Isocyanate moisture sensitivity

The blocked isocyanate function of aminimides also allows their use as polyurethane adhesives. Thus bis(aminimides) crosslink with polyester or polyether diols to yield a range of elastomers dependent upon the structure of the bis(aminimide) and the co-reactant chosen. For example, bis(aminimides) mixed with polyhydroxyl components can provide stable, single-package prepolymer compositions which yield polyurethanes on heating without the problem of isocyanate moisture sensitivity which can plague polyurethane applications. 

At this point the product consisted mostly of the isocyanate, since the reaction with tert-butyl alcohol is relatively slow at 35-40°. If the photolysis is carried out in an aprotic solvent such as tetrahydrofuran, the isocyanate may be isolated. However, care must be exercised to avoid losses of this rather volatile and moisture-sensitive compound. 

Owing to the rapid decomposition of the cyanate ion in water, the use of aprotic solvents was necessary for the preparation of the Ag(NCO)J ion. Since alkali cyanates are poorly soluble in aprotic solvents, the cyanate salts used were the tetraethylammonium, tetramethylammonium and tetraphenylarsonium cyanates. Either dry acetone or acetonitrile could be used as solvent as silver isocyanate was reasonably soluble in both. Once prepared the silver salts were found to be light- and moisture-sensitive.136-137... 

Following the same strategy, the dihydrotriazinyl derivative 140 has been obtained by deprotonation and the use of triazine as the C-electrophile reagent. 4-Nitro-/3-sultam 38 has been prepared for the first time as a very moisture-sensitive and unstable liquid by silylation to the 4-monosilylated product 141, followed by reaction with nitropropane at — 78 °C. Reaction of iV-TBDMS /3-sultam with phenyl isocyanate yields mixtures of 4-mono- and 4,4-disubstituted products 142 and 143, respectively (Scheme 42) <2004HCA1574>. 

Isocyanates are sensitive to moisture therefore, the reaction needs to be done on dry wood (82). As wood moisture content increases before reaction, more nonbonded polymers are formed after reaction. Reacted moist wood shows very high ASE values on the first water-soak test, but leaching causes a significant loss in ASE. This shows that the bulking chemical is not bonded to the cell wall but comes out upon water leaching. 

Proprietary bonding agents are used almost exclusively in modern manufacturing processes for metal-rubber bonded products. Isocyanates were proved to be of value in the immediate postwar period, but their moisture sensitivity and tendency to be wiped off the metal during processing have proved as disadvantages. The majority of commercially available adhesives in use today are a complex mixture of undisclosed composition, and in many instances are specifically used for particular rubbers and substrates. 

Caution. Methyl isocyanate is malodorous and toxic. Avoid skin contact and inhalation. All procedures should be carried out in a well-ventilated hood. Due to the moisture sensitivity of the starting materials and the product, all substance transfers must be carried out under an atmosphere of nitrogen. 

Blocked isocyanates offer a number of advantages to unblocked isocyanates. The traditional concern for moisture sensitivity can be addressed by blocking the isocyanate. Heat activation is then required, but most commercial adhesive applications can meet this requirement. Water-based dispersions and dispersions of the isocyanate in the polyol or other reactive media become possible using blocked isocyanates. There are a number of blocked isocyanates commercially available that could be used in adhesive... 

Hazardous Decomp. Prods. Heated to decomp, emits CO, CO2, NOx, hydrogen cyanide Storage Air- and moisture-sensitive store under nitrogen reacts slowly with water Uses In isocyanate-based adhesives component in polyurethane elastomers high strength backbone or crosslinking intermediate... 

This work was underway at the time J. H. Grezlak and G. L. Wilkes (3) published on a similar synthetic approach to block copolymers. In their process a preformed, isocyanate terminated polyester-urethane is reacted with monohydroxyfunctional polymethyl methacrylate. In the new procedure reported here a monohydroxyfunctional polymethyl methacrylate-polyester diol mixture is azeotropically dried in toluene solution and then simultaneously extended and end capped by reaction with diisocyanate. This approach has the advantage of simplicity and avoids unnecessary manipulations of moisture sensitive materials. 

There are, however, certain limitations associated with polyurethane structural adhesives, the most significant being their elevated temperature performance. It is typical of such adhesives to lose 50%, or more, of their room temperature strength on aluminum or steel at 80-100°C as shown in Table I. Urethanes produce only moderate strength bonds to metals, and adhesives which contain free isocyanate groups suffer from limited shelf stability due to their moisture sensitivity. 

Preparative Method readily prepared in high yield from the reaction of chlorosulfonyl isocyanate and anhydrous methanol. Handling, Storage, and Precautions is moisture sensitive and should be stored in a dark bottle, protected from light. Violent decomposition has been observed when the product is stored in a clear-glass container or when advertently exposed to sunlight. 

Two-component polyurethanes are extremely versatile in plastics bonding and are used widely for polyester SMC bonding where their good adhesion and high flexibility are key properties. Limitations include the moisture-sensitivity of the isocyanates leading to foam formation, the need for primers for some surfaces, and some health and safety concerns concerning the toxicity and irritancy of isocyanates. 

The most important types of two-component adhesives are moisture-sensitive polyurethane, comprising polyol resin and isocyanate catalyst, and heat-sensitive epoxy, comprising bisphenol A or F resins and polyamine catalyst. Both single- and two-component adhesive systems are available in the market. Single-component reactive adhesives, which include cyanoacrylate and silicone, are also widely known, with the latter often being used as a sealant. 

Single-component polyurethanes consist of pre-polymers, a fraction of which is pre-reacted polyurethanes with terminal isocyanate groups. Due to their moisture sensitivity, they have to be stored away from moisture or possible contact with water, preferably in metal containers. In this case, water acts as a reaction partner. They require similar storage conditions as the MDI hardeners, although in the reduced forms, they are less reactive. In the absence of moisture, the viscosity increases during storage. As such, manufacturers usually recommend storage stabilities of 3-6 months at 20-25°C. 

Urethane hydrolyzes into an amine, an alcohol, and carbon dioxide. So the possible degradation products of a poly(phosphoester-urethane) are diamines, diols, phosphates, carbon dioxide, and even ureas. Urea is possible because the isocyanate is extremely sensitive to moisture, which would convert the isocyanate to an amino group. One is therefore bound to have traces of diamine in the polymerization that leads to a urea bond in the backbone. We think the cytotoxicity seen in the macrophage functional assay comes from the TDI structure. 

It reacts with zinc oxide (1, 1294 additional suppliers Alfa Inorganics, ROC/RIC) to give isopropyl isocyanate (S). The yield is high if the complex (I) is not isolated owing to its high sensitivity to moisture. The reaction of (I) with silver oxide was not successful owing lo the violence of reaction. Reaction of (I) with sodium acetate gave (S) in 24% yield. 

NIPU networks are created by the reaction between polycyclic carbonate oligomers and aliphatic or cycloaliphatic polyamines with primary amino groups [4], This forms a cross-linked polymer with p-hydroxy urethane groups of a different structure—polyhydroxyurethane polymer. Since NIPU is obtained without using highly toxic isocyanates, the process of synthesis is relatively safe for both humans and the environment in comparison to the production of conventional polyurethanes. Moreover, NIPU is not sensitive to moisture in the surrounding environment. 

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