Radicals isocyanate

SAFETY PROFILE Compounds containing the isocyanate radical -NCO. Derivatives of isocyanic acid (cyanic acid). Usually the term refers to a diisocyanate. Inorganic isocyanates are only slightly toxic. Organic isocyanates (diisocy anates) can cause local irritation and allergic reactions. When heated to decomposition they emit toxic fumes of NO.. 

Substituted urea linkages also result from the presence of moisture which reacts with the Isocyanate radical. (Subsequently, B can represent any portion of the system including polymer segments). ... 

Other hydrolyzable groups consist of biuret and allophanate crosslinks formed from the reaction of Isocyanate radicals with active hydrogen atoms of the urea and urethane linkages, respectively. 

CSI acts as a chlorinating agent when allowed to react with an alkane (under free radical conditions,viz, UV irradiation or thermal initiation). Tertiary hydrogens are selectively replaced by chlorine compared to primary hydrogens (120 1) and the H- abstracting entity in the isocyanate radical. 

Participation of an intermediate such as isocyanate, radicals, or oxygen-contaiiiiiig compound (73-76). 

Chlorosnlfonyl isocyanate radical reactions with ethylene derivs. 26, 613... 

A number of methods such as ultrasonics (137), radiation (138), and chemical techniques (139—141), including the use of polymer radicals, polymer ions, and organometaUic initiators, have been used to prepare acrylonitrile block copolymers (142). Block comonomers include styrene, methyl acrylate, methyl methacrylate, vinyl chloride, vinyl acetate, 4-vinylpyridine, acryUc acid, and -butyl isocyanate. 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Type AD-G is used in an entirely different sort of formulation. The polymer is designed for graft polymerisation with methyl methacrylate. Typically, equal amounts of AD-G and methyl methacrylate are dissolved together in toluene, and the reaction driven to completion with a free-radical catalyst, such as bensoyl peroxide. The graft polymer is usually mixed with an isocyanate just prior to use. It is not normally compounded with resin. The resulting adhesive has very good adhesion to plasticised vinyl, EVA sponge, thermoplastic mbber, and other difficult to bond substrates, and is of particular importance to the shoe industry (42,43). 

Irradiation of the A-bromo- or N- chloro-azetidin-2-ones (71) in the presence of alkenes, alkynes or radical donors induces rearrangement to the /3-haloalkyl isocyanates (72) via a... 

The Preparation and Reactions of Fluoromethyleiies Fluorinated Isocyanates and Their Denvatives as Intermediates for Biologically Active Stibsianccs (Ccr) Radical Reactions of Polyfliioroaromatic Compounds (Russ )... 

Cyanates contain the OCN group. Inorganic cyanates that are formed industrially by the oxidation of cyanide salts hydrolyze in water to form ammonia and bicarbonate ion. Alkyl cyanates are insoluble in water and form cyanurates. Alkyl isocyanates contain the OCN radical, are formed from cyanates, and, like cyanates, are readily hydrolyzed. Thiocyanates (SCN group) are formed from cyanides and sulfur-containing materials and are relatively stable. 

Oxidation, hydrolysis, and photolysis are the three predominant chemical processes that may cause loss of simple cyanides in aquatic media are. Cyanides are oxidized to isocyanates by strong oxidizing agents the isocyanates may be further hydrolyzed to ammonia and carbon dioxide (Towill et al. 1978). However, it has not yet been determined whether such oxidation and subsequent hydrolysis of isocyanate is a significant fate process in natural waters known to contain peroxy radicals (EPA 1992f). 

Hydroxy-4-methylthiazole-2(3//)thione carbamates, e.g. the cyclohexyl derivative 336, are precursors for monoalkylaminium cation radicals, which cannot be prepared from 2-thioxopyridinyloxycarbamates. The carbamate is obtained from 3-hydroxy-4-methylthiazole-2(3//)-thione and cyclohexyl isocyanate. When irradiated in the presence of malonic acid and /-butyl hydrogen sulphide it yields the cyclohexylaminium cation... 

Trialkylsilyl radicals add to alkyl isocyanate to form imidoyl radicals 56 (Reaction 5.38). Detailed EPR studies established intermediates 56 to be strongly bent at the carbon bearing the unpaired electron [76], The absolute rate constant for the reaction of Et3Si radical with ieri-butyl isocyanate was found to be 5.5 x 10 s at 27 °C [13], whereas the relative rate of the addition of MesSi radicals to alkyl isocyanates was found to decrease in the... 

At this juncture. It was decided to make a radical formulation change. First, because of the Incompatibility of the Freon 11 with the polyol, the Freon 11 would be removed from the polyol and placed In the Isocyanate component. Second, since 1/1 component ratios are necessary to accommodate the mixing machine, different Isocyanate and polyol components were formulated to establish appropriate viscosities. The final formulation Is shown below. 

Some phenyl esters give rise to photodecarbonylation as a side reaction [37], This is also the case for certain phenylpropionamides, which implies cleavage of the CO—C bond in the acyl radical, after the breaking of the N—CO bond [99], If CO—C cleavage occurs prior to N—CO cleavage, then an isocyanate is formed (Scheme 38) and PFR does not occur. 

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