Allophanic ether

By passing the vapour of cyanic acid into alcohol, Liebig and Wohler (1830) obtained what they called cyanic ether (ethyl cyanate), but fifteen years later they found that the crystalline product contains neither cyanic acid nor cyanuric acid, and named it allophanic ether, because it is different from what was expected (oAAo , other av p6sy manifest). The constitution of allophanic... 

Catalysts such as dibutyl tin dilaurate or tertiary amines are added to promote the urethane reaction and/or subsequent moisture cure. Dimorpholine diethyl ether is particularly effective at promoting moisture cure without promoting allophanate side reactions at the application temperature (which leads to instability in the hot melt pot) [29]. 

Methyl Allophanate. Three hundred five milliliters of methyl chlorocarbonate (4.0 mols) and 480 g. of finely powdered urea (8.0 mols) are placed in a 2-1. standard-taper round-bottomed flask equipped with a 60-cm. reflux condenser. The mixture is heated on a steam bath for 90 minutes. Four hundred milliliters of water is added to the warm reaction cake to decompose any unreacted chlorocarbonic ester and to remove by solution both unchanged urea and urea hydrochloride, t Methyl allophanate remains behind as a relatively water-insoluble residue. The suspension is filtered and the white product washed with three 250-ml. portions of water, then with 95% ethanol (two 250-ml. portions), and finally with 500 ml. of ethyl ether. It is air-dried. The yield of product will vary from 227 to 274 g. (48 to 58%). The product thus obtained is pure enough to use as the starting material for other reactions. It can be further purified by recrystallization from hot water using 27.5 ml. of water per gram of compound (85% recovery m.p. 215 to 216° with decomposition). 

Ethyl Allophanate. A mixture consisting of 252 g. of finely powdered urea (4.2 mols) and 217 g. of ethyl chlorocarbonate (2 mols) is refluxed for 3 hours in a 1-1. round-bottomed flask equipped with a 60-cm. reflux condenser and heated by a steam bath. Two hundred milliliters of water is subsequently added to the warm reaction cake. After mechanical agitation to form an aqueous slurry, the suspension is filtered and the residue washed well with water (600 ml. in three portions), 95% ethanol (400 ml. in three portions), and ethyl ether (400 ml. in three portions). 

From Ethyl Allophanate. One hundred thirty-two grams of ethyl allophanate (1.0 mol), 100 ml. of 95% hydrazine (3.0 mols), and 1.5 1. of methanol are placed in a 3-1. standard-taper round-bottomed flask equipped with a reflux condenser and heating mantle. A few charcoal chips are added to prevent bumping. The reaction mixture is refluxed for 8 to 10 hours, after which it is cooled overnight in a freezer ( — 14°). The crystalline product is removed, washed with ethanol and ethyl ether, and air-dried. The yield is 63.7 g. (54% of theory) of allophanyl hydrazide, melting at 165 to 166° with decomposition. 

Tetrabromide, C,0HiaBr4O. crystals, mp 118% Allophanate. C 3HWN203> needles from petr ether, mp 84-86%... 

A typical polyurethane adhesive may contain, in addition to the urethane linkages, aliphatic and aromatic hydrocarbons, esters, ethers, amides, urea, and allophanate groups. Polyurethanes are formed by the addition reaction of diisocyanates or polyisocyanates with polyols (Figure 3.12) through a step-growth polymerization... 

The acellular (hydrolytic) mode of hiodegradation is identical in model media in vitro) and in hving organisms in vivo). It consists in hreaking ester urethane, and then ether bonds [423, 424]. Biodegradation of polyurethane is also accompanied hy hreaking of the secondary hiiu ethic and allophane bonds, a decrease in the effective density of the polymer suture, and a change in its supramolecular structure [422—424],... 

Procedure C [93] Formation of diastereomeric allophanates from (4R, 5S-c s-4,5-diphenyl-2-oxazolidone-3-carbamyl chloride (DOCC) Heat a mixture of DOCC (1 mM), the amine (1.1 mM), triethylamine (1.1 mM) and dry benzene (3 ml) under reflux for approximately 3 h. Cool, dilute with ether and partition with hydrochloric acid (IM) and finally water. Evaporate the organic phase and dissolve the residue in a solvent suitable for chromatography. 

The initial step to prepare polyurethane polymers for solution wet or dry spinning includes reaction of 1000-3500 molecular weight macroglycol with a diisocyanate at molar ratios of between about 1 1.4 and 1 2.0. Reaction conditions must be carefully selected and controlled to minimize side reactions, eg, allophanate and biuret formation, which can result in trifunctional branched chains and ultimately to insoluble cross-linked poljuners. For the prepolymer reaction, poly(tetramethylene ether) glycol [25190-06-1] and bis(4-isocyanatophenyl) methane [101-68-8] are currently the most commonly used macroglycol and diisocyanate. Several types of polyester-based macroglycols are included in spandex producers product lines, but with the exception of Dorlastan, made by Bayer AG in Germany, the polyester-based products represent only a minor part of their spandex fiber production. 

Allophanates from urethans s. 11, 591 o co-Chlorobromides from cyclic ethers... 

Thus, a urethane adhesive can be based on a wide range of polymers as long as they can be reacted to form a urethane linkage. In practice, polymers can contain aliphatic and aromatic hydrocarbons, esters, ethers, amides, urea and allophanate groups. This leads to a very wide range of raw materials being available, and formulations tend to differ in the type of polymer used rather than on the variations in additives, as seen with many other adhesives. 

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