| abstract |
The invention relates to a multistage process for the continuous preparation of organic, distillable polyisocyanates, preferably of diisocyanates, particularly preferably of aliphatic or cycloaliphatic diisocyanates, by reacting the corresponding organic polyamines with carbonic acid derivatives and alcohols in low molecular weight monomeric polyurethanes and their thermal cleavage, in which, at certain stages in the reaction, the prepared polyisocyanates and unutilizable residues are separated off and reusable by-products and intermediate products are returned to initial stages. |