Isocyanate Route

Figure 1-11 The upper reaction is the methyl isocyanate route used at Bhopal. The lower reaction suggests an alternative reaction scheme using a less hazardous intermediate. Adapted from Chemical and Engineering News (Feb. 11, 1985), p. 30.

The most successful substitution reaction is via the isocyanate route. The poly (paraphenylene) backbone polymer chosen for this work... 

Certain fibers and non-wovens are made commercially by the isocyanate route, such as P84. For this family, 4,4 -BTDA and PMDA are used as dianhydride components, and toluene diisocyanate and diisocyan-atodiphenyl methane are used as diisocyanate components. ... 

The isocyanate route comprises the condensation of aromatic diisocyanate with aromatic tricarboxylic acid... 

Fig. 2.10 Scheme illustrating the synthesis of a polyurethane pol5nner via non-isocyanate route... 

There are currently two popular commercial methods to synthesize polyamide-imides. One is the acid chloride route, and the other is the isocyanate route. The sjmthesis method used will determine and limit to some extent the applications in which the resultant polymer is used. The chemistry of these two methods is outlined helow. 

The other most popular method of synthesizing commercial PAI uses the so-called isocyanate route. This is the primary route to polyamide-imides which are then utilized as wire enamels or fibers. This PAI chemistry involves the reaction of a di-isocyanate, often -methylenediphenyldi-isocyanate (MDI) (Fig. 12.3) with trimellitic anhydride (TMA) (Fig. 12.4). To overcome the lower reactivity of the carboxylic acid functionality in... 

Commercially the isocyanate process is also done in a dipolar aprotic solvent, typically NMP. The isocyanate route is performed at higher temperatures to evolve CO2 gases and promote imidization reactions. The reaction temperature is ramped over time to promote aU the various reactions shown above. One typical profQe starts the reaction at 80 C with the temperature increased at a rate of 30°C/h to 200°C over 4 h. Here the maximum CO2 evolution occurs in the 120 to 130°C range, with no more evidence of isocyanate functional groups present [13]. 

M. Fleischer, H. Blattmann, R. Mulhaupt, Glycerol-, pentaerythritol- and trimethylol-propane-based polyurethanes and their cellulose carbonate composites prepared via the non-isocyanate route with catalytic carbon dioxide fixation. Green Chem. 15 (2013) 934-942. 

Propham Phenyl isocyanate Not made by isocyanate route... 

The second way to obtain ammonia during the NSR regeneration is the isocyanate route [23]. This intermediate reaction is observed when a carbon source is present in the reaction mixture, especially CO [11]. However, CO can also be produced in situ, for instance by the reverse water gas shift (RWGS) reaction between H2 and CO2, the later being always present in large amounts in a real exhaust gas (see also the influence of the WGS equilibrium Sect. 19.2.3). 

Finally, signihcant ammonia emissions are possible at the NSR catalyst outlet. Two pathways are described, the direct route with H2 and the isocyanate route with CO. However, the ammonia formation is especially favored in the presence of hydrogen, which can be produced in situ or upstream the NSR catalyst. Whatever the ammonia production pathway, ammonia emission strongly depends on the balance between the ammonia formation rate and the ammonia reactivity (with NOx or oxygen from the support). Ammonia emission is particularly linked to the presence of unconsumed hydrogen. In addition, Ce-based oxides are proved to enhance the ammonia reactivity in the NSR catalyst. 

Method of synthesis polymer can be obtained by reacting the trimellitic anhydride chloride with m-phenylenediamine and 4,4 -oxydianiline, followed by dehydratation other methods Include isocyanate route and direct polymerization Robertson, G P Guiver, M D Yoshikawa, M Brownstein, S, Polymer, 45,1111-17, 2004 Fink, J K, High Performance Polymers, William Andrew, 2008. 

---