Polyurethane urethane linkage formation

The synthesis of polyurethanes is usually presented as proceeding via the formation of carbamate (urethane) linkages by the reaction of isocyanates and alcohols ... 

The analysis of pyrolysate shown in Table 14.1.2 indicates only derivatives for the polyether sequences from the polymer. No traces of methylaniline were seen in the pyrogram, and the elution of an amino derivative of benzylbenzene is not likely to happen in the conditions used for this separation. Therefore, the use of pyrolysis results for the identification of this type of polyurethane is not conclusive. At lower temperatures three main paths for decomposition were indicated. One first process is the dissociation of the urethane linkage, taking place as the reverse of urethane formation, as shown below ... 

The crystalline structure of polyurethanes is controlled by the formation of hydrogen bonds between NH and C=0 groups of the urethane linkages [28, 29]. From the IR analysis, the hydrogen bonded C=0 present in the crystalline domain can be identified by the peak absorbance at 1699-1706 cm and the non-bonded or free C=0 group shows peaks at 1735 cm and 1748 cm. ... 

Polyurethanes (PUs), one of the most commonly used polymers for various blood-contacting biomedical applications, are generally prepared by the polycondensation reactions of diisocyanates with diols or amines [35, 36]. Reactions of diisocyanates with diols result in the formation of urethane linkages while diisocyanates reactions with amines result in urea linkages. Both aliphatic, as well as aromatic diisocyanate monomers, are commonly used for preparing polyurethane biomaterials. Examples include 1,4-butane diisocyanate (BDI), 1,6-hexamethylene diisocyanate (HDI), 4,4-dicyclohexylmethane diisocyanate (HMDI), and 4,4-diphenylmethane diisocyanate (MDl) [37]. Commonly used diols (or termed as polyols) for preparing polyurethanes includes poly ethers, polycaprolactone, and polyesters with molecular weights up to 5000 Da. 

Isocyanate Resins n Resins synthesized from isocyanates (—N = C = O) and alcohols (—OH). The reactants are joined through the formation of the urethane linkage and hence this field of technology is generally known as urethane chemistry. See Polyurethanes. (Odian, G. C., Principles of Polymerization, Wiley, New York, 2004). 

In any case, the principal chemistry used in making a polyurethane foam is the formation of urethane linkages from hydroxyl groups and isocyanate groups and the simultaneous generation of a gas that will enormously expand the reacting mass. This gas highly dilutes the polymeric network as it forms and remains as either open or closed gas cells in the final foamed product. 

The reaction of NCO groups and carboxylic acid groups resulted in the formation of amide linkages and carbon dioxide as blowing agent. This reaction has led to the invention of urethane foam preparation, and the polyurethane industry has become one of the biggest plastic industries. A model reaction of a polyamide foam formation is shown below ... 

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