A PROCESS FOR THE PRODUCTION OF POLYISOCYANATES

A process for the continuous catalyst-free production of polyisocyanates by thermal decomposition of the N-substituted carbamic acid esters corresponding to the polyisocyanates, in which the carbamic acid esters to be decomposed, in the form of a 5 to 90% by weight solution in an inert high-boiling solvent, are heated to a temperature of 100 to 400.degree.C and are subsequently introduced with expansion as a sidestream into a distillation column (4), in the sump of which a pressure of 0.001 to 5 bar and a temperature of 150 to 400.degree.C are maintained so that the high boiler is kept boiling in the sump, and the decomposition products are simultaneously condensed continuously and selectively at the head of the distillation column. The high boiler, which optionally contains impurities, is continuously removed via the sump outlet in a quantity substantially corresponding to the quantity of high boiler introduced into 'the column as solvent for the carbamic acid ester.