P-phenylene diisocyanate

In the late 1990s high quality elastomers were produced using p-phenylene diisocyanate (PPDI) but because of its high vapour pressure it has to be used in a prepolymer formulation. 

Phenylenediamines, alkylation, 2 197 p-Phenylene diisocyanate (PPDI), 25 462 p-Phenylene ladder oligomers, sulfonio-bridged, 23 709, 716... 

Fig. 2. Reactivity of aromatic diisocyanates 0.02 M with 2-ethyihexanol 0.4 M and diethylene glycol adipate polyester in benzene at 28°C. (A) l-Chloro-2,4-phenylene diisocyanate. (B) m-Phenylene diisocyanate. (C) p-Phenylene diisocyanate. (D) 4,4 -Methylene bis(phenyl isocyanate). (E) 2,4-Tolylene diisocyanate. (F) Tolylene diisocyanate (60%, 2,4-isomer, 40% 2,6-isomer). (G) 2,6-Tolylene diisocyanate. (H) 3,3 -Dimethyl-4,4 -biphenylene diisocyanate (0.002 M) in 0.04 M 2-ethylhexanol. (I) 4,4 -Methylene bis(2-methylphenyl isocyanate). (J) 3,3 -Dimethoxy-4,4 -biphenylene diisocyanate. (K) 2,2,5,5 -Tetramethyl-4,4 -biphenylene diisocyanate. (L) 80% 2,4- and 20% 2,6-isomer of tolylene diisocyanate with diethylene glycol adipate polyester (hydroxyl No. 57, acid No. 1.6, and average molecular weight 1900). Reprinted from M. E. Bailey, V. Kirss, and R. G. Spaunburgh, Ind. Eng. Chem. 48, 794 (1956). (Copyright 1956 by the American Chemical Society. Reprinted by permission of the copyright owner.)...

Also, p-phenylene diisocyanate 74 upon reaction of two equivalents of the imino-phosphorane 75 and subsequent refluxing in p-xylene, affords the bis-heterocycle 76 in 66%yield. ... 

The reactions of several diisocyanates with a large excess of 2-ethyl-hexanol have been reported by Bailey et al. [122]. Reactions were run in benzene with the extent of reaction being followed by loss of infrared absorption at 4.4 pm, characteristic for the isocyanate group. A sharp decrease in the rate of reaction of 2,4-tolylene diisocyanate and the 80 20 isomer ratio of tolylene diisocyanate at approximately 50% reaction was found. In contrast, 2,6-tolylene diisocyanate, 4,4 -diphenyImethane diisocyanate, p-phenylene diisocyanate and m-phenylene diisocyanate showed only a slight decrease in rate as the reaction proceeded. 

Some data on the effect of structure of the hydroxyl compound on reactivity with p-phenylene diisocyanate were given by Cooper et al. [155]. The system was not specified except that the temperature was... 

Fig. 13. Effect of temperature on reactivity of p-phenylene diisocyanate with model compounds (ref. 155).

Abbreviations TDI, tolylene diisocyanate p-PDI, p-phenylene diisocyanate HDI, hexamethylene diisocyanate MDI, methylene bis(4-phenyl isocyanate) PPG, polypropylene glycol of indicated molecular weight DEG, diethylene glycol TEG, triethylene glycol EG, ethylene glycol PEG, polyethylene glycol. 

Another phosgene-free method was developed by Akzo Co. to product p-phenylene diisocyanate (32). 

Although p-phenylene diisocyanate (PPDI) has been synthesized as early as 1913 (18). the Akzo Corp. has developed more recently a modified Hofmann process for the preparation of PPDI (19). A comparison of the reactivity of PPDI in comparison with MDI and NDI (1,5-naphthalene diisocyanate) as well as with aliphatic diisocyanates (H12MDI, IPDI, and CHDI—see Aliphatic Isocyanates) was reported by Wong and Frisch (20). 

Among other aromatic diisocyanates in commercial use are p-phenylene diisocyanate, m-phenylene diisocyanate, l-chloro-2,4-phenylene diisocyanate, 3,3 -dimethyl-4,4 -bisphenylene diisocyanate, 4,4 -bis(2-methylisocyanophenyl)methane, and 4,4 -bis(2-methoxyisocyano-phenyl)methane. 

