Diphenylmethane diamine

From the hydrolysis of a polyether-based PU a diamine (or a polyamine) such as toluene diamine or diphenylmethane diamine, a polyol and carbon dioxide are formed. The resulting diamines are the precursors used for the synthesis of isocyanates [11,12,16,18]. The resulting polyol is the polyether polyol used for the initial synthesis of PU. Carbon dioxide results from the decomposition of the very unstable carbamic acid formed by the hydrolysis (20.2) ... 

The diamine (for example diphenylmethane diamine) is transformed into a rigid polyether polyol by alkoxylation with PO and EO (reaction 20.18). 

The recovered polyols shown in Table 20.2 have a lower acidity due to the alkoxylation of acidic groups, lower hydroxyl numbers and higher viscosities (due to the alkoxylation of diphenylmethane diamine, which leads to high viscosity polyols) compared to the polyols resulting directly from glycolysis (Table 20.1). 

The toxicity of phosgene has spawned a lot of research into alternates for both MDI and TDI, as well as polycarbonates. In addition to safety, there are economic incentives for developing alternate routes. In the conventional MDI process, methylene diphenylmethane diamine (MDA) is formed by reacting aniline with formaldehyde. Separating excess aniline from crude MDA is an expensive operation. Also, by-product HCl formed in the conversion of MDA to MDI is an environmental issue. The final isocyanate product contains hydrolyzable chloride compounds that are difficult to separate and dispose of. The reactants must be kept bone dry to prevent corrosion, and the introduction of water can cause a runaway reaction. Similar concerns influence the search for nonphosgene routes for TDl. Conventional routes to polycarbonates also employ phosgene, which produces chlorine waste products, primarily sodium chloride, that present disposal problems. The elimination of chlorine from the polycarbonate process would constitute a major improvement. 

Phosgene produced by chlorinating carbon monoxide is used as a carbonylating agent to convert amines to isocyanates, as shown by reactions (8) and (9). Thus, the reaction of phosgene with diphenylmethane diamine results in the formation of methylene diphenyl diisocyanate (MDI), and with toluenediamine to form toluene diisocyanate (TDI). The isocyanates are used to produce polyurethanes for flexible and rigid foams, elastomers, coatings, and adhesives, for the construction and automotive industries. 

Synonyms Tonox HT 972 MDA DDM 4,4 -diaminodiphenylmethane methylenebis(aniline) 4,4 -methylenebisbenzeneamine diaminodiphenylmethane p,p -diaminodiphenylmethane bis(p-aminophenyl)methane DADPM DAPM dianilinomethane 4,4 -diaminoditan 4-(4-aminobenzyl)aniline Ancamine TL araldite hardener 972 curithane dianilinemethane 4,4 -diphenylmethane-diamine Epicure DDM Epikure DDM Jeffamine AP-20 Sumicure M... 

Based on the above studies, the identity of the diisocyanate component in BPUla was deduced by the presence of fragments at ra/z 250 [methylene-bis(4)phenyl-isocyanate] (MDI), 224 (4-amino-4 -iso-cyanato-diphenylmethane), and 198(diamino-diphenylmethane).27 The presence of the diamine, as the chain extender was evident from the presence of the fragments m/z 324, assignable to 1,l -bisCB-iso-jg cyanatoethyl)ferrocene, and 298, assignable to the structure 10. 

Fig. 3.6 shows the results of viscosity determination for a linear temperature increase in a polyurethane based on poly (butadiene diol), diphenylmethane diisocyanate, and diamine. 

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). 

Fig. 21 Comparison of fracture surfaces of (a) neat diethyltoluene diamine cured tetraglycedyl diamino diphenylmethane resin system (top) and (b) its corresponding nanocomposite containing 7.5% octadecyl ammoninm modified layered silicate...

In general, PAI is prepared by the following two processes diamine process and diisocyanate process. Diisocyanate process is achieved by the direct polycondensation of trimellitic anhydride (TMAH) with aromatic diisocyanate, such as 4,4 -diphenylmethane diisocyanate, in a polar solvent such as N-methyl-2-pyrrolidone (NMP) as shown in Eq. [13.4.On the other hand, the diamine process is achieved by a two-step reaction ... 

Similar observations were made by Born et al [262], for PUs extended with aliphatic glycols or diamines. The model compounds studied by them were prepared by the reaction between diphenylmethane-4-mono-isocyanate and glycols of the H0-(CH2)-0H structure with n = 2 to 6. The series of materials showed a characteristic fluctuation in their thermal and hydrothermal properties which was dependent on the number ( even or odd ), of CH2 groups in the chain extender. 

However it is also established that the commonly used diphenylmethane and naphthalene diisocyanate-based elastomers are frequently chain-extended with glycols. Table 3.12 contrasts the effects of diamine and glycol chain extenders with a toluene diisocyanate/polyether-based prepolymer, Adiprene LI00. With the unsymmetrical diisocyanates, such as TDI and MDI, polyol chain extenders give elastomers of poorer properties than diamines, and it is usually desirable to introduce additional crosslinking into diol-extender elastomers by the use of a proportion of a triol such as... 

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. 

Triphosgene is used as a carbonylating agent in the synthesis of 2-tolyl isocyanate 262 and in the synthesis of 4,4 -diphenylmethane diisocyanate (MDI) 264 from the corresponding diamine in high yield (92%) [53]. 

Whereas Hunter did not obtain the catenane 16 directly from 14 and 17, but only after preparation of the intermediate 15, we independently succeeded in the same year in a one-step synthesis of a substituted representative of the same catenane type 16 (R = OCH3) starting from the simple components 17 and 18 [31], In connection with earlier syntheses of basket-shaped host molecules [32], we had applied the cyclohexylidene-substituted diamine 17 [33] instead of unsubstituted diphenylmethane, p-phenylene and naphthalene units in order to increase the solubility of macropolycyclic lactams of type 19. The OCH3-substituents introduced via 18 are intended to be cleaved to OH-groups after the cyclization process. This should be useful for further bridging and, in particular, for attaching the bottom of the basket (spacer in 20). 

This limitation is overcome when the elastomer is cast from a mixture consisting of a linear polyester or poly ether, diisocyanate and glycol or diamine. In this process, the hydroxy-terminated polymer (e.g., poly(ethylene adipate) or poly(oxytetramethylene) glycol) is treated with an excess of diisocyanate (e.g., naphthylene 1,5-diisocyanate, tolylene diisocyanate or diphenylmethane 4,4 -diisocyanate). The product is a pre-polymer which is, in effect, a mixture of isocyanate-terminated polymer and unreacted diisocyanate. The pre-polymer is then mixed with either a glycol (e.g., 1,4-butanediol or 1,6-hexanediol) or diamine (which is usually a deactivated amine such as 3,3 -dichloro4,4 -diamino-diphenylmethane (MOCA)). The mixture is poured into a heated mould where it quickly sets. After about 30 mins the casting is removed from the mould and cured at about 110°C for 24 hours. 

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