Isocyanate functional group

Nitrocellulose based lacquers often contain short or medium oil alkyds to improve flexibiUty and adhesion. The most commonly used are short oil non drying alkyds. Amino resins or urethane resins with residual isocyanate functional groups may be added to cross-link the coating film for improved solvent and chemical resistance. The principal appHcations are furniture coatings, top lacquer for printed paper, and automotive refinishing primers. 

Processing of rigid foams from two part formulations involves combining measured quantities of the polyisocyanate with a polyhydroxyl such that there are no or limited reactive isocyanate functional groups. Moisture is not required to complete the cure. Once the reactants are combined the mixture is poured into a form where expansion and polymerization take place simultaneously. Cure times are usually very fast, on the order of minutes. 

Both chemically and toxicologically, the most significant property of isocyanates is the high chemical reactivity of the isocyanate functional group. Industrially, the most significant such reaction is with alcohols to yield urethane (carbamate) compounds, as shown by reaction 15.8.2. Multiple... 

The formation of a single urethane bond by the addition reaction of hydroxyl and isocyanate functional groups is represented simply by ... 

Coreactive and prereacted. All polyurethanes can be subdivided into two broad categories, using the reactive isocyanate functional group to distinguish them. Those that have available NCO (for further reaction) can be called coreactive and those that have essentially no pendant NCO are prereacted. Table I contains an outline and description of some of the available materials that fit each type. It should be noted that some of the prereacted urethanes do contain other chemical functional groups that may be available for non-urethane forming reactions. 

Figure 1.5 Preparation of (a) UPy possessing an isocyanate functional group (3) and (b) a difunctional UPy compound (4) which forms a supramolecular polymer by hydrogen bonding (cf. Fig. 1.4). (After Folmer et al., 2000 Brunsveld et al., 2001.)...

These compounds are highly reactive due to the high unsaturation in the isocyanate functional group. They undergo addition reactions to the carbon-nitrogen double bond. Isocyanates react readily with alcohols to form urethanes ... 

Owing to the highly unsaturated isocyanate functional group, methyl isocyanate exhibits high reactivity. It decomposes with water and reacts vigorously with acids, bases, amines, and metals and their salts. 

Figure 1.20 The term polyurethane commonly describes a linear segmented copolymer which comprises hard and soft blocks stemming from the use of a mixture of low and high molecular weight diols in the polymerization formulation. The amount of each block-type in the polymer can be adjusted by altering the relative amount of low molecular weight diol to polyol while preserving the ratio of isocyanate functional groups to alcohol groups of all types.

Step addition and step condensation polymerization processes give rise to polymers containing distinctive functional groups at chain ends. The nature of the end groups will depend on the precise chemistry of the polymerization process. For example, linear polyurethanes are produced by reaction between diisocyanates and diols. If a perfect 1 1 stoichiometry of the reactants is used in the synthesis, on average each polymer chain must contain one isocyanate functional group and one alcohol group. If a 2 1 molar ratio of reactants is used, when the isocyanate is in excess, all the chain ends will have isocyanate functionality, and all will have alcohol functionality at the chain ends if a two-fold excess of diol is used. 

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]. 

Karmarkar, A., Chauhan, S. S., Modak, J. M., and Chanda, M. (2007). Mechanical Properties of Wood-Fiber Reinforced Polypropylene Composites Effect of a Novel Compatibilizer with Isocyanate Functional Group. Composites—Part A 38,227 233. 

Urethane bond-hastd polymers, called polyurethane (PU), include a wide family of polymers obtained from the reaction of starting monomers and/or prepolymers containing alcoholic and isocyanate functional groups typically, polyesters-polyols (polyesters with alcoholic termination) and diisocyanates are reacted to obtain PU. Final products often consist of reticulated polymers rather than linear ones, depending on the final use and desired properties. 

Polyurethane (PU) is a polymer composed of a chain of organic units joined by carbamate (urethane) links. PU polymers are formed by combining two bi-fimctional (or higher) monomers, one of which contains two or more isocyanate functional groups with the formula — N=C=0, while the other contains two or more hydroxyl groups. The isocyanate and hydroxyl groups combine to form a urethane linkage ... 

When the two paekages are mixed, the isocyanate functional groups react with the polyol hydroxyls, as in Figure 13. It is not uncommon for water vapor present to also enter into the reaction resulting in urea crosslinks as well. 

Spandex" Fibers. It is the name of polyurethane-based elastic fibers these are materials experiencing a very significant development in the textile industry. These spandex fibers have an initial molecular structure close to that of previously described TPU, but their preparation is performed out of stoichiometry in order to limit their molar mass and to produce two-ended chains carrying isocyanate functional groups. 

In order to produce flexible urethane foam, a blowing agent (e.g., water) is added to the reaction mass, which reacts with isocyanate functional group, giving CO2 as follows ... 

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