Metaphenylene diamine

Metaphenylene diamine (MPDA) is one of the most common of the aromatic amines used to cure epoxies. This product is amber to very dark in color. It is a solid that melts at 65°C and is generally mixed with the epoxy resin at that temperature. The molten liquid or vapors from MPDA can stain the skin and nearby structures rather badly. The para-isomer is reported to be carcinogenic, but the meta-isomer is free from this disadvantage. 

MPDA has four active hydrogens and is used stoichiometrically with DGEBA at 14.5 pph. Once it is in solution within an epoxy resin, the resulting mixture has excellent 

FIGURE 5.5 Chemical structures of common aromatic amine curing agents. 

Heat both the MPDA and the epoxy resin to 65°C the two components can then be blended. 

Heat the resin to about 80°C and then, while stirring continuously, dissolve the curing agent into the resin. 

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Figure 2. Solid-state spectra of four different epoxies (hosed on the resin diglycidyl ether of bisphenol-A) are compared with the liquid-state spectra of their respective unreacted components, The chemical compositions are in Table I. Here the epoxies are identified by their main curing agent (a) PIP—piperidine (b) MPDA—metaphenylene diamine (c) HHPA—hexahydro-phthalic anhydride (d) NMA—nadic methyl anhydride.

Epoxy adhesives are generally more resistant to a wide variety of liquid environments than other structural adhesives. However, the resistance to a specific environment is greatly dependent on the type of epoxy curing agent used. Aromatic amine (e.g., metaphenylene diamine) cured systems are frequently preferred for long-term chemical resistance. 

Older epoxy resins were noticed to cause skin cancer in laboratory animals. This was most likely due to the epichlorohydrin. Most newer epoxy resins, which contain less epichlorohydrin, do not seem to cause cancer in animals. Certain curing agents, such as metaphenylene diamine (MPDA) and diaminodiphenyl sulfone (DADPS), and certain gly-cidyl ethers are carcinogenic in laboratory animals. It is not known if these materials cause cancer in humans. 

Lime gives a vdute turbidity on addition of saturated ammonium oxalate solution, and sulphates with barium chloride acidified with hydrochloric acid. A useful reagent for nitrites is metaphenylene diamine, 5 grams of which are dissolved in water, acidified with dilute sulphuric acid, and made up to one litre. It may be necessary to previously decolorise the solution with charcoal. If nitrites are present in the water to be tested, on addition of the diamine, a yellow colour is produced, either immediately or upon standing. Starch-iodide solution acidified with dilute sulphuric acid may also be used, the characteristic blue colour of the starch-iodine complex indicating nitrites, but this test is not altogether satisfactory. 

Lu et al. [2] fabricated TFC NF membranes, in which the skin layer was either polyesters or polyamides. The monomers used in the polycondensation reactions are as follows (1) alcohol (bisphenol-A, BPA), (2) amine (metaphenylene diamine and piperazine), and (3) acid chloride (isophthaloyl chloride, terephthaloyl chloride [3,4], and trimesoyl chloride). They reported that the composite layer (active layer) was smoother than that of the substrate membrane. Upon formation of the active layer, the pore size decreased, which resulted in a flux decrease and a retention increase. Although it is unclear, they seem to maintain that their results confirm Hirose et al.s conclusion, i.e., the flux increases with an increase in surface roughness [Ij. 

One of the most commonly used aromatic amines is metaphenylene diamine (MPDA), a solid with a melting point around 63" C... 

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