Aromatic amine eutectic

Aromatic Amine Eutectics. There are several curing agents available that consist of eutectics of various aromatic amines. These perform very much as MPDA and MDA do. However, the eutectics are liquids with viscosity of approximately 2000 cP at room temperature. They are readily miscible with liquid epoxy resins at room temperature. 

The aromatic amine eutectics may crystallize on storage. They can be reliquefied by heating to 40°C with stirring. This liquefaction can be accomplished without sacrificing either the curing properties or the final physical and chemical properties of the cured resins. 

Metaphenylenediamine (MPDA) is the best known of these aromatic amines. Methylene dianiline (MDA) requires somewhat longer cures and has a higher processing viscosity. Both products are solids and generally must be melted before being blended with resin. The difficulty in handling these materials as hot melts has led to the development of aromatic amine eutectics, which are liquid at room temperature. 

Similarly to the aromatic amines, eutectic mixtures of two anhydrides are sometimes used to overcome difficult mixing procedures such as the requirement for high temperature mixing. One such example is a 70/30 mixture of chlorendic anhydride and hexahydrophthalic anhydride which imparts nearly the same properties on the cured system as pure chlorendic anhydride yet allows much simpler mixing to be achieved. 

Examples of aromatic amines are shown in Fig. 5.5. Of these compounds the most common are mefa-phenylene diamine (MPDA), methylene dianiline (MDA), and eutectics of the two. 

Temperature-resistant two-part, elevated-temperature curing epoxy adhesives can be formulated with aromatic amines, such as metaphenylenediamine (MPDA), methylene dianiline (MDA), or a eutectic blend of the two. These adhesives will provide relatively high temperature strength, but they are generally brittle. When mixed with epoxy resin at concentrations of about 15 pph for MPDA and 26 pph for MDA, they provide complete cure in about 30 min at 175°C. The aromatic amines also provide a working life of several hours at room temperature. Starting formulations for aromatic amine cured epoxy adhesives are shown in Table 12.4. 

BUT liquid eutectic mixture of aromatic amines MOCA 3,3 -dichloro-4,4 -diphenylmethane DDS diaminodiphenylsulfone... 

Other aromatic amines can also be used in place of MOCA. These include methylene dianiline (MDA), m-phenylene diamine (w-PDA), and a eutectic mixture of m-PDA and cumene diamine (Caytur 7). MDA is so reactive that conventional compounds cannot be handled by normal processing methods. Blends of this material and MOCA can be used where shorter setting-up times are required with little change in final properties. 

Aromatic amines are solids at room temperature and are routinely melted at elevated temperatures and blended with warmed resin. Eutectic mixtures of metaphenylene and methylene dianiline exhibit a depressed melting point, producing an aromatic hardener that remains liquid over short periods of time. Pot life is considerably longer that that of aliphatic polyamines. Cure at elevated temperature is needed to develop optimum properties, which are maintained at up to 15()°C. Aromatic amines have better chemical and thermal resistance than aliphatic polyamines. 

Aromatic Amines. Because of conjugation, aromatic amines have lower electron density on nitrogen than do the aliphatic and cycloaliphatic amines. Consequently, they are much less reactive toward aromatic epoxies. They have longer pot-lives and usually require elevated temperature cures. Aromatic amines are usually solid at room temperature. These hardeners are routinely melted at elevated temperatures and blended with warmed resins to improve solubility. Eutectic mixtures of meto-phenylenediamine (MPD) and methylenedianiline (MDA or DDM) exhibit a depressed melting point resulting in an aromatic hardener that remains a liquid over a short period of time. MDA or 4,4 -diaminodiphenylmethane (DDM), 4,4 -diaminodiphenyl sulfone (DDS or DADPS), and MPD are the principal commercial aromatic amines. A new aromatic amine, diethyltoluenediamine (DETDA) has gained more significant uses in recent years. 

Only a few commercial uses for TDA per se have been found. In epoxy curing appHcations, 2,4- I DA has been used as a component of a eutectic mixture with short chain aUphatic glycidal ether resins (46) as well as by itself (46,47) TDA (46) and single isomers (47) are also used as amine curatives. TDA can be used as a chain extender in polyurethanes (48,49). TDA is cited as a monomer in making aromatic polymers with unique properties, eg, amorphous polyamides (50), powdered polyamides (51), and low melting, whoUy aromatic polyamides (52). 

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