Terepthalonitrile disulfite, obtained from the corresponding hydroxamic acid (s. Synth. Meth. 23, 119), added with stirring to -octane, and rapidly heated to reflux at which time SOg-evolution has ceased -> p-phenylene diisocyanate. Y 96%. Also m-isomer in the presence of Supercel, and prepn. of 1,3,2,4-dioxathiazole 2-oxides from nitrile oxides, s. E. H. Burk and D. D. Carlos, J. Heterocyclic Chem. 7, 177 (1970). 

EFFECT OF DIOL MOLECULAR WEIGHT ON REACTIVITY (p-PHENYLENE DIISOCYANATE... 

Elastopan S, Shoe sole polyurethane materials, BASF Corp., Urethanes Specialties Elastopor, Rigid polyurethane foam systems, BASF Corp., Urethanes Specialties Elate, p-Phenylene diisocyanate, Akzo Nobel Chemicals Inc. 

Synonyms 4,4 -diphenyl methane diisocyanate 4,4 -diisocyanodiphenylmethane MBI 4,4 -methylenediphenyl diisocyanate PMDI methylene bis(phenylisocyanate) diphenyl methane diisocyanate 4,4 -methylene bisphenyl isocyanate methylene diphenyl diisocyanate i,i -methylene bis(4-isocyanato)-benzene methylenebis(4-isocyanatobenzene) bis(p-isocyanatophenyl)methane i,i-methylenebis(4-isocyanatobenzene) bis(i,4-isocyanatophenyl)methane methylene bis(p-phenylene isocyanate) Caradate 30 Desmodur 44 4,4 diisocyanatodiphenylmethane Hylene M50 Isonate 125M Isonate 125MF methylene bis(p-phenyl isocyanate) methylene di-p-phenylene diisocyanate 4,4 -methylene diphenylene isocyanate Nocconate 300 methylene di-p-phenyl diisocyanate diphenylmethyl diisocyanate methylene bisphenyl isocyanate MDI... 

Polyimides are also obtained in one step in the reaction of diisocyanates with tetracarboxylic acid dianhydrides. As an example, BTDA is reacted with a mixture of 2,4-TDI and MDI in DMF (93). This copolyimide, PI 2080, is used as a high temperature fiber and it is also sinter molded into solid shapes with exceptional mechanical properties. From PMDI and benzophenone-tetracarboxylic acid dianhydride polyimide foams with outstanding thermal properties and flame resistance are produced (94). Pol5fimides derived from p-phenylene diisocyanate (PPDI) or naphthalene diisocyanate (NDI) and pyromellitic dianhydride or BTDA are also synthesized using DMAc as solvent (95). 

Several higher-priced aromatic diisocyanates, such as p-phenylene diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI), and bitolylene diisocyanate (TODI), are also available. These symmetrical high melting diisocyanates give high melting hard segments in polyurethane elastomers. 

For example, toluene-2,4-diyl diisocyanate (TDI), p-phenylene diisocyanate (PDI), and 4,4 -methylenehis(phenyl isocyanate) (MDI), which are large-scale raw materials for the manufacture of polyurethane foams [248], can be isolated as spectroscopically pure materials from their corresponding methyl carbamate esters in yields of 70-79%. Toluene-2,4-diyl diisocyanate can also be isolated in good yield from its methyl carbamate ester when the reaction is performed in toluene (65% isolated yield) or hexanes (41% isolated yield). Chlorinated solvents, however, are not suitable media for this reaction. As expected, BCI3 is converted to trialkyl borate (identifiable by GC-MS after the reaction), consistent with Scheme 4.4. 

The formation of oligomeric four-membered ring dimers is especially pronounced in the highly symmetrical p-phenylene diisocyanate (PPDl) and diphenylmethane-4,4 -diisocyanate (MDI). On heating, the MDI dimer converts back to the monomer, while no dissociation occurs on heating of the PPDI dimer. The dimerization tendency of the large-volume diisocyanate MDI requires storage at low temperatures. Even in the solid state, dimerization of MDI occurs . 

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