| 摘要 |
Polyisocyanates are prepared by thermally splitting a carbamate corresponding to the formula: R1(NH-CO-O-R2)n in which R1, R2 and n are as defined herein into the corresponding isocyanate and alcohol. The splitting reaction is carried out at a temperature of from 150 DEG to 350 DEG C., at a pressure of from 0.001 to 20 bar and in the presence of an auxiliary agent. Suitable auxiliary agents are hydrogen chloride, organic acid chlorides, compounds having an alkylating effect and organotin (IV) chlorides. Inert solvents and catalysts may also be employed in the splitting products. The thus-produced isocyanate and alcohol are then separated, if necessary. |
