| 摘要 |
A process is disclosed for the preparation of light coloured, stable to storage uretonimine-modified polyisocyanates, wherein organic isocyanates based on one or more 4,4'-diphenyl-methane-diisocyanate (MDI) are partially carbodiimidized in the presence of a phospholene type catalyst, characterized in that
(a) the concentration of the catalyst based on the weight of the starting isocyanates is between 150 ppb and 1000 ppb;
(b) the reaction is performed at a temperature between 180 °C and 280 °C;
(c) at the intermediate, after achieving an isocyanate content between 24 to 27.5% the reaction is stopped by decreasing the reaction temperature below 100 °C. |
