Methyl isocyanate polymerization

The owner of tlie plant. Union Carbide Corporation, reported tliat tlie accident was "tlie result of a unique combination of unusual events." The methyl isocyanate (MIC) was driven out of a storage tank by pressure generated from a water-induced runaway polymerization reaction. The last batch of MIC put into the tank before the accident contained more chloroform tlian product specifications allowed. Cliloroform promotes the polymerization of MIC altliough cliloroform alone cannot react without the higli temperatures caused by tlie presence of water. The excess chloroform is one of tlie "unusual events" preceding tlie disaster, altliough the presence of water appears to be tlie primaiy culprit. 

In a study concerned with the decay resistance provided by isocyanate bonding to wood, the distribution of the methyl isocyanate reaction in southern pine showed that 60% of the lignin hydroxyls and 12% of the holocellulose hydroxyls are substituted at the point where resistance to biological attack occurs. Therefore, it can be surmised that the chemical bonding of wood by isocyanates through the urethane link can contribute significantly to the excellent performance of diphenylmethane-diisocyanate X or polymeric isocyanates XI as adhesive binder in particle boards (24, 25). 

The Bhopal incident (India, 1984) has dramatically outlined the high toxicity level of methyl isocyanate and moreover its very exothermic self-polymerization which requires extreme care during its production and storage (Ref. 270),... 

Potentially hazardous reactants. Spontaneons polymerizations with exothermic heat generation inclnde styrene, snbstitnted styrene, vinyl chloride, vinyl pyridine, acrylonitrile, bntadience, isoprene cyclopentadience, and methyl isocyanate reactions involving peroxides as illnstrated in Table 16.17, azides, perchlorates, or nitro componnds and decompositions, nitrations, oxidations, alkylations, aminations, combnstions, condensations, diazotizations, halogenations, or hydrogenations. 

METHYL ISOCYANATE (624-83-9) Forms explosive mixture with air (flash point 0°F/— 18 C). Reacts slowly with water, violently with warm water or steam, forming carbon dioxide and heat. Decomposes above 100 F/38°C. Violent reaction with acetaldehyde, amines, alcohols, acids, alkalis, strong oxidizers. Unless inhibited, can produce unstable peroxides contact with iron, tin, copper, or salts of these elements, or with certain catalysts such as triphenylarsenic oxide, triethylphosphine, or tributyltin oxide, or elevated temperatures may cause polymerization. Incompatible with glycols, amides, ammonia, caprolactam. Attacks some plastics, mbber, or coatings. The uninhibited monomer vapor may block vents and confined spaces by forming a solid piolymer material. 

Hyperbranchedpolytriallylsilanes functionalized with NCN [C H3X(CH2NMe2)2-2,6] ligands were reported by van Koten and Frey [19]. The soluble supports were used as ligands for the Pd-catalyzed aldol condensation of benzaldehyde and methyl isocyanate. Activities similar to that of parent NCN-Pd complexes were observed (Scheme 2). The hyperbranched polymeric systems showed similar properties to those of analogous dendritic compounds, indicating that structural perfection is not always required. The polymers were purified by means of dialysis, showing a potential application in continuous-flow membrane reactors. 

The Bhopal disaster, in terms of loss of life and human injury, is the most serious disaster in the history of the chemical and process industries. It took the form of a runaway polymerization of a highly toxic substance — methyl isocyanate (MIC). This took place not in a reactor, but in a storage tank. 

B. Polymeric Urea [Benzene, diethenyl-, polymer with ethenylbenzene, [[[[(1 methylethyl)amino]carbonyt]amino]methyl] deriv.] A 10.0-g. portion of benzylamine polymer beads prepared as in Part A and 125 ml. of tetrahydrofuran (Note 6) are combined in a 300-ml., three-necked, round-bottomed flask equipped with a magnetic stirrer, a dropping funnel, and a condenser fitted with a gas-inlet tube A nitrogen atmosphere is established in the system, and the slurry is stirred while 1.35 g. (0.0159 mole) of isopropyl isocyanate [Propane, 2-isocyanato-] is added. This causes an exothermic reaction, which subsides after about 20 minutes. The mixture is then stirred at room temperature for 22 hours and at reflux for an additional 4 hours. The beads are collected by filtration, washed with 150-ml. portions of tetrahydrofuran (Note 6) and methanol, and dried under reduced pressure over calcium chloride to yield 9.09 g, of the isopropyl urea polymer. 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

The instability of the 3-hydroxymethylindoles over a wide pH range results in the lack of success in acetylation of the hydroxy compound and also in the failure to hydrolyze the acetoxymethylindole without conversion into the bis(3-indolyl)methane (79HC(25-3)l). In contrast with the 3-isomer, 2-hydroxymethylindoles are stable to bases, but are polymerized by acids (79HC(25-3)l). Similarly, it is possible to convert 3-hydroxymethylpyrroles into their acetates and methyl ethers under basic conditions, and reaction with isocyanates yields the expected urethanes (79JMC977). Under acidic conditions, however, they produce the bis(3-pyrrolyl)methanes (B-77MI30504). 

Southern pine with a dual treatment of chemical modification with butylene oxide or butyl isocyanate followed by lumen-fill treatment with methyl methacrylate, or southern pine impregnated with methyl methacrylate and polymerized in situ, resulted in modified woods that were resistant to accelerated weathering and to ultraviolet light alone. Physical, chemical, and microscopic changes occurring as a result of ultraviolet light irradiation are described. 

Allyl isothiocyanate treatment also gave a high decay resistance of wood comparable to methyl and allyl isocyanates, but the main reaction appaeared to be polymerization, which left isothiocyanate groups intact [15]. 

Catalysts which have been found to promote dimerization of phenyl isocyanate include pyridine (11), methylpyridine (12), triethylamine (13), X-methyl- (or ethyl-)morpholine, triethylphosphine, and other alkyl or alkyl-arylphosphines (14, 15). Alkylphosphines bring about a very violent polymerization since they act as active catalysts and the polymerization is quite exothermic. Triphenylphosphine is inactive. Alkyl-arylphosphines are not as active as alkylphosphines and permit better control of the reaction. Another convenient method (14, 16) for control of phosphine-catalyzed dimerization involves the addition of an alkylating agent such as benzyl chloride in an amount stoichioraetrically equivalent to the substituted phosphine present. Complete deactivation of the catalyst results. By this means the reaction may be mitigated or even quenched and then activated by the addition of more catalyst. 

The structure of the isocyanate affects its tendency to polymerize. While diisocyanates can polymerize to form resins due to cross-linking, the dimer of toluene 2,4-diisocyanate is readily formed as a separate compound. This is because the isocyanate group ortho to the methyl is relatively much less active than the para-isocyanate group ... 

One-Step Process. Into 100 g of polymeric isocyanate, 0.8 g of 1-phenyl-3-methyl-l-phospholine oxide, 2.1 g of methanol and 2.1 g of 2,4,6-tris(dimethylaminomethyl) phenol are mixed and stirred for 15 sec. After 10 sec of mixing, foam rise starts, and the rise time is 60 sec. Low-friable foamed products result. 

A foam was prepared firom polymeric isocyanate (134 pbw) 3,3, 4,4 -benzophenonetetracarboxylic dianhydride (45 pbw) epoxy novolak resin (20 pbw) wetting agent (1 pbw) methanol (2.5 pbw) N,N, N -tris(dimethylaminopropyl)-s-hexahydrotriazine (2.5 pbw) triethylenediamine (2.5 pbw) and l-phenyl-3-methyl-2-phospholene 1-oxide (2.5 pbw). 

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