Diphenylmethane-4,4-Diisocyanate MDI

4 -Diphenylmethane diisocyanate is the second-most important aromatic isocyanate, next to toluene diisocyanate (see Chapter 6.1.2). 

The reaction of formaldehyde with aniline in the presence of adds (e.g. HCl) also includes an attack of the formaldehyde on the amino nitrogen, which can then further react with aniline to give p-aminobenzylaniline and higher-molecular secondary amines. In the second reaction stage, these secondary amines are iso-merized to primary amines, with a reaction time of around 4 hours. 

In the acid-catalyzed process, condensation in the first stage is carried out at 50 to 70 °C, while in the second stage a temperature of around 105 °C and a pressure of 3 bar are used. Subsequent neutralization is carried out at 90 to 100 °C, to keep the polyamines in the liquid state. The crude amine mixture is refined by distillation, with around 60% 4,4 -diamine, 5% 2,4 -diamine and 35% polyamines being recovered. 

Increasing the temperature and raising the aniline/formaldehyde ratio favors the formation of the 2,4 -isomer, at the expense of the 4,4 -isomer. 

Following the distillation of the amines to recover 4,4 -diaminodiphenylme-thane and the polyamine fraction, a reaction with phosgene is performed at temperatures up to 140 °C in solvents such as dichlorobenzene. 

MDl is one of the most commonly used diisocyanates in polyurethane chemistry. 

More MDI is produced by way of p,p -diaminodiphenylmethane than by the nitrobenzene synthesis route. 

A distillation process is sometimes used to produce pure MDI. However, about of the MDI output is sold in a polymeric form. Much of the MDI production is used in making polyurethane foam. However, significant quantities of the pure MDI are used in making specialty polyurethane elastomers. 

An annual total of approximately 9 billion pounds of MDI was produced worldwide in 2010, with oniy a relatively small quantity going into polyurethane specialty elastomers. 

Note Production of nitrobenzene Is one of the most dangerous prooesses conducted In the chemical Industry, because It Is extremely exothermic. 

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Isocyanates are capable of co-reacting to form dimers, oligomers and polymers. For example, aromatic isocyanates will readily dimerize when heated, although the presence of a substituent ortho to the -NCO group reduces this tendency. For example, toluene diisocyanate (TDI) is less susceptible to dimer formation than diphenylmethane diisocyanate (MDI). The dimerization reaction is reversible, with dissociation being complete above 200 °C. It is unusual for aliphatic isocyanates to form dimers, but they will readily form trimers, as do aromatic isocyanates. The polymerization of aromatic isocyanates is known, but requires the use of metallic sodium in DMF. 

We have prepared and characterized three linear isosorbide containing polyurethanes with toluene diisocyanate (TDI), 4,4 -diphenylmethane diisocyanate (MDI), and 1,6-hexamethylene diisocyanate (HMDI) P(I-TDI), P(I-MDI), and P(I-HMDI). These polyurethanes have been synthesized as described in the experimental section by solution polymerization of isosorbide with the corresponding diisocyanate in dimethylacetamide using dibutyl-tin dilaurate as the catalyst at 75 C for 24 hours. All polymers have been isolated in quantitative yield by precipitation in methanol or water (5). 

World Health Organization Concise International Chemical Assessment Document(CICAD) 21 Diphenylmethane Diisocyanate (MDI), pp 1-25. International Programme on Chemical Safety (IPCS), Geneva, 2001... 

Polyurethanes (PU s). SL and 4,4 -diphenylmethane diisocyanate (MDI) were dissolved in tetrahydrofuran (THF), and the solution was stirred for 1 hr at 60°C. A THF solution of polyethylene glycol (PEG 400) and diethyl bis(2-hydroxyethyl)aminomethylphosphonate (polyol containing phosphorous) was added to the reaction mixture, and the reaction time was extended for 1 hr. In all reactions, the molar ratio of the total amount of isocyanate groups to the total amount of hydroxyl groups (NCO/OH) was maintained at 1.2. The lignin content in PU was 20 wt%. Each solution was drawn on a glass plate, and allowed to dry for 48 hr. The residual solvent in a sample was removed under vacuum and curing of each PU film was carried out at 120°C for 3 hr under a pressure of 50 kg/cm2. 

