Diisocyanates cross-reactivity

HDI exposure has also been reported to induce the production of immunoglobulins, mainly IgG and IgE (Belin et al. 1981 Grammar et al. 1988, 1990 Patterson et al. 1990), making this response a potential for use as a biomarker of exposure. Several difficulties arise when attempting to use blood immimoglobulin levels specifically as an HDI biomarker of exposme. As discussed earlier, there is no one specific test to detect the antibodies produced exclusively in response to HDI exposure. Cross-reactivity does occur with the HDI-HSA antigen and other aromatic isocyanates, such as TDI and MDI (Belin et al. 1981), making serum or skin antibody measmements of limited value as a biomarker of HDI exposure when workers may have been exposed to more than one diisocyanate. The presence and quantity of antibodies found in the serum or after RAST and skin prick tests do not always correlate to the occurrence of ocular, nasal. 

Erasure. Only one biomarker of exposure, HD A, was located in the surveyed literature (Brorson et al. 1990). This biomarker may be some use for acute-duration exposmes, but only if urine is collected from the exposed person within 6-12 hours after exposure. No reliable biomarkers of exposure are available for chronic, low-level exposures in humans, although blood immunoglobulins (in particular IgG) may be useful in determining exposures to the diisocyanates as a group, and not a specific exposme to HDl. Studies to determine other biomarkers that would be sensitive enough to detect chronic, low-level exposures to HDl/HDl prepolymers and be specific to HDl only, with low cross-reactivity to other diisocyanates, would be extremely useful, and would enhance the database. 

Thome PS, Hillebrand JA, Lewis GR, et al. 1987. Contact sensitivity by diisocyanates potencies and cross-reactivities. Toxicol Appl Pharmacol 87(1) 155-165. 

I. Mechanism of toxicity. Toluene diisocyanate and related isocyanates act as irritants and sensitizers at very low concentrations. The mechanism is poorly understood, but it is thought that they act as haptens. Once a person is sensitized to one isooyanate, cross-reactivity to others may occur. 

Curing with Atmospheric Moisture. Type 2 in Table 2.5. High molecular mass polyaddition products of polyols with excess diisocyanate contain reactive isocyanate groups. They are used to formulate one-pack polyurethane paints that cross-link with the formation of urea groups under the influence of atmospheric moisture to produce paint films with excellent resistance to chemical and mechanical attack. Solvent-free products and dissolved products with isocyanate contents of 5- 15% (based on the solid resin) are commercially available. 

In two sensitised workers exposed to diphenylmethane diisocyanate (MDI), used for coating pipes with a polyurethane foam, tests with an MDI-human serum albumin conjugate showed the presence of specific IgE antibodies as measured by polystyrene tube radioimmunoassay (PTRIA) procedures (Zeiss et al. 1979). High levels of specific IgG antibody were found, with some cross-reactivity with a TDI-human serum albumin conjugate. The serum of one of the workers gave a positive precipitin reaction in the double diffusion test in gel. The authors suggest that these antibodies may be related to the respiratory reactions to the inhaled chemical. 

The use of hydroxyethyl (also hydroxypropyl) methacrylate as a monomer permits the introduction of reactive hydroxyl groups into the copolymers. This offers the possibility for subsequent cross-linking with an HO-reactive difunctional agent (diisocyanate, diepoxide, or melamine-formaldehyde resin). Hydroxyl groups promote adhesion to polar substrates. 

Following this work, the y -12F-diol was used for the direct reaction with hexamethylene-1,6-diisocyanate in the presence of dibutyltin dilaurate to produce a cross-linked elastomer or a reactive prepolymer which was terminated with either isocyanate or hydroxyl groups, depending on which reactant was in excess (142,143). 

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

Telechelic polymers rank among the oldest designed precursors. The position of reactive groups at the ends of a sequence of repeating units makes it possible to incorporate various chemical structures into the network (polyether, polyester, polyamide, aliphatic, cycloaliphatic or aromatic hydrocarbon, etc.). The cross-linking density can be controlled by the length of precursor chain and functionality of the crosslinker, by molar ratio of functional groups, or by addition of a monofunctional component. Formation of elastically inactive loops is usually weak. Typical polyurethane systems composed of a macromolecular triol and a diisocyanate are statistically simple and when different theories listed above are... 

Malo JL, Ouimet G, Cartier A, et al. 1983. Combined alveolitis and asthma due to hexamethylene diisocyanate, with demonstration of crossed respiratory and immunologic reactivities to diphenylmethane diisocyanate. J Allergy Clin Immunol 72(4) 413-419. 

The functionalization of SAMs via ruthenium-catalyzed cross metathesis of vinyl-terminated SAMs has been reported by Lee et al.76 to install a variety of acrylic derivatives on SAMs bearing vinyl groups on their outer surface. The major drawback of this approach is the intra-SAM metathesis which causes the formation of a mixture of surface-bound products, limiting the reproducibility of the method. The formation of urethanes by the reaction of diisocyanates77 or isothiocyanates78 with hydroxyl- and amino-terminated SAMs has been reported as well. The reaction of hydroxyl-terminated SAMs with diisocyanates, allowed the preparation of isocyanate SAMs that proved to be reactive towards amines, alcohols, and water, displaying the standard chemistry of the isocyanate groups.77... 

On adding a reagent enzyme with two or more reactive groups to the solution, the protein globules are cross-linked with the formation of a space lattice. The compounds most often used for this purpose are glutaraldehyde (1), hexamethylene diisocyanate (2), adipimidate (3), diazobenzidine-3,3-dianisidine (4), 4,4-diisothiocyanatediphenyl-2,2-disulfonic acid (5), and sym-trichlortriazine (6) ... 

Isocyanates are used as a cross-linker in EPI adhesive systems. Theoretically, any isocyanate with two or more NCO groups would be suitable. In practice two main parameters are important for the choice of isocyanate The volatility and reactivity of the isocyanate [1, 12]. The use of isocyanates with low volatility, low vapor pressure, is preferred to minimize the health risks concerned with the use and handling of the isocyanate. Isocyanates that are typically used, or have been used, as cross-linkers in EPI adhesive systems are based on the following isocyanate monomers toluene diisocyanate (TDl), diphenylmethane diisocyanate (MDl), hexamethylene diisocyanate (HMDI), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) and triphenylmethane-triisocyanate (TTl)... 

Both aromatic and aliphatic isocyanates are used in coatings the former are less expensive and the latter provide films with better color retention and exterior durability. Diisocyanates are used in two broad types of ways (1) as raw materials in the synthesis of resins and (2) as cross-linkers for resins with multiple substituent groups that are reactive with isocyanate groups. Isocyanates are toxic materials. When used as cross-linkers for coatings, they are reacted to form higher molecular weight isocyanate products with lower toxic hazards. 

Cross-Linkable PUDs. Cross-linkable PUDs are also made. For example, a hydroxy-fiinctional polyurethane can be made using a diisocyanate, a diol, a triol, and 2,2-dimethylolpropionic acid (DMPA) in aone-step process. The sterically hindered carboxylic acid group on DMPA is so low in reactivity with isocyanate that few amide bonds are formed. After neutralization of carboxylic acid groups with an amine, the resin is diluted with water to yield a dispersion stabilized by... 

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