Diphenylmethane di-isocyanate

This tri-isocyanate is reported to impart good light stability and weather resistanee in polyurethane eoatings and is probably the most widely used aliphatic isocyanate. A number of other aliphatic polyisocyanates have been introduced recently in attempts to produce polyurethanes with improved light stability. Amine derivatives of diphenylmethane are made by reacting aniline of toluidines with formaldehyde. These can lead to a mixture of di-isoeyanates, the diphenylmethane di-isocyanates (MDIs) of commerce. Triphenylmethane-pp p"-tny tri-isocyanate is produced from leucorosaniline. 

Formulations for one-shot polyether systems are similar to those used for flexible foams and contain polyether, isocyanate, catalyst, surfactant and water. Trichloroethyl phosphate is also often used as a flame retardant. As with polyesters, diphenylmethane di-isocyanate is usually preferred to TDI because of its lower volatility. Tertiary amines and organo-tin catalysts are used as with the flexible foams but not necessarily in combination. Silicone oil surfactants are again found to be good foam stabilisers. Volatile liquids such as trichlorofluoro-methane have been widely used as supplementary blowing agents and give products of low density and of very low thermal conductivity. 

In addition to one-shot processes, quasi-prepolymer systems are used commercially with rigid polyether foams. The quasi-prepolymer is commonly produced using excess TDI rather than diphenylmethane di-isocyanate. Sinee the former isocyanate is light in colour and the latter dark, quasi-prepolymer foams... 

Zeiss CLR, Kanellakes T, Bellone J, Levitz D, Pruzansky JJ, Patterson R (1979) IgG and IgE antibody in two workers with diphenylmethane di-isocyanate induced respiratory reactions (Abstr). J Allergy Clin Immunol 63 150... 

Materials Investigated. The linear polyether-polyurethane investigated herein was obtained courtesy of Richard Oertel at the Upjohn Company in North Haven, CT. The polydisperse urethane hard segment is based on 4,4 -diphenylmethane di-isocyanate (MDI), chain extended with... 

MPEG Methoxy polyethylene glycol-amine DEG Diethylene glycol MDI 4,4 -diphenylmethane di-isocyanate... 

Polyurethanes are synthetized from di-isocyanates and polyols. The most frequently used di-isocyanates are toluylene di-isocyanate (TDI) and 4,4 -diphenylmethane di-isocyanate (MDI) as well as oligomers of the latter, poly(arylmethane) polyisocyanates (PAPI). 

Chemistry Polyurethane is produced by the reaction of a polyol with an diisocyanate (or in some instances a polyisocyanate) in the presence of catalysts. The polyols of choice are poly(propylene glycol), block copolymers of ethylene oxide (10-15%) with propylene oxide, or the newer polymer polyols (based on polymers such as polystyrene or styrene-acrylonitrile copolymer). Polyester diols such as polycaprolactone diol can be used in place of the polyether polyol in this reaction. The isocyanate of choice is a mixture of the 2,4 and 2,6 isomers of tolylene di-isocyanate in the ratio of 80 20, generally referred to as 80 20TDI. Other isocyanates such as diphenylmethane di-isocyanate (MDI), hexamethylene di-isocyanate (HMDI), and isophorone di-isocyanate (IPDI) are also used. A tin-based or amine catalyst is used to promote the reaction. Given the wide choice of reactants available, the reaction can yield foams with a range of different mechanical and thermal characteristics. 

Isocyanate as diphenylmethane di-isocyanate (MDI) is commonly used in the manufacture of composite wood products. MDI is used primarily in the manufacture of OSB. Facilities that use MDI are required to take special precautionary protective measures due to its toxicity. These adhesives have been chosen based upon their suitability for the particular product under consideration. Factors that must be taken into account include the materials to be bonded together, moisture content at time of bonding, mechanical property and durability requirements of the resultant composite products, and of course, resin system costs. 

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