Isocyanates analysis

Wu WS, Stoyanoff RE, Szklar RS, et al. 1990. Application of Tryptamine as a derivatising agent for airborne Isocyanate determination. Part 3 evaluation of total isocyanates analysis by high-performanee liquid chromatography with fluorescence and amperometric deteetion. Analyst 115 801-807. 

When sampling for isocyanate analysis the mixer rotors were stopped and a sample was quickly withdrawn from the sticky polymerizing mixture by dipping two or three clean spatulas in quick succession through the reactor throat, then resuming mixing and data taking. 

Isocyanate analysis performed during the polymerization of Polymers 6, 7, and 8 after 7 and 16 minutes of reaction time afforded the interesting results of Table V. 

Liquid Ghromatography/Mass Spectrometry. Increased use of Hquid chromatography/mass spectrometry (Ic/ms) for stmctural identification and trace analysis has become apparent. Thermospray Ic/ms has been used to identify by-products in phenyl isocyanate precolumn derivatization reactions (74). Five compounds resulting from the reaction of phenyUsocyanate and the reaction medium were identified two from a reaction between phenyl isocyanate and methanol, two from the reaction between phenyl isocyanate and water, and one from the polymerisation of phenyl isocyanate. There were also two reports of derivatisation to enhance either the response or stmctural information from thermospray Ic/ms for linoleic acid hpoxygenase metabohtes (75) and for cortisol (76). 

Organic isocyanates in air Lab method with sampling either onto coated glass-fibre filters followed by solvent desorption, or into impingers and analysis using high performance liquid chromatography 25/3... 

F-NMR analysis not only permits an accurate quantitative determination erf hydroxy groups but also provides valuable information on their nature and their location. This not the case with lH-NMR measurements which have been carried out on samples modified by reaction with (CH3)3SiCl329 or with naphthalene isocyanate. 

A full development of the rate law for the bimolecular reaction of MDI to yield carbodiimide and CO indicates that the reaction should truly be 2nd-order in MDI. This would be observed experimentally under conditions in which MDI is at limiting concentrations. This is not the case for these experimements MDI is present in considerable excess (usually 5.5-6 g of MDI (4.7-5.1 ml) are used in an 8.8 ml vessel). So at least at the early stages of reaction, the carbon dioxide evolution would be expected to display pseudo-zero order kinetics. As the amount of MDI is depleted, then 2nd-order kinetics should be observed. In fact, the asymptotic portion of the 225 C Isotherm can be fitted to a 2nd-order rate law. This kinetic analysis is consistent with a more detailed mechanism for the decomposition, in which 2 molecules of MDI form a cyclic intermediate through a thermally allowed [2+2] cycloaddition, which is formed at steady state concentrations and may then decompose to carbodiimide and carbon dioxide. Isocyanates and other related compounds have been reported to participate in [2 + 2] and [4 + 2] cycloaddition reactions (8.91. 

Another example involved a batch of isocyanate crosslinker which was too tacky. Upon comparing the HPGPC trace of this sample with that of a control as shown in Figure 9, it is seen that the major difference between these two samples was the level of free caprolactam. The high content of free caprolactam in sample CX-006 depressed the glass transition temperature (Tg) of the sample to such an extent that CX-006 became too tacky. This method of analysis has proved to be a reliable and useful technique for detecting low levels of free caprolactam in this type of oligomeric crosslinker. 

Flame retardants in polyurethane foams were determined by SFE-SFC [117]. Off-line SFE-SFC-FID was used for the analysis of additives in polyurethanes [52], and on-line SFE-SFC for extraction of additives from isocyanate formulations [107]. 

It is well established that primary amino-functional groups, particularly aliphatic ones, react instantaneously with isocyanates to form ureas at ambient temperature. Indeed this was observed when 6-aminoethylferrocene (3) and freshly distilled phenylisocyanate were shaken vigorously. A yellow precipitate separated out immediately. Elemental analysis and an IR spectrum of the product indicate this compound to have the structure 6. ... 

Many practical applications of cure characterization involve samples for which the data required to convert isocyanate absorbance to concentration is unavailable. The emphasis is often placed on rapid analysis of many samples rather than an exhaustive characterization of a single sample. It is particularly desirable to develop a procedure which can determine the rate constants describing the cure reaction without converting the infrared absorbance curve to concentration. This has been accomplished by normalizing the data in such a way that the rate constants are determined from the shape of the cure curve. 

The isocyanates were added to the respective resin-bound amines suspended in dichloromethane in open glass tubes. The resulting reaction mixtures were each irradiated in a single-mode microwave cavity for 2 min intervals (no temperature measurement given) (Scheme 7.52). After each step, samples were collected for on-bead FTIR analysis. Within 12 min (six irradiation cycles), each reaction had reached completion. Acid cleavage of the polymer-bound ureas furnished the corresponding hydrouracils. 

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