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【求助】NCO基团测定
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木虫 (知名作家)
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lumeng(金币+2): 2010-03-23 09:00
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Determination of % NCO in Prepolymer The method for the determination of the isocyanate level is based on that given by Wright and Cummins (1969). The NCO content of diisocyanates can be determined by the reaction with an excess of a standard solution of dibutylamine in chlorobenzene (or dry toluene) and titration of the excess with hydrochloric acid. The dibutylamine is prepared by dissolving 129 g of freshly distilled dibutylamine in 871 g of redistilled chlorobenzene and storing the resultant solution in the dark. The solution is relatively stable, but it is advisable to determine the amine content weekly by titration with 1 N hydrochloric acid in methanol. In the determination, 2 g of the diisocyanate should be accurately weighed out into a conical flask and 5 ml of chlorobenzene added. In the case of naphthalene diisocyanate, it is recommended that the mixture be warmed slightly to assist dissolution. To this mixture there is then added 25 ml of the standard dibutylamine solution. The reaction is rapid and takes only a few minutes for completion, when a clear solution is obtained. After adding 2 or 3 drops of a 1% alcoholic solution of bromophenol blue and 100 ml of methanol, the excess dibutylamine can be titrated with 1 N hydrochloric acid. If W = weight of sample in grams V1 = volume in ml of HCl solution required for titration of the sample V2 = volume in ml of HCl solution required for 25 ml of dibutylamine solution (blank) %NCO={[4.2*（v2-V1）*N]/1000W}*100 贴上一段 |
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8楼2010-03-23 20:46:31
