| 摘要 |
The invention relates to polyphenylene polymethylene polyisocyanates having an NCO number of at least 29% and containing less than 2 wt% of carbamides, less than 8 wt% of carbodiimides or uretonimines, and less than 1000 ppm of organic chlorine compounds. According to the invention, the polyphenylene polymethylene polyisocyanates can be produced in that (i) polyphenylene polymethylene polyamines are reacted with organic carbonates in order to form the corresponding polyphenylene polymethylene polycarbamates, (ii) the polyphenylene polymethylene carbamates are thermally cleaved in order to form the polyphenylene polymethylene polyisocyanates, wherein, before the thermal cleavage, the free amino groups or carbamide groups present in the carbamate raw mixture containing the polyphenylene polymethylene polycarbamates are reacted with a derivatization reactant in order to form amide groups or urethane groups. According to the invention, the polyphenylene polymethylene polyisocyanates can also be produced in that, before the thermal cleavage, compounds having free amino groups or carbamide groups that are present in the carbamate raw mixture are separated from the carbamate raw mixture by filtration of the carbamate raw mixture containing the polyphenylene polymethylene polycarbamates by means of a solid acidic adsorbent in the presence of an acid dissolved in the carbamate raw mixture. |
