| 摘要 |
Liquid polyisocyanates, which have been made by phosgenating polyamines, are freed from accompanying polymeric polyisocyanates and reaction by-products, by treating with a mixture of (a) a solvent for the entire phosgenation product and (b) a non-solvent for the polymers and by-products only, and then separating the two layers which form. The solvent (a) comprises at least 5 vol. per cent, and the mixture (a) + (b) comprises at least 75 vol. per cent, of the system [phosgenation product + (a) + (b)]. The preferred extraction mixture is CCl4 + n-hexane, and exemplified polyisocyanates are CH2(C6H4NCO)2 with higher methylene-bridged phenyleneisocyanates, and tolylene diisocyanates. Numerous other extraction mixtures and polyisocyanates are specified. |
