ester alone. Such epoxy/cyanate ester thermoset blends exhibit improvements in processability, toughness, hot-wet performance, and low dielectric properties. 

Epoxy/cyanate ester thermoset blend-based composites have low dielectric constant desirable for advanced radomes, microwave anteimas, and stealth aircraft composite applications. Other applications include its use in copper clad laminates, semiconductor devices, and fire-resistant aircraft structural composites. 

Table 8.3. Typical properties of phenolics, polyimide, bismaleimide and cyanate ester thermoset resins...

Currendy, epoxy resins (qv) constitute over 90% of the matrix resin material used in advanced composites. The total usage of advanced composites is expected to grow to around 45,500 t by the year 2000, with the total resin usage around 18,000 t in 2000. Epoxy resins are expected to stiH constitute about 80% of the total matrix-resin-systems market in 2000. The largest share of the remaining market will be divided between bismaleimides and polyimide systems (12 to 15%) and what are classified as other polymers, including thermoplastics and thermoset resins other than epoxies, bismaleimides, cyanate esters, and polyimide systems (see Composites,polymer-matrix-thermoplastics). 

Modified Bismaleimides. Bismaleknide resins may be further modified and blended with other thermoset resins or reactive diluents to achieve either specific end-use properties or processibiUty. Thermoset resins that can be used for modification are unsaturated polyesters, vinylesters, cyanate esters, and epoxies. 

The fluorine content for the fluoromethylene cyanate ester resin system is clearly significantly greater than that for AroCy F and also significantly less than that for PTFE (76.0%). Correspondingly, the density reflects the fluorine content. As a homologous series, the contribution of incremental CF2 units can be quantified. From the density data, the volume equivalent of 41. 0 A1 /CF, structural unit in an amorphous thermoset matrix has been determined.8... 

FRP materials are made up of the polymer and reinforcing fibers. The polymer is typically a thermoset polymer thermoplastics can be used as well. Some typical thermoset polymers used are epoxy resins, unsaturated polyester resins, epoxy vinyl ester resins, phenolic resins, and high performance aerospace resins such as cyanate esters, polyimides, and bismaleimides. These resins... 

Within the past several years, improvements in the toughening of high-temperature epoxies and other reactive thermosets, such as cyanate esters and bismaleimides, have been accomplished through the incorporation of engineering thermoplastics. Additions of poly(arylene ether ketone) or PEK and poly(aryl ether sulfone) or PES have been found to improve fracture toughness. Direct addition of these thermoplastics generally improves fracture toughness but results in decreased tensile properties and reduced chemical resistance. 

The slightly altered form of the Pascault-Williams equation [136] was employed by Venditti and Gillham for describing the conversion-Tg dependency for many thermosetting resin including cyanate ester [139] ... 

Like other thermoset resins, cyanate esters are amenable to processing by a large variety of conventional techniques and their processing versatility in contrast to... 

Curing of liquid crystalline cyanate ester resins in electric fields is a new trend in thermoset design and processing and can be used to control directly their mechanical and physical properties. Combining new LC materials with non-LC cyanate monomers leads to a variety of novel ordered network structures and is a convenient method for modifying and controlling their chemical and physical properties [294]. 

The preceding review on the recent developments in the science and technology of cyanate esters clearly shows that this system emerges as a new generation of thermosetting polymer, encompassing several characteristics required of an... 

Crosslinked cyanate ester systems typically exhibit higher glass transition temperatures (T S 250°C), lower moisture absorption and lower dielectric constants than conventional epoxy thermosets. Hence by mixing dicyanates or their corresponding prepolymers with epoxy resins, and then co-curing, the desired level of property improvements can be achieved. Such hybrid thermosets have been used in printed circuit board manufacture. 

Other thermosetting polymers are cyanate esters (CEs), benzoxazines, PU acrylates, bismaleimides (BMIs), dicy-clopentadienes (DCPDs), diallyl phthalates (DAPs), etc. Formulations based on these polymers are used for specific applications where their particular properties are required. For example, DAP has long been the material of choice for electrical components where long-term reliability is required. 

The matrix is the weakest component of the composite determining the allowed maximum stress and the maximum service temperature. Great efforts have been undertaken to develop thermosetting polymers with increased temperature resistance. Cyanate-esters (CEs), BMI, and polyimides are the actual thermosetting matrices with higher thermal resistance. 

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