HDI is one of the most commercially important isocyanate compounds currently used in the United States. HDI, toluene diisoeyanate (TDI) and 4,4 -diphenylmethane diisocyanate (MDI) are widely used in... 

Synonyms Bis(l,4-isocyanatophenyl)methane diphenylmethane diisocyanate MDI methylenedi-/ ara-phenylene isocyanate and for 26447-40-5 crude MDI polymeric MDI PMDI generic MDI non-isomeric-specific MDI... 

M.A. Grammer, L.C. (1993) Hypersensitivity pneumonitis-like reaction among workers exposed to diphenylmethane diisocyanate (MDI). Am. Rev. respir. Dis., 147, 338-346... 

The catalysts of reactions between 4,4 -diphenylmethane diisocyanate (MDI) and alcohols in N,N-dimethylformamide (DMF) by dibutylin dilaurate has been investigated. The reaction rate of the catalyzed urethane formation in DMF is proportional to the square root of dibutylin dilaurate concentration. This result differs from that of similar studies on apolar solvents. The catalysis in DMF can be explained very well by a mechanism in which a small amount of the dibutylin dilaurate dissociates into a catalytic active species. 

Diisocyanites have two reacting groups and they can form chains or even networks. The two most commonly used diisocyanites are toluenediisocyanites (TDI) and diphenylmethane diisocyanates (MDI) (Fig. 12.17). With each bond formed one molecule of gaseous carbon dioxide is released. This is responsible for the foaming effect. 

The isocyanates form the major part of the hard or rigid phase of the polyurethane. The three main isocyanates used in industry for castable materials are toluene diisocyanate (TDI), 4,4 diphenylmethane diisocyanate (MDI), and 1,5-naphthalene diisocyanate(NDI). Aliphatic diisocyanates form a small segment of the diisocyanate market. 

In the production of polyurethane elastomers, only diisocyanates are of any important use. The major diisocyanates manufactured and used are the 2,4 and 2,6-toluene diisocyanates (TDI) and 4,4 -diphenylmethane diisocyanates (MDI). See Figure 2.15. 

In this chapter we investigate the morphology of a series of polyurethanes based on polycaprolactone polyol (PCP), diphenylmethane diisocyanate (MDI), and butanediol (BDO). Samples of as-batch-reacted and solution-cast polymers were examined by optical microscopy, transmission electron microscopy, electron and x-ray diffraction, and differential scanning calorimetry. Our interest is to provide a mapping of the size and shape of the domains (and any superstructure such as spherulites) and the degree of order as a function of the fraction of each phase present. 

The polyurethane samples were kindly supplied by F. E. Critchfield of Union Carbide Corporation. The samples were made by a one-step batch process with curing at 145°C for 16 hr. Details of the polyurethane polymerization are described elsewhere (9). The hard segment consists of 4,4 -diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) (MDI/BDO)i, and the soft segment consists of MDI and polycaprolac-tone diol (PCP) with Mn — 2000 (PCP/MDI),. 

The reaction of sterically hindered aromatic diisocyanates with bases or phospholene oxide catalysts afford oligomeric carbodiimides having terminal isocyanate groups. If the catalytic conversion of 4,4 -diphenylmethane diisocyanate (MDI) is conducted in the... 

MIC is less frequently used than toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), and other isocyanates. In order to highhght the distinctiveness of MIC toxicity, the toxicity of diisocyanates is described briefly. 

Diphenylmethane diisocyanate (MDI) is another important raw material in polyurethane manufacture. It is a solid, melting at 37°C, and has a tendency to dimerise at room temperature. Several other aromatic isocyanates are used in the preparation of polyurethanes but are not widely used. Various aromatic isocyanates are illustrated in Figure 2.14. 

The International Isocyanate Institute,lnc., (a) Technical Information No. 1, Recommendation for the Handling of Toluene Diisocyante, (b) ibid, A report on the International Institute,Inc., Second Edition, September, 1981 (c) ibid. Recommendations for the Handling of 4,4 - Diphenylmethane Diisocyanate MDI, momeric and Polymeric. 

Di-n-butyltin catalysts are being used in the preparation of polyurethane foams. Most polyurethane foams utilize aromatic isocyanates such as toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) as the isocyanate, and a polyester or polyether polyols as the coreactant. Tertiary amine catalysts are used to accelerate the reaction with water and formation of the carbon dioxide blowing agent. To achieve a controlled rate of reaction with the polyol, an organotin catalyst can be used. Polyurethane foams are not only applied in place, but are also cast in a factory as slabstocks. These foam slabs are then cut for use in car seats, mattresses, or home furnishings. DBTDL is an excellent catalyst in high resiliency slabstock foams. DBTDL shows an excellent reaction profile for this application replacement for DBTDL in such an end-use is difficult and requires a substantial reformulation of the foam. 

ZEISS, C.R., KANELLAKES, T.M., BELLONE, J.D., LEVITZ, D PRUZANSKY, JJ. PATTERSON, R. (1980) Immunoglobulin E-mediated asthma and hypersensitivity pneumonitis with precipitating anti-hapten antibodies due to diphenylmethane diisocyanate (MDI) exposure. Journal of Allergy and Clinical Immunology, 65, 346-352. 

A guinea pig inhalation model was developed by Karol (1983) to examine immune and pulmonary responses to TDI. Since that time, this model has been used by other investigators to examine immune and pulmonary responses to TDI and other chemical respiratory allergens such as diphenylmethane diisocyanate (MDI) (Karol and Thome, 1988), trimeric hexamethylene diisocyanate (Des-N) (Pauluhn and Eben, 1991), trimellitic anhydride (TMA) (Botham el al., 1988 Pauluhn and Eben,... 

A number of different hindered diamines have been investigated as a substitute for MOCA (1). In addition to diamine curing agents, which are used most frequently with elastomers based on polyether polyols and toluene diisocyanate (TDI), prepolymers based on polyether or polyester polyols and 4,4 -diphenylmethane diisocyanate (MDI), can be cured with diols to yield elastomers with similar properties to those of diamine-cured polyester-TDI elastomers. The most common chain extender is butanediol. However, to achieve improved mechanical properties, especially at elevated temperatures, aromatic diols are often used. The most common one is hydroquinone di-(beta-hydroxy-ethyl) ether (HEQ). 

Polyurethanes are produced by the chemical action of di-isocyanate and polyol. The properties can be varied by the type of isocyanate used and the proportion of the two monomers. There are four main groups of classification for the thermoplastic groups of polyurethane, i.e. rigid foam, flexible foam, non-cellular and cellular polymers. Two main isocyanates used are toluene di-isocyanate (TDI) and diphenylmethane diisocyanate (MDI). Polyurethanes have limited application in the pharmaceutical or medical industries. Polyurethane is used as an adhesive for laminations (thermosetting material). Like thermosetting polyurethane, thermoplastic polyurethanes can be found as esters and ethers. 

A reliable method to determine the oligo-polyol reactivity is the study of the kinetics of the oligo-polyol s reaction with phenyl isocyanate, a model for the -NCO groups of toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) ... 

A similar structure to the one in Figure 6.6 is obtained by using instead of epoxy resins diphenylmethane diisocyanate (MDI pure or crude ). For example by using crude MDI with the functionality of around 2.2-2.5 -NCO groups/mol, by the reaction with terminal groups of high molecular weight polyether triols (5000-6500 daltons), nonreactive NAD... 

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