4,4 -Diaminodiphenylmethane diisocyanate

It should be stressed that the viscosity changes during formation of polyurethanes even from bifiinctional compounds can be correlated with gelation most likely they are connected with the formation of a physical network then crosslinks arise from sufficiently strong specific interactions like hydrogen bonds [50]. An example of such a process is the reaction of macro (diisocyanate) with 3,3 -dichloro-4,4 -diaminodiphenylmethane [43]. 

The production of aniline is a major international business, carried on in the US, Europe and Asia, mainly for the conversion, by reaction with formaldehyde under acid-catalyzed conditions, into diaminodiphenylmethanes 9a, 9b and 9c, and then into isocyanates, mainly 4,4/-methylenebis(phenylisocyanate) (MDI, also known as 4,4 -methylene-di-paraphenylene isocyanate, 4,4 -diphenylmethane diisocyanate, methylene diphenylene diisocyanate and diisocyanato diphenyl methane) (9d), from which polyurethanes are produced. This accounts for well over 60% of total demand (Figure 1). Aniline is also used in bulk for the production of antioxidants and vulcanization accelerators for rubber. Some 15.5 million lbs. of cyclohexylamine are made each year mainly by catalytic hydrogenation of aniline. Half the demand is for use as a boiler water additive. Other major uses include in the manufacture of herbicides, plasticizers, emulsifying agents, dyes, dry-cleaning soaps, acid gas absorbents and, in Asia, cyclamate sweeteners. Apart from India, the use of aniline for dyestuff manufacture represents about 10% of demand. 

In the last few years, however, 4,4 -diphenylmethane diisocyanate (methane diphenyldi isocyanate, MDI), whose precursor 4,4 -diaminodiphenylmethane is obtained from the condensation of aniline with formaldehyde, has overtaken TDI. In 1990, capacities in Western Europe, the United States, and Japan for MDI were 600,000, 530,000, and 190,000, tons, respectively for TDI, they were 400,000, 360,000, and 110,000 tons [91]. 

Diaminodiphenylmethane is an aromatic diamine used as a curing agent in epoxy resins of the bisphenol A type, as in the production of plastics, isocyanates, adhesives, elastomers, polyurethane (elastic and rigid foams, paints, lacquers, adhesives, binding agents, synthetics rubbers, and elastomeric fibers) and butyl rubber. Diaminodiphenylmethane is also a by-product of azo dyes. It is also possibly formed by hydrolysis of diphenylmethane-4,4 -diisocyanate. 

The precise composition of the mixture depends principally on the aniline to formaldehyde ratio used increasing amounts of aniline favour the formation of diaminodiphenylmethanes. Sometimes the amine mixture is fractionated to give pure 4,4 -diaminodiphenylmethane which is then phosgenated to form diphenylmethane 4,4 -diisocyanate. More commonly, the amine mixture is phosgenated without separation to give crude diphenylmethane diisocyanate which typically contains about 55% diphenylmethane diisocyanates (4,4 - and 2,4 -isomers), 25% triisocyanates and 20% higher polyisocyanates. 

Diaminodiphenylmethane n (DDM, methyl-enediamine, MD). A silvery, crystalline material obtained by heating formaldehyde aniline with aniline hydrochloride and aniline. It is used as a curing agent for epoxy resins and as an intermediate in making diisocyanates for urethane elastomers and foams by reaction with phosgene. Possible occupational hazards in the use of DDM are toxic hepatitis and liver damage. 